Calcineurin (CN) is a conserved Ca2+/calmodulin-dependent phosphoprotein phosphatase that plays a key role in Ca2+ signaling. Regulator of calcineurin 1 (RCAN1), also known as Down syndrome critical region gene 1 (DSCR1), interacts with calcineurin and inhibits calcineurin-dependent signaling in various organisms. Ppb1, the fission yeast calcineurin regulates Cl--homeostasis, and Ppb1 deletion induces MgCl2 hypersensitivity. Here, we characterize the conserved and novel roles of the fission yeast RCAN1 homolog rcn1+. Consistent with its role as an endogenous calcineurin inhibitor, Rcn1 overproduction reproduced the calcineurin-null phenotypes, including MgCl2 hypersensitivity and inhibition of calcineurin signaling upon extracellular Ca2+ stimuli as evaluated by the nuclear translocation and transcriptional activation of the calcineurin substrate Prz1. Notably, overexpression of rcn1+ causes hypersensitivity to arsenite, whereas calcineurin deletion induces arsenite tolerance, showing a phenotypic discrepancy between Rcn1 overexpression and calcineurin deletion. Importantly, although Rcn1 deletion induces modest sensitivities to arsenite and MgCl2 in wild-type cells, the arsenite tolerance, but not MgCl2 sensitivity, associated with Ppb1 deletion was markedly suppressed by Rcn1 deletion. Collectively, our findings reveal a previously unrecognized functional collaboration between Rcn1 and calcineurin, wherein Rcn1 not only negatively regulates calcineurin in the Cl- homeostasis, but also Rcn1 mediates calcineurin signaling to modulate arsenite cytotoxicity.

Various stress conditions, such as heat stress (HS) and oxidative stress, can cause biomolecular condensates represented by stress granules (SGs) via liquid-liquid phase separation. We have previously shown that Hsp90 forms aggregates in response to HS and that Hsp90 aggregates transiently co-localize with SGs as visualized by Pabp. Here, we showed that arsenite, one of the well-described SG-inducing stimuli, induces Hsp90 aggregates distinct from conventional SGs in fission yeast. Arsenite induced Hsp90 granules in a dose-dependent manner, and these granules were significantly diminished by the co-treatment with a ROS scavenger N-acetyl cysteine (NAC), indicating that ROS are required for the formation of Hsp90 granules upon arsenite stress. Notably, Hsp90 granules induced by arsenite do not overlap with conventional SGs as represented by eIF4G or Pabp, while HS-induced Hsp90 granules co-localize with SGs. Nrd1, an RNA-binding protein known as a HS-induced SG component, was recruited into Hsp90 aggregates but not to the conventional SGs upon arsenite stress. The non-phosphorylatable eIF2α mutants significantly delayed the Hsp90 granule formation upon arsenite treatment. Importantly, inhibition of Hsp90 by geldanamycin impaired the Hsp90 granule formation and reduced the arsenite tolerance. Collectively, arsenite stimulates two types of distinct aggregates, namely conventional SGs and a novel type of aggregates containing Hsp90 and Nrd1, wherein Hsp90 plays a role as a center for aggregation, and stress-specific compartmentalization of biomolecular condensates.

The extracellular signal-regulated kinase (ERK) MAPK pathway is dysregulated in various human cancers and is considered an attractive therapeutic target for cancer. Therefore, several inhibitors of this pathway are being developed, and some are already used in the clinic. We have previously identified an anticancer compound, ACA-28, with a unique property to preferentially induce ERK-dependent apoptosis in melanoma cells. To comprehensively understand the biological cellular impact induced by ACA-28, we performed a global gene expression analysis of human melanoma SK-MEL-28 cells exposed to ACA-28 using a DNA microarray. The transcriptome analysis identified nuclear factor erythroid 2-related factor 2 (Nrf2), a master transcription factor that combats oxidative stress, as the most upregulated genetic pathway after ACA-28 treatment. Consistently, ACA-28 showed properties to increase the levels of reactive oxygen species (ROS) as well as Nrf2 protein, which is normally repressed by proteasomal degradation and activated in response to oxidative stresses. Furthermore, the ROS scavenger N-acetyl cysteine significantly attenuated the anticancer activity of ACA-28. Thus, ACA-28 activates Nrf2 signaling and exerts anticancer activity partly via its ROS-stimulating property. Interestingly, human A549 cancer cells with constitutively high levels of Nrf2 protein showed resistance to ACA-28, as compared with SK-MEL-28. Transient overexpression of Nrf2 also increased the resistance of cells to ACA-28, while knockdown of Nrf2 exerted the opposite effect. Thus, upregulation of Nrf2 signaling protects cancer cells from ACA-28-mediated cell death. Notably, the Nrf2 inhibitor ML385 substantially enhanced the cell death-inducing property of ACA-28 in pancreatic cancer cells, T3M4 and PANC-1. Our data suggest that Nrf2 plays a key role in determining cancer cell susceptibility to ACA-28 and provides a novel strategy for cancer therapy to combine the Nrf2 inhibitor and ACA-28.

Autophagy promotes or inhibits cell death depending on the environment and cell type. Our previous findings suggested that Atg1 is genetically involved in the regulation of Pmk1 MAPK in fission yeast. Here, we showed that Δatg1 displays lower levels of Pmk1 MAPK phosphorylation than did the wild-type (WT) cells upon treatment with a 1,3-β-D-glucan synthase inhibitor micafungin or CaCl2, both of which activate Pmk1. Moreover, the overproduction of Atg1, but not that of the kinase inactivating Atg1D193A activates Pmk1 without any extracellular stimuli, suggesting that Atg1 may promote Pmk1 MAPK signaling activation. Notably, the overproduction of Atg1 induces a toxic effect on the growth of WT cells and the deletion of Pmk1 failed to suppress the cell death induced by Atg1, indicating that the Atg1-mediated cell death requires additional mechanism(s) other than Pmk1 activation. Moreover, atg1 gene deletion induces tolerance to micafungin and CaCl2, whereas pmk1 deletion induces severe sensitivities to these compounds. The Δatg1Δpmk1 double mutants display intermediate sensitivities to these compounds, showing that atg1 deletion partly suppressed growth inhibition induced by Δpmk1. Thus, Atg1 may act to promote cell death upon micafungin and CaCl2 stimuli regardless of Pmk1 MAPK activity. Since micafungin and CaCl2 are intracellular calcium inducers, our data reveal a novel role of the autophagy regulator Atg1 to induce cell death upon calcium overload independent of its role in Pmk1 MAPK activation.

The extracellular-signal-regulated-kinase (ERK) signaling pathway is essential for cell proliferation and is frequently deregulated in human tumors such as pancreatic cancers. ACAGT-007a (GT-7), an anti-cancer compound, stimulates ERK phosphorylation, thereby inducing growth inhibition and apoptosis in T3M4 pancreatic cancer cells. However, how GT-7 stimulates ERK phosphorylation and induces apoptosis in ERK-active T3M4 cells remains unclear. To look into the mechanism, we performed a spatiotemporal analysis of ERK phosphorylation mediated by GT-7 in T3M4 cells. The immunoblotting showed that GT-7 stimulates ERK phosphorylation within 1 hr, which was more remarkable after 2 hr. Importantly, apoptosis induction as evaluated by the cleaved Caspase-3 was observed only after 2 hr incubation with GT-7. The immunofluorescence staining revealed the enrichment of phosphorylated ERK (phospho-ERK) in the nucleus upon 1 hr incubation with GT-7. Fractionation experiments showed that GT-7 increases phospho-ERK levels in the cytoplasm within 1 hr, whereas nuclear phospho-ERK accumulation is observed after 2 hr incubation with GT-7. MEK inhibition by U0126 significantly diminishes nuclear phospho-ERK distribution and apoptosis induction stimulated by GT-7. Thus, GT-7 may initiate the induction of ERK phosphorylation in the cytoplasm, which leads to phospho-ERK enrichment in the nucleus. This nuclear phospho-ERK accumulation by GT-7 precedes and may underlie apoptosis induction in T3M4.

Phosphatidylinositol-4-phosphate 5-kinase (PI4P5K) is a highly conserved enzyme that generates phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) by phosphorylating phosphatidylinositol 4-phosphate (PI(4)P). Schizosaccharomyces pombe (S. pombe) its3-1 is a loss-of-function mutation in the essential its3+ gene that encodes a PI4P5K. Its3 regulates cell proliferation, cytokinesis, cell integrity, and membrane trafficking, but little is known about the regulatory mechanisms of Its3. To identify regulators of Its3, we performed a genetic screening utilizing the high-temperature sensitivity (TS) of its3-1 and identified puf3+ and puf4+, encoding Pumilio/PUF family RNA-binding proteins as multicopy suppressors of its3-1 cells. The deletions of the PUF domains in the puf3+ and puf4+ genes resulted in the reduced ability to suppress its3-1, suggesting that the suppression by Puf3 and Puf4 may involve their RNA-binding activities. The gene knockout of Puf4, but not that of Puf3, exacerbated the TS of its3-1. Interestingly, mutant Its3 expression levels both at mRNA and protein levels were lower than those of the wild-type (WT) Its3. Consistently, the overexpression of the mutant its3-1 gene suppressed the its3-1 phenotypes. Notably, Puf3 and Puf4 overexpression increased the mRNA and protein expression levels of both Its3 and Its3-1. Collectively, our genetic screening revealed a functional relationship between the Pumilio/PUF family RNA-binding proteins and PI4P5K.

The nucleocytoplasmic transport of proteins is an important mechanism to control cell fate. Pap1 is a fission yeast nucleocytoplasmic shuttling transcription factor of which localization is redox regulated. The nuclear export factor Crm1/exportin negatively regulates Pap1 by exporting it from the nucleus to the cytoplasm. Here, we describe the effect of an anti-cancer compound ACA-28, an improved derivative of 1'-acetoxychavicol acetate (ACA), on the subcellular distribution of Pap1. ACA-28 induced nuclear accumulation of Pap1 more strongly than did ACA. ROS inhibitor N-acetyl-L-cysteine (NAC) partly antagonized the Pap1 nuclear accumulation induced by ACA-28. NAC almost abolished Pap1 nuclear localization upon H 2 O 2 , whereas leptomycin B (LMB)-mediated inhibition of Pap1 nuclear export was resistant to NAC. Collectively, ACA-28-mediated apoptosis in cancer cells may involve ROS-dependent and -independent mechanisms.

The mitogen-activated protein kinase (MAPK)/ERK and phosphatidylinositol-3 kinase (PI3K)/AKT pathways are dysregulated in various human cancers, including pancreatic ductal adenocarcinoma (PDAC), which has a very poor prognosis due to its lack of efficient therapies. We have previously identified ACAGT-007a (GT-7), an anti-cancer compound that kills ERK-active melanoma cells by inducing ERK-dependent apoptosis. Here, we investigated the apoptosis-inducing effect of GT-7 on three PDAC cell lines and its relevance with the MAPK/ERK and PI3K/AKT signaling pathways. GT-7 induced apoptosis in PDAC cells with different KRAS mutations (MIA-Pa-Ca-2 (KRAS G12C), T3M4 (KRAS Q61H), and PANC-1 (KRAS G12D)), being T3M4 most susceptible, followed by MIA-Pa-Ca-2, and PANC-1 was most resistant to apoptosis induction by GT-7. GT-7 stimulated ERK phosphorylation in the three PDAC cells, but only T3M4 displayed ERK-activation-dependent apoptosis. Furthermore, GT-7 induced a marked down-regulation of AKT phosphorylation after a transient peak in T3M4, whereas PANC-1 displayed the strongest and most sustained AKT activation, followed by MIA-Pa-Ca-2, suggesting that sustained AKT phosphorylation as a determinant for the resistance to GT-7-mediated apoptosis. Consistently, a PI3K inhibitor, Wortmannin, abolished AKT phosphorylation and enhanced GT-7-mediated apoptosis in T3M4 and MIA-Pa-Ca-2, but not in PANC-1, which showed residual AKT phosphorylation. This is the first report that ERK stimulation alone or in combination with AKT signaling inhibition can effectively induce apoptosis in PDAC and provides a rationale for a novel concurrent targeting of the PI3K/AKT and ERK pathways.

Recent studies reveal that tumor microenvironment contributes to breast cancer (BRCA) development, progression, and therapeutic response. However, the contribution of the tumor microenvironment-related genes in routine diagnostic testing or therapeutic decision making for BRCA remains elusive. Immune/stromal/ESTIMATE scores calculated by the ESTIMATE algorithm quantify immune and stromal components in a tumor, and thus can reflect tumor microenvironment. To investigate the association of the tumor microenvironment-related genes with invasive BRCA prognosis, here we analyzed the immune/stromal/ESTIMATE scores in combination with The Cancer Genome Atlas (TCGA) database in invasive BRCA. We found that immune/stromal/ESTIMATE scores were significantly correlated with the invasive BRCA clinicopathological factors. Based on the immune/stromal/ESTIMATE scores, we extracted a series of differential expression genes (DEGs) related to the tumor microenvironment. Survival analysis was further performed to identify a list of high-frequency DEGs (HF-DEGs), which exhibited prognostic value in invasive BRCA. Importantly, consistent with the results of bioinformatics analysis, immunohistochemistry results showed that high SASH3 expression was associated with a good prognosis in invasive BRCA patients. Our findings suggest that the tumor microenvironment-related HF-DEGs identified in this study have prognostic values and may serve as potential biomarkers and therapeutic targets for invasive BRCA.

Apart from the highly conserved role in the cellular degradation process, autophagy also appears to play a key role in cellular proliferation. Here, we describe the genetic interaction of autophagy-related genes and Pmk1 MAPK signaling in fission yeast. atg1 deletion cells (Δ atg1 ) exhibit the vic (viable in the presence of immunosuppressant and Cl - ) phenotype, indicative of Pmk1 signaling inhibition. Moreover, the Δ atg1 Δ pmk1 double mutant resembles the single Δ pmk1 mutant, suggesting that Atg1 functions in the Pmk1 pathway. In addition, the growth defect induced by overexpression of Pck2, an upstream activator of Pmk1 MAPK was alleviated by the deletion of atg1 + . Finally, the deletion of autophagy-related genes recapitulates Pmk1 MAPK signaling inhibition. Our data suggest a novel role for autophagy in MAPK signaling regulation.

Calcineurin (CN) is a conserved Ca2+-calmodulin activated protein phosphatase, which plays important roles in immune regulation, cardiac hypertrophy, and apoptosis in humans. In pathogenic fungi, CN is essential for stress survival, sexual development, and virulence. The immunosuppressant tacrolimus (FK506) is a specific inhibitor of CN in humans and fungi including nonpathogenic fission yeast. Although calcineurin inhibition by FK506 or CN deletion in fission yeast does not induce growth defects, treatment with some anti-fungal drugs such as micafungin and valproic acid, induced synthetic lethality with calcineurin inhibition. Here, we searched for the compounds that induce synthetic growth defects with CN inhibition in fission yeast. We found that ellagic acid (EA) preferentially induced growth inhibition in CN deletion cells. Consistently, co-treatment with EA and FK506 induced severe growth inhibition in the wild-type cells, whereas neither of the single treatment with each compound did so. Moreover, deletion of the calcineurin-regulated transcription factor Prz1 also induced a marked EA sensitivity. Intriguingly, EA also enhanced the growth inhibitory effect of other anti-fungal drugs, including micafungin and miconazole. Thus, our data suggesting the synergistic growth inhibitory effect of the calcineurin inhibitor FK506 and EA may be useful to understand the mechanism to overcome the antifungal resistance.

Stress granule (SG) assembly is a conserved cellular strategy that copes with stress-related damage and promotes cell survival. SGs form through a process of liquid-liquid phase separation. Cellular signaling also appears to employ SG assembly as a mechanism for controlling cell survival and cell death by spatial compartmentalization of signal-transducing factors. While several lines of evidence highlight the importance of SGs as signaling hubs, where protein components of signaling pathways can be temporarily sequestered, shielded from the cytoplasm, the regulation and physiological significance of SGs in this aspect remain largely obscure. A recent study of the heat-shock response in the fission yeast Schizosaaccharomyces pombe provides an unexpected answer to this question. Recently, we demonstrated that the PKC orthologue Pck2 in fission yeast translocates into SGs through phase separation in a PKC kinase activity-dependent manner upon high-heat stress (HHS). Importantly, the downstream MAPK Pmk1 promotes Pck2 recruitment into SGs, which intercepts MAPK hyperactivation and cell death, thus posing SGs as a negative feedback circuit in controlling MAPK signaling. Intriguingly, HHS, but not modest-heat stress targets Pck2 to SGs, independent of canonical SG machinery. Finally, cells fail to activate MAPK signaling when Pck2 is sequestrated into SGs. In this review, we will discuss how SGs have a role as signaling hubs beyond serving as a repository for non-translated mRNAs during acute stress.

HER1-and HER2-targeted drugs are effective in cancer therapy, especially against lung, breast and colon malignancies; however, resistance of cancer cells to HER1-and HER2-targeted therapies is becoming a serious problem. The avidity/affinity constant (KA) and growth inhibitory effect of anti-HER3 rat monoclonal antibodies (mAb, Ab1∼Ab6) in the presence of therapeutic mAb or low-molecular-weight inhibitors against HER family proteins were analyzed by flow cytometry-based Scatchard plots (Splot) and cell proliferation assay. The KA of Ab3 and Ab6, but not Ab1 or Ab4, split into dual (high and low) modes of KA, and Ab6 exhibited greater anti-proliferative effects against LS-174T colon cancer cells in the presence of Pertuzumab (anti-HER2 mAb). A high KA by Ab6 and Ab6-mediated increased growth inhibition were observed against NCI-H1838 lung or BT474 breast cancer cells, respectively, in the presence of Panitumumab (anti-HER1 mAb) or Perutuzumab. A high KA by Ab6 and Ab6-mediated increased anti-proliferative effects against NCI-H1838 or BT474 were also respectively observed in the presence of Erlotinib (HER1 inhibitor) or Lapatinib (HER1/HER2 inhibitor). In HER1-knockout (KO) NCI-H1838, the reactivity and KA of Ab4 increased compared with in parent NCI-H1838. In HER1-KO or HER3-KO SW1116 colon cancer cells, dual modes of KA with Pertuzumab were noted, and the combination Ab6 and Pertuzumab promoted growth inhibition of HER1-KO, but not of parent SW1116.

The RAF/MEK/ERK signaling pathway regulates diverse cellular processes as exemplified by cell proliferation, differentiation, motility, and survival. Activation of ERK1/2 generally promotes cell proliferation, and its deregulated activity is a hallmark of many cancers. Therefore, components and regulators of the ERK pathway are considered potential therapeutic targets for cancer, and inhibitors of this pathway, including some MEK and BRAF inhibitors, are already being used in the clinic. Notably, ERK1/2 kinases also have pro-apoptotic functions under certain conditions and enhanced ERK1/2 signaling can cause tumor cell death. Although the repertoire of the compounds which mediate ERK activation and apoptosis is expanding, and various anti-cancer compounds induce ERK activation while exerting their anti-proliferative effects, the mechanisms underlying ERK1/2-mediated cell death are still vague. Recent studies highlight the importance of dual-specificity phosphatases (DUSPs) in determining the pro- versus anti-apoptotic function of ERK in cancer. In this review, we will summarize the recent major findings in understanding the role of ERK in apoptosis, focusing on the major compounds mediating ERK-dependent apoptosis. Studies that further define the molecular targets of these compounds relevant to cell death will be essential to harnessing these compounds for developing effective cancer treatments.

In receptor-type transcription factors-mediated cytochrome P450 (P450)s induction, few studies have attempted to clarify the roles of protein kinase N (PKN) in the transcriptional regulation of P450s. This study aimed to examine the involvement of PKN in the transcriptional regulation of P450s by receptor-type transcription factors, including the aryl hydrocarbon receptor, constitutive androstane receptor (CAR), and pregnane X receptor. The mRNA and protein levels, and metabolic activity, of P450s in the livers of wild-type (WT) and double-mutant (D) mice harboring both PKN1 kinase-negative knock-in and PKN3 knockout mutations [PKN1 T778A/T778A; PKN3 -/-] were determined following treatment with activators for receptor-type transcription factors. mRNA and protein levels, and metabolic activity, of CYP2B10 were significantly higher in D mice treated with the CAR activator phenobarbital (PB), but not with 1,4-bis((3,5-dichloropyridin-2-yl)oxy)benzene, compared with WT mice. We examined the CAR-dependent pathway regulated by PKN following PB treatment, because the extent of CYP2B10 induction in WT and D mice was notably different in response to treatment with different CAR activators. The mRNA levels of Cyp2b10 in primary hepatocytes from WT and D mice treated with PB alone or in combination with SKI-1 (a Src inhibitor), or U0126 (a MEK inhibitor), were evaluated. Treatment of hepatocytes from D mice with the combination of PB with U0126, but not SKI-1, significantly increased the mRNA levels of Cyp2b10 compared with those from the corresponding WT mice. These findings suggest that PKN may have inhibitory effects on the Src-RACK1 pathway in the CAR-mediated induction of Cyp2b10 in mice livers. Significance Statement This is the first report of involvement of PKN in the transcriptional regulation of P450s. The elucidation of mechanisms responsible for induction of P450s could help optimize the pharmacotherapy and improve drug development. We examined whether the mRNA and protein levels, and activities of P450s were altered in double-mutant mice harboring both PKN1 kinase-negative knock-in and PKN3 knockout mutations. PKN1/3 negatively regulates CAR-mediated induction of Cyp2b10 through phosphorylation of a signaling molecule in the Src-RACK1 pathway.

L-type amino acid transporter 1 (LAT1)/SLC7A5 is the first identified CD98 light chain disulfide linked to the CD98 heavy chain (CD98hc/SLC3A2). LAT1 transports large neutral amino acids, including leucine, which activates mTOR, and is highly expressed in human cancers. We investigated the oncogenicity of human LAT1 introduced to NIH/3T3 cells by retrovirus infection. NIH/3T3 cell lines stably expressing human native (164C) or mutant (164S) LAT1 (naLAT1/3T3 or muLAT1/3T3, respectively) were established. We confirmed that endogenous mouse CD98hc forms a disulfide bond with exogenous human LAT1 in naLAT1/3T3, but not in muLAT1/3T3. Endogenous mouse CD98hc mRNA increased in both naNIH/3T3 and muLAT1/3T3, and a similar amount of exogenous human LAT1 protein was detected in both cell lines. Furthermore, naLAT1/3T3 and muLAT1/3T3 cell lines were evaluated for cell growth-related phenotypes (phosphorylation of ERK, cell-cycle progression) and cell malignancy-related phenotypes (anchorage-independent cell growth, tumor formation in nude mice). naLAT1/3T3 had stronger growth- and malignancy- related phenotypes than NIH/3T3 and muLAT1/3T3, suggesting the oncogenicity of native LAT1 through its interaction with CD98hc. Anti-LAT1 monoclonal antibodies significantly inhibited in vitro cell proliferation and in vivo tumor growth of naLAT1/3T3 cells in nude mice, demonstrating LAT1 to be a promising anti-cancer target.

The molecular chaperone Hsp90 is highly conserved from bacteria to mammals. In fission yeast, Hsp90 is essential in many cellular processes and its expression is known to be increased by heat stress (HS). Here, we describe the distinct spatiotemporal distribution of Hsp90 under high-heat stress (HHS: 45˚C) and mild-heat stress (MHS: 37˚C). Hsp90 is largely distributed in the cytoplasm under non-stressed conditions (27˚C). Under HHS, Hsp90 forms several cytoplasmic granules within 5 minutes, then the granules disappear within 60 minutes. Under MHS, Hsp90 forms fewer granules than under HHS within 5 minutes and strikingly the granules persist and grow in size. In addition, nuclear enrichment of Hsp90 was observed after 60 minutes under both HS conditions. Our data suggest that assembly/disassembly of Hsp90 granules is differentially regulated by temperatures.

The PKC signaling is a highly conserved signaling module, which plays a central role in a myriad of physiological processes, ranging from cell proliferation to cell death via various signaling pathways, including MAPK. Stress granules (SGs) are non-membranous cytoplasmic foci that aggregate in cells exposed to environmental stresses. Here we explored the role of SGs in PKC/MAPK signaling activation in fission yeast. High heat-stress (HHS) induced Pmk1 MAPK activation and Pck2/PKC translocation from the cell tips into poly(A)-binding protein (Pabp)-positive SGs. Pck2 dispersal from the cell tips required Pck2 kinase activity and the constitutively active Pck2 promotes its translocation to SGs. Importantly, Pmk1 deletion impaired Pck2 recruitment into SGs, indicating that MAPK activation stimulates Pck2 SG translocation. Consistently, HHS-induced SGs delayed Pck2 relocalization at the cell tips, thereby blocking subsequent Pmk1 reactivation after recovery from HHS. HHS partitioned Pck2 into the Pabp-positive SG-containing fraction, which resulted in the reduced Pck2 abundance and kinase activity in the soluble fraction. Collectively, MAPK-dependent Pck2 SG recruitment serves as a feedback mechanism to intercept PKC/MAPK activation induced by HHS, which might underlie PKC-related diseases.

Copy number alterations detected by comparative genomic hybridization (CGH) can lead to the identification of novel cancer-related genes. We analyzed chromosomal aberrations in a set of 100 human primary colorectal cancers (CRCs) using CGH and found a solute carrier (SLC) 7A1 gene, which encodes cationic amino acid transporter 1 (CAT1) with 14 putative transmembrane domains, in a chromosome region (13q12.3) with a high frequency of gene amplifications. SLC7A1/CAT1 is a transporter responsible for the uptake of cationic amino acids (arginine, lysine, and ornithine) essential for cellular growth. Microarray and PCR analyses have revealed that mRNA transcribed from CAT1 is overexpressed in more than 70% of human CRC samples, and RNA interference-mediated knockdown of CAT1 inhibited the cell growth of CRCs. Rats were immunized with rat hepatoma cells expressing CAT1 tagged with green fluorescent protein (GFP), and rat splenocytes were fused with mouse myeloma cells. Five rat monoclonal antibodies (mAbs) (CA1 ~ CA5) reacting with HEK293 cells expressing CAT1-GFP in a GFP expression-dependent manner were selected from established hybridoma clones. Novel anti-CAT1 mAbs selectively reacted with human CRC tumor tissues compared with adjacent normal tissues according to immuno-histochemical staining and bound strongly to numerous human cancer cell lines by flow cytometry. Anti-CAT1 mAbs exhibited internalization activity, antibody-dependent cellular cytotoxicity, and migration inhibition activity against CRC cell lines. Furthermore, CA2 inhibited the in vivo growth of human HT29 and SW-C4 CRC tumors in nude mice. This study suggested CAT1 to be a promising target for mAb therapy against CRCs.

