title: Isolation of a fission yeast mutant that is sensitive to valproic acid and defective in the gene encoding Ric1, a putative component of Ypt/Rab-specific GEF for Ryh1 GTPase.
abstract: 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 (Deltaryh1) cells and Deltaric1 cells exhibited similar phenotypes. The double knockout Deltaric1Deltaryh1 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 Deltaric1 cells, and they failed to localize to the Golgi/endosomes in ric1-v3 and Deltaric1 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 Deltaric1 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.
authors.affiliation: Division of Molecular Pharmacology and Pharmacogenomics, Department of Biochemistry and Molecular Biology, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan. mayan@med.kobe-u.ac.jp
authors.forename: Yan
authors.initials: Y
authors.lastname: Ma
authors.forename: Reiko
authors.initials: R
authors.lastname: Sugiura
authors.forename: Lili
authors.initials: L
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Zhou
authors.forename: Mai
authors.initials: M
authors.lastname: Takeuchi
authors.forename: Yi
authors.initials: Y
authors.lastname: He
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kuno
mesh_terms: D000927:Anticonvulsants / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D055785:Gene Knockdown Techniques; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics* / Q000378:metabolism; D015151:Immunoblotting; D008856:Microscopy, Fluorescence; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics* / Q000254:growth & development; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000378:metabolism; D058571:Vacuolar Sorting Protein VPS15; D014635:Valproic Acid / Q000494:pharmacology*
chemical_list: D000927:Anticonvulsants; D056827:Endosomal Sorting Complexes Required for Transport; D020662:Guanine Nucleotide Exchange Factors; C552252:Ric1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D049452:Green Fluorescent Proteins; D014635:Valproic Acid; D017346:Protein Serine-Threonine Kinases; D058571:Vacuolar Sorting Protein VPS15; C064392:ryh1 protein, S pombe; D020559:Monomeric GTP-Binding Proteins