title: The requirement for the hydrophobic motif phosphorylation of Ypk1 in yeast differs depending on the downstream events, including endocytosis, cell growth, and resistance to a sphingolipid biosynthesis inhibitor, ISP-1.
abstract: ISP-1 inhibits de novo sphingolipid biosynthesis and induces growth defects in both mammals and yeast (Saccharomyces cerevisiae). In our previous study, YPK1/SLI2 was identified as one of multicopy suppressor genes for ISP-1 in yeast. Ypk1 is proposed to be a downstream serine/threonine kinase of the sphingolipid signaling pathway in yeast. Other than resistance against ISP-1, Ypk1 is involved in at least two downstream events, namely cell growth and endocytosis. In this study, the effect of mutants of Ypk1 on these three downstream events was investigated. Among Ypk1 mutants, no 'kinase-dead' mutants complemented the defects in any of these three downstream events in the ypk1 null strain. One of the hydrophobic motif phosphorylation-deficient mutants of Ypk1, Ypk1(T662A) had the moderate kinase activity compared with the wild-type Ypk1. Ypk1(T662A) and the wild-type Ypk1 completely restored the slow-growth phenotype and fluid-phase endocytosis defect of the ypk1 null strain. However, unlike the wild-type Ypk1, Ypk1(T662A) lost the ability for the recovery of the ISP-1 resistance in the ypk1 null strain. Furthermore, the expression of Ypk1(T662A) in the wild-type strain showed a dominant-negative effect on the ISP-1-resistance activity. On the other hand, the cell growth revertant of the ypk1 null strain still showed the hypersensitive phenotype to ISP-1. These data suggest that the ISP-1-resistance pathway is under the regulation of the hydrophobic motif phosphorylation and is separated from the other pathways downstream of Ypk1.
authors.affiliation: Laboratory of Membrane Biochemistry and Biophysics, Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Tanoue
authors.forename: Takafumi
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Yidi
authors.initials: Y
authors.lastname: Sun
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Fujita
authors.forename: Hiromu
authors.initials: H
authors.lastname: Takematsu
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kozutsumi
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics / Q000502:physiology; D019943:Amino Acid Substitution; D000935:Antifungal Agents / Q000494:pharmacology; D049108:Cell Enlargement / Q000187:drug effects; D025141:Drug Resistance, Fungal / Q000235:genetics / Q000502:physiology; D004705:Endocytosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D005229:Fatty Acids, Monounsaturated / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3; D010641:Phenotype; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*
chemical_list: D000935:Antifungal Agents; D005229:Fatty Acids, Monounsaturated; D029701:Saccharomyces cerevisiae Proteins; D011505:Protein-Tyrosine Kinases; D038362:Glycogen Synthase Kinase 3; C068124:MCK1 protein, S cerevisiae; C001996:thermozymocidin