Dual-specificity phosphatase 6 (DUSP6) is a key negative feedback regulator of the member of the RAS-ERK MAPK signaling pathway that is associated with cellular proliferation and differentiation. Deterioration of DUSP6 expression could therefore result in deregulated growth activity. We have previously discovered ACA-28, a novel anticancer compound with a unique property to stimulate ERK phosphorylation and induce apoptosis in ERK-active melanoma cells. However, the mechanism of cancer cell-specific-apoptosis by ACA-28 remains obscure. Here, we investigated the involvement of DUSP6 in the mechanisms of the ACA-28-mediated apoptosis by using the NIH/3T3 cells overexpressing HER2/ErbB2 (A4-15 cells), as A4-15 exhibited higher ERK phosphorylation and are more susceptible to ACA-28 than NIH/3T3. We showed that A4-15 exhibited high DUSP6 protein levels, which require ERK activation. Notably, the silencing of the DUDSP6 gene by siRNA inhibited proliferation and induced apoptosis in A4-15, but not in NIH/3T3, indicating that A4-15 requires high DUSP6 expression for growth. Importantly, ACA-28 preferentially down-regulated the DUSP6 protein and proliferation in A4-15 via the proteasome, while it stimulated ERK phosphorylation. Collectively, the up-regulation of DUSP6 may exert a growth-promoting role in cancer cells overexpressing HER2. DUSP6 down-regulation in ERK-active cancer cells might have the potential as a novel cancer measure.

The recent discovery that an ERK signaling modulator [ACA-28 (2a)] preferentially kills human melanoma cell lines by inducing ERK-dependent apoptosis has generated significant interest in the field of anti-cancer therapy. In the first SAR study on 2a, here, we successfully developed candidates (2b, 2c) both of which induce more potent and selective apoptosis towards ERK-active melanoma cells than 2a, thus revealing the structural basis for inducing the ERK-dependent apoptosis and proposing the therapeutic prospect of these candidates against ERK-dependent cancers represented by melanoma.

FTY720, a sphingosine-1-phosphate (S1P) analog, is used as an immune modulator to treat multiple sclerosis. Accumulating evidence has suggested the mode of action of FTY720 independent of an S1P modulator. In fission yeast, FTY720 induces an increase in intracellular Ca2+ and ROS levels. We have previously identified 49 genes of which deletion causes FTY720 sensitivity. Here, we characterized the FTY720-sensitive mutants in terms of their relevance to the Ca2+ homeostasis and identified the 16 FTY720- and Ca2+ - sensitive mutants (fcs mutants). Most of the FTY720-sensitive mutants showed elevated Ca2+ levels and exhibited Ca2+ dysregulation by FTY720 treatment. One of the functional categories among the genes whose deletion renders cells susceptible to FTY720 and Ca2+ include the Golgi/endosomal membrane trafficking. Notably, FTY720, but not phosphorylated FTY720 incapable of inducing Ca2+ increase, inhibited the secretion of acid phosphatase in the wild-type cells. Importantly, secretory defects of the Golgi/endosomal trafficking mutants, Vps45, or Ryh1 deletion, were further exacerbated by FTY720. Our fcs mutant screen also identified the adenylyl cyclase-associated protein Cap1 and a Rictor homolog Ste20, whose deletion markedly exacerbated FTY720-sensitive secretory impairment. Collectively, our data may suggest a synergistic impact of FTY720 combined with secretion perturbation on proliferation and Ca2+ homeostasis.

Structural study of multidomain proteins using NMR is an emerging issue for understanding biological functions. To this end, domain-specific labeling is expected to be a key technology for facilitating the NMR-assignment process and for collecting distance information via spin labeling. To obtain domain-specific labeled samples, use of sortase A as a protein ligation tool is a viable approach. Sortase A enables ligation of separately expressed proteins (domains) through the Leu-Pro-X-Thr-Gly linker. However, the ligation reaction mediated by sortase A is not efficient. Poor yield and long reaction times hamper large-scale preparation using sortase A. Here we report the application of highly active sortases to NMR analyses. Optimal yields can be achieved within several hours when the ligation reaction are mediated by highly active sortases at 4 °C. We propose that this protocol can contribute to structural analyses of multidomain proteins by NMR.

Protein kinase N1 (PKN1) knockout (KO) mice spontaneously form germinal centers (GCs) and develop an autoimmune-like disease with age. Here, we investigated the function of PKN1 kinase activity in vivo using aged mice deficient in kinase activity resulting from the introduction of a point mutation (T778A) in the activation loop of the enzyme. PKN1[T778A] mice reached adulthood without external abnormalities; however, the average spleen size and weight of aged PKN1[T778A] mice increased significantly compared to aged wild type (WT) mice. Histologic examination and Southern blot analyses of spleens showed extramedullary hematopoiesis and/or lymphomagenesis in some cases, although without significantly different incidences between PKN1[T778A] and WT mice. Additionally, flow cytometry revealed increased numbers in B220+, CD3+, Gr1+ and CD193+ leukocytes in the spleen of aged PKN1[T778A] mice, whereas the number of lymphocytes, neutrophils, eosinophils, and monocytes was reduced in the peripheral blood, suggesting an advanced impairment of leukocyte trafficking with age. Moreover, aged PKN1[T778A] mice showed no obvious GC formation nor autoimmune-like phenotypes, such as glomerulonephritis or increased anti-dsDNA antibody titer, in peripheral blood. Our results showing phenotypic differences between aged Pkn1-KO and PKN1[T778A] mice may provide insight into the importance of PKN1-specific kinase-independent functions in vivo.

Protein kinase C (PKC) family plays crucial roles in a wide variety of cellular functions and dysregulation of PKC signaling leads to pathophysiological states including cancer and neurodegenerative disease. PKC activity is rigorously fine-tuned by multiple mechanisms, but the spatial regulatory mechanism of PKC signaling remains fully understood. Here, we have shown that RNA granules, widely conserved non-membranous cytoplasmic structures composed of RNA-protein complexes, play a key role in spatially regulating PKC and its downstream MAPK signaling activation. Upon heat stress, PKC and downstream MAPK signaling activation was induced, which stimulates recruitment of the PKC homologue in fission yeast, from the plasma membrane into RNA granules. Intriguingly, Inhibition of the downstream MAPK signaling impaired PKC translocation to the RNA granules, whereas the constitutively active MAPKK stimulated PKC translocation to the RNA granules. We also demonstrated that the kinase activity of PKC influenced its intracellular distribution from the cell membranes to the RNA granules.  Our data is the first demonstration that PKC translocation into RNA granules is a novel feedback mechanism mediated by MAPK signaling.

Mitogen-activated protein kinase (MAPK) pathways are evolutionarily conserved kinase modules that link extracellular signals to the machinery that controls fundamental cellular processes such as growth, proliferation, differentiation, and apoptosis. The Ras/Raf/MEK/ERK MAPK pathway is one of the most studied of the mammalian MAPK pathways and has attracted intense research interest because of its critical involvement in the regulation of cell proliferation. The mutational activation of upstream signaling components that constitutively activate ERK MAPKs as seen in various primary tumor samples has validated this pathway for drug discovery. The fission yeast Schizosaccharomyces pombe is an important tool for cancer research. This well-studied model organism has enabled groundbreaking, Nobel Prize-winning discoveries and has provided insights into how both normal and cancerous cells grow and divide. We performed chemical genetic screening using a fission yeast phenotypic assay and demonstrated that ACA-28, a synthetic derivative of 1'-acetoxychavicol acetate (ACA), effectively inhibited the growth of melanoma cancer cells wherein ERK MAPK signaling is hyperactivated due to mutations in the upstream activating regulators. Importantly, the growth of normal human epidermal melanocytes was less affected by ACA-28. In addition, ACA-28 specifically induced apoptosis in NIH/3T3 cells oncogenically transformed with HER2/ErbB2 but not in the parental cells. Notably, the ACA-28-induced apoptosis was abrogated when ERK activation was blocked with the specific MEK inhibitor U0126. Consistently, ACA-28 more strongly stimulated ERK phosphorylation in melanoma cells as compared with normal human epidermal melanocytes. ACA-28 might serve as a promising seed compound to combat ERK-dependent cancers by stimulating oncogenic signaling.

Fingolimod hydrochloride (FTY720) is a first-in-class of sphingosine-1-phosphate (S1P) receptor modulator approved to treat multiple sclerosis by its phosphorylated form (FTY720-P). In this review, we introduce our recent discoveries using a chemical genomics approach to uncover a signaling network relevant to FTY720-mediated ROS signaling and apoptosis, thereby proposing new potential targets for combination therapy as a means to enhance the antitumor efficacy of FTY720 as a ROS generator. We extend our knowledge by summarizing various measures targeting the vulnerability of cancer cells' defense mechanisms against oxidative stress. Future directions that may lead to the best use of FTY720 and ROS-targeted strategies as a promising cancer treatment are also discussed.

In fission yeast, a KH-type RBP Rnc1 negatively regulates MAPK signaling activation via mRNA stabilization of the dual-specificity MAPK phosphatase Pmp1, which dephosphorylates MAPK Pmk1. Rnc1 also serves as a target of MAPK phosphorylation, which makes a feedback loop mediated by an RBP. We recently discovered that the nuclear export of Rnc1 requires mRNA-binding ability and the mRNA export factor Rae1. This strongly suggested the presence of an mRNA-export system, which recognizes the mRNA/RBP complex and dictates the location and post-transcriptional regulation of mRNA cargo. Here, we briefly review the known mechanisms of general nuclear transporting systems, with an emphasis on our recent findings on the spatial regulation of Rnc1 and its impact on the regulation of the MAPK signal transduction cascade.

Negative regulator differentiation 1 (Nrd1), a fission yeast RNA binding protein, modulates cytokinesis and sexual development and contributes to stress granule formation in response to environmental stresses. Nrd1 comprises four RRM domains and binds and stabilizes Cdc4 mRNA that encodes the myosin II light chain. Nrd1 binds the Cpc2 fission-yeast RACK1 homolog, and the interaction promotes Nrd1 localization to stress granules. Interestingly, Pmk1 mitogen-activated protein kinase phosphorylates Thr40 in the unstructured N-terminal region and Thr126 in the first RRM domain of Nrd1. Phosphorylation significantly reduces RNA-binding activity and likely modulates Nrd1 function. To reveal the relationship between the structure and function of Nrd1 and how phosphorylation affects structure, we used heteronuclear NMR techniques to investigate the three-dimensional structure of Nrd1. Here we report the H-1, C-13, and N-15 resonance assignments of RRM1-RRM2 (residues 108-284) comprising the first and second RRMs obtained using heteronuclear NMR techniques. Secondary structures derived from the chemical shifts are reported. These data should contribute to the understanding of the three-dimensional structure of the RRM1-RRM2 region of Nrd1 and the perturbation caused by phosphorylation.

A method was developed for the specific entrapment and separation of phosphorylated compounds using a Phos-tag polyacrylamide gel fabricated at the channel crossing point of a microfluidic electrophoresis chip. The channel intersection of the poly(methyl methacrylate)-made microchip was filled with a solution comprising acrylamide, N, N-methylene-bis-acrylamide, Phos-tag acrylamide, and 2,2'-azobis [2-methyl-N-(2-hydroxyethyl) propionamide], which functioned as a photocatalytic initiator. In situ polymerization at the channel crossing point was performed by irradiation with a UV LED laser beam. The fabricated Phos-tag gel (100 x 100 x 30 mu m) contains ca. 20 fmol of the Phos-tag group and therefore could entrap phosphorylated compounds at the femtomolar level. The electrophoretically trapped phosphorylated compounds were released from the gel by switching the voltage to deliver high concentrations of phosphate and EDTA in a background electrolyte. The broad sample band eluted from the gel was effectively reconcentrated at the boundary of a pH junction generated by sodium ions delivered from the outlet reservoir. The reconcentrated sample components were then separated and fluorometrically detected at the end of the separation channel. Under the optimized conditions, the phosphorylated compounds were concentrated by a factor of 100-fold, and the peak resolution was comparable to that obtained by pinched injection. This method was successfully utilized to preconcentrate and analyze phosphorylated peptides in a complex peptide mixture.

Knock-in mice lacking PKN1 kinase activity were generated by introducing a T778A point mutation in the catalytic domain. PKN1[T778A] mutant mice developed to adulthood without apparent external abnormalities, but exhibited lower T and B lymphocyte counts in the peripheral blood than those of wild-type (WT) mice. T and B cell development proceeded in an apparently normal fashion in bone marrow and thymus of PKN1[T778A] mice, however, the number of T and B cell counts were significantly higher in the lymph nodes and spleen of mutant mice in those of WT mice. After transfusion into WT recipients, EGFP-labelled PKN1[T778A] donor lymphocytes were significantly less abundant in the peripheral circulation and more abundant in the spleen and lymph nodes of recipient mice compared with EGFP-labelled WT donor lymphocytes, likely reflecting lymphocyte sequestration in the spleen and lymph nodes in a cell-autonomous fashion. PKN1[T778A] lymphocytes showed significantly lower chemotaxis towards chemokines and sphingosine 1-phosphate (S1P) than WT cells in vitro. The biggest migration defect was observed in response to S1P, which is essential for lymphocyte egress from secondary lymphoid organs. These results reveal a novel role of PKN1 in lymphocyte migration and localization.

The extracellular signal-regulated kinase (ERK) signaling pathway is essential for cell proliferation and is frequently deregulated in human tumors such as melanoma. Melanoma remains incurable despite the use of conventional chemotherapy; consequently, development of new therapeutic agents for melanoma is highly desirable. Here, we carried out a chemical genetic screen using a fission yeast phenotypic assay and showed that ACA-28, a synthetic derivative of 1'-acetoxychavicol acetate (ACA), which is a natural ginger compound, effectively inhibited the growth of melanoma cancer cells wherein ERK MAPK signaling is hyperactivated due to mutations in the upstream activating regulators. ACA-28 more potently inhibited the growth of melanoma cells than did the parental compound ACA. Importantly, the growth of normal human epidermal melanocytes (NHEM) was less affected by ACA-28 at the same 50% inhibitory concentration. In addition, ACA-28 specifically induced apoptosis in NIH/3T3 cells which were oncogenically transformed with human epidermal growth factor receptor-2 (HER2/ErbB2), but not in the parental cells. Notably, the ACA-28-induced apoptosis in melanoma and HER2-transformed cells was abrogated when ERK activation was blocked with a specific MEK inhibitor U0126. Consistently, ACA-28 more strongly stimulated ERK phosphorylation in melanoma cells, as compared in NHEM. ACA-28 might serve as a promising seed compound for melanoma treatment.

The extracellular signal-regulated kinase (ERK) signaling pathway is essential for cell proliferation and is frequently deregulated in human tumors such as melanoma. Melanoma remains incurable despite the use of conventional chemotherapy; consequently, development of new therapeutic agents for melanoma is highly desirable. Here, we carried out a chemical genetic screen using a fission yeast phenotypic assay and showed that ACA-28, a synthetic derivative of 10-acetoxychavicol acetate (ACA), which is a natural ginger compound, effectively inhibited the growth of melanoma cancer cells wherein ERK MAPK signaling is hyperactivated due to mutations in the upstream activating regulators. ACA-28 more potently inhibited the growth of melanoma cells than did the parental compound ACA. Importantly, the growth of normal human epidermal melanocytes (NHEM) was less affected by ACA-28 at the same 50% inhibitory concentration. In addition, ACA-28 specifically induced apoptosis in NIH/3T3 cells which were oncogenically transformed with human epidermal growth factor receptor-2 (HER2/ErbB2), but not in the parental cells. Notably, the ACA-28-induced apoptosis in melanoma and HER2-transformed cells was abrogated when ERK activation was blocked with a specific MEK inhibitor U0126. Consistently, ACA-28 more strongly stimulated ERK phosphorylation in melanoma cells, as compared in NHEM. ACA-28 might serve as a promising seed compound for melanoma treatment.

RNA-binding proteins (RBPs) play important roles in the posttranscriptional regulation of gene expression, including mRNA stability, transport and translation. Fission yeast rnc1+ encodes a K Homology (KH)-type RBP, which binds and stabilizes the Pmp1 MAPK phosphatase mRNA thereby suppressing the Cl− hypersensitivity of calcineurin deletion and MAPK signaling mutants. Here, we analyzed the spatial regulation of Rnc1 and discovered a putative nuclear export signal (NES)Rnc1, which dictates the cytoplasmic localization of Rnc1 in a Crm1-independent manner. Notably, mutations in the NESRnc1 altered nucleocytoplasmic distribution of Rnc1 and abolished its function to suppress calcineurin deletion, although the Rnc1 NES mutant maintains the ability to bind Pmp1 mRNA. Intriguingly, the Rnc1 NES mutant destabilized Pmp1 mRNA, suggesting the functional importance of the Rnc1 cytoplasmic localization. Mutation in Rae1, but not Mex67 deletion or overproduction, induced Rnc1 accumulation in the nucleus, suggesting that Rnc1 is exported from the nucleus to the cytoplasm via the mRNA export pathway involving Rae1. Importantly, mutations in the Rnc1 KH-domains abolished the mRNA-binding ability and induced nuclear localization, suggesting that Rnc1 may be exported from the nucleus together with its target mRNAs. Collectively, the functional Rae1-dependent mRNA export system may influence the cytoplasmic localization and function of Rnc1.

RNA-binding proteins (RBPs) play important roles in the posttranscriptional regulation of gene expression, including mRNA stability, transport and translation. Fission yeast rnc1(+) encodes a K Homology (KH)-type RBP, which binds and stabilizes the Pmp1 MAPK phosphatase mRNA thereby suppressing the Cl- hypersensitivity of calcineurin deletion and MAPK signaling mutants. Here, we analyzed the spatial regulation of Rnc1 and discovered a putative nuclear export signal (NES)(Rnc1), which dictates the cytoplasmic localization of Rnc1 in a Crm1-independent manner. Notably, mutations in the NESRnc1 altered nucleocytoplasmic distribution of Rnc1 and abolished its function to suppress calcineurin deletion, although the Rnc1 NES mutant maintains the ability to bind Pmp1 mRNA. Intriguingly, the Rnc1 NES mutant destabilized Pmp1 mRNA, suggesting the functional importance of the Rnc1 cytoplasmic localization. Mutation in Rae1, but not Mex67 deletion or overproduction, induced Rnc1 accumulation in the nucleus, suggesting that Rnc1 is exported from the nucleus to the cytoplasm via the mRNA export pathway involving Rae1. Importantly, mutations in the Rnc1 KH-domains abolished the mRNA-binding ability and induced nuclear localization, suggesting that Rnc1 may be exported from the nucleus together with its target mRNAs. Collectively, the functional Rae1-dependent mRNA export system may influence the cytoplasmic localization and function of Rnc1.

The distribution of metal and metalloid species in each of the cell compartments is termed as "metallome". It is important to elucidate the molecular mechanism underlying the beneficial or toxic effects exerted by a given metal or metalloid on human health. Therefore, we developed a method to measure intracellular metal ion concentration (particularly, intracellular calcium ion) in fission yeast. We evaluated the effects of nitric acid (HNO3), zymolyase, and westase treatment on cytolysis in fission yeast. Moreover, we evaluated the changes in the intracellular calcium ion concentration in fission yeast in response to treatment with/without micafungin. The fission yeast undergoes lysis when treated with 60% HNO3, which is simpler and cheaper compared to the other treatments. Additionally, the intracellular calcium ion concentration in 60% HNO3-treated fission yeast was determined by inductively coupled plasma atomic emission spectrometry. This study yields significant information pertaining to measurement of the intracellular calcium ion concentration in fission yeast, which is useful for elucidating the physiological or pathological functions of calcium ion in the biological systems. This study is the first step to obtain perspective view on the effect of the metallome in biological systems.

As part of an ongoing study on the structure-activity relationship of acremomannolipin A (1)-the novel glycolipid isolated from Acremonium strictum possessing potent calcium signal-modulating activity-the role of acyl substituents on the D-mannose moiety was examined. Three partially deacylated homologs (2a-2c) and 20 homologs (2d-2w) bearing different acyloxy side chains were synthesized via the stereoselective beta-mannosylation of appropriately protected mannosyl sulfoxides (3) with D-mannitol derivatives (4), and their calcium signal-modulating activities were examined. The activities of 2a-2c were completely lost. Homologs bearing relatively short acyloxy groups at C-3, C-4, and C-6 positions (2t-2v) exhibited less activity than 1, whereas a heptanoyl homolog (2w: C-7) maintained activity nearly equal to that of 1. When the acyl groups at these three positions were substituted by an octanoyl group (2i: C-8), the activity was completely lost. On the other hand, of the 10 homologs in which the octanoyl at C-2 was substituted by other acyloxy moieties (2j-2s), three (2m: C-7, 2n: C-9, 2o: C-10) maintained potent activity. These results suggested that peracylated mannose structure is critical for calcium signal modulating activity, and this activity is precisely dependent on the length of four acyl side chains on D-mannose. (C) 2016 Published by Elsevier Masson SAS.

The mitogen-activated protein kinase (MAPK) cascade is a highly conserved signaling module composed of MAPK kinase kinases (MAPKKKs), MAPK kinases (MAPKK) and MAPKs. The MAPKKK Mkh1 is an initiating kinase in Pmk1 MAPK signaling, which regulates cell integrity in fission yeast (Schizosaccharomyces pombe). Our genetic screen for regulators of Pmk1 signaling identified Shk1 kinase binding protein 5 (Skb5), an SH3-domain-containing adaptor protein. Here, we show that Skb5 serves as an inhibitor of Pmk1 MAPK signaling activation by downregulating Mkh1 localization to cell tips through its interaction with the SH3 domain. Consistent with this, the Mkh13PA mutant protein, with impaired Skb5 binding, remained in the cell tips, even when Skb5 was overproduced. Intriguingly, Skb5 needs Mkh1 to localize to the growing ends as Mkh1 deletion and disruption of Mkh1 binding impairs Skb5 localization. Deletion of Pck2, an upstream activator of Mkh1, impaired the cell tip localization of Mkh1 and Skb5 as well as the Mkh1-Skb5 interaction. Interestingly, both Pck2 and Mkh1 localized to the cell tips at the G1/S phase, which coincided with Pmk1 MAPK activation. Taken together, Mkh1 localization to cell tips is important for transmitting upstream signaling to Pmk1, and Skb5 spatially regulates this process.

The mitogen-activated protein kinase (MAPK) cascade is a highly conserved signaling module composed of MAPK kinase kinases (MAPKKKs), MAPK kinases (MAPKK) and MAPKs. The MAPKKK Mkh1 is an initiating kinase in Pmk1 MAPK signaling, which regulates cell integrity in fission yeast (Schizosaccharomyces pombe). Our genetic screen for regulators of Pmk1 signaling identified Shk1 kinase binding protein 5 (Skb5), an SH3-domain-containing adaptor protein. Here, we show that Skb5 serves as an inhibitor of Pmk1 MAPK signaling activation by downregulating Mkh1 localization to cell tips through its interaction with the SH3 domain. Consistent with this, the Mkh13PA mutant protein, with impaired Skb5 binding, remained in the cell tips, even when Skb5 was overproduced. Intriguingly, Skb5 needs Mkh1 to localize to the growing ends as Mkh1 deletion and disruption of Mkh1 binding impairs Skb5 localization. Deletion of Pck2, an upstream activator of Mkh1, impaired the cell tip localization of Mkh1 and Skb5 as well as the Mkh1-Skb5 interaction. Interestingly, both Pck2 and Mkh1 localized to the cell tips at the G1/S phase, which coincided with Pmk1 MAPK activation. Taken together, Mkh1 localization to cell tips is important for transmitting upstream signaling to Pmk1, and Skb5 spatially regulates this process.

PKN, a conserved family member related to PKC, was the first protein kinase identified as a target of the small GTPase Rho. PKN is involved in various functions including cytoskeletal arrangement and cell adhesion. Furthermore, the enrichment of PKN3 mRNA in some cancer cell lines as well as its requirement in malignant prostate cell growth suggested its involvement in oncogenesis. Despite intensive research efforts, physiological as well as pathological roles of PKN3 in vivo remain elusive. Here, we generated mice with a targeted deletion of PKN3. The PKN3 knockout (KO) mice are viable and develop normally. However, the absence of PKN3 had an impact on angiogenesis as evidenced by marked suppressions of micro-vessel sprouting in ex vivo aortic ring assay and in vivo corneal pocket assay. Furthermore, the PKN3 KO mice exhibited an impaired lung metastasis of melanoma cells when administered from the tail vein. Importantly, PKN3 knock-down by small interfering RNA (siRNA) induced a glycosylation defect of cell-surface glycoproteins, including ICAM-1, integrin beta 1 and integrin a5 in HUVECs. Our data provide the first in vivo genetic demonstration that PKN3 plays critical roles in angiogenesis and tumor metastasis, and that defective maturation of cell surface glycoproteins might underlie these phenotypes.

Five homologs of a novel glycolipid acremomannolipin A (1a), the potential Ca2+ signal modulator isolated from Acremonium strictum, bearing alditols of different length (1g-1k) were synthesized by a stereoselective beta-mannosylation of appropriately protected mannosyl sulfoxide (2) with five alditols (1g: C2, 1h: C3, 1i: C4, 1j: C5 and 1k: C7 units), and their potential in modulating Ca2+ signaling were evaluated. Homologs with alditols of more than 4 carbons (1i, 1j and 1k) were equally or more potent than the parent compound (1a) regardless of the length of the alditol chain. Whereas activities of two homologs with shorter chains (1g and 1h) decreased to a considerable extent. The results indicated that the length of the alditol side chain was a crucial determinant for the potent calcium signal modulating activity. (C) 2015 Elsevier Ltd. All rights reserved.

