TOR complex 2 (TORC2) signaling and the ESCRT machinery cooperate in the protection of plasma membrane integrity in yeast

J Biol Chem. 2020 Aug 21;295(34):12028-12044. doi: 10.1074/jbc.RA120.013222. Epub 2020 Jul 1.

Abstract

The endosomal sorting complexes required for transport (ESCRT) mediate evolutionarily conserved membrane remodeling processes. Here, we used budding yeast (Saccharomyces cerevisiae) to explore how the ESCRT machinery contributes to plasma membrane (PM) homeostasis. We found that in response to reduced membrane tension and inhibition of TOR complex 2 (TORC2), ESCRT-III/Vps4 assemblies form at the PM and help maintain membrane integrity. In turn, the growth of ESCRT mutants strongly depended on TORC2-mediated homeostatic regulation of sphingolipid (SL) metabolism. This was caused by calcineurin-dependent dephosphorylation of Orm2, a repressor of SL biosynthesis. Calcineurin activity impaired Orm2 export from the endoplasmic reticulum (ER) and thereby hampered its subsequent endosome and Golgi-associated degradation (EGAD). The ensuing accumulation of Orm2 at the ER in ESCRT mutants necessitated TORC2 signaling through its downstream kinase Ypk1, which repressed Orm2 and prevented a detrimental imbalance of SL metabolism. Our findings reveal compensatory cross-talk between the ESCRT machinery, calcineurin/TORC2 signaling, and the EGAD pathway important for the regulation of SL biosynthesis and the maintenance of PM homeostasis.

Keywords: ORMDL family; TORC2; calcineurin; endosomal sorting complexes required for transport (ESCRT); endosome and Golgi-associated degradation (EGAD); mTOR complex (mTORC); membrane; membrane stress; sphingolipid; stress.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Endosomal Sorting Complexes Required for Transport / genetics
  • Endosomal Sorting Complexes Required for Transport / metabolism*
  • Glycogen Synthase Kinase 3 / genetics
  • Glycogen Synthase Kinase 3 / metabolism
  • Mechanistic Target of Rapamycin Complex 2 / genetics
  • Mechanistic Target of Rapamycin Complex 2 / metabolism*
  • Mutation
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Signal Transduction*

Substances

  • Endosomal Sorting Complexes Required for Transport
  • Orm2 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • VPS4 protein, S cerevisiae
  • Mechanistic Target of Rapamycin Complex 2
  • Glycogen Synthase Kinase 3
  • MCK1 protein, S cerevisiae
  • Adenosine Triphosphatases