title: TORC2-dependent protein kinase Ypk1 phosphorylates ceramide synthase to stimulate synthesis of complex sphingolipids.
abstract: Plasma membrane lipid composition must be maintained during growth and under environmental insult. In yeast, signaling mediated by TOR Complex 2 (TORC2)-dependent protein kinase Ypk1 controls lipid abundance and distribution in response to membrane stress. Ypk1, among other actions, alleviates negative regulation of L-serine:palmitoyl-CoA acyltransferase, upregulating production of long-chain base precursors to sphingolipids. To explore other roles for TORC2-Ypk1 signaling in membrane homeostasis, we devised a three-tiered genome-wide screen to identify additional Ypk1 substrates, which pinpointed both catalytic subunits of the ceramide synthase complex. Ypk1-dependent phosphorylation of both proteins increased upon either sphingolipid depletion or heat shock and was important for cell survival. Sphingolipidomics, other biochemical measurements and genetic analysis demonstrated that these modifications of ceramide synthase increased its specific activity and stimulated channeling of long-chain base precursors into sphingolipid end-products. Control at this branch point also prevents accumulation of intermediates that could compromise cell growth by stimulating autophagy.
authors.affiliation: Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Muir
authors.affiliation: Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
authors.forename: Subramaniam
authors.initials: S
authors.lastname: Ramachandran
authors.affiliation: Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
authors.forename: Françoise M
authors.initials: FM
authors.lastname: Roelants
authors.affiliation: Department of Chemistry, University of California, Berkeley, Berkeley, United States.
authors.forename: Garrett
authors.initials: G
authors.lastname: Timmons
authors.affiliation: Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Thorner
mesh_terms: D001343:Autophagy; D019703:Calcineurin / Q000378:metabolism; D002470:Cell Survival; D015536:Down-Regulation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D018869:Heat-Shock Response; D000076225:Mechanistic Target of Rapamycin Complex 2; D008565:Membrane Proteins / Q000378:metabolism*; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction; D013107:Sphingolipids / Q000096:biosynthesis*; D013312:Stress, Physiological; D013379:Substrate Specificity; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C087436:LAG1 protein, S cerevisiae; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; D010768:Phosphoserine; D010088:Oxidoreductases; C513563:LAC1 protein, S cerevisiae; C108138:dihydroceramide desaturase; D000076225:Mechanistic Target of Rapamycin Complex 2; D058570:TOR Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C068124:MCK1 protein, S cerevisiae; D019703:Calcineurin
keywords: S. cerevisiae; biochemistry; cell biology; lipids; mutants; phosphorylation; plasma membrane; regulation; substrates