Pmk1, a fission yeast homologue of mammalian ERK MAPK, regulates cell wall integrity, cytokinesis, RNA granule formation and ion homeostasis. Our screen for vic (viable in the presence of immunosuppressant and chloride ion) mutants identified regulators of the Pmk1 MAPK signaling, including Cpp1 and Rho2, based on the genetic interaction between calcineurin and Pmk1 MAPK. Here, we identified the vic2-1 mutants carrying a mis-sense mutation in the cwg2(+) gene encoding a beta subunit of geranylgeranyltransferase I (GGTase I), which participates in the post-translational C-terminal modification of several small GTPases, allowing their targeting to the membrane. Analysis of the vic2-1/cwg2-v2 mutant strain showed that the localization of Rho1, Rho4, Rho5 and Cdc42, both at the plasma and vacuolar membranes, was impaired in the vic2-1/cwg2-v2 mutant cells. In addition, Rho4 and Rho5 deletion cells exhibited the vic phenotype and cell wall integrity defects, shared phenotypes among the components of the Pmk1 MAPK pathway. Consistently, the phosphorylation of Pmk1 MAPK on heat shock was decreased in the cwg2-v2 mutants, and rho4- and rho5-null cells. Moreover, Rho4 and Rho5 associate with Pck1/Pck2. Possible roles of Cwg2, Rho4 and Rho5 in the Pmk1 signaling will be discussed.

Rapamycin and its derivatives have now emerged as an attractive therapeutic strategy with both immunosuppressant and antitumor properties. In addition, rapamycin has been proposed as a calorie restriction mimetic to extend the life span of various organisms. The fission yeast Schizosaccharomyces pombe (S.pombe) serves as a valuable genetic model system to study the mechanism(s) of drug action as well as to determine genetic contexts associated with drug sensitivity or resistance. Here, we identified genes that when deleted modulate the rapamycin-sensitive strains in S.pombe. We carried out a chemical genomics screen for rapamycin-sensitive mutants using the genome-deletion library which covers 95.3% of all nonessential fission yeast genes and confirmed 59 genes to be rapamycin sensitive. Gene Ontology (GO) enrichment analysis showed that strains sensitive to rapamycin are highly enriched in processes regulating tRNA modification and mitochondria as well as other ontologies, including cellular metabolic process, chromatin organization, cell cycle, signaling, translation, transport and other cellular processes. Analysis also showed that components of the Elongator complex are overrepresented in the sensitive strains. Here, the data obtained will provide valuable information for speculation on the actions of rapamycin as well as on TORC signaling, thereby presenting a strategy to enhance sensitivity to rapamycin.

In fission yeast, Ppb1, the Ca2+/calmodulin-dependent protein phosphatase calcineurin regulates multiple biological processes, such as cytokinesis, Ca2+-homeostasis, membrane trafficking and cell wall integrity. Calcineurin dephosphorylates the Prz1 transcription factor, leading to its nuclear translocation and gene expression under the control of CDRE (calcineurin-dependent response element). Although the calcineurin-mediated spatial control of downstream transcription factors has been intensively studied in many organisms, less is known about the spatial regulation of calcineurin on stresses. Here, we show that heat shock stimulates calcineurin-dependent nuclear translocation of Prz1 and CDRE-dependent gene expression. Notably, calcineurin exhibited a dramatic change in subcellular localization, translocating from diffuse cytoplasmic to dot-like structures on heat shock. The calcineurin dots colocalized with Dcp2 or Pabp, the constituent of P-bodies or stress granules, respectively, thus suggesting that calcineurin is a component of RNA granules under heat shock. Importantly, the calcineurin inhibitor FK506 markedly inhibited the accumulation of calcineurin granules, whereas the constitutively active calcineurin strongly accumulated in the granules on heat shock, suggesting that phosphatase activity is important for calcineurin localization. Notably, the depletion of calcineurin induced a rapid appearance of Nrd1- and Pabp-positive RNA granules. The possible roles of calcineurin in response to heat shock will be discussed.

In fission yeast, Ppb1, the Ca2+/calmodulin-dependent protein phosphatase calcineurin regulates multiple biological processes, such as cytokinesis, Ca2+-homeostasis, membrane trafficking and cell wall integrity. Calcineurin dephosphorylates the Prz1 transcription factor, leading to its nuclear translocation and gene expression under the control of CDRE (calcineurin-dependent response element). Although the calcineurin-mediated spatial control of downstream transcription factors has been intensively studied in many organisms, less is known about the spatial regulation of calcineurin on stresses. Here, we show that heat shock stimulates calcineurin-dependent nuclear translocation of Prz1 and CDRE-dependent gene expression. Notably, calcineurin exhibited a dramatic change in subcellular localization, translocating from diffuse cytoplasmic to dot-like structures on heat shock. The calcineurin dots colocalized with Dcp2 or Pabp, the constituent of P-bodies or stress granules, respectively, thus suggesting that calcineurin is a component of RNA granules under heat shock. Importantly, the calcineurin inhibitor FK506 markedly inhibited the accumulation of calcineurin granules, whereas the constitutively active calcineurin strongly accumulated in the granules on heat shock, suggesting that phosphatase activity is important for calcineurin localization. Notably, the depletion of calcineurin induced a rapid appearance of Nrd1- and Pabp-positive RNA granules. The possible roles of calcineurin in response to heat shock will be discussed.

Cytokinesis is a highly ordered process that divides one cell into two cells, which is functionally linked to the dynamic remodeling of the plasma membrane coordinately with various events such as membrane trafficking. Calcineurin is a highly conserved serine/threonine protein phosphatase, which regulates multiple biological functions, such as membrane trafficking and cytokinesis. Here, we isolated imp2-c3, a mutant allele of the imp2(+) gene, encoding a homolog of the mouse PSTPIP1 (proline-serine-threonine phosphatase interacting protein 1), using a genetic screen for mutations that are synthetically lethal with calcineurin deletion in fission yeast. The imp2-c3 mutants showed a defect in cytokinesis with multi-septated phenotypes, which was further enhanced upon treatment with the calcineurin inhibitor FK506. Notably, electron micrographs revealed that the imp2-c3 mutant cells accumulated aberrant multi-lamella Golgi structures and putative post-Golgi secretory vesicles, and exhibited fragmented vacuoles in addition to thickened septa. Consistently, imp2-c3 mutants showed a reduced secretion of acid phosphatase and defects in vacuole fusion. The imp2-c3 mutant cells exhibited a weakened cell wall, similar to the membrane trafficking mutants identified in the same genetic screen such as ypt3-i5. These findings implicate the PSTPIP1 homolog Imp2 in Golgi/vacuole function, thereby affecting various cellular processes, including cytokinesis and cell integrity. (C) 2015 Elsevier Inc. All rights reserved.

Aim: The aim of this study was to identify the age and sex-specific reference ranges for the non-highdensity lipoprotein cholesterol (non-HDLC) levels in Japanese children. Methods: The subjects included 441,431 schoolchildren (207,015 boys, 234,416 girls) 9-16 years of age who participated in a screening and care program for lifestyle-related diseases from 2006 to 2011. The serum total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and triglyceride (TG) levels were measured, and the non-HDL-C levels were calculated. The serum lipid levels were analyzed according to age and sex. Results: The overall mean non-HDL-C level was 105.7 +/- 24.0 mg/dL, with a sex difference: boys 103.0 +/- 24.0 mg/dL and girls 108.2 +/- 23.8 mg/dL. In boys, the median non-HDL-C level decreased gradually from 104 mg/dL in the 9-year-old age group to 96 mg/dL in the 15-year-old age group. The 75th percentile level was approximately 120 mg/dL in the 9- to 11-year-old groups and decreased at approximately 113 mg/dL in the 12- to 15-year-old groups, whereas the 95th percentile level was approximately 150 mg/dL in the 9- to 11-year-old groups and decreased at approximately 140 mg/dL in the 13- to 15-year-old groups. In girls, the median non-HDL-C level remained unchanged at approximately 105 mg/dL, with 75th and 95th percentile levels of approximately 122 and 150 mg/dL, respectively. Conclusions: The non-HDL-C levels vary by age and sex. The age-and sex-specific reference ranges for the non-HDL-C levels may be a valuable tool for management with respect to preventing the development of atherosclerosis in childhood.

Fingolimod hydrochloride (FTY720) is the first-in-class immune modulator known as sphingosine 1-phosphate (S1P) receptor agonists. FTY720 has also been reported to exert a variety of physiological functions such as antitumor effect, angiogenesis inhibition, and Ca2+ mobilization. Here, we show that FTY720 treatment induced reactive oxygen species (ROS) accumulation, and investigated the effect of FTY720 on the stress-activated MAP kinaseSpc1/Sty1, a functional homologue of p38 MAPK, using a Renilla luciferase reporter construct fused to the CRE, which gives an accurate measure of the transcriptional activity of Atf1 and thus serves as a faithful readout of the Spc1/Sty1 MAPK signaling in response to oxidative stresses. FTY720 stimulated the CRE responses in a concentration-dependent manner, which was markedly reduced by deletion of the components of the Spc1/Sty1 MAPK pathway. The blockade of ROS production by NAC (N-acetyl-l-cysteine) significantly reversed the FTY720-induced ROS accumulation, subsequent activation of the Spc1/Sty1 MAPK pathway, and inhibition of cell proliferation. Cells lacking the components of the Spc1/Sty1 MAPK exhibited higher sensitivity to FTY720 and higher ROS levels upon FTY720 treatment than in wild-type cells. Thus, our results demonstrate the usefulness of fission yeast for elucidating the FTY720-mediated signaling pathways involving ROS.

Fission yeast its3(+) encodes an essential phosphatidylinositol-4-phosphate 5-kinase (PI4P5K) that regulates cell integrity and cytokinesis. We performed a genetic screen to identify genes that function in PI4P5K-mediated signaling, and identified gyp10(+) encoding a Rab GTPase-activating protein (GAP), a negative regulator for Rab GTPase signaling. Its3 overproduction caused growth defects and abnormal cytoplasmic accumulation of the Its3 protein, which can be stained by calcofluor. Notably, Its3 overproducing cells displayed abnormal membranous structures, multilamella Golgi and fragmented vacuoles showed by Electron microscopy. Furthermore, the excess cytoplasmic Its3 structure partly colocalized with the fluorescence of FM4-64. Gyp10 rescued both growth defects and abnormal Its3 localization when it was over-expressed. Gyp10 functionally interacted with the Rab GTPases Ypt3 and Ryh1, both of which regulate Golgi membrane trafficking. Consistently, mutation or deletion of Ypt3 and Ryh1 suppressed phenotypes associated with Its3 overproduction. Importantly, the plasma membrane localization of Its3 was also affected by the impairment of the Ypt3/Ryh1 Rab membrane trafficking, thus suggesting that membrane trafficking events regulated by two Rab GTPases functionally interacts with PI4,5P(2) signaling. These results suggest a mechanism whereby PI4P5K signaling/localization is affected by Golgi membrane trafficking, thus provide a functional link between the PI4,5P(2) signaling and Rab-mediated trafficking.

Five alditol analogs 1b-1f of a novel glycolipid acremomannolipin A (1a), the potential Ca2+ signal modulator isolated from Acremonium strictum, were synthesized by employing a stereoselective beta-mannosylation of appropriately protected mannose with five hexitols with different stereochemistry, and their potential on modulating Ca2+ signaling were evaluated. All these analogs were more potent compared to the original compound 1a, and proved that mannitol stereochemistry of 1a was not critical for the potent calcium signal modulating. (C) 2014 Elsevier Ltd. All rights reserved.

Fingolimod hydrochloride (FTY720) is the first-in-class immune modulator known as sphingosine 1-phosphate (S1P) receptor agonists. FTY720 has also been reported to exert a variety of physiological functions such as antitumor effect, angiogenesis inhibition, and Ca2+ mobilization. Here, we show that FTY720 treatment induced reactive oxygen species (ROS) accumulation, and investigated the effect of FTY720 on the stress-activated MAP kinase Spc1/Sty1, a functional homologue of p38 MAPK, using a Renilla luciferase reporter construct fused to the CRE, which gives an accurate measure of the transcriptional activity of Atf1 and thus serves as a faithful readout of the Spc1/Sty1 MAPK signaling in response to oxidative stresses. FTY720 stimulated the CRE responses in a concentration-dependent manner, which was markedly reduced by deletion of the components of the Spc1/Sty1 MAPK pathway. The blockade of ROS production by NAC (N-acetyl-l-cysteine) significantly reversed the FTY720-induced ROS accumulation, subsequent activation of the Spc1/Sty1 MAPK pathway, and inhibition of cell proliferation. Cells lacking the components of the Spc1/Sty1 MAPK exhibited higher sensitivity to FTY720 and higher ROS levels upon FTY720 treatment than in wild-type cells. Thus, our results demonstrate the usefulness of fission yeast for elucidating the FTY720-mediated signaling pathways involving ROS. © 2014 by the Molecular Biology Society of Japan and Wiley Publishing Asia Pty Ltd.

Calcium signals trigger the translocation of the Prz1 transcription factor from the cytoplasm to the nucleus. The process is regulated by the calcium-activated phosphatase calcineurin, which activates Prz1 thereby maintaining active transcription during calcium signalling. When calcium signalling ceases, Prz1 is inactivated by phosphorylation and exported to the cytoplasm. In budding yeast and mammalian cells, different kinases have been reported to counter calcineurin activity and regulate nuclear export. Here, we show that the Ca2+/calmodulin-dependent kinase Cmk1 is first phosphorylated and activated by the newly identified kinase CaMKK2 homologue, Ckk2, in response to Ca2+. Then, active Cmk1 binds, phosphorylates and inactivates Prz1 transcription activity whilst at the same time cmk1 expression is enhanced by Prz1 in response to Ca2+. Furthermore, Cdc25 phosphatase is also phosphorylated by Cmk1, inducing cell cycle arrest in response to an increase in Ca2+. Moreover, cmk1 deletion shows a high tolerance to chronic exposure to Ca2+, due to the lack of cell cycle inhibition and elevated Prz1 activity. This work reveals that Cmk1 kinase activated by the newly identified Ckk2 counteracts calcineurin function by negatively regulating Prz1 activity which in turn is involved in activating cmk1 gene transcription. These results are the first insights into Cmk1 and Ckk2 function in Schizosaccharomyces pombe.

Fingolimod hydrochloride (FTY720) is the first in class of sphingosine 1-phosphate (S1P) receptor modulator approved to treat multiple sclerosis via down-regulation of G protein-coupled S1P receptor 1 by its phosphorylated form (FTY720-P). Many studies have revealed that FTY720 exerts various biological effects, including antitumor activities, angiogenesis inhibition, Ca 2+ mobilization and apoptosis, independently of S1P receptors. However, the exact mechanisms underlying their effects or signaling pathways mediated by FTY720 have not been completely established. To gain further insights into molecular mechanisms of FTY720 action, the effect of FTY720 on Ca2+ signaling in fission yeast was analyzed. The addition of Ca 2+ enhanced the sensitivity induced by FTY720, and mutants lacking genes required for calcium homeostasis, including calcineurin and its downstream transcription factor, Ppb1-responsive zinc finger protein (Prz1), were hypersensitive to FTY720 and CaCl2. The effect of FTY720 on calcineurin signaling was monitored by utilizing a luciferase reporter construct fused to three tandem repeats of the calcineurin-dependent response element (CDRE), which gives an accurate measure of calcineurin activity. The addition of FTY720 increased calcineurin activity as well as Ca2+ influx in a concentration-dependent manner. Notably, the FTY720-mediated Ca2+ influx and calcineurin activation were reduced markedly by the deletion of yam8+ or cch1+ encoding putative subunits of a Ca 2+ channel. Consistently, the deletion of Pmk1 mitogen-activated protein kinase (MAPK), which plays an important role in the activation of the Yam8/Cch1 channel, markedly decreased the intracellular Ca2+ levels upon FTY720 treatment. These results suggest that the FTY720-stimulated Ca 2+/calcineurin signaling activation partly involves the Yam8/Cch1 channel in fission yeast. © 2013 Hagihara et al.

A full account of stereoselective total synthesis of a novel glycolipid, acremomannolipin A (1), the potent calcium signal modulator isolated from Acremonium strictum, by employing the stereoselective beta-mannosylation of 4,6-O-benzylidene-protected mannosyl sulfoxide with D-mannitol as the key reaction is described. The alpha-anomer (epi-1) of 1 was also synthesized selectively. The calcium modulating activity was reduced upon inversion of the configuration at the anomeric center, indicating that the beta-configuration of the mannose moiety is preferable for the activity. (C) 2013 Elsevier Ltd. All rights reserved.

Negative regulator of differentiation 1 (Nrd1) is known as a negative regulator of sexual differentiation in fission yeast. Recently, it has been revealed that Nrd1 also regulates cytokinesis, in which physical separation of the cell is achieved by a contractile ring comprising many proteins including actin and myosin. Cdc4, a myosin II light chain, is known to be required for cytokinesis. Nrd1 binds and stabilizes Cdc4 mRNA, and thereby suppressing the cytokinesis defects of the cdc4 mutants. Interestingly, Pmk1 MAPK phosphorylates Nrd1, resulting in markedly reduced RNA binding activity. Furthermore, Nrd1 localizes to stress granules in response to various stresses, and Pmk1 phosphorylation enhances the localization. Nrd1 consists of four RRM domains, although the mechanism by which Pmk1 regulates the RNA binding activity of Nrd1 is unknown. In an effort to delineate the relationship between Nrd1 structure and function, we prepared each RNA binding domain of Nrd1 and examined RNA binding to chemically synthesized oligo RNA using NMR. The structure of the second RRM domain of Nrd1 was determined and the RNA binding site on the second RRM domain was mapped by NMR. A plausible mechanism pertaining to the regulation of RNA binding activity by phosphorylation is also discussed. (c) 2013 Elsevier Inc. All rights reserved.

Rho family GTPases act as molecular switches to regulate a range of physiological functions, including the regulation of the actin-based cytoskeleton, membrane trafficking, cell morphology, nuclear gene expression, and cell growth. Rho function is regulated by its ability to bind GTP and by its localization. We previously demonstrated functional and physical interactions between Rho3 and the clathrin-associated adaptor protein-1 (AP-1) complex, which revealed a role of Rho3 in regulating Golgi/endosomal trafficking in fission yeast. Sip1, a conserved AP-1 accessory protein, recruits the AP-1 complex to the Golgi/endosomes through physical interaction. In this study, we showed that Sip1 is required for Rho3 localization. First, overexpression of rho3(+) suppressed defective membrane trafficking associated with sip1-i4 mutant cells, including defects in vacuolar fusion, Golgi/endosomal trafficking and secretion. Notably, Sip1 interacted with Rho3, and GFP-Rho3, similar to Apm1-GFP, did not properly localize to the Golgi/endosomes in sip1-i4 mutant cells at 27 degrees C. Interestingly, the C-terminal region of Sip1 is required for its localization to the Golgi/endosomes, because Sip1-i4-GFP protein failed to properly localize to Golgi/endosomes, whereas the fluorescence of Sip1 Delta N mutant protein co-localized with that of FM4-64. Consistently, in the sip1-i4 mutant cells, which lack the C-terminal region of Sip1, binding between Apm1 and Rho3 was greatly impaired, presumably due to mislocalization of these proteins in the sip1-i4 mutant cells. Furthermore, the interaction between Apm1 and Rho3 as well as Rho3 localization to the Golgi/endosomes were significantly rescued in sip1-i4 mutant cells by the expression of Sip1 Delta N. Taken together, these results suggest that Sip1 recruits Rho3 to the Golgi/endosomes through physical interaction and enhances the formation of the Golgi/endosome AP-1/Rho3 complex, thereby promoting crosstalk between AP-1 and Rho3 in the regulation of Golgi/endosomal trafficking in fission yeast.

実験用ゴム栓1は通常のバイアル用ゴム栓(対照)の脚部に厚さ2mmのシリコンゴムを貼付し、実験用ゴム栓2はブチルゴムで作製し、上下2片を嵌合させて用いた。平均漏液量は対照用ゴム栓で8.2μL、実験用ゴム栓1で1.8μLと1/5に減少した。検体数を9とした場合の平均漏液量は対照用ゴム栓で16.7μL、実験用ゴム栓2で1.0μLと1/17に減少した。次いで実験用ゴム栓2の嵌合部空間にウレタン系連泡スポンジの吸収体を入れた場合、平均漏液量は0.3μLと更に減少した。吸収体を入れた実験用ゴム栓2を装着したバイアルを用い、注射針の抜針途中でバイアルを反転正立させ、その後に抜針する方法では、全ての検体で漏液量は検出限界以下であった。今回開発した二重底構造のゴム栓は漏液防止効果を有し、無菌性や異物排除などの条件を満たし、工場出荷時に本ゴム栓が装着されれば、医療従事者は従来のゴム栓と同じ要領で操作可能と考えられた。

The first total synthesis of acremomannolipin A, the potential Ca2+ signal modulator isolated from Acremonium strictum, was achieved by employing the characteristic stereoselective beta-mannosylation of 4,6-O-benzylidene-protected mannosyl sulfoxide with a D-mannitol derivative in the presence of trifluoromethanesulfonic anhydride as the key reaction. (C) 2012 Elsevier Ltd. All rights reserved.

By the newly developed assay method, the glycolipid Acremomannolipin A (1) was isolated from a filamentous fungus Acremonium strictum as a potential calcium signal modulator. The structure of 1 elucidated on the basis of intensive spectroscopic analyses as well as its degradation studies is quite unique: the d-mannopyranose is connected to d-mannitol through a β-glycoside linkage all the hydroxyls in the mannose are highly masked as peresters with aliphatic acids, and this moiety is made hydrophobic, whereas the mannitol part exhibits a highly hydrophilic property. The compound (1) showed the characteristic bioactivity property, enabling calcineurin deletion cells to grow in the presence of Cl-, which would be caused by calcium signal modulating. The activity was so potent as to exert the effect at a concentration of 200 nM. © 2012 Elsevier Ltd. All rights reserved.

By the newly developed assay method, the glycolipid Acremomannolipin A (1) was isolated from a filamentous fungus Acremonium strictum as a potential calcium signal modulator. The structure of 1 elucidated on the basis of intensive spectroscopic analyses as well as its degradation studies is quite unique: the D-mannopyranose is connected to D-mannitol through a beta-glycoside linkage; all the hydroxyls in the mannose are highly masked as peresters with aliphatic acids, and this moiety is made hydrophobic, whereas the mannitol part exhibits a highly hydrophilic property. The compound (1) showed the characteristic bioactivity property, enabling calcineurin deletion cells to grow in the presence of Cl-, which would be caused by calcium signal modulating. The activity was so potent as to exert the effect at a concentration of 200 nM. (C) 2012 Elsevier Ltd. All rights reserved.

We had previously identified the mutant allele of apm1(+) that encodes a homolog of the mammalian mu 1A subunit of the clathrin-associated adaptor protein-1 (AP-1) complex and demonstrated that the AP-1 complex plays a role in Golgi/endosome trafficking, secretion, and vacuole fusion in fission yeast. Here, we isolated a mutant allele of its4(+)/sip1(+), which encodes a conserved AP-1 accessory protein. The its4-1/sip1-i4 mutants and apm1-deletion cells exhibited similar phenotypes, including sensitivity to the calcineurin inhibitor FK506, Cl- and valproic acid as well as various defects in Golgi/endosomal trafficking and cytokinesis. Electron micrographs of sip1-i4 mutants revealed vacuole fragmentation and accumulation of abnormal Golgi-like structures and secretory vesicles. Overexpression of Apm1 suppressed defective membrane trafficking in sip1-i4 mutants. The Sip1-green fluorescent protein (GFP) co-localized with Apm1-mCherry at Golgi/endosomes, and Sip1 physically interacted with each subunit of the AP-1 complex. We found that Sip1 was a Golgi/endosomal protein and the sip1-i4 mutation affected AP-1 localization at Golgi/endosomes, thus indicating that Sip1 recruited the AP-1 complex to endosomal membranes by physically interacting with each subunit of this complex. Furthermore, Sip1 is required for the correct localization of Bgs1/Cps1, 1,3-beta-D-glucan synthase to polarized growth sites. Consistently, the sip1-i4 mutants displayed a severe sensitivity to micafungin, a potent inhibitor of 1,3-beta-D-glucan synthase. Taken together, our findings reveal a role for Sip1 in the regulation of Golgi/endosome trafficking in coordination with the AP-1 complex, and identified Bgs1, required for cell wall synthesis, as the new cargo of AP-1-dependent trafficking.

We previously identified Cis4, a zinc transporter belonging to the cation diffusion facilitator protein family, and we demonstrated that Cis4 is implicated in Golgi membrane trafficking in fission yeast. Here, we identified three glycosylphosphatidylinositol (GPI)-anchored proteins, namely Ecm33, Aah3, and Gaz2, as multicopy suppressors of the MgCl2-sensitive phenotype of cis4-1 mutant. The phenotypes of ecm33, aah3 and gaz2 deletion cells were distinct from each other, and Cis4 overexpression suppressed Delta ecm33 phenotypes but did not suppress Delta aah3 defects. Notably, green fluorescent protein-tagged Ecm33, which was observed at the cell surface in wild-type cells, mostly localized as intracellular dots that are presumed to be the Golgi and endosomes in membrane-trafficking mutants, including Delta apm1, ypt3-i5, and chc1-1 mutants. Interestingly, all these membrane-trafficking mutants showed hypersensitivity to BE49385A, an inhibitor of Its8 that is involved in GPI-anchored protein synthesis. Taken together, these results suggest that GPI-anchored proteins are transported through a clathrin-mediated post-Golgi membrane trafficking pathway and that zinc transporter Cis4 may play roles in membrane trafficking of GPI-anchored proteins in fission yeast.

