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Rab-family GTPase regulates TOR complex 2 signaling in fission yeast

Hisashi Tatebe1, Susumu Morigasaki, Shinichi Murayama

  • 1Department of Microbiology, University of California, Davis, Davis, CA 95616, USA.

Current Biology : CB
|November 2, 2010
PubMed
Abstract

Insights

Ryh1 GTPase activates TORC2 signaling to Gad8 kinase in yeast. This pathway is crucial for maintaining vacuolar integrity and cellular stress resistance, with potential mammalian homologs.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Yeast genetics

Background:

  • The target of rapamycin (TOR) kinase is a central regulator of cell growth and metabolism, operating in two complexes: TORC1 and TORC2.
  • TORC1 is regulated by Rheb, but the regulators of TORC2 remain largely uncharacterized.
  • Understanding TORC2 regulation is key to deciphering cellular responses to extracellular stimuli.

Purpose of the Study:

  • To identify novel regulators of TORC2 signaling.