TORC2-dependent protein kinase Ypk1 phosphorylates ceramide synthase to stimulate synthesis of complex sphingolipids
Alexander Muir,
Subramaniam Ramachandran,
Françoise M Roelants,
Garrett Timmons,
Jeremy Thorner
Affiliations
Alexander Muir
Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States; Chemical Biology Graduate Program, University of California, Berkeley, Berkeley, United States
Subramaniam Ramachandran
Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
Françoise M Roelants
Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
Garrett Timmons
Department of Chemistry, University of California, Berkeley, Berkeley, United States
Jeremy Thorner
Division of Biochemistry, Biophysics and Structural Biology, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
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.