簡便かつ再現性よく、針の穿刺→抜針までの1単位の操作ごとの液漏れ量を測定する方法を確立し、確立した測定法を用いて、注射針の太さおよびベベルの形状と漏液との関連性を定量的に検討した。確立した抽出および測定法を用いて、注射針形状が漏液量に与える影響について調べた。18G RB針からの漏れの平均値は19.7μL、18G SB針からの漏れの平均値は14.4μLであった。22G RB針および22G SB針からの漏れ量の平均値は、それぞれ2.6μLおよび2.5μLと低値であった。18G RBと22G RB、あるいは、18G SBと22G SBとの漏液量の差は有意であった。18G RBからの漏液量は18G SBの値より高値を示したが、両者の間に有意差は認められず、22G RBからの漏液量は22G SBの値とほぼ同等の値を示した。

Calcineurin phosphatase plays crucial roles in a wide variety of cell types and organisms. Dephosphorylation of the nuclear factor of activated T-cell (NFAT) family of transcriptional factors by calcineurin is essential for activating immune-responsive genes in mammals. NFAT activity is also regulated by diverse signaling pathways, which affect NFAT kinases and nuclear partner proteins. In fission yeast, calcineurin dephosphorylates and activates Prz1, a C2H2-type zinc finger transcriptional factor. Calcineurin-Prz1 signaling regulates the expression of the Pmc1 Ca2+ pump. Prz1-overexpressing cells showed extremely slow growth and high transcriptional activity of Prz1 in the absence of stimulation. Here, we isolated seven genes as dosage-dependent suppressors of this slow growth phenotype. These seven genes encode Rad24, Rad25, Pka1, Msn5 (SPAC328.01c), Pac1, Ape2, and Tfs1. All of them decreased the high transcriptional activity caused by Prz1 overexpression. Overexpression of Pka1, Rad24, and Rad25 also repressed the Ca2+-induced transcriptional activity in cells with Prz1 expressed at wild-type levels. Knock-out of rad24 or rad25 significantly enhanced the transcriptional activity of Prz1, whereas knock-out or mutation of other genes did not enhance the activity. The 14-3-3 proteins, Rad24 and Rad25, bound Prz1 and the Rad24-binding site located at residues 421-426 of Prz1. In msn5 deletion mutants, GFP-Prz1 localized at nucleus in the absence of Ca2+ stimulation, suggesting that Msn5 functions as an exportin for Prz1. In summary, our data suggest that Rad24 and Rad25 negatively regulate Prz1 and that Pka1, Msn5, Pac1, Tfs1, and Ape2 also regulate Prz1.

Calcineurin phosphatase plays crucial roles in a wide variety of cell types and organisms. Dephosphorylation of the nuclear factor of activated T-cell (NFAT) family of transcriptional factors by calcineurin is essential for activating immune-responsive genes in mammals. NFAT activity is also regulated by diverse signaling pathways, which affect NFAT kinases and nuclear partner proteins. In fission yeast, calcineurin dephosphorylates and activates Prz1, a C2H2-type zinc finger transcriptional factor. Calcineurin-Prz1 signaling regulates the expression of the Pmc1 Ca2+ pump. Prz1-overexpressing cells showed extremely slow growth and high transcriptional activity of Prz1 in the absence of stimulation. Here, we isolated seven genes as dosage-dependent suppressors of this slow growth phenotype. These seven genes encode Rad24, Rad25, Pka1, Msn5 (SPAC328.01c), Pac1, Ape2, and Tfs1. All of them decreased the high transcriptional activity caused by Prz1 overexpression. Overexpression of Pka1, Rad24, and Rad25 also repressed the Ca2+-induced transcriptional activity in cells with Prz1 expressed at wild-type levels. Knock-out of rad24 or rad25 significantly enhanced the transcriptional activity of Prz1, whereas knock-out or mutation of other genes did not enhance the activity. The 14-3-3 proteins, Rad24 and Rad25, bound Prz1 and the Rad24-binding site located at residues 421-426 of Prz1. In msn5 deletion mutants, GFP-Prz1 localized at nucleus in the absence of Ca2+ stimulation, suggesting that Msn5 functions as an exportin for Prz1. In summary, our data suggest that Rad24 and Rad25 negatively regulate Prz1 and that Pka1, Msn5, Pac1, Tfs1, and Ape2 also regulate Prz1.

We have previously identified the RNA recognition motif (RRM)-type RNA-binding protein Nrd1 as an important regulator of the posttranscriptional expression of myosin in fission yeast. Pmk1 MAPK-dependent phosphorylation negatively regulates the RNA-binding activity of Nrd1. Here, we report the role of Nrd1 in stress-induced RNA granules. Nrd1 can localize to poly(A)-binding protein (Pabp)-positive RNA granules in response to various stress stimuli, including heat shock, arsenite treatment, and oxidative stress. Interestingly, compared with the unphosphorylatable Nrd1, Nrd1(DD) (phosphorylation-mimic version of Nrd1) translocates more quickly from the cytoplasm to the stress granules in response to various stimuli; this suggests that the phosphorylation of Nrd1 by MAPK enhances its localization to stress-induced cytoplasmic granules. Nrd1 binds to Cpc2 (fission yeast RACK) in a phosphorylation-dependent manner and deletion of Cpc2 affects the formation of Nrd1-positive granules upon arsenite treatment. Moreover, the depletion of Nrd1 leads to a delay in Pabp-positive RNA granule formation, and overexpression of Nrd1 results in an increased size and number of Pabp-positive granules. Interestingly, Nrd1 deletion induced resistance to sustained stresses and enhanced sensitivity to transient stresses. In conclusion, our results indicate that Nrd1 plays a role in stress-induced granule formation, which affects stress resistance in fission yeast.

We have previously identified the RNA recognition motif (RRM)-type RNA-binding protein Nrd1 as an important regulator of the posttranscriptional expression of myosin in fission yeast. Pmk1 MAPK-dependent phosphorylation negatively regulates the RNA-binding activity of Nrd1. Here, we report the role of Nrd1 in stress-induced RNA granules. Nrd1 can localize to poly(A)-binding protein (Pabp)-positive RNA granules in response to various stress stimuli, including heat shock, arsenite treatment, and oxidative stress. Interestingly, compared with the unphosphorylatable Nrd1, Nrd1(DD) (phosphorylation-mimic version of Nrd1) translocates more quickly from the cytoplasm to the stress granules in response to various stimuli; this suggests that the phosphorylation of Nrd1 by MAPK enhances its localization to stress-induced cytoplasmic granules. Nrd1 binds to Cpc2 (fission yeast RACK) in a phosphorylation-dependent manner and deletion of Cpc2 affects the formation of Nrd1-positive granules upon arsenite treatment. Moreover, the depletion of Nrd1 leads to a delay in Pabp-positive RNA granule formation, and overexpression of Nrd1 results in an increased size and number of Pabp-positive granules. Interestingly, Nrd1 deletion induced resistance to sustained stresses and enhanced sensitivity to transient stresses. In conclusion, our results indicate that Nrd1 plays a role in stress-induced granule formation, which affects stress resistance in fission yeast.

Doxorubicin is an anthracycline antibiotic widely used for chemotherapy. Although doxorubicin is effective in the treatment of several cancers, including solid tumors and leukemias, the basis of its mechanism of action is not completely understood. Here, we describe the effects of doxorubicin and its relationship with stress granules formation in the fission yeast, Schizosaccharomyces pombe. We show that disruption of genes encoding the components of stress granules, including vgl1(+), which encodes a multi-KH type RNA-binding protein, and pab1(+), which encodes a poly(A)-binding protein, resulted in greater sensitivity to doxorubicin than seen in wild-type cells. Disruption of the vgl1(+) and pab1(+) genes did not confer sensitivity to other anti-cancer drugs such as cisplatin, 5-fluorouracil, and paclitaxel. We also showed that doxorubicin treatment promoted stress granule formation when combined with heat shock. Notably, doxorubicin treatment did not induce hyperphosphorylation of eIF2 alpha, suggesting that doxorubicin is involved in stress granule assembly independent of eIF2 alpha( phosphorylation. Our results demonstrate the usefulness of fission yeast for elucidating the molecular targets of doxorubicin toxicity and suggest a novel drug-resistance mechanism involving stress granule assembly. (C) 2011 Elsevier Inc. All rights reserved.

The regulation of cytoplasmic Ca2+ is crucial for various cellular processes. Here, we examined the cytoplasmic Ca2+ levels in living fission yeast cells by a highly sensitive bioluminescence resonance energy transfer-based assay using GFP-aequorin fusion protein linked by 19 amino acid. We monitored the cytoplasmic Ca2+ level and its change caused by extracellular stimulants such as CaCl2 or NaCl plus FK506 (calcineurin inhibitor). We found that the extracellularly added Ca2+ caused a dose-dependent increase in the cytoplasmic Ca2+ level and resulted in a burst-like peak. The overexpression of two transient receptor potential (TRP) channel homologues, Trp1322 or Pkd2, markedly enhanced this response. Interestingly, the burst-like peak upon TRP overexpression was completely abolished by gene deletion of calcineurin and was dramatically decreased by gene deletion of Prz1, a downstream transcription factor activated by calcineurin. Furthermore, 1 hour treatment with FK506 failed to suppress the burst-like peak. These results suggest that the burst-like Ca2+ peak is dependent on the transcriptional activity of Prz1, but not on the direct TRP dephosphorylation. We also found that extracellularly added NaCl plus FK506 caused a synergistic cytosolic Ca2+ increase that is dependent on the inhibition of calcineurin activity, but not on the inhibition of Prz1. The synergistic Ca2+ increase is abolished by the addition of the Ca2+ chelator BAPTA into the media, and is also abolished by deletion of the gene encoding a subunit of the Cch1-Yam8 Ca2+ channel complex, indicating that the synergistic increase is caused by the Ca2+ influx from the extracellular medium via the Cch1-Yam8 complex. Furthermore, deletion of Pmk1 MAPK abolished the Ca2+ influx, and overexpression of the constitutively active Pek1 MAPKK enhanced the influx. These results suggest that Pmk1 MAPK and calcineurin positively and negatively regulate the Cch1-Yam8 complex, respectively, via modulating the balance between phosphorylation and dyphosphorylation state.

Mitogen-activated protein kinases (MAPKs), which are found in all eukaryotes, are signal transducing enzymes playing a central role in diverse biological processes, such as cell proliferation, sexual differentiation, and apoptosis. The MAPK signaling pathway plays a key role in the regulation of gene expression through the phosphorylation of transcription factors. Recent studies have identified several RNA-binding proteins (RBPs) as regulators of MAPK signaling because these RBPs bind to the mRNAs encoding the components of the MAPK pathway and regulate the stability of their transcripts. Moreover, RBPs also serve as targets of MAPKs because MAPK phosphorylate and regulate the ability of RBPs to bind and stabilize target mRNAs, thus controlling various cellular functions. In this review, we present evidence for the significance of the MAPK signaling in the regulation of RBPs and their target mRNAs, which provides additional information about the regulatory mechanism underlying gene expression. We further present evidence for the clinical importance of the posttranscriptional regulation of mRNA stability and its implications for drug discovery.

Background: We had previously identified the mutant allele of apm1(+) that encodes a homolog of the mammalian mu 1A subunit of the clathrin-associated adaptor protein-1 (AP-1) complex, and we demonstrated the role of Apm1 in Golgi/endosome trafficking, secretion, and vacuole fusion in fission yeast. Methodology/Principal Findings: In the present study, we isolated rho3+, which encodes a Rho-family small GTPase, an important regulator of exocystosis, as a multicopy-suppressor of the temperature-sensitive growth of the apm1-1 mutant cells. Overexpression of Rho3 suppressed the Cl- sensitivity and immunosuppressant sensitivity of the apm1-1 mutant cells. Overexpression of Rho3 also suppressed the fragmentation of vacuoles, and the accumulation of v-SNARE Syb1 in Golgi/endosomes and partially suppressed the defective secretion associated with apm1-deletion cells. Notably, electron microscopic observation of the rho3-deletion cells revealed the accumulation of abnormal Golgi-like structures, vacuole fragmentation, and accumulation of secretory vesicles; these phenotypes were very similar to those of the apm1-deletion cells. Furthermore, the rho3-deletion cells and apm1-deletion cells showed very similar phenotypic characteristics, including the sensitivity to the immunosuppressant FK506, the cell wall-damaging agent micafungin, Cl-, and valproic acid. Green fluorescent protein (GFP)-Rho3 was localized at Golgi/endosomes as well as the plasma membrane and division site. Finally, Rho3 was shown to form a complex with Apm1 as well as with other subunits of the clathrin-associated AP-1 complex in a GTP- and effector domain-dependent manner. Conclusions/Significance: Taken together, our findings reveal a novel role of Rho3 in the regulation of Golgi/endosome trafficking and suggest that clathrin-associated adaptor protein-1 and Rho3 co-ordinate in intracellular transport in fission yeast. To the best of our knowledge, this study provides the first evidence of a direct link between the small GTPase Rho and the clathrin-associated adaptor protein-1 in membrane trafficking.

Deviation of driving behavior from usual could be a sign of human error that increases the risk of traffic accidents. This paper proposes a novel method for predicting the possibility a driving behavior leads to an accident from the information on the driving behavior and the situation. In a previous work, a method of predicting the possibility by detecting the deviation of driving behavior from usual one in that situation has been proposed. In contrast, the method proposed in this paper predicts the possibility by detecting the deviation of the situation from usual one when the behavior is observed. An advantage of the proposed method is the number of the required models is independent of the variety of the situations. The method was applied to a problem of predicting accidents by right-turn driving behavior at an intersection, and the performance of the method was evaluated by experiments on a driving simulator. © 2011 The Institute of Electrical Engineers of Japan.

Personnel who prepare and administer chemotherapeutic agents have been reported to develop untoward effects. The use of appropriate techniques for preparing these agents is encouraged, and educational training systems that involve the use of a fluorescent or chemiluminescence reagent as placebos have been established to minimize potential exposure to these agents. However, the optimum conditions for the use and visibility of these placebos remain obscure. In this study, our results indicated that the fluorescence intensity of fluorescent reagent decreased when it was used at a concentration greater than 0.01%. Because drops created due to splashes and leaks are extremely small and easily evaporate, it is possible that the fluorescence resulting from such drops readily disappears despite using an anti-evaporation reagent. We also developed a method to evaluate the visibility of the small drop using this method, we determined the distance at which the drop present on the pin could be seen by the observer. The distance at which the drop was clearly recognized as a pinpoint by using the fluorescence method was almost comparable to that for the chemiluminescence method. In the chemiluminescence method, the drop on the pin was faintly visible as a slightly bright area because of low background when observed at a certain distance that was much greater than that at which the drop was clearly visible however, such an area was not observed in the fluorescence method. The results of our study will help in the selection of a training method depending on the situation. © 2011 The Pharmaceutical Society of Japan.

The interaction between Rnc1, an RNA interactive protein, and a Pmp1 mRNA was investigated by affinity capillary electrophoresis (ACE). Prior to the ACE experiments, the column performances of three capillaries (an untreated fused silica capillary, a polybrene-polyacrylic acid (PB-PAA) double layer coating capillary, and a carboxylated capillary with a covalent modification) were studied with model proteins including ribonuclease B (RNase B) and bovine serum albumin (BSA) Using an untreated fused silica and a PB-PAA double layer coating capillaries, both of the protein peaks were broad and tailing. However, using a carboxylated capillary, the protein peaks were sharp and symmetric, and migration times were repeatable (RSD < 0 4%) Further, the proteins in human serum also gave sharp peaks and its repeatability was kept at a high level by pre-treatment of a capillary inner wall with 1 M sodium chloride solution before each run. An Rnc1 protein was analyzed by ACE with background electrolytes containing various concentrations of Pmp1 sense mRNA using a carboxylated capillary. Increase in the concentration of the mRNA was found to delay the migration time of the protein. But the migration time of the protein was kept constant with increasing Pmp1 anti-sense mRNA instead of Pmp1 sense mRNA A straight line (r=0.987) was obtained by plotting 1/(migration time shift) versus 1/(Pmp1 sense mRNA concentration) and the association constant of Rnc1 protein with Pmp1 sense mRNA could be estimated to be 4 15 x 10(6) M(-1). These results suggest that the association constants of proteins with mRNAs as ligands were easily determined by the proposed method. (C) 2010 Elsevier B.V. All rights reserved.

In fission yeast, the Sty1/Spc1/Phh1 mitogen-activated protein kinase (MAPK) pathway is known to be involved in multiple-stress responses. It is currently thought that the Sty1 MAPK cascade is mediated by histidine kinases and phosphorelay proteins in response to oxidative stress signals. However, studies of the exact transduction mechanism of multiple-stress responses are lacking. Thus, in response to various stimuli, we monitored the Sty1 MAPK pathway through the downstream transcription factor Atf1 in living cells using a highly sensitive luciferase reporter gene. Surprisingly, in cadmium and low glucose (LG) medium, Atf1 activation was observed even in the absence of all of the four fission yeast MAPK kinase kinases (MAPKKKs); whereas in osmotic stress, Atf1 activation was abolished. Thus, the osmotic stress likely mediates the MAPK activation via MAPKKKs, whereas a cadmium or LG condition activates the MAPKin a MAPKKK-independent manner. On the other hand, knockout of tyrosine phosphatase gene pyp1(+) abolished the Atf1 response to cadmium and LG, but not to osmotic stress, suggesting that Pyp1 is a sensor for cadmium and LG.

In fission yeast, the Sty1/Spc1/Phh1 mitogen-activated protein kinase (MAPK) pathway is known to be involved in multiple-stress responses. It is currently thought that the Sty1 MAPK cascade is mediated by histidine kinases and phosphorelay proteins in response to oxidative stress signals. However, studies of the exact transduction mechanism of multiple-stress responses are lacking. Thus, in response to various stimuli, we monitored the Sty1 MAPK pathway through the downstream transcription factor Atf1 in living cells using a highly sensitive luciferase reporter gene. Surprisingly, in cadmium and low glucose (LG) medium, Atf1 activation was observed even in the absence of all of the four fission yeast MAPK kinase kinases (MAPKKKs); whereas in osmotic stress, Atf1 activation was abolished. Thus, the osmotic stress likely mediates the MAPK activation via MAPKKKs, whereas a cadmium or LG condition activates the MAPKin a MAPKKK-independent manner. On the other hand, knockout of tyrosine phosphatase gene pyp1(+) abolished the Atf1 response to cadmium and LG, but not to osmotic stress, suggesting that Pyp1 is a sensor for cadmium and LG.

Valproic acid (VPA) causes various therapeutic and biological effects, but the exact mechanisms underlying these effects, however, remain elusive. To gain insights into the molecular mechanisms of VPA action, we performed in fission yeast a genetic screen for mutants that show VPA hypersensitivity and have identified several membrane-trafficking mutants including vas1-1/vps45 and vas2-1/aps1. Here, we describe the isolation and characterization of vas3-1/ric1-v3, a mutant allele of the ric1 (+) gene encoding a fission yeast homolog of the budding yeast Ric1p, a component of Ypt/Rab-specific guanyl-nucleotide exchange factor (GEF). The Rab GTPase Ryh1 knockout (Delta ryh1) cells and Delta ric1 cells exhibited similar phenotypes. The double knockout Delta ric1 Delta ryh1 cells did not display synthetic growth defects. These results are consistent with the notion that Ric1 may be a component of the GEF complex for Ryh1. Overexpression of wild-type Ryh1 and the constitutively active Ryh1Q70L only partially suppressed the phenotypes of ric1-v3 and Delta ric1 cells, and they failed to localize to the Golgi/endosomes in ric1-v3 and Delta ric1 cells. Furthermore, we isolated vps15 (+) gene, encoding a serine/threonine protein kinase, as a dosage-dependent suppressor of the temperature-sensitive phenotype of ric1-v3 mutant, but not that of Delta ric1 cells. Our results showed that the ric1-v3 mutant allele has some residual functional activity and suggest that Vps15 plays a role in the regulation of Ric1 function. In conclusion, Ric1 is a putative component of GEF for Ryh1 and might be regulated by Vps15. Further studies are needed to reveal the mechanism underlying the regulation.

The highly conserved fission yeast Pmk1 MAPK pathway plays a key role in cell integrity by regulating Atf1, which belongs to the ATF/cAMP-responsive element-binding (CREB) protein family. We identified and characterized ecm33(+), which encodes a glycosyl-phosphatidylinositol (GPI)-anchored cell surface protein as a transcriptional target of Pmk1 and Atf1. We demonstrated that the gene expression of Ecm33 is regulated by two transcription factors Atf1 and a MADS-box-type transcription factor Mbx1. We identified a putative ATF/CREB-binding site and an RLM1-binding site in the ecm33(+) promoter region and monitored the transcriptional activity of Atf1 or Mbx1 in living cells using a destabilized luciferase reporter gene fused to three tandem repeats of the CRE and six tandem repeats of the Rlm1-binding sequence, respectively. These reporter genes reflect the activation of the Pmk1 pathway by various stimuli, thereby enabling the real-time monitoring of the Pmk1 cell integrity pathway. Notably, the Delta ecm33 cells displayed hyperactivation of the Pmk1 signaling together with hypersensitivity to Ca2+ and an abnormal morphology, which were almost abolished by simultaneous deletion of the components of the Rho2/Pck2/Pmk1 pathway. Our results suggest that Ecm33 is involved in the negative feedback regulation of Pmk1 cell integrity signaling and is linked to cellular Ca2+ signaling.

Adaptins are subunits of the heterotetrameric (beta/mu/gamma/sigma) adaptor protein (AP) complexes that are involved in clathrin-mediated membrane trafficking. Here, we show that in Schizosaccharomyces pombe the deletion strains of each individual subunit of the AP-1 complex [Apl2 (beta), Apl4 (gamma), Apm1 (mu) and Aps1 (sigma)] caused distinct phenotypes on growth sensitivity to temperature or drugs. We also show that the Delta apm1 and Delta apl2 mutants displayed similar but more severe phenotypes than those of Delta aps1 or Delta apl4 mutants. Furthermore, the Delta apl2 Delta aps1 and Delta apl2 Delta apl4 double mutants displayed synthetic growth defects, whereas the Delta aps1 Delta apl4 and Delta apl2 Delta apm1 double mutants did not. In pull-down assay, Apm1 binds Apl2 even in the absence of Aps1 and Apl4, and Apl4 binds Aps1 even in the absence of Apm1 and Apl2. Consistently, the deletion of any subunit generally caused the disassociation of the heterotetrameric complex from endosomes, although some subunits weakly localized to endosomes. In addition, the deletion of individual subunits caused similar endosomal accumulation of v-SNARE synaptobrevin Syb1. Altogether, results suggest that the four subunits are all essential for the heterotetrameric complex formation and for the AP-1 function in exit transport from endosomes.

Schizosaccharomyces pombe genome contains an essential gene hmg1(+) encoding the sterol biosynthetic enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR). Here, we isolated an allele of the hmg1(+) gene, hmg1-1/its12, as a mutant that showed sensitivities to high temperature and to FK506, a calcineurin inhibitor. The hmg1-1 allele contained an opal nonsense mutation in its N-terminal transmembrane domain, yet in spite of the mutation a full-length protein was produced, suggesting a read-through termination codon. Consistently, overexpression of the hmg1-1 mutant gene suppressed the mutant phenotypes. The hmg1-1 mutant showed hypersensitivity to pravastatin, an HMGR inhibitor, suggesting a defective HMGR activity. The mutant treated with FK506 caused dramatic morphological changes and showed defects in cell wall integrity, as well as displayed synthetic growth phenotypes with the mutant alleles of genes involved in cytokinesis and cell wall integrity. The mutant exhibited different phenotypes from those of the disruption mutants of ergosterol biosynthesis genes, and it showed normal filipin staining as well as showed normal subcellular localization of small GTPases. These data suggest that the pleiotropic phenotypes reflect the integrated effects of the reduced availability of ergosterol and various intermediates of the mevalonate pathway.

Myosin II is an essential component of the actomyosin contractile ring and plays a crucial role in cytokinesis by generating the forces necessary for contraction of the actomyosin ring. Cdc4 is an essential myosin II light chain in fission yeast and is required for cytokinesis. In various eukaryotes, the phosphorylation of myosin is well documented as a primary means of activating myosin II, but little is known about the regulatory mechanisms of Cdc4. Here, we isolated Nrd1, an RNA-binding protein with RNA-recognition motifs, as a multicopy suppressor of cdc4 mutants. Notably, we demonstrated that Nrd1 binds and stabilizes Cdc4 mRNA, thereby suppressing the cytokinesis defects of the cdc4 mutants. Importantly, Pmk1 mitogen-activated protein kinase (MAPK) directly phosphorylates Nrd1, thereby negatively regulating the binding activity of Nrd1 to Cdc4 mRNA. Consistently, the inactivation of Pmk1 MAPK signaling, as well as Nrd1 overexpression, stabilized the Cdc4 mRNA level, thereby suppressing the cytokinesis defects associated with the cdc4 mutants. In addition, we demonstrated the cell cycle-dependent regulation of Pmk1/Nrd1 signaling. Together, our results indicate that Nrd1 plays a role in the regulation of Cdc4 mRNA stability; moreover, our study is the first to demonstrate the posttranscriptional regulation of myosin expression by MAPK signaling.

Myosin II is an essential component of the actomyosin contractile ring and plays a crucial role in cytokinesis by generating the forces necessary for contraction of the actomyosin ring. Cdc4 is an essential myosin II light chain in fission yeast and is required for cytokinesis. In various eukaryotes, the phosphorylation of myosin is well documented as a primary means of activating myosin II, but little is known about the regulatory mechanisms of Cdc4. Here, we isolated Nrd1, an RNA-binding protein with RNA-recognition motifs, as a multicopy suppressor of cdc4 mutants. Notably, we demonstrated that Nrd1 binds and stabilizes Cdc4 mRNA, thereby suppressing the cytokinesis defects of the cdc4 mutants. Importantly, Pmk1 mitogen-activated protein kinase (MAPK) directly phosphorylates Nrd1, thereby negatively regulating the binding activity of Nrd1 to Cdc4 mRNA. Consistently, the inactivation of Pmk1 MAPK signaling, as well as Nrd1 overexpression, stabilized the Cdc4 mRNA level, thereby suppressing the cytokinesis defects associated with the cdc4 mutants. In addition, we demonstrated the cell cycle-dependent regulation of Pmk1/Nrd1 signaling. Together, our results indicate that Nrd1 plays a role in the regulation of Cdc4 mRNA stability; moreover, our study is the first to demonstrate the posttranscriptional regulation of myosin expression by MAPK signaling.

We have previously demonstrated that calcineurin and the Pmk1 MAP kinase pathway play an antagonistic role in Cl- homeostasis. Using this relationship, we screened for mutations that show vic (viable in the presence of immunosuppressant and chloride ion) phenotype and isolated a vic6 mutant cell. The vic6 mutant cells also showed sensitivity to high temperature. Using this phenotype, we isolated hmg1+ gene, encoding a HMG-CoA reductase. Consistently, the vic6 mutant cells exhibited hypersensitivity to miconazole, an inhibitor of ergosterol biosynthesis and showed aberrant intracellular localization of filipin, suggesting that the mutant cells are affected in the sterol biosynthesis. In addition, overexpression of the hmg1+ gene complemented the phenotype of vic1-1/cpp1-v1 mutant cells, an allele of the gene encoding a farnesyltransferase, whereas overexpression of the cpp1+ gene exacerbated the temperature-sensitive phenotype of the vic6 mutant cells.

We screened for mutations that confer sensitivities to the calcineurin inhibitor FK506 and to a high concentration of MgCl2 and isolated the cis4-1 mutant, an allele of the gene encoding a cation diffusion facilitator (CDF) protein that is structurally related to zinc transporters. Consistently, the addition of extracellular Zn2+ suppressed the phenotypes of the cis4 mutant cells. The cis4 mutants and the mutant cells of another CDF-encoding gene SPBC16E9.14c ( we named zrg(17+)) shared common and nonadditive zinc-suppressible phenotypes, and Cis4 and Zrg17 physically interacted. Cis4 localized at the cis-Golgi, suggesting that Cis4 is responsible for Zn2+ uptake to the cis-Golgi. The cis4 mutant cells showed phenotypes such as weak cell wall and decreased acid phosphatase secretion that are thought to be resulting from impaired membrane trafficking. In addition, the cis4 deletion cells showed synthetic growth defects with all the four membrane-trafficking mutants tested, namely ypt3-i5, ryh1-i6, gdi1-i11, and apm1-1. Interestingly, the addition of extracellular Zn2+ significantly suppressed the phenotypes of the ypt3-i5 and apm1-1 mutant cells. These results suggest that Cis4 forms a heteromeric functional complex with Zrg17 and that Cis4 is implicated in Golgi membrane trafficking through the regulation of zinc homeostasis in fission yeast.

The fission yeast Schizosaccharomyces pombe (S. pombe) has become a valuable model system to elucidate the mechanisms of basic cellular functions of higher eukaryotes, including cell cycle control, membrane trafficking, and signal transduction. Having the smallest genome size among eukaryotes and with its powerful genetics, this organism is also an excellent model system for drug discovery. In addition, many signaling molecules targeted by the drug or the homologues of disease-linked human genes are highly conserved. We have been studying the signal transduction pathway in fission yeast with special emphasis on calcineurin phosphatase and mitogen-activated protein kinase (MAPK) signal transduction pathways. Our molecular genetic approach, which utilizes a crosstalk between calcineurin and MAPK signaling, has identified several regulators of Pmk1 MAPK, which is a homologue of extracellular signal-regulated kinase (ERK) in mammals. As MAPK signal transduction pathways are one of the most attractive targets for cancer therapy, inhibitors that target this signaling appear to be promising drug candidates for the treatment of cancer. Here, we first give an overview of the use of yeast as a model system for drug discovery and then we introduce our molecular genetic strategy to identify regulators of MAPK signaling and the application of this approach to drug discovery. © 2008 Humana Press Inc.

In fission yeast, knockout of the calcineurin gene resulted in hypersensitivity to Cl-, and the overexpression of pmp1(+) encoding a dual-specificity phosphatase for Pmk1 mitogen-activated protein kinase (MAPK) or the knockout of the components of the Pmk1 pathway complemented the Cl- hypersensitivity of calcineurin deletion. Here, we showed that the overexpression of ptcl(+) and ptc3(+), both encoding type 2C protein phosphatase (PP2C), previously known to inactivate the Wis1Spc1Atf1 stress-activated MAPK signaling pathway, suppressed the Cl- hypersensitivity of calcineurin deletion. We also demonstrated that the mRNA levels of these two PP2Cs and pyp2(+), another negative regulator of Spc1, are dependent on Pmk1. Notably, the deletion of Atf1, but not that of Spc1, displayed hypersensitivity to the cell wall-damaging agents and also suppressed the Cl- hypersensitivity of calcineurin deletion, both of which are characteristic phenotypes shared by the mutation of the components of the Pmk1 MAPK pathway. Moreover, micafungin treatment induced Pmk1 hyperactivation that resulted in Atf1 hyperphosphorylation. Together, our results suggest that PP2C is involved in a negative feedback loop of the Pmk1 signaling, and results also demonstrate that Atf1 is a key component of the cell integrity signaling downstream of Pmk1 MAPK.

In fission yeast, knockout of the calcineurin gene resulted in hypersensitivity to Cl-, and the overexpression of pmp1(+) encoding a dual-specificity phosphatase for Pmk1 mitogen-activated protein kinase (MAPK) or the knockout of the components of the Pmk1 pathway complemented the Cl- hypersensitivity of calcineurin deletion. Here, we showed that the overexpression of ptcl(+) and ptc3(+), both encoding type 2C protein phosphatase (PP2C), previously known to inactivate the Wis1Spc1Atf1 stress-activated MAPK signaling pathway, suppressed the Cl- hypersensitivity of calcineurin deletion. We also demonstrated that the mRNA levels of these two PP2Cs and pyp2(+), another negative regulator of Spc1, are dependent on Pmk1. Notably, the deletion of Atf1, but not that of Spc1, displayed hypersensitivity to the cell wall-damaging agents and also suppressed the Cl- hypersensitivity of calcineurin deletion, both of which are characteristic phenotypes shared by the mutation of the components of the Pmk1 MAPK pathway. Moreover, micafungin treatment induced Pmk1 hyperactivation that resulted in Atf1 hyperphosphorylation. Together, our results suggest that PP2C is involved in a negative feedback loop of the Pmk1 signaling, and results also demonstrate that Atf1 is a key component of the cell integrity signaling downstream of Pmk1 MAPK.

Inosine (I) at position 34 (wobble position) of tRNA is formed by the hydrolytic deamination of a genomically encoded adenosine (A). The enzyme catalyzing this reaction, termed tRNA A: 34 deaminase, is the heterodimeric Tad2p/ADAT2 center dot Tad3p/ADAT3 complex in eukaryotes. In budding yeast, deletion of each subunitis lethal, indicating that the wobble inosine tRNA modification is essential for viability; however, most of its physiological roles remain unknown. To identify novel cell cycle mutants in fission yeast, we isolated the tad3-1 mutant that is allelic to the tad3(+) gene encoding a homolog of budding yeast Tad3p. Interestingly, the tad3-1 mutant cells principally exhibited cell cycle-specific phenotype, namely temperature-sensitive and irreversible cell cycle arrest both in G(1) and G(2). Further analyses revealed that in the tad3-1 mutant cells, the S257N mutation that occurred in the catalytically inactive Tad3 subunit affected its association with catalytically active Tad2 subunit, leading to an impairment in the A to I conversion at position 34 of tRNA. In tad3-1 mutant cells, the over expression of the tad3(+) gene completely suppressed the decreased tRNA inosine content. Notably, the overexpression of the tad2(+) gene partially suppressed the temperature-sensitive phenotype and the decreased tRNA inosine content, indicating that the tad3-1 mutant phenotype is because of the insufficient I-34 formation of tRNA. These results suggest that the wobble inosine tRNA modification is essential for cell cycle progression in the G1/S and G2/M transitions in fission yeast.

The multivesicular body (MVB) sorting pathway is required for a number of biological processes, including downregulation of cell-surface proteins and protein sorting into the vacuolar lumen. The function of this pathway requires endosomal sorting complexes required for transport (ESCRT) composed of class E vacuolar protein sorting (Vps) proteins in Saccharomyces cerevisiae, many of which are conserved in Schizosaccharomyces pombe. Of these, sst4/vps27 (homologous to VPS27) and sst6 (similar to VPS23) have been identified as suppressors of sterility in ste12 Delta (sst), although their functions have not been uncovered to date. In this report, these two sst genes are shown to be required for vacuoiar sorting of carboxypeptidase Y (CPY) and an MVB marker, the ubiquitin-GFP-carboxypeptidase S (Ub-GFP-CPS) fusion protein, despite the lack of the ubiquitin E2 variant domain in Sst6p. Disruption mutants of a variety of other class E vps homologues also had defects in sorting of CPY and Ub-GFP-CPS. Sch. pombe has a mammalian AMSH homologue, sst2. Phenotypic analyses suggested that Sst2p is a class E Vps protein. Taken together, these results suggest that sorting into multivesicular bodies is dependent on class E Vps proteins, including Sst2p, in Sch. pombe.

Fission yeast Schizosaccharomyces pombe is amenable to genetics and is an excellent model system for studying eukaryotic cell biology. However, auxotrophic markers that can be used for both targeted gene integration and disruption are very limited. Here we performed a forward genetic screen in an effort to develop a new set of selectable markers for use in this yeast. Mutants that were auxotrophic for arginine, asparagine, cysteine, lysine, methionine and phenylalanine were isolated. Six genes were analyzed in detail and the mutations in the genes were identified. Among these six are three new genes: asn1(+), cys2(+) and pha2(+) were required for biosynthesis of asparagine, cysteine and phenylalanine, respectively. New alleles of arg1(+), lys3(+) and met6(+) were also identified. All of these genes proved to be suitable as selectable markers for targeted gene integration and disruption. We also showed that in Schizosaccharomyces pombe there are two apparent homologues of Saccharomyces cerevisiae MET2: the previously known met6(+), and SPBC106.17c (named cys2(+)). The cys2 mutation required cysteine rather than methionine. These new tools, specifically, new selectable markers, will be useful in further genetic and biological studies in fission yeast.

Valproic acid (VPA) is widely used to treat epilepsy and manic-depressive illness. Although VPA has been reported to exert a variety of biochemical effects, the exact mechanisms underlying its therapeutic effects remain elusive. To gain further insights into the molecular mechanisms of VPA action, a genetic screen for fission yeast mutants that show hypersensitivity to VPA was performed. One of the genes that we identified was vps45(+), which encodes a member of the Sec1/Munc18 family that is implicated in membrane trafficking. Notably, several mutations affecting membrane trafficking also resulted in hypersensitivity to VPA. These include ypt3(+) and ryh1(+), both encoding a Rab family protein, and apm1(+), encoding the mu 1 subunit of the adaptor protein complex AP-1. More importantly, VPA caused vacuolar fragmentation and inhibited the glycosylation and the secretion of acid phosphatase in wild-type cells, suggesting that VPA affects membrane trafficking. Interestingly, the cell-wall-damaging agents such as micafungin or the inhibition of calcineurin dramatically enhanced the sensitivity of wild-type cells to VPA. Consistently, VPA treatment of wild-type cells enhanced their sensitivity to the cell-wall-digesting enzymes. Altogether, our results suggest that VPA affects membrane trafficking, which leads to the enhanced sensitivity to cell-wall damage in fission yeast.

The genes belonging to Pumilio gene family of the fission yeast Schizosaccharomyces pombe (S. pombe) were compared with genome information of the several fungi and their functions have been inferred using public-access databases disclosed on the internet websites. The Pumilio-family genes are conserved from yeast to man and have been considered to suppress the expression of other genes by binding their specific target messenger RNAs. In S. pombe genome, nine genes belonging to Pumilio gene family were found and were clustered into four groups by homology of their amino acid sequences. Each gene has been analyzed to search 'close orthologue' in the genomes of Saccharomyces cerevisiae, Candida parapsilosis, Aspergillus fumigatus, Phytophthora infestans, Pneumocystis carinii and Neurospora crassa, using protein-protein blast P search. Consequently, we found several genes belonging to Pumilio gene family in the genomes of Saccharomyces cerevisiae, Candida parapsilosis, and Neurospora crassa. Evolution and function of these genes can be expected from the analysis based on the molecular phylogenies.

We have previously demonstrated that knockout of the calcineurin gene or inhibition of calcineurin activity by immunosuppressants resulted in hypersensitivity to Cl- in fission yeast. We also demonstrated that knockout of the components of the Pmk1 mitogen-activated protein kinase (MAPK) pathway, such as Pmk1 or Pek1 complemented the hypersensitivity to Cl-. Using this interaction between calcineurin and Pmk1 MAPK, here we developed a genetic screen that aims to identify new regulators of the Pmk1 signaling and isolated vic (viable in the presence of immunosuppressant and chloride ion) mutants. One of the mutants, vic1-1, carried a missense mutation in the cpp(1+) gene encoding a 13 subunit of the protein farnesyltransferase, which caused an amino acid substitution of aspartate 155 of Cpp1 to asparagine (Cpp1(D115N)). Analysis of the mutant strain revealed that Rho2 is a novel target of Cpp1. Moreover, Cpp1 and Rho2 act upstream of Pck2-Pmk1 MAPK signaling pathway, thereby resulting in the vic phenotype upon their mutations. Interestingly, compared with other substrates of Cpp1, defects of Rho2 function were more phenotypically manifested by the Cpp1(D155N) mutation. Together, our results demonstrate that Cpp1 is a key component of the Pck2-Pmk1 signaling through the spatial control of the small GTPase Rho2.

We have previously demonstrated that knockout of the calcineurin gene or inhibition of calcineurin activity by immunosuppressants resulted in hypersensitivity to Cl- in fission yeast. We also demonstrated that knockout of the components of the Pmk1 mitogen-activated protein kinase (MAPK) pathway, such as Pmk1 or Pek1 complemented the hypersensitivity to Cl-. Using this interaction between calcineurin and Pmk1 MAPK, here we developed a genetic screen that aims to identify new regulators of the Pmk1 signaling and isolated vic (viable in the presence of immunosuppressant and chloride ion) mutants. One of the mutants, vic1-1, carried a missense mutation in the cpp(1+) gene encoding a 13 subunit of the protein farnesyltransferase, which caused an amino acid substitution of aspartate 155 of Cpp1 to asparagine (Cpp1(D115N)). Analysis of the mutant strain revealed that Rho2 is a novel target of Cpp1. Moreover, Cpp1 and Rho2 act upstream of Pck2-Pmk1 MAPK signaling pathway, thereby resulting in the vic phenotype upon their mutations. Interestingly, compared with other substrates of Cpp1, defects of Rho2 function were more phenotypically manifested by the Cpp1(D155N) mutation. Together, our results demonstrate that Cpp1 is a key component of the Pck2-Pmk1 signaling through the spatial control of the small GTPase Rho2.

In fission yeast, calcineurin dephosphorylates and activates the Prz1 transcription factor. Here, we identified the calcineurin-dependent response element (CDRE) in the promoter region of prz1(+) gene and monitored the calcineurin activity in living cells using a destabilized luciferase reporter gene fused to three tandem repeats of CDRE. Elevated extracellular CaCl2, caused an increase in calcineurin activity with an initial peak and then approached a sustained constant level in a concentration-dependent manner. In CaCl2-sensitive mutants such as Delta pmc1, the response was markedly enhanced, reflecting its high intracellular Ca2+. Agents expected to induce Ca2+ influx showed distinct patterns of the CDRE-reporter activity, suggesting different mechanisms of calcineurin activation. Knockout of yam(8+) or cch1(+) encoding putative subunits of a Ca2+ channel abolished the activation of calcineurin upon exposure to various stimuli, including high extracellular NaCl and cell wall-damaging agents. However, knockout of yam8(+) or cch1(+) did not affect the activation of calcineurin upon stimulation by elevated extracellular Ca2+. The Pck2 protein kinase C-Pmk1 mitogen-activate protein kinase pathway was required for the stimulation of calcineurin via Yam8/Cch1-mediated Ca2+ influx, but it was not required for the stimulation by elevated extracellular Ca2+, suggesting two distinct pathways for calcineurin activation.

We have previously identified mutant alleles of genes encoding two Rab proteins, Ypt3 and Ryh1, through a genetic screen using the immunosuppressant drug FK506 in fission yeast. In the same screen, we isolated gdi1-i11, a mutant allele of the essential gdi1(+) gene encoding Rab GDP-dissociation inhibitor. In gdi1-i11, a conserved Gly267 was substituted by Asp. The Gdil(G267D) protein failed to extract Rabs from membrane and Rabs were depleted from the cytosolic fraction in the gdi1-i11 mutant cells. Consistently, the Gdi1(G267D) protein was found mostly in the membrane fraction, whereas wild-type Gdi1 was found in both the cytosolic and the membrane fraction. Notably, overexpression of spo20(+), encoding a phosphatidylcholine/ phosphatidylinositol transfer protein, rescued gdi1-i11 mutation, but not ypt3-i5 or ryh1-i6 The gdi1-i11 and spo20-KC104 mutations are synthetically lethal, and the wild-type Gdi1 failed to extract Rabs from the membrane in the spo20-KC104 mutant. The phosphatidylinositol-transfer activity of Spo20 is dispensable for the suppression of the gdi1-i11 mutation, suggesting that the phosphatidylcholine-transfer activity is important for the suppression. Furthermore, knockout of the pct1(+) gene encoding a choline phosphate cytidyltransferase rescued the gdi1-i11 mutation. Together, our findings suggest that Spo20 modulates Gdi1 function via regulation of phospholipid metabolism of the membranes.

We have previously isolated ypt3-i5 mutant and showed that Ypt3 GTPase functions in the fission yeast secretory pathway. Here, the same genetic screen led to the isolation of ryh1-i6, a mutant allele of the ryh1(+) gene encoding a homolog of Rab6. The ryh1-i6 mutant showed phenotypes that support its role in retrograde traffic from endosome to the Golgi. Interestingly, ryh1(+) gene deletion was synthetically lethal with ypt3-i5 mutation. Consistently, the over-expression of the GDP-conformational mutant, Ryh1T25 N, inhibited the growth of ypt3-i5 mutant but had no effect on that of wild-type cells. Furthermore, the over-expression of the Ryh1T25N mutant inhibited the acid phosphatase glycosylation and exacerbated the cell wall integrity of ypt3-i5 mutant, but had no effect on those of wild-type cells. GFP-Ryh1 and GFP-Ypt3 both localized at the Golgi/endosome, but showed distinct subcellular localizations. The localization of GFP-Ryh1 in ypt3-i5 mutant and that of GFP-Ypt3 in ryh1-i6 mutant were distinct from those in wild-type cells. In addition, Ryh1 as well as Ypt3 were shown to be involved in acid phosphatase secretion. These results suggest that Ryh1 is involved in the secretory pathway and may have a potential overlapping function with Ypt3 in addition to its role in recycling.

Fission yeast its3-1 mutant is an allele of the essential gene its3(+) that encodes a phosphatidylinositol-4-phosphate 5-kinase (PIP5K) that produces phosphatidylinositol 4,5-bisphosphate. We found that the its3-1 mutant is sensitive to micafungin, a (1,3)-beta-D-glucan synthase inhibitor, suggesting a cell wall integrity defect. Consistently, its3-1 mutation caused synthetic lethality with a (1,3)-beta-D-glucan synthase mutant, bgs1-i2, and its3-1 mutant cells showed aberrant localization of green fluorescent protein-Bgs1. Similar aberrant localization of green fluorescent protein-tagged Rgf1, a putative phosphatidylinositol 4,5-bisphosphate-binding guanine nucleotide exchange factor for Rho protein, in its3-1 mutants was observed, suggesting a defective Rgf1/Rho pathway. To unravel the molecular mechanism(s), putative downstream components of PIP5K signaling were analyzed. Unexpectedly, overexpression of phospholipase C (Plc1), but not that of protein kinase C (PKC; Pck1 and Pck2), suppressed the phenotypes of the its3-1 mutant. These findings indicate that PKCs are not involved in the suppression, and further analysis revealed that PKCs are not downstream of Plc1 in fission yeast. Also, the enzymatic activity of Plc1 is essential for the suppression of the phenotypes and for the viability of the its3-1 mutant. These findings suggest that Its3 PIP5K regulates cell integrity through a Plc1-mediated PKC-independent pathway, in addition to the Rho/PKC pathway.

Fission yeast its3-1 mutant is an allele of the essential gene its3(+) that encodes a phosphatidylinositol-4-phosphate 5-kinase (PIP5K) that produces phosphatidylinositol 4,5-bisphosphate. We found that the its3-1 mutant is sensitive to micafungin, a (1,3)-beta-D-glucan synthase inhibitor, suggesting a cell wall integrity defect. Consistently, its3-1 mutation caused synthetic lethality with a (1,3)-beta-D-glucan synthase mutant, bgs1-i2, and its3-1 mutant cells showed aberrant localization of green fluorescent protein-Bgs1. Similar aberrant localization of green fluorescent protein-tagged Rgf1, a putative phosphatidylinositol 4,5-bisphosphate-binding guanine nucleotide exchange factor for Rho protein, in its3-1 mutants was observed, suggesting a defective Rgf1/Rho pathway. To unravel the molecular mechanism(s), putative downstream components of PIP5K signaling were analyzed. Unexpectedly, overexpression of phospholipase C (Plc1), but not that of protein kinase C (PKC; Pck1 and Pck2), suppressed the phenotypes of the its3-1 mutant. These findings indicate that PKCs are not involved in the suppression, and further analysis revealed that PKCs are not downstream of Plc1 in fission yeast. Also, the enzymatic activity of Plc1 is essential for the suppression of the phenotypes and for the viability of the its3-1 mutant. These findings suggest that Its3 PIP5K regulates cell integrity through a Plc1-mediated PKC-independent pathway, in addition to the Rho/PKC pathway.

ここ数年間各種生物のゲノムシークエンスプロジェクトが進行し，多くの生物種のゲノムの全構造が次々と明らかにされている．この成果を生かした遺伝子機能の網羅的解析により，生命現象を理解することを目的にしたいわゆるポストゲノム研究に入り，比較的早い時期に全塩基配列決定が終了した酵母，線虫，ショウジョウバエなどの生物は，高等生物のモデルとして，医学，薬学および生命科学の分野で大きな役割を果たすようになってきた．中でも酵母は，強力な遺伝学的解析と組み合わせた膨大なゲノミクス情報が得られ，酵母ホモログが存在するような高等動物の遺伝子機能解析に有力な情報を提供している．近年ゲノム創薬に酵母ゲノミクスを応用することにより，ハイスループットスクリーニングなどの網羅的な遺伝子機能解析により，薬物の作用様式や標的分子あるいは経路に関する新たな情報が蓄積しつつある．本稿では創薬研究における酵母ゲノミクスの活用について，具体的な例を挙げてモデル生物としての酵母の役割について述べたい．

ここ数年間各種生物のゲノムシークエンスプロジェクトが進行し，多くの生物種のゲノムの全構造が次々と明らかにされている．この成果を生かした遺伝子機能の網羅的解析により，生命現象を理解することを目的にしたいわゆるポストゲノム研究に入り，比較的早い時期に全塩基配列決定が終了した酵母，線虫，ショウジョウバエなどの生物は，高等生物のモデルとして，医学，薬学および生命科学の分野で大きな役割を果たすようになってきた．中でも酵母は，強力な遺伝学的解析と組み合わせた膨大なゲノミクス情報が得られ，酵母ホモログが存在するような高等動物の遺伝子機能解析に有力な情報を提供している．近年ゲノム創薬に酵母ゲノミクスを応用することにより，ハイスループットスクリーニングなどの網羅的な遺伝子機能解析により，薬物の作用様式や標的分子あるいは経路に関する新たな情報が蓄積しつつある．本稿では創薬研究における酵母ゲノミクスの活用について，具体的な例を挙げてモデル生物としての酵母の役割について述べたい．

Calcineurin, a protein phosphatase required for Ca2+ signaling in many cell types, is a heterodimer composed of catalytic and regulatory subunits. The fission yeast genome encodes a single set of catalytic (Ppb1) and regulatory (Cnb1) subunits, providing an ideal model system to study the functions of these subunits in vivo. Here, we cloned the cnb1(+) gene and showed that the cnb1 knock-out (Delta cnb1) exhibits identical phenotypes with Delta ppb1 and that overexpression of Ppb1 failed to suppress the phenotypes of Delta cnb1. Interestingly, overexpression of the C-terminal-deleted Ppb1 (Ppb1 Delta C), the constitutively active form of Ppb1, also failed to suppress the phenotypes of Delta cnb1. FK506 caused MgCl2 sensitivity to the wild-type cells in an FKBP12-dependent manner. Co-overexpression of Ppb1 and Cnb1 suppressed the FK506-induced MgCl2 sensitivity, but the suppression was only partial, suggesting that an excess amount of the Ppb1-Cnb1 complex cannot compete out the FKBP12-FK506 complex. Although overexpression of Ppb1 Delta C alone had little effect on cell growth, co-overexpression of Ppb1 Delta C and Cnb1 caused a distinct growth defect. FK506 suppressed the growth defect when Cnb1 was co-expressed using the attenuated nmt1 promoter, but it failed to suppress the defect when Cnb1 was co-expressed using the wild-type nmt1 promoter. Knock-out of the prz1(+) gene, encoding a downstream target transcription factor of calcineurin, suppressed the growth defect irrespective of the promoter potency. These results suggest that Cnb1 is essential for the activation of calcineurin and that the activated calcineurin is the pharmacological target of the FKBP12-FK506 complex in vivo.

ここ数年間各種生物のゲノムシークエンスプロジェクトが進行し，多くの生物種のゲノムの全構造が次々と明らかにされている．この成果を生かした遺伝子機能の網羅的解析により，生命現象を理解することを目的にしたいわゆるポストゲノム研究に入り，比較的早い時期に全塩基配列決定が終了した酵母，線虫，ショウジョウバエなどの生物は，高等生物のモデルとして，医学，薬学および生命科学の分野で大きな役割を果たすようになってきた．中でも酵母は，強力な遺伝学的解析と組み合わせた膨大なゲノミクス情報が得られ，酵母ホモログが存在するような高等動物の遺伝子機能解析に有力な情報を提供している．近年ゲノム創薬に酵母ゲノミクスを応用することにより，ハイスループットスクリーニングなどの網羅的な遺伝子機能解析により，薬物の作用様式や標的分子あるいは経路に関する新たな情報が蓄積しつつある．本稿では創薬研究における酵母ゲノミクスの活用について，具体的な例を挙げてモデル生物としての酵母の役割について述べたい．

We have investigated the toxicity of an alpha(1L)-adrenoceptor agonist, ESR 1150 CL, and compared the toxicokinetics and pharmacokinetics in rats and monkeys. In rats, this compound induced death with remarkable sacculated aneurysms of the aorta in groups given more than 3 mg/kg per day in a 4-week repeated oral administration study. On the other hand, these findings were not observed in monkeys during a 2-week repeated oral administration study at doses up to 30 mg/kg per day. Orally administered ESR 1150 CL raised blood pressure transiently and dose-dependently during the 4-week repeated study in rats, whereas no increase of blood pressure was observed during the 2-week oral toxicity study in monkeys. Contrary to our expectation, the exposure level of ESR 1150 CL in rats was not higher than that in monkeys in the toxicokinetic evaluation. Pharmacokinetic evaluation indicated good absorption of the compound, but the bioavailability was very low in both rats and monkeys. These findings suggest that the potent species difference in toxicity of ESR 1150 CL between rats and monkeys does not depend on differences of toxicokinetics/pharmacokinetics. Rather, we suggest that the reason is likely to be species difference in the biological susceptibility of the alpha(1L)-adrenoceptor subtypes between rats and monkeys, which would be closely related with the effect on blood pressure by alpha(1L)-adrenoceptor agonist.

We have investigated the toxicity of an alpha(1L)-adrenoceptor agonist, ESR 1150 CL, and compared the toxicokinetics and pharmacokinetics in rats and monkeys. In rats, this compound induced death with remarkable sacculated aneurysms of the aorta in groups given more than 3 mg/kg per day in a 4-week repeated oral administration study. On the other hand, these findings were not observed in monkeys during a 2-week repeated oral administration study at doses up to 30 mg/kg per day. Orally administered ESR 1150 CL raised blood pressure transiently and dose-dependently during the 4-week repeated study in rats, whereas no increase of blood pressure was observed during the 2-week oral toxicity study in monkeys. Contrary to our expectation, the exposure level of ESR 1150 CL in rats was not higher than that in monkeys in the toxicokinetic evaluation. Pharmacokinetic evaluation indicated good absorption of the compound, but the bioavailability was very low in both rats and monkeys. These findings suggest that the potent species difference in toxicity of ESR 1150 CL between rats and monkeys does not depend on differences of toxicokinetics/pharmacokinetics. Rather, we suggest that the reason is likely to be species difference in the biological susceptibility of the alpha(1L)-adrenoceptor subtypes between rats and monkeys, which would be closely related with the effect on blood pressure by alpha(1L)-adrenoceptor agonist.

Calcineurin is a highly conserved regulator of Ca2+ signaling in eukaryotes. In fission yeast, calcineurin is not essential for viability but is required for cytokinesis and Cl- homeostasis. In a genetic screen for mutations that are synthetically lethal with calcineurin deletion, we isolated a mutant, cis1-1/apm1-1, an allele of the apm1(+) gene that encodes a homolog of the mammalian mu1A subunit of the clathrin-associated adaptor protein-1 (AP-1) complex. The cis1-1/apm1-1 mutant as well as the apm1-deleted (Deltaapm1) cells showed distinct phenotypes: temperature sensitivity; tacrolimus (FK506) sensitivity; and pleiotropic defects in cytokinesis, cell integrity, and vacuole fusion. Electron micrographs revealed that Deltaapm1 cells showed large vesicular structures associated with Golgi stacks and accumulated post-Golgi secretory vesicles. Deltaapm1 cells also showed the massive accumulation of the exocytic v-SNARE Syb1 in the Golgi/endosomes and a reduced secretion of acid phosphatase. These phenotypes observed in apm1 mutations were accentuated upon temperature up-shift and FK506 treatment. Notably, Apm1-GFP localized to the Golgi/endosomes, the spindle pole bodies, and the medial region. These findings suggest a role for Apm1 associated with the Golgi/endosome function, thereby affecting various cellular processes, including secretion, cytokinesis, vacuole fusion, and cell integrity and also suggest that calcineurin is involved in these events.

Calcineurin is a highly conserved regulator of Ca2+ signaling in eukaryotes. In fission yeast, calcineurin is not essential for viability but is required for cytokinesis and Cl- homeostasis. In a genetic screen for mutations that are synthetically lethal with calcineurin deletion, we isolated a mutant, cis1-1/apm1-1, an allele of the apm1(+) gene that encodes a homolog of the mammalian mu1A subunit of the clathrin-associated adaptor protein-1 (AP-1) complex. The cis1-1/apm1-1 mutant as well as the apm1-deleted (Deltaapm1) cells showed distinct phenotypes: temperature sensitivity; tacrolimus (FK506) sensitivity; and pleiotropic defects in cytokinesis, cell integrity, and vacuole fusion. Electron micrographs revealed that Deltaapm1 cells showed large vesicular structures associated with Golgi stacks and accumulated post-Golgi secretory vesicles. Deltaapm1 cells also showed the massive accumulation of the exocytic v-SNARE Syb1 in the Golgi/endosomes and a reduced secretion of acid phosphatase. These phenotypes observed in apm1 mutations were accentuated upon temperature up-shift and FK506 treatment. Notably, Apm1-GFP localized to the Golgi/endosomes, the spindle pole bodies, and the medial region. These findings suggest a role for Apm1 associated with the Golgi/endosome function, thereby affecting various cellular processes, including secretion, cytokinesis, vacuole fusion, and cell integrity and also suggest that calcineurin is involved in these events.

Ubiquitin-dependent proteolysis plays a pivotal role in stress responses. To investigate the mechanisms of these cellular processes, we have been studying Schizosaccharomyces pombe mutants that have altered sensitivities to various stress conditions. Here, we showed that Lub1, a homologue of Ufd3p/Zzz4p/Doa1p in budding yeast, is involved in the regulation of ubiquitin contents. Disruption of the lub1(+) gene resulted in monoubiquitin as well as multiubiquitin depletion without change in mRNA level and in hypersensitivity to various stress conditions. Consistently, overexpression of genes encoding ubiquitin suppressed the defects associated with lub1 mutation, indicating that the phenotypes of the lub1 mutants under stress conditions were due to cellular ubiquitin shortage at the posttranscriptional level. In addition, the lub1-deleted cells showed aberrant functions in ubiquitin/proteasome-dependent proteolysis, with accelerated degradation of ubiquitin. Also Cdc48, a stress-induced chaperon-like essential ATPase, was found to interact with Lub1, and this association might contribute to the stabilization of Lub1. Our results indicated that Lub1 is responsible for ubiquitin homeostasis at the protein level through a negative regulation of ubiquitin degradation.

Ubiquitin-dependent proteolysis plays a pivotal role in stress responses. To investigate the mechanisms of these cellular processes, we have been studying Schizosaccharomyces pombe mutants that have altered sensitivities to various stress conditions. Here, we showed that Lub1, a homologue of Ufd3p/Zzz4p/Doa1p in budding yeast, is involved in the regulation of ubiquitin contents. Disruption of the lub1(+) gene resulted in monoubiquitin as well as multiubiquitin depletion without change in mRNA level and in hypersensitivity to various stress conditions. Consistently, overexpression of genes encoding ubiquitin suppressed the defects associated with lub1 mutation, indicating that the phenotypes of the lub1 mutants under stress conditions were due to cellular ubiquitin shortage at the posttranscriptional level. In addition, the lub1-deleted cells showed aberrant functions in ubiquitin/proteasome-dependent proteolysis, with accelerated degradation of ubiquitin. Also Cdc48, a stress-induced chaperon-like essential ATPase, was found to interact with Lub1, and this association might contribute to the stabilization of Lub1. Our results indicated that Lub1 is responsible for ubiquitin homeostasis at the protein level through a negative regulation of ubiquitin degradation.

Mitogen-activated protein kinases (MAPKs), found in all eukaryotes, are signal-transducing enzymes playing a central role in a variety of biological processes. MAPK phosphatase has dual catalytic activity toward phosphotyrosine- and phosphothreonine-containing proteins, and is known to inactivate ERKs, and JNKs/SAPKs, thus playing a crucial role in MAPK regulation. Although MAPK phosphatase has been implicated in a feedback loop that inactivates MAPKs after stimulation by mitogens and during the cellular response to stress, signaling pathways leading to MAPK phosphatase gene expression have not been fully elucidated. Recently, we have shown that a novel RNA-binding protein Rnc1 plays a crucial role in negative feedback regulation of MAPK signaling, by stabilizing the mRNA of a MAPK phosphatase at the post-transcriptional level. One important aspect of our findings is that the increase in mRNA levels involves not only the transcriptional up-regulation, but also the post-transcriptional gene regulation, especially the regulation of mRNA stability. Our discovery highlights a potential role and an emerging view of RNA-binding protein as a regulator of cell signaling and as a future target of drug discovery.

Schizosaccharomyces pombe pmr1(+) gene is homologous to Saccharomyces cerevisiae PMR1 gene, which encodes the P-type Ca2+/Mn2+-ATPase. Addition of Mn2+, as well as Ca2+, to the medium induced pmr1(+) gene expression in a calcineurin-dependent manner. The pmr1 knockout (Deltapmr1) cells exhibited hypersensitivity to EGTA. A screen for high gene dosage-suppressors of the EGTA-hypersensitive phenotype of Deltapmr1 led to the identification of pdt1(+) gene, which encodes an Nramp-related metal transporter. The Deltapmr1 cells showed round cell morphology. Although Deltapdt1 cells appeared normal in the regular medium, it showed round cell morphology similar to that of the Deltapmr1 cells when Mn2+ was removed from the medium. The removal of Mn2+ also exacerbated the round morphology of the Deltapmr1 cells. The Deltapmr1Deltapdt1 double mutants grew very slowly and showed extremely aberrant cell morphology with round, enlarged and depolarized shape. The addition of Mn2+, but not Ca2+, to the medium completely suppressed the morphological defects, while both Mn2+ and Ca2+ markedly improved the slow growth of the double mutants. These results suggest that Pmr1 and Pdt1 cooperatively regulate cell morphogenesis through the control of Mn2+ homeostasis, and that calcineurin functions as a Mn2+ sensor as well as a Mn2+ homeostasis regulator.

Schizosaccharomyces pombe pmr1(+) gene is homologous to Saccharomyces cerevisiae PMR1 gene, which encodes the P-type Ca2+/Mn2+-ATPase. Addition of Mn2+, as well as Ca2+, to the medium induced pmr1(+) gene expression in a calcineurin-dependent manner. The pmr1 knockout (Deltapmr1) cells exhibited hypersensitivity to EGTA. A screen for high gene dosage-suppressors of the EGTA-hypersensitive phenotype of Deltapmr1 led to the identification of pdt1(+) gene, which encodes an Nramp-related metal transporter. The Deltapmr1 cells showed round cell morphology. Although Deltapdt1 cells appeared normal in the regular medium, it showed round cell morphology similar to that of the Deltapmr1 cells when Mn2+ was removed from the medium. The removal of Mn2+ also exacerbated the round morphology of the Deltapmr1 cells. The Deltapmr1Deltapdt1 double mutants grew very slowly and showed extremely aberrant cell morphology with round, enlarged and depolarized shape. The addition of Mn2+, but not Ca2+, to the medium completely suppressed the morphological defects, while both Mn2+ and Ca2+ markedly improved the slow growth of the double mutants. These results suggest that Pmr1 and Pdt1 cooperatively regulate cell morphogenesis through the control of Mn2+ homeostasis, and that calcineurin functions as a Mn2+ sensor as well as a Mn2+ homeostasis regulator.

Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved enzymes that convert extracellular signals into various outputs such as cell growth, differentiation and cell death(1-4). MAPK phosphatases selectively inactivate MAPKs by dephosphorylating critical phosphothreonine and phosphotyrosine residues(5,6). The transcriptional induction of MAPK phosphatase expression by various stimuli, including MAPK activation, has been well documented as a negative-feedback mechanism of MAPK signalling(7,8). Here we show that Rnc1, a novel K-homology-type RNA-binding protein in fission yeast, binds and stabilizes Pmp1 messenger RNA(9), the MAPK phosphatase for Pmk1 (refs 10, 11). Rnc1 therefore acts as a negative regulator of Pmk1 signalling. Notably, Pmk1 phosphorylates Rnc1, causing enhancement of the RNA-binding activity of Rnc1. Thus, Rnc1 is a component of a new negative-feedback loop that regulates the Pmk1 pathway through its binding to Pmp1 mRNA. Our findings-the post-transcriptional mRNA stabilization of a MAPK phosphatase mediated by an RNA-binding protein-provide an additional regulatory mechanism for fine-tuning of MAPK signalling pathways.

Calcineurin is an important mediator that connects the Ca2+-dependent signaling to various cellular responses in a wide variety of cell types and organisms. In budding yeast, activated calcineurin exerts its function mainly by regulating the Crz1p/Tcn1 transcription factor. Here, we cloned the fission yeast prz1(+) gene, which encodes a zinc finger transcription factor highly homologous to Crz1/Tcn1. Similar to the results in budding yeast, calcineurin dephosphorylated Prz1 and resulted in the trans-location of Prz1 from the cytoplasm to the nucleus. Prz1 expression was stimulated by high extracellular Ca2+ in a calcineurin-dependent fashion. However, unlike in budding yeast, the prz1-null cells did not show any phenotype similar to those previously reported in calcineurin deletion such as aberrant cell morphology, mating defect, or hypersensitivity to Cl-. Instead, the prz1-null cells showed hypersensitivity to Ca2+, consistent with a dramatic decrease in transcription of Pmc1 Ca2+ pump. Interestingly, overexpression of Prz1 did not suppress the Cl- hypersensitivity of calcineurin deletion, and overexpression of Pmp1 MAPK phosphatase suppressed the Cl- hypersensitivity of calcineurin deletion but not the Ca2+ hypersensitivity of prz1 deletion. In addition, mutations in the its2(+)/cps1(+), its8(+), and its10(+)/cdc7(+) genes that showed synthetic lethal genetic interaction with calcineurin deletion did not exhibit synthetic lethality with the prz1 deletion. Our results suggest that calcineurin activates at least two distinct signaling branches, i.e. the Prz1-dependent transcriptional regulation and an unknown mechanism, which functions antagonistically with the Pmk1 MAPK pathway.

Background: In fission yeast, calcineurin has been implicated in cytokinesis because calcineurin-deleted cells form multiple septa and cell separation is impeded. However, this mechanism remains unclear. Results: We screened for mutations that confer syn-thetic lethality with calcineurin deletion and isolated a mutant, its10-1 /cdc7-i10 , a novel allele of the cdc7 (+) gene involved in the septation initiation network (SIN). The mutation created a termination codon, resulting in the truncation of Cdc7 by 162 amino acids, which is not localized in the spindle pole body. Following treatment with the immune suppressive drug FK506, cdc7-i10 and the original cdc7-24 mutant cells showed highly elongated multinuclear morphology with few visible septa, closely resembling the phenotype at the restrictive temperature. Other SIN mutants, cdc11 , spg1 , sid2 and mob1 showed similar phenotypes following FK506 treatment. Consistent with this, expression of the constitutively active calcineurin suppressed the growth defects and septum initiation deficiency of these SIN mutants at the restrictive temperature. Moreover, electron microscopy revealed that calcineurin-deleted cells had very thick multiple septa which were partially and ectopically formed. Conclusion: These results suggest that calcineurin is involved in the regulation of the SIN pathway, and is required for the proper formation and maturation of the septum in fission yeast.

A genetic screen for mutations synthetically lethal with fission yeast calcineurin deletion led to the identification of Ypt3, a homolog of mammalian Rab11 GTP-binding protein. A mutant with the temperature-sensitive ypt3-i5 allele showed pleiotropic phenotypes such as defects in cytokinesis, cell wall integrity, and vacuole fusion, and these were exacerbated by FK506-treatment, a specific inhibitor of calcineurin. Green fluorescent protein (GFP)-tagged Ypt3 showed cytoplasmic staining that was concentrated at growth sites, and this polarized localization required the actin cytoskeleton. It was also detected as a punctate staining in an actin-independent manner. Electron microscopy revealed that ypt3-i5 mutants accumulated aberrant Golgi-like structures and putative post-Golgi vesicles, which increased remarkably at the restrictive temperature. Consistently, the secretion of GFP fused with the pho1(+) leader peptide (SPL-GFP) was abolished at the restrictive temperature in ypt3-i5 mutants. FK506-treatment accentuated the accumulation of aberrant Golgi-like structures and caused a significant decrease of SPL-GFP secretion at a permissive temperature. These results suggest that Ypt3 is required at multiple steps of the exocytic pathway and its mutation affects diverse cellular processes and that calcineurin is functionally connected to these cellular processes.

Calcineurin (protein phosphatase 2B), the only serine/threonine phosphatase under the control of Ca2+ /calmodulin, is an important mediator in signal transmission, connecting the Ca2+ -dependent signalling to a wide variety of cellular responses. Furthermore, calcineurin is specifically inhibited by the immunosuppressant drugs cyclosporin A and tacrolimus (FK506), and these drugs have been a powerful tool for identifying many of the roles of calcineurin. Calcineurin is enriched in the neural tissues, and also distributes broadly in other tissues. The structure of the protein is highly conserved from yeast to man. The combined use of powerful genetics and of specific calcineurin inhibitors in fission yeast Schizosaccharomyces pombe (S. pombe ) identified new components of the calcineurin pathway, and defined new roles of calcineurin in the regulation of the many cellular processes. Recent data has revealed functional interactions in which calcineurin phosphatase is involved, such as the cross-talk between the Pmk1 MAP kinase signalling, or the PI signalling. Calcineurin also participates in membrane traffic and cytokinesis of fission yeast through its functional connection with members of the small GTPase Rab/Ypt family, and Type II myosin, respectively. These findings highlight the potential of fission yeast genetic studies to elucidate conserved elements of signal transduction cascades.

Calcineurin plays a critical role in Ca2+ signaling in various cell types. In fission yeast, calcineurin is required for cytokinesis and chloride ion homeostasis. However, most of its physiological functions remain obscure. A genetic screen was performed to identify genes that share an essential function with calcineurin. We screened for mutations that confer sensitivity to the calcineurin inhibitor FK506 and to a high concentration of chloride ion and isolated a mutant, cis2-1/myp2-c2, which contains a novel allele of the myp2(+)/myo3(+) gene that encodes a type 2 myosin heavy chain. The myp2-c2 mutant showed morphological defects similar to those associated with a calcineurin deletion mutant, such as multiseptated and branched cells. Consistently, myp2-null cells were hypersensitive to chloride ion and showed the multiseptated phenotype in the presence of immunosuppressants or at high chloride concentrations. Overexpression of constitutively active calcineurin suppressed the chloride ion-sensitive growth defect and cytokinesis abnormality of the myp2-c2 mutant and myp2-null cells. Interestingly, the essential myosin light chain mutant cdc4-8 failed to grow and could not form a normal contractile ring in the presence of immunosuppressants. Furthermore, calcineurin-null cells exhibited aberrant contractile rings, suggesting impaired contraction of the rings. These results indicate that calcineurin is involved in the regulation of cytokinesis and that chloride ion homeostasis is mediated by type 2 myosin.

Calcineurin is a conserved Ca^<2+>/calmodulin-dependent protein phosphatase that plays a critical role in Ca^<2+>-mediated signaling in eucaryotic cells. In fission yeast a calcineurin homologue (Ppb1) is required for cytokinesis and for chloide ion homeostasis but is not essential for cell viability. To elucidate further the functions of calcineurin, we screened for mutations that are synthetically lethal in combination with calcineurin deletion and identified its4^+ gene. The its4^+ gene contains an open reading frame (ORF), encoding a protein of 1807 amino acid residues with calculated molecular weight of 200 Kda. Its4 is a novel evolutionarily highly conserved pretein in mammals, Drosophila melanogaster, Caenorhabditis elegans, and fission yeast Gene disruption experiments were performed and demonstrated that its4^+ gene was essential for vegetative forwth in fission yeast. Interestingly, overexpression of pck1^+gene encoding a protein kinase C and constitutively active calcineurin suppressed the temperature-sensitivity and cytokinesis defect of its4^+ mutant. Together, these results suggest that calcineurin and Its4 seem to share an essential function in cytokinesis and cell growth.

Calcineurin (CN), a highly conserved Ca2+/calmodulin-regulated phosphatase, is a critical component of many calcium-regulated processes in mammalian cells, including T cell activation, cardiac hypertrophy, learning and memory. CN is specifically inhibited by the immunosuppressant drugs cyclosporin A and tacrolimus (FK506), and these drugs have served as valuable reagents in identifying the role of CN in a wide variety of cell types. CN may have additional functions in other cell types, and the loss of these functions may contribute to the side effects of these drugs, which include nephrotoxicity and neurotoxicity. A better understanding of the biological roles of CN in different cell types may promote the development of improved strategies for immunosuppression. We have been studying the CN signal transduction pathway in fission yeast because this system is amenable to genetics and has many advantages in terms of relevance to higher systems. Fission yeast has a single gene encoding the catalytic subunit of CN, ppb1+, that is essential for cytokinesis. We have shown that in fission yeast CN plays an essential role in maintaining chloride ion homeostasis and acts antagonistically with the Pmk1 MAP kinase pathway. We also carried out an isolation and a screening for several FK506-sensitive mutants in order to identify genes that share an essential function for viability with CN. Possible roles of these gene products in cellular functions in relation to calcineurin are discussed.

In fission yeast, calcineurin is required for cytokinesis and ion homeostasis; however, most of its physiological roles remain obscure. To identify genes that share an essential function with calcineurin, we screened for mutations that confer sensitivity to the calcineurin inhibitor FK506 and high temperature and isolated the mutant its8-1. its8(+) encodes a homolog of the budding yeast MCD4 and human Pig-n that are involved in glycosylphosphatidylinositol (GPI) anchor synthesis. Consistently, reduced inositol labeling of proteins suggested impaired GPI anchor synthesis in its8-1 mutants. The temperature upshift induced a further decrease in inositol labeling and caused dramatic increases in the frequency of septation in its8-1 mutants. BE49385A, an inhibitor of MCD4 and Pig-n, also increased the septation index of the wild-type cell. Osmotic stabilization suppressed these morphological defects, indicating that cell wall weakness caused by impaired GPI anchor synthesis resulted in abnormal cytokinesis. Furthermore, calcineurin-deleted cells exhibited hypersensitivity to BE49385A, and FK506 exacerbated the cytokinesis defects of the its8-1 mutant, Thus, calcineurin and Its8 may share an essential function in cytokinesis and cell viability through the regulation of cell wall integrity.

Calcineurin is a Ca2+- and calmodulin-regulated protein phosphatase that is important in Ca2+-mediated signal transduction. Recent application of the powerful techniques of molecular genetics has demonstrated that calcineurin is involved in the regulation of critical biological processes such as T cell activation, muscle hypertrophy, memory development, glucan synthesis, ion homeostasis, and cell cycle control. Notably, specific transcription factors have been shown to play a key role in regulating these functions, and their calcineurin-mediated dephosphorylation and nuclear translocation appear to be a central event in the signal transduction pathways. This review focuses on recent progress in these areas and discusses the evidence for cross-talk between calcineurin and other signaling pathways.

1. Cyclic guanosine monophosphate (cyclic GMP)-mediated mechanism plays an important role in vasodilatation and blood pressure regulation. We investigated the effects of high salt intake on the nitric oxide (NO)-cyclic GMP signal transduction pathway regulating relaxation in aortas of spontaneously hypertensive rats (SHR). 2. Four-week-old SHR and normotensive Wistar-Kyoto rats (WKY) received a normal salt diet (0.3% NaCl) or a high salt diet (8% NaCl) for 4 weeks. 3. In aortic rings from SHR, endothelium-dependent relaxations in response to acetylcholine (ACh), adenosine diphosphate (ADP) and calcium ionophore A23187 were significantly impaired by the high salt intake. The endothelium-independent relaxations in response to sodium nitroprusside (SNP) and nitroglycerin were also impaired, but that to 8-bromo-cyclic GMP remained unchanged. On the other hand, high salt diet had no significant effects on the relaxations of aortic rings from WKY. 4. In aortas from SHR, the release of NO stimulated by ACh was significantly enhanced, whereas the production of cyclic GMP induced by either ACh or SNP was decreased by the high salt intake. 5. Western blot analysis showed that the protein level of endothelial NO synthase (eNOS) was slightly increased, whereas that of soluble guanylate cyclase (sGC) was dramatically reduced by the high salt intake. 6. These results indicate that in SHR, excessive dietary salt can result in downregulation of sGC followed by decreased cyclic GMP production, which leads to impairment of vascular relaxation in responses to NO. It is notable that chronic high salt intake impairs the sGC/cyclic GMP pathway but not the eNOS/NO pathway.

The ppb1(+) gene encodes a fission yeast homologue of the mammalian calcineurin. We have recently shown that Ppb1 is essential for chloride ion homeostasis, and acts antagonistically with Pmk1 mitogen-activated protein kinase pathway. In an attempt to identify genes that share an essential function with calcineurin, we screened for mutations that confer sensitivity to the calcineurin inhibitor FR506 and high temperature, and isolated a mutant, its3-1. its3(+) was shown to be an essential gene encoding a functional homologue of phosphatidylinositol-4-phosphate 5-kinase (PI(4)P5K), The temperature:upshift or addition of FK506 induced marked disorganization of actin patches and dramatic increase in the frequency of septation in the its3-1 mutants but not in: the wild-type cells. Expression of a green fluorescent protein-tagged Its3 and the phospholipase C delta pleckstrin homology domain indicated plasma membrane localization of PI(4)P5K and phosphatidylinositol 4,5-bisphosphate. These green fluorescent protein-tagged proteins were concentrated at the septum of dividing cells, and the mutant Its3 was no longer localized to the plasma membrane. These data suggest that fission yeast PI(4)P5K Its3 functions coordinately with calcineurin and plays a key role in cytokinesis, and that the plasma membrane localization of Its3 is the crucial event in:cytokinesis.

Lithium is the drug of choice for the treatment of bipolar affective disorder. The identification of an in vivo target of lithium in fission yeast as a model organism may help in the understanding of lithium therapy. For this purpose, we have isolated genes whose overexpression improved cell growth under high LiCl concentrations. Overexpression of tol1(+), one of the isolated genes, increased the tolerance of wild-type yeast cells for LiCl but not for NaCl. tol1(+) encodes a member of the lithium-sensitive phosphomonoesterase protein family, and it exerts dual enzymatic activities, 3'(2'),5'-bisphosphate nucleotidase and inositol polyphosphate 1-phosphatase. tol1(+) gene-disrupted cells required high concentrations of sulfite in the medium for growth. Consistently, sulfite repressed the sulfate assimilation pathway in fission yeast. However, tol1(+) gene-disrupted cells could not fully recover from their growth defect and abnormal morphology even when the medium was supplemented with sulfite, suggesting the possible implication of inositol polyphosphate 1-phosphatase activity for cell growth and morphology. Given the remarkable functional conservation of the lithium-sensitive dual-specificity phosphomonoesterase between fission yeast and higher-eukaryotic cells during evolution, it may represent a likely in vivo target of Lithium action across many species.

Calcineurin is a conserved Ca2+/calmodulin-dependent protein phosphate that plays a critical role in Ca2+-mediated signaling in various cell types and is a target molecule of immunosuppressants, FK506 and cyclosporin A. Fission yeast cells lacking functional calcineurin (Δppb1) are viable: however, showed cytokinesis abnormality and Cl--sensitive growth defect. Wild-type cells treated with FK506 showed an identical phenotype to Δppb1, suggesting that FK506 inhibited calcineurin activity in fission yeast. To characterize regulatory pathways that overlap with calcineurin, we have isolated mutants that show. Immunosuppressant-and chloride ion-sensitivity (cis mutant) in fission yeast. We have identified 5 genetic loci (cis1-5) that display its mutant phenotype. cis2 mutant showed abnormal cell morphology (multiseptated, and branched). Cells displayed increased sensitivity to β-glucanase. These data suggest that cis2+ gene is involved in maintaining cell wall integrity. cis2+ gene encoded for a type 2 myosin heavy chain. cis2 mutation was synthetically lethal with calcineurin deletion, indicating that cis2+ and calcineurin shared an essential function for cell viability. These results suggest that calcineurin plays an important role in cell morphogenesis through regulation type 2 myosin heavy chain.

The mitogen-activated protein kinase (MAPK) pathway is a highly conserved eukaryotic signalling: cascade that converts extracellular signals into various outputs, such as cell growth and differentiation(1-3), MAPK is phosphorylated and activated by a specific MAPK kinase (MAPKK)(4): MAPKK is therefore considered to be an activating regulator of MAPK. Pmk1 is a MAPK that regulates cell integrity(5) and which, with calcineurin phosphatase, antagonizes chloride homeostasis(6) in fission yeast. We have now identified Pek1, a MAPKK for Pmk1 MAPK. We show here that Pek1, in its unphosphorylated form, acts as a potent negative regulator of Pmk1 MAPK sig-nailing. Mkh1(7), an upstream MAPKK kinase (MAPKKK), converts Pek1 from being an inhibitor to an activator. Our results indicate that Pek1 has a dual stimulatory and inhibitory function which depends on its phosphorylation state. This switch-like mechanism could contribute to the all-or-none physiological response mediated by the MAPK signalling pathway.

Calcineurin is a highly conserved and ubiquitously expressed Ca2+- and calmodulin-dependent protein phosphatase. The in vivo role of calcineurin, however, is not fully understood. Here, we show that disruption of the calcineurin gene (ppb1(+)) in fission yeast results in a drastic chloride ion (Cl-)-sensitive growth defect and that a high copy number of a novel gene pmp1(+) suppresses this defect, pmp1(+) encodes a phosphatase, most closely related to mitogen-activated protein (MAP) kinase phosphatases of the CL100/MKP-1 family, Pmp1 and calcineurin share an essential function in Cl- homeostasis, cytokinesis and cell viability Pmp1 phosphatase dephosphorylates Pmk1, the third MAP kinase in fission yeast, in vitro and in vivo, and is bound to Pmk1 in vivo, strongly suggesting that Pmp1 negatively regulates Pmk1 MAP kinase by direct dephosphorylation. Consistently, the deletion of pmk1+ suppresses the Cl--sensitive growth defect of ppb1 null. Thus, calcineurin and the Pmk1 MAP kinase pathway may play antagonistic functional roles in the Cl- homeostasis.

A heat shock cognate gene from the fission yeast Schizosaccharomyces pombe (Sp), designated hsc1(+), was cloned. The putative translation product of hsc1(+) contains 613 aa, with an estimated molecular mass of 67 205 Da, and is more similar to the Saccharomyces cerevisiae (Sc) heat shock cognate protein SSB1 (69% identity) than the Sp heat-inducible ssp1(+) gene product (41% identity). The hsc1(+) mRNA was abundant during steady-state growth at 23 degrees C and decreased upon heat shock. Immunoblot analysis showed that the hsc1 protein is also abundant and constitutively expressed, however, we could not observe significant change in the protein level upon heat shock. DNA blot analyses indicated that hsc1(+) is localized in Sp chromosome II, and suggested that the Sp genome contains a relatively smaller number of HSP70 genes compared with the Sc genome.

We have isolated a gene, pmk1+, a third mitogen-activated protein kinase (MAPK) gene homolog from the fission yeast Schizosaccharomyces pombe. The predicted amino acid sequence shows the most homology (63 to 65% identity) to those of budding yeast Saccharomyces Mpk1 and Candida Mkc1. The Pmk1 protein contains phosphorylated tyrosines, and the level of tyrosine phosphorylation was increased in the dsp1 mutant which lacks an attenuating phosphatase for Pmk1. The level of tyrosine phosphorylation appears constant during hypotonic or heat shock treatment. The cells with pmk1 deleted (Δpmk1) are viable but show various defective phenotypes, including cell wall weakness, abnormal cell shape, a cytokinesis defect, and altered sensitivities to cations, such as hypersensitivity to potassium and resistance to sodium. Consistent with a high degree of conservation of amino acid sequence, multicopy plasmids containing the MPK1 gene rescued the defective phenotypes of the Δpmk1 mutant. The frog MAPK gene also suppressed the pmk1 disruptant. The results of genetic analysis indicated that Pmk1 lies on a novel MAPK pathway which does not overlap functionally with the other two MAPK pathways, the Spk1-dependent mating signal pathway and Sty1/Spc1/Phh1-dependent stress-sensing pathway. In Saccharomyces cerevisiae, Mpk1 is involved in cell wall integrity and functions downstream of the protein kinase C homolog. In contrast, in S. pombe, Pmk1 may not act in a linear manner with respect to fission yeast protein kinase C homologs. Interestingly, however, these two pathways are not independent instead, they regulate cell integrity in a coordinate manner.

杉浦が独自の創薬探索手法により発見したERK MAPKシグナル調節剤である＜ACA-28＞は、ERK活性依存的細胞死を、がん細胞選択的に誘導することにより、抗腫瘍効果を発揮する。本研究の目的は「ACA-28は、いかなる分子を標的として、ERK MAPKを活性化するのか？」「ACA-28を介するがん細胞選択的な増殖抑制メカニズムは？」という問いを明らかにすることにより、＜ERK依存的細胞死＞に関わる細胞内シグナル伝達経路を浮き彫りにすることである。今年度は、ACA-28およびそのリード化合物であるGT-7が各種のRas変異を有する膵臓がんに対して細胞死を誘導できることを証明した。特にKRasQ61H変異を有する膵臓がん細胞であるT3M4に対して、ERK依存的細胞死を誘導できることを世界で初めて証明した。一方、KRasG12V変異を有するPANC-1細胞はGT-7依存的な細胞死に抵抗性を示すこと、AKTの活性化がGT-7依存的な細胞死抵抗性のメカニズムであることも証明した。本研究により、KRAS変異を有する膵臓がん細胞に対してGT-7は有効なERK依存的細胞死を誘導するとともに、GT-7とAKT阻害剤の併用が膵臓がんの新たな治療戦略となりうることも明らかになった。ACA-28およびGT-7の標的分子に関しては、ACA-28にビオチン修飾を行った標識化合物を合成し、プルダウン実験と質量分析の手法によりACA-28結合タンパク質を複数同定した。また、リン酸化プロテオミクスの手法を用いてACA-28の標的候補因子群を同定している。現在これらの分子とACA-28の結合やACA-28依存的リン酸化のvalidationを行うとともに、これらの標的候補分子のノックダウンがACA-28あるいはGT-7依存的な細胞死に与える影響を解析している段階である。

The purpose of this research project was to elucidate novel regulatory mechanisms of the Pmk1 MAPK signaling pathway in fission yeast and its application to genome-based drug discovery. We performed chemicalgenomics screens, utilizing the functional interaction between MAPK and calcineurin, and identified regulators (such as Cwg2, Rho4 and Rho5) and targets of Pmk1 MAPK in addition to several compounds that modify the ERK MAPK signaling pathway in mammals. Furthermore, we performed genome-wide identification of the genes involved in the sensitivities to FK506, Rapamycin and FTY720 and elucidated as-yet-unidentified functional interactions between MAPK and these gene products. Collectively, our data will contribute to the development of novel and effective therapeutic approaches for diseases associated with abrogated MAPK signaling activity.

生物の持つ複雑で巧妙な形態・機能の獲得には、RNA段階での遺伝子発現制御プログラムが極めて重要な役割を果たします。発生・分化の基本原理としての「非対称性」と遺伝子産物の「多様性」の獲得原理を理解するためには、RNAレベルでの制御（RNAプログラム）を包括的に理解する必要があります。本新学術領域研究「多様性と非対称性を獲得するRNAプログラム（RNA制御学）」は、このRNAプログラムの分子機構とその生理的意義の解明を目指しました。RNAレベルでの制御を研究する若手ならびに中堅の研究者を中心とした組織を構成し、手法、材料や情報を共有しながら交流を行い、研究を進めました。分子・細胞レベルから遺伝学を用いた高次生命現象解析まで、幅広いアプローチでRNA研究を展開し必要に応じて共同研究を積極的に進めました。平成２０－２４年度までの研究期間において、計画研究のみならず公募研究においても優れた研究成果を上げる事ができ、当初の目的を概ね達成できました。また、多数の若手ならびに中堅研究者がプロモーションされました。領域内の連携を促進する支援班活動等を行った結果、共著論文も発表することが出来ました。平成２５年度は、理化学研究所や関連する新学術領域研究「非コードRNA」とRNA Sciences in Cell and Developmental Biology III共催した、内外のRNA研究者から高い評価をうけ、本領域における優れた研究を国内外に宣伝する非常に良い機会となりました。また、研究成果報告書を作成し、班員と評価者の先生方、関連分野の研究者に配布しました。

We identified the mRNA-binding protein Nrd1 and demonstrated that Nrd1 binds to and regulates mRNA stability of the Myosin mRNA. We also showed that Pmk1 MAPK, a homologue of ERK in fission yeast regulates the RNA-binding activity of Nrd1 in a phosphorylation-dependent manner. Moreover, Nrd1 translocated to the stress granules in a MAPK-mediated phosphorylation-dependent manner, thereby regulates stress tolerance in fission yeast.

This project aims to identify regulators of MAPK signaling using fission yeast S. pombe as a model organism. We identified negative regulators of Pmk1 MAPK, such as ptc1+, ptc3+, encoding PP2Cs, and ecm33+, encoding a cell surface protein. We also identified targets of Pmk1 including the Atf1 transcription factor and the Nrd1 RNA-binding protein. We also demonstrated feedback mechanisms involving these regulators of Pmk1 MAPK and identified several compounds with potent MAPK inhibitory action.

本研究では,高等生物と極めて近い細胞周期システムを有する分裂酵母モデル生物を用いた<分子遺伝学的アプローチ>と<リン酸化プロテオーム解析>を軸として、細胞増殖と分化のスイッチ機構を分子レベルで明らかにすることを試みた。 特に、細胞増殖と細胞質分裂に重要な働きをするMAPキナーゼであるPmk1の細胞周期における働きに焦点をあてた解析を行った。Pmk1 MAPキナーゼの標的基質として、従来減数分裂において重要な働きをしていると報告されていたRNA結合タンパク質であるNrdlを同定した。また、Pmk1は外界からの刺激に応じてリン酸化、活性化されることは報告されていたが、今回Pmk1 MAPキナーゼの活性化が細胞周期依存的に変動することも発見した。このような細胞周期依存的なMAPキナーゼの活性や標的遺伝子群のリン酸化あるいは発現状態を定量的にアッセイできるレポーターシステムも構築した。Pmk1 MAPKはミオシン重鎖や軽鎖の変異体と遺伝学的な関係を示すことも明らかとなった。すなわち、ミオシン軽鎖の変異体や重鎖変異体の示す温度感受性がPmk 1MAPKノックアウト細胞では回復した。これらの結果から、Pmk1 MAPKはミオシンとの機能的な関係を通して、細胞質分裂を制御する可能性が示唆された。 また、新たに細胞質分裂に異常を示す変異体の取得を行い、高等生物のPSTPIPとホモロジーの高いタンパク質を同定した。このタンパク質はPmk1 MAPKと機能的な関係があることも明らかにした。具体的にはPSTPIPホモログを過剰発現するとMAPキナーゼが活性化することから、PSTPIPホモログはMAPキナーゼの上流で細胞質分裂シグナルを伝達すると考えられる。

1.カルシニューリン活性のリアルタイムモニタリング:カルシニューリンは細胞内Ca^<2+>により活性化されるタンパク質脱リン酸化酵素で,酵母からヒトにまで保存されたカルシウムシグナル系の中心的分子であり,臓器移植時に用いられる免疫抑制薬の分子標的である。本研究では,生細胞におけるカルシニューリン活性をリアルタイムにモニターするシステムを確立し,分裂酵母には細胞壁の異常を感知するMAPキナーゼに依存した経路と細胞外Ca^<2+>を感知するMAPキナーゼに依存しない経路の2っが存在することを発見した。 2.バルプロ酸(VPA)の細胞内輸送に対する影響:VPAは抗てんかん薬として良く知られており,最近はがん化学療法の奏功性をあげることが報告されているが,そのメカニズムたついては不明である。VPA感受性を示す変異体を単離し,その原因遺伝子を決定したところ細胞内輸送で重要な働きをするVps45をコードする遺伝子だった。さらに,治療濃度に相当する低濃度のVPAが分泌などの細胞内輸送に影響を与えることを発見した。分裂酵母ではVPAを投与すると細胞内輸送が抑制されることで細胞壁に異常を来たし,上記1で述べたMAPキナーゼを介する経路によりCa^<2+>/カルシニューリン系が活性化されることも示した。 3.細胞内輸送で重要な働きを担うRab GDI (GDP dissociation inhibitor)の活性のリン脂質による制御:免疫抑制薬(カルシニューリン阻害薬)感受性と高温感受性を同時に示す分裂酵母変異体を単離し,その遺伝子を決定したところ細胞内輸送で重要な役割を果たすRab GDIをコードしていた。さらに,本変異体の高温感受性を相補する遺伝子としてリン脂質輸送体をコードする遺伝子を単離した。さらに,Rab GDIの活性がリン脂質により制御されていることを明らかにした。

This research aims to unravel the regulatory mechanisms of the signal transduction pathway regulated by RNA-binding proteins. We utilized the fission yeast model system and molecular genetic approach to identify RNA binding proteins that regulate various signaling pathways including MAP kinase pathways. We identified several RNA-binding proteins including Rncl that encodes a highly conserved KH-type RNA-binding protein. Rncl overexpression decreased the activation of the Pmkl MAPK signaling and Rncl deletion increased the phosphorylation level of the Pmk1 MAPK signaling thus indicating that Rncl acts as a negative regulator of the Pmkl MAPK signaling. We demonstrated that Rncl binds and stabilizes Pmpl mRNA that encodes a MAPK phosphatase for Pmkl MAPK Moreover, Pmk1 MAPK phosphorylates Rncl which regulates the RNA-binding activity of Rncl to bind and stabilize Pmpl mRNA. We also identified the tad3-1 mutant that encodes a mutation in the tRNA deaminase. Notably, we demonstrated that the tad3-1 mutants displayed defects in cell cycle progression at G1/S and G2/M transitions thus indicating that the wobble tRNA modification is essential to cell cycle in fission yeast. We also identified an RRM-type RNA binding protein that stabilizes the mRNA encoding an actin-binding protein. Notably, the MAPK Pmk1 directly phosphorylates the RRM-type RNA-binding protein and this phosphorylation negatively regulates the activity of the RNA-binding protein to bind target mRNAs. The MAPK pathways have long been known as a transcriptional regulator of cellular signaling by phosphorylating various transcription factors. Our data suggest a novel paradigm involving the MAPK-mediated regulation of the post-transcriptional RNAmetabolism.

Recent progress in the Schizosaccharomyces pombe genome project has revealed that most of genes required for the synthesis of phosphoinositides are conserved between S.pombe and Saccharomyces cerevisiae. We have cloned the gene, vps34/pik3, encoding a phosphatidylinositol (PtdIns) 3-kinase from S.pombe. In this project, we have identified and characterized PX and FYVE domain-containing proteins in S. pombe. 1.Among various PX domain-containing proteins, Vps5p and Vps17p, homologues of sorting nexins, were found to be required for efficient sporulation, vacuolar protein sorting and vacuolar biogenesis in S.pombe cells. 2.The FYVE-domain containing Ste12 protein catalyzes a PtdIns 3-P 5-kinase, which is required for efficient mating. Suppressor mutants for sterility of ste12 cells were identified. Of these, sst4/vps27 has been identified. The fission yeast Sst4p contain FYVE domain, and Sst4p is shown to be required for vacuolar protein and multivesicular sortings in S.pombe. 3.Valproic acid (VPA) is widely used to treat epilepsy and manic-depressive illness. A genetic screen for fission yeast mutants that show hypersensitivity to VPA was isolated. One of the genes that we identified was vps45+, which encodes a member of Sec1/Munc18 family that is implicated PtdIns-dependent membrane trafficking.

1. In fission yeast, calcineurin dephosphorylates and activates the Przl transcription factor. Here, we identified the calcineurin-dependent response element (CDRE) in the promoter region of przl(+) gene and monitored the calcineurin activity in living cells using a destabilized luciferase reporter gene fused to three tandem repeats of CDRE. The Pck2 protein kinase C-Pmkl mitogen-activate protein kinase pathway was required for the stimulation of calcineurin via Yam8/Cchl-mediated Ca(2+) influx, but it was not required for the stimulation by elevated extracellular Ca(2+), suggesting two distinct pathways for calcineurin activation. 2. Here we isolated vic (viable in the presence of immunosuppressant and chloride ion) mutants. One of the mutants, vicl-1, carried a missense mutation in the cppl+ gene encoding a beta subunit of the protein farnesyltransferase. Analysis of the mutant strain revealed that Rho2 is a novel target of Cppl. Moreover, Cppl and Rho2 act upstream of Pck2-Pmk1 MAPK signaling pathway, thereby resulting in the vic phenotype upon their mutations. 3. To gain further insights into the molecular mechanisms of valproic acid action (VPA), a genetic screen for fission yeast mutants that show hypersensitivity to VPA was performed. One of the genes we identified was vps45+ which encodes a member of the Sec1/Munc18 family that is implicated in membrane trafficking. Our results suggest that VPA affects membrane trafficking, which leads to the enhanced sensitivity to cell wall damage in fission yeast. 4. In the same screen using the immunosuppressant drug FK506 in fission yeast, we isolated gdil-ill, a mutant allele of the essential gdil+ gene encoding Rab GDP-dissociation inhibitor. Notably, overexpression of spo20+, encoding a phosphatidylcholine/phosphatidylinositol transfer protein, rescued gdil-ill mutation. The gdil-ill and spo20-KC104 mutations are synthetically lethal. Our findings suggest that Spo20 modulates Gdil function via regulation of phospholipid metabolism of the membranes.

1.2つのRas関連Rabファミリータンパク質ryh1とypt3の相互作用 Rabファミリータンパク質は,Ras関連タンパク質の中でも最大のファミリーを形成しており,ヒトでは60以上の遺伝子でコードされている。また,細胞内小胞輸送を介して,がん細胞の増殖や転移にも関与している。分裂酵母ゲノムはこれまで報告された真核細胞の中で最も少ない9個のRabファミリータンパク質をコードしており,Rabの機能解析に最適のモデル生物である。本研究では,小胞をエンドソームからリサイクルするRab6ホモログのRyh1をコードする遺伝子を単離,解析した。さらに,Ryh1は別のRabをコードするYpt3変異体と遺伝学的関係を示し,機能的関係も示すことから,これら2つのRabタンパク質が共同的に働くこと,さらに細胞内シグナル伝達により制御されることが示唆された。 2.PI4P5キナーゼとPKC/マップキナーゼの細胞統合性制御機構における関係 its3変異体は高温感受性と免疫抑制薬感受性を同時に示す分裂酵母変異体で,必須遺伝子であるPI4P5キナーゼをコードしている。今回,我々は高発現によりこれらの表現型を抑圧する遺伝子としてホスフォリパーゼCをコードするplc1を単離した。遺伝学的,細胞生物学的,生化学的解析により,plc1はジアシルグリセロールを産生することで,しかし,PKC/マップキナーゼ系は介さずに細胞統合性を制御することが明らかになった。 3.カルシニューリンの活性化と抑制における制御サブユニットの役割 モデル生物の系を用いて,制御サブユニットがないとカルシニューリンの生理的活性化が起こらないことを示した。さらに,分裂酵母モデル系を用いて,分子遺伝学的解析により,免疫抑制薬・結合タンパク質複合体は,活性化したカルシニューリンにのみ結合し,不活性化状態のものには結合しないことを明らかにした。

高等生物に極めて近い細胞内情報伝達経路を有する分裂酵母モデル生物を用いて、カルシウムシグナル伝達経路による細胞周期制御機構を解析した。特にカルシウム依存性に活性化されるカルシニューリン、およびProtein Kinase C, MAPキナーゼなどを中心に解析を行った。カルシニューリンの特異的阻害薬であるFK506に対して感受性を示す変異体を取得した。これらの変異体は<細胞増殖に対してカルシニューリン活性が必須である>ことからこれらの変異体の原因遺伝子を同定することで、カルシニューリン経路と密接に関連する遺伝子が同定できると考えられる。現在までにこれらの変異体の原因遺伝子として、細胞内輸送に関与する低分子量Gタンパク質Rab11のホモログ,Ypt6のホモログ、クラスリンアダプター複合体のμ1サブユニットApm1、などを同定してきた。 さらに、これらのタンパク質は細胞内輸送におけるゴルジ・エンドゾームから細胞膜へ至る分泌の過程を制御することによってカルシニューリンと共同的に細胞質分裂に関与することを報告した。 また、Protein Kinase C経路において機能する分子を同定した結果、細胞質分裂に関与するセプチンを同定した。セプチンノックアウト細胞は細胞質分裂の異常を示し、細胞の成長端やmedial regionに局在するが、これらの局在がProtein kinase Cをノックアウトすることで異常になること、さらに、Protein Kinase Cとセプチンが複合体を形成することも見出した。またセプチンのPKCコンセンサス配列に変異を入れるとセプチンの機能低下が起こることを証明した。これらの結果から、セプチンはProtein kinase C経路において細胞質分裂をコントロールしている可能性が示唆された。

高等生物に極めて近い細胞内情報伝達経路を有する分裂酵母モデル生物を用いて、細胞内シグナル伝達による細胞内輸送の制御機構を解析した。特にカルシウム依存性に活性化されるタンパク質脱リン酸化酵素であるカルシニューリンを介するシグナル経路を中心に解析を行った。カルシニューリンの特異的阻害薬であるFK506に対して感受性を示す変異体を取得した。これらの変異体は<細胞増殖に対してカルシニューリン活性が必須である>ことからこれらの変異体の原因遺伝子を同定することで、カルシニューリン経路と密接に関連する遺伝子が同定できると考えられる。我々は現在までにこれらの変異体の原因遺伝子として、低分子量Gタンパク質であるRab11のホモログであるYpt3,クラスリンアダプター複合体のμ1サブユニットであるApm1などを同定してきた。さらに、Apmはゴルジ・エンドゾームにおいて小胞形成に重要な働きをするとともに、分泌の過程においても関与することで細胞質分裂や細胞壁合成を制御すること、これらの働きにカルシニューリン活性が必須であることを示した。さらに、Apm1はゴルジ・エンドゾームのみならずmedial regionに局在するとともに、核とSpindle pole bodyにも局在することを明らかにした。 また、低分子量Gタンパク質Ypt6のホモログRyh1を同定し、Ryh1とYpt3という二つの低分子量Gタンパク質がゴルジから細胞膜へいたる分泌の過程で協同的に機能することを証明した。新たに免疫抑制薬感受性変異体原因遺伝子としてRab GDIも同定した。Gdi1変異蛋白質は細胞質におけるタンパク量が激減していることを見出すとともに、gdi1変異体の示す細胞内輸送の異常をPhosphatidyl inositol transfer proteinであるSpo20が回復できるということを明らかにした。

研究代表者らが発見した分裂酵母新規マップキナーゼPmk1系は,細胞増殖とともに細胞形態形成,特に細胞質分裂において重要であり,カルシニューリンと機能的関連性をもつことが既に明らかにされている。また,その構造はヒトの細胞増殖を制御するマップキナーゼと高い相同性を示すので,分裂酵母におけるマップキナーゼの機能解析は,ヒトのマップキナーゼ異常による病態や分子標的治療に直結している。本年度は以下のような結果を得た。 1.カルシニューリン制御サブユニットの役割の解明 分裂酵母のカルシニューリン制御サブユニットを新たにクローニングし,遺伝子ノックアウトを行なった。ノックアウト細胞に種々の遺伝子を過剰発現することで表現型の変化を調べたところ,制御サブユニットがin vivoにおけるカルシニューリン活性に必須であることが明らかになった。 2.マップキナーゼ経路におけるmRNA安定性制御の重要性 カルシニユーリンのノックアウト表現型を相補する多コピー抑圧遺伝子の一つを単離し,配列決定をしたところ,RNA結合蛋白質をコードしていた。このRNA結合蛋白質は,Pmk1マップキナーゼを抑制すると思われるPmp1マップキナーゼホスファターゼのmRNAと結合し,安定化するマップキナーゼの抑制因子であることが明らかになった。 3.カルシニューリンと機能的に関連する細胞内輸送因子アダプチンApm1の発見 温度感受性と免疫抑制薬感受性を指標とした遺伝学的スクリーニングにより遺伝子apm1を発見した。apm1遺伝子ノックアウト細胞は、カルシニューリン活性に対する依存性を示すとともに,ゴルジ体から細胞膜への輸送に異常を示し,Apm1がゴルジから細胞膜への輸送に働いていることが明らかになった。また,Apm1は核にも局在し,機能していることが示唆された。

研究代表者等は、哺乳動物細胞に極めて近い細胞内情報伝達系を持ち、厳密な分子遺伝学的解析が可能な分裂酵母モデル系を用いて、カルシウム依存性脱リン酸化酵素であるカルシニューリンが細胞質分裂等の多様な細胞機能を制御することを明らかにしてきた。この過程で、カルシウムシグナルがタンパク質の分解や輸送系の制御を示唆する多くの結果を得ている。本研究は、分裂酵母モデル系の分子遺伝学的解析を行うことでカルシウムシグナルによるタンパク質の産生・輸送・分解の制御機構を解明し、この制御機構の破綻による細胞病態を明らかにする事を目的とした。 1)細胞内小胞輸送を担うアダプチン遺伝子とカルシニューリンの遺伝学的関連について 高温感受性と免疫抑制薬感受性を同時に示す分裂酵母変異体を単離し,その遺伝子を決定した。その結果,変異遺伝子は,ゴルジ・エンドソームからの小胞輸送を担うことが知られているミュー・アダプチンをコードしていることが明らかになった。また,アダプチン遺伝子ノックアウトでも同様の表現型が認められることも確認した。これらの結果から,細胞内輸送とカルシニューリンとの関連が明らかになった。 2)mRNA制御における安定性制御の重要性について タンパク質産生においては,mRNA量制御がきわめて重要である。これまでは,シグナル伝達系によりmRNA量が制御される場合は,主に転写の制御が考えられていたが,我々は,分裂酵母ではカルシニューリンとマップキナーゼがクロライドイオンホメオスタシスに関して拮抗的関係にあることを利用し,RNA結合タンパク質のリン酸化によるmRNAの安定性制御が重要であることを明らかにした。

分裂酵母は高等生物に極めて近い細胞内情報伝達経路を有する優れたモデル生物である。我々はMAPKシグナルのフィードバック制御に関わるRNA結合タンパク質Rnc1を同定した。本研究は分子遺伝学的手法を用いてRNA結合タンパク質の標的分子および機能的関連因子を同定し、MAPKシグナル制御におけるRNA結合タンパク質の役割を明らかにすることを目的とする。まずDNAマイクロアレイを用いてRnc1ノックアウト細胞と野生細胞で発現が変化している遺伝子群を同定した。その結果複数の翻訳に関与すると考えられる遺伝子群がノックアウト細胞で発現上昇していることが明らかとなったのでこれらの遺伝子をPCR法によりクローニングし、遺伝子破壊などの機能解析を開始した。 さらに、分子遺伝学的手法により新たにRRM型のRNA結合タンパク質であるNrd1を同定した。Nrd1は従来減数分裂や分化に関与することが報告されていたが、我々はNrd1を過剰発現することで細胞分裂が異常になる変異体の温度感受性や細胞形態異常を正常に回復することを示した。この結果は、Nrd1は減数分裂や分化のステップのみならず細胞分裂や細胞形態にも重要な働きをしていることを示唆している。また、Nrd1と結合するタンパク質としてProtein kinase Cのターゲットでもある高等生物のRACK1のホモログであるcpc2+遺伝子を取得した。Cpc2ノックアウトは接合に異常を示すことからCpc2は減数分裂に重要な働きをしていることがわかった。Nrd1タンパク質とCpc2タンパク質のGFP融合タンパク質を作製し、細胞内局在を観察した結果どちらのタンパクも細胞質内に均一に局在していることが明らかとなった。

Calcineurin (protein phosphatase 2B), the only serine/threonine phosphatase under the control of Ca2+/calmodulin, is an important mediator in signal transmission, connecting the Ca2+-dependent signalling to a wide variety of cellular responses. Calcineurin is an in vivo target of the immunosuppressant drug FK506 in fission yeast, and inhibition of calcineurin activity by gene disruption or by the addition of FK506 to the media does not affect the vegetative growth of fission yeast. We performed a genetic screen to search for the mutations that show sensitivity to the immunosuppressive drug FK506, and identified eight complementation groups. We identified PI4P5K Ypt3 small GTPase, subunits of clathrin-adaptor complex and demonstrated that these molecules and calcineurin share an essential function in cellular events such as cytokinesis, cell integrity and membrane trafficking. We also identified a downstream target of calcinerin ; Prz1, a zinc finger-type transcription factor. Prz1 was shown to be dephosphorylated by calcineurin and its transcriptional activity was also under the control of calcineurin-mediated signalling. Another approach to identify molecules that functionally interact with calcineurin signalling utilizes our discovery that calcineurin and the Pmk1 MAPK signalling function antagonistically in the Cl- homeostasis of fission yeast. Using this approach, we identified pmp1+ encoding MAPK phosphatase, pek1+ encoding MAPK kinase, and rnc1+, encoding an RNA-bindign protein. We also demonstrated that Pmp1 dephosphorylates and inactivates Pmk1, thereby negatively regulates Pmk1 siganlling. Rnc1 is a KH-type RNA-binding protein that binds and stabilizes the Pmp1 mRNA, thus acting as a negative feedback regulator of MAPK signalling.

1.マップキナーゼ経路を制御する新規RNA結合蛋白質Rnc1の発見:カルシニューリンのKO表現型を相補する多コピー抑圧遺伝子の一つを単離し,配列決定をしたところ,酵母からヒトまで高度に保存されたKHドメインを持つ新規RNA結合蛋白質をコードしていた。Rnc1の遺伝子をノックアウトするとPmk1マップキナーゼの燐酸化が亢進している事が確認された。また、このRNA結合蛋白質は、Pmk1マップキナーゼを抑制すると思われるPmp1マップキナーゼホスファターゼのmRNAと結合する事が示された。Rnc1KO株ではPmp1mRNAが不安定である事も示された。さらに,Pmk1はRnc1を直接燐酸化し,燐酸化されたRnc1は燐酸化されていないRnc1よりも強くPmp1mRNAに結合し,安定化することが明らかになった。この結果,mRNAの増加は転写制御だけではなく,mRNAの安定性制御という別のメカニズムの存在が明らかになった。 2.zinc finger型転写因子Prz1の同定:カルシニューリンの下流で働く転写因子Prz1を同定した。さらにカルシニューリンの下流にPrz1を介する経路と介さない経路があり,マップキナーゼと括抗するのはPrz1を介さない系であることも明らかにした。 3.ユビキチンホメオスターシスとストレス応答に関与するLub1の発見:ストレス感受性を指標としたスクリーニングによりlub1遺伝子を発見したlub1遺伝子KO細胞は,細胞内ユビキチン量が著しく低下したことから,lub1遺伝子はユビキチン代謝に重要な役割を果たすことが示された。

研究成果:分裂酵母にカルシニューリンが存在することに着目し、細胞増殖にカルシニューリン(CN)の活性が必須であるような変異体(免疫抑制薬に感受性を示す)を10種分離し、its(immunosuppressant and temperature sensitive)変異体と命名し,原因遺伝子の同定と機能解析を行った。本年度はits3変異体およびits8変異体についての解析結果を報告する。 1)its3変異体の原因遺伝子はPI45P2合成酵素であるPI4(P)5 kinaseをコードしており,種を越えて高度に保存されている。its3変異体ではPI(45)P2の量が著明に低下しており,its3遺伝子を発現するとPI(45)P2の量が増加した。its3変異体は制限温度,あるいはFK506処理により,アクチンパッチの異常と細胞質分裂異常を示すことを明らかにした。さらに,GFP-Its3は細胞膜と中隔に局在し,PI(45)P2と高い親和性を示すPLC-PHドメインの局在と一致した。以上の結果から,カルシニューリンとPI4(P)5 kinaseは協同的に分裂酵母の細胞質分裂,アクチン細胞骨格系の維持に関与していることが示唆された。(業績1) 2)its8変異体の原因遺伝子はGPIアンカー合成酵素をコードしており,酵母から高等動物まで高度に保存されている。its8変異体は高温下でinositolの取り込みが著明に低下していたことから,its8変異体ではGPIアンカー合成が低下していることを明らかにした。さらに,its8変異体の表現型を解析した結果,its8変異体は細胞壁が脆弱であること,細胞質分裂と細胞極性が異常であることを示した。以上の結果から,カルシニューリンとGPIアンカー合成酵素は細胞増殖のみならず,細胞壁のintegrityの維持,細胞質分裂に重要な機能をシェアしていることが示唆された。(業績2)

カルシニューリンは酵母から哺乳動物に至るまで高度に保存されたタンパク質脱燐酸化酵素である。野生型分裂酵母では免疫抑制薬であるFK506によりカルシニューリンの機能を抑制しても成育に影響がない。この現象に基づいて、我々は分裂酵母をモデル生物として用いて、FK506の存在下で致死となる変異体(its変異体)の網羅的スクリーニングを展開し、多数の変異体を単離している。本研究では、これらのカルシニューリンと機能的に関連する遺伝子産物とカルシニューリンとの相互作用の解析を通して、カルシニューリンが関与する蛋白質脱リン酸化及びリン酸化ネットワークを明らかにする事を目的としている。本年度は以下の2つの点について解析し、成果を発表した。 1.低分子量GTP結合タンパク質RabファミリーであるYpt3/Its5の機能解析を行った。Its5は細胞質分裂、細胞壁形成,および液胞の融合などの生理機能に重要な役割を示すことが明らかとなった。さらに、Its5はエキソサイトーシスのゴルジ、およびポストゴルジのステップにおいてカルシニューリンと協同的に働いていることが証明された。これらの結果より、カルシニューリンが細胞内輸送系の制御に重要な役割を果たしていることが示唆された。 2.細胞隔壁形成に関与するタンパク質リン酸化酵素Its10/Cdc7の機能解析を行った。分裂酵母カルシニューリンは細胞質分裂のcell separationのステップに重要であるため、カルシニューリンノックアウトは多核・多隔壁の表現型を示すと考えられてきた。しかし、われわれが単離したits10/cdc7変異体の解析から、カルシニューリンがseptation initiation network (SIN)の経路をターゲットにして機能することが示唆された。この結果より、カルシニューリンは隔壁形成とcell separationの両方のステップで重要な役割を果たしていることが示唆された。

研究代表者らが発見した新規マップキナーゼPmk1系は,細胞増殖とともに細胞形態形成,特に細胞質分裂において重要であり,カルシニューリンと機能的関連性をもつことが既に明らかにされている。また,その構造はヒトの細胞増殖を制御するマップキナーゼと高い相同性を示すので,分裂酵母における本マップキナーゼの機能解析は,ヒトのマップキナーゼ異常による病態や分子標的治療に直結している。本研究では,研究代表者らが発見した分裂酵母マップキナーゼとカルシニューリンとの拮抗的関係を利用し,カルシニューリンノックアウトの表現型を過剰発現で相補する遺伝子をクローニングすることで,マップキナーゼ系の制御因子を同定することを目的としている。本年度は,Pmk1マップキナーゼ系のネガティブフィードバックに重要と思われる新規RNA結合蛋白質を単離した。また,マップキナーゼ/カルシニューリン系と機能的に関連する遺伝子として,細胞質分裂制御,特にSIN (septation initiation network)経路において重要な働きをしている蛋白質燐酸化酵素をコードする遺伝子を同定した。本研究で発見した新規RNA結合蛋白質はマップキナーゼの抑制因子であるマップキナーゼホスファターゼのmRNAを安定化することでマップキナーゼ系を抑制する事が示唆された。また,Pmk1マップキナーゼノックアウトでは細胞質分裂が異常になる事が知られているが,本研究でその下流にSIN経路や細胞内輸送経路が存在する事が示唆された。

本研究は,哺乳動物細胞に極めて近い細胞内情報伝達系を持つ分裂酵母モデル系を用いて,カルシウムによる蛋白質の一生の制御機構を分子遺伝学的に解明しようとするものである。カルシウムにより蛋白分解や細胞内輸送が制御される現象は良く知られているが,その分子機構は殆ど不明である。我々は,分裂酵母を材料として,カルシウムシグナリングとストレス応答の分子遺伝学的研究を進め,本年度は以下の結果を得た。 (1)カルシウムによるユビキチン系制御に関連する遺伝子を単離,解析するため,変異により様々なストレスに対して超感受性を示す変異体を解析した結果,lub1^+という新規遺伝子を単離した。この遺伝子を破壊すると細胞内ユビキチン量が非常に低下し,細胞外のカルシウムに対して超感受性を示した。Lub1ノックアウトはカルシウム以外にも紫外線,高温などに対して感受性を示した。Lub1はCdc48と結合することが示され,Cdc48はLub1の機能に対して抑制的に働いていることが示唆された。(2)カルシウム/カルモデュリン依存性タンパク質脱燐酸化酵素カルシニューリン遺伝子破壊株において,小胞体ストレスに対する応答の異常が示唆される結果を得ている。本現象を解明する目的で,遺伝学的解析をすすめた結果,細胞質分裂を制御する蛋白質燐酸化酵素Cdc7,細胞内輸送に関わる低分子量G蛋白質Ypt3,ミオシン重鎖Myp2/Myo3がカルシニューリンと遺伝学的関係を示すことが明らかになった。

本研究は、分裂酵母において蛋白質脱リン酸化酵素であるカルシニューリン(CN)の遺伝子破壊が細胞質分裂異常を惹起する事に注目し、CNと細胞質分裂において機能的に関連する遺伝子群を分子遺伝学的アプローチで取得し,機能解析を行うことにより,細胞質分裂制御のネットワークとメカニズムを分子レベルで解明することを目的としている。分裂酵母においてCNをノックアウトしても通常の増殖には影響がないが、細胞質分裂に著しい異常が認められる。我々は<細胞増殖に活性型のCNを必須とする分裂酵母変異体(免疫抑制薬に感受性を示す)>の取得と解析により,多くの変異体が細胞質分裂異常を示すことを見いだした。昨年度の成果として、変異体の原因遺伝子のクローニングにより,Type II Myosinをコードするmyp2,低分子量GTP結合蛋白質rabファミリーに属するypt3,およびSeptation Initiation Network (SIN)の構成因子であるCdc7をコードする遺伝子群の同定を行った。本年度は引き続きこれらの遺伝子群とCNがどのように細胞質分裂という現象に関わるのかを解析した。その結果、myp2変異体とypt3変異体はCNの活性を抑制すると多核・多隔壁という表現型を示し,細胞増殖を停止する。CNの活性を高めるとこれらの変異体の異常な細胞質分裂は改善する。一方cdc7変異体はCNの活性を抑制すると,多核だが中隔を形成できないSIN欠損(septation initiation defective (sid))の表現型が増悪した。他のSINの構成因子であるcdc11やcdc14の変異体も同様の表現型を示した。さらにCNの構成的活性型を発現するとこれらの変異体のsid表現型が改善した。以上の結果から,CNは細胞質分裂においてSINの制御を含めて複数のステップに関与することが示唆された。

本研究の目的は,哺乳動物細胞に極めて近い細胞内情報伝達系をもつ分裂酵母モデル系を用いてRNA結合蛋白質を介するシグナル伝達経路を解明することである。研究代表者等は、哺乳動物のがん化・増殖に関与するMAPK/ERKと相同な経路である分裂酵母のPmk1MAPK経路を世界に先駆けて発見し、その生理機能と作用経路を解析してきた。この過程で、MAPKシグナルを制御する因子として高度に保存された新規RNA結合蛋白質Rnc1をクローニングした。このスクリーニングは分裂酵母のカルシニューリン遺伝子をノックアウトした細胞の表現型を過剰発現で抑圧する因子を取得するというものであり,現在までにMAPキナーゼホスファターゼなどのMAPキナーゼの抑制因子を同定してきた。この結果は、RNA結合蛋白質Rnc1の制御するRNA代謝がPmk1MAPKシグナルと密接な機能的関連をもつことを示唆している。そこで,Rnc1がMAPキナーゼホスファターゼを標的とする可能性を検討した結果,予想通りRnc1を過剰発現細胞することでMAPキナーゼホスファターゼのmRNA量が上昇し,ノックアウト株ではMAPキナーゼホスファターゼのmRNAが不安定になっていることを見いだした。また、生化学的手法を用いてMAPキナーゼホスファターゼとRnc1の結合を証明した。さらにPmk1MAPKがリン酸化によりPrn1のRNA結合能を制御するという結果を得ている。このことは、RNA結合蛋白質を介するMAPキナーゼ経路のフィードバック制御という極めて斬新なモデルを提唱するものである。また、他の遺伝学的アプローチにより、RRM型のRNA結合蛋白質であるNrd1を同定した。現在標的分子の同定を目的に遺伝学的・生化学的アプローチを行っているところである。

Calcineurin, a Ca^<2+>- and calmodulin-dependent protein phosphatase (protein phosphatase 2B), is a molecular target for the specific immunosuppressive drugs, such as cyclosporin A or FK506, used in organ transplantation. Calcineurin is enriched in the neural tissues, and also distributes broadly in other tissues. The structure of the protein is highly conserved from yeast to man. We are studying immunosuppressive drug sensitivity in the fission yeast Schizosaccharomyces pombe (S. pombe) because this system is amenable to genetics and has many advantages in terms of relevance to higher systems. We have screened for mutations that confer sensitivity to immunosuppressant, FK506 and cyclosporin A, and have identified ten complementation groups (its1~10 for immunosuppressant and temperature-sensitive). The combined use of powerful genetics and of specific calcineurin inhibitors in fission yeast identified new components of the calcineurin pathway, and defined new roles of calcineurin in the regulation of the many cellular processes. Recent our data have revealed functional interactions between calcineurin and IP signaling through Its5/PI4P 5 kinase. Calcineurin also participates in membrane traffic and separation initiation network (SIN) of fission yeast through its functional connection with the small GTPase Rab/Ypt family protein Its5/Ypt3, and Its10/Cdc7 protein kinase, respectively. Taking account of the conservation of the signal transduction pathway between human and the fission yeast, these findings provide further insight into the molecular mechanisms of adverse effects of immunosuppressant therapy upon organ transplantation.

カルシニューリンは酵母から哺乳動物に至るまで高度に保存された蛋白質脱燐酸化酵素である。野生型分裂酵母では免疫抑制薬によりカルシニューリンの機能を抑制しても成育に影響がない。この現象に基づいて,我々は分裂酵母をモデル生物として用いて,免疫抑制薬の存在下で致死となる変異体(its 変異体)の網羅的スクリーニングを展開し,多数の変異体を単離している。本研究では,これらのカルシニューリンと機能的に関連する遺伝子群の産物とCNとの相互作用の解析を通して,カルシニューリンが関与する蛋白質脱燐酸化及び燐酸化ネットワークを明らかにする事を目的としている。本年度の成果は以下の通りである。 1.免疫抑制薬感受性遺伝子座位の解析 its8変異体の原因遺伝子はGPIアンカー合成酵素であるPig-n(ヒト)及びMCD4(出芽酵母)の分裂酵母ホモログをコードしていた。its8変異体はGPIアンカー合成障害の結果,細胞壁の脆弱性,細胞形態異常,及び細胞質分裂異常を示した。CNとits8^+遺伝子産物は細胞質分裂と細胞壁integrityの維持において重要な機能をシェアしていることが示唆された。 2.分裂酵母のプロテオーム解析 (1)分裂酵母発現蛋白質のプロファイリング:分裂酵母可溶性および膜画分をSDS-PAGEで分離後,LC/MS/MSにて測定し配列タグ法により同定を行った。その結果,1302種類の蛋白質を検出できた。(2)CNにより制御される蛋白質発現のプロテオーム解析:野生株とCN破壊株のそれぞれから抽出した可溶性および膜画分を二次元電気泳動で解析し,発現蛋白質を比較した。その結果,CN欠損で発現量が減少した蛋白質31種類,増加した蛋白質17種類,等電点が変化した蛋白質11種類が検出された。

本研究は、分裂酵母においてカルシニューリン(CN)遺伝子破壊カミ細胞賛分裂異常を惹起する事に注目し、CNと細胞質分裂において機能的に関連する遺伝子群を分子遺伝学的アプローチで取得し,機能解析を行うことにより,細胞質分裂制御のネットワークとメカニズムを分子レベルで解明することを目的としている。分裂酵母においてCNの活性を抑制しても(CN遺伝子を破壊した場合、あるいは免疫抑制薬FK506の存在下)通常の増殖には影響がないが、細胞質分裂に著しい異常が認められる。我々は<細胞増殖に活性型のCNを必須とする分裂酵母変異体(免疫抑制薬に感受性を示す)>の取得と解析により,多くの変異体が細胞質分裂異常を示すことを見いだした。本年度はこれらの変異体の原因遺伝子のクローニングにより,Type II Myosinをコードするmp2,低分子量GTP結合蛋白質rabファミリーに属するypt3,およびSeptation Initiation Network(SlN)の構成因子であるCdc7をコードする遺伝子を同定し,これらの遺伝子群が細胞質分裂においてCNと機能的に関連することを見いだした。myp2変異体とypt3変異体はCNの活性を抑制すると多核・多隔壁という表現型を示し,細胞増殖を停止する。一方cdc7変異体はCNの活性を抑制すると,制限温度にシフトしたときと同様に多核だが中隔を形成できないSIN欠損(septation initiation defective(sid)の表現型が増悪した。他のSINの構成因子であるcdc11やcdc14の変異体も同様の表現型を示した。さらにCNの構成的活性型を発現するとこれらの変異体のsidの表現型が改善した。以上の結果から,CNは細胞質分裂においてSINの制御を含めて複数のステップに関与することが示唆された。また,CNが細胞内輸送を制御する可能性も示唆された。

カルシニューリンは酵母から哺乳動物に至るまで高度に保存された蛋白質脱燐酸化酵素である。野生型分裂酵母では免疫抑制薬によりカルシニューリンの機能を抑制しても成育に影響がない。この現象に基づいて、我々は分裂酵母をモデル生物として用いて、免疫抑制薬の存在下で致死となる変異体(its変異体)の網羅的スクリーニングを展開し、多数の変異体を単離している。本研究では、これらのカルシニューリンと機能的に関連する遺伝子群の産物とカルシニューリンとの相互作用の解析を通して、カルシニューリンが関与する蛋白質脱燐酸化及び燐酸化ネットワークを明らかにする事を目的としている。 本年度はits3及びits8変異体の原因遺伝子を同定し、解析を行った。 its3遺伝子は必須遺伝子であり、ホスファチジルイノシトール4リン酸(PI4P)をリン酸化し、PI(4,5)P2を産生するPI4P5キナーゼをコードしていた。PI4P5キナーゼは細胞膜上にPI(4,5)P2と共局在し、細胞周期とともにその局在が変化した。its3変異体は制限温度下あるいは免疫抑制薬存在下でアクチンの局在異常及び細胞質分裂異常を呈した。 its8遺伝子はGPIアンカー合成酵素の一つであるヒトPig-nと高い相同性を有する蛋白質をコードしていた。its8破壊体は非常に成育が遅く、多核多隔壁の細胞形態を示した。Its8融合蛋白質は小胞体に局在していた。 its3及びits8変異体はともに、制限温度下あるいは免疫抑制薬存在下で、多くの細胞が分裂中隔を持った状態で増殖停止していたことから、細胞質分裂や細胞形態の制御に関与する事が示唆された。これらの遺伝子は哺乳動物細胞にもホモログが存在しており、酵母細胞と同様、細胞形態の維持に関与していると考えられる。

本研究は、哺乳動物細胞に極めて近い細胞内情報伝達系を持つ分裂酵母モデル系を用いて、マップキナーゼ制御機構を分子遺伝学的に解明しようとするものである。細胞形態は,癌細胞の転移における重要な因子の一つである。研究代表者らが発見した新規マップキナーゼPmk1系は,細胞増殖とともに細胞形態形成,特に細胞質分裂において重要であり,カルシニューリンと機能的関連性をもつことがすでに明らかにされている。 本年度は,さらに新たな機能的関連遺伝子を単離するために遺伝学的スクリーニングを行い,ホスファチジル・イノシトール代謝において中心的な役割を果たしているPI4P5キナーゼをコードする遺伝子と細胞膜に存在し細胞外において様々な役割を果たすGPIアンカー蛋白質の合成酵素の一つをコードする遺伝子を得た。生化学的および細胞生物学的解析を行った結果,これらの遺伝子産物はともにマップキナーゼと同様,細胞質分裂においてカルシニューリンと重要な役割をシェアしていることを明らかにした。ヒトに於いても,これらの遺伝子に非常に類似した機能的ホモログが存在しているので,これらの機能的ホモログはヒトマップキナーゼ系の制御機構に深くかかわっている事が示唆された。PI4P5キナーゼはPIP2の産生によりマップキナーゼの上流における制御因子として,一方,GPIアンカー合成酵素は下流における標的因子として,細胞質分裂にかかわっていることが示唆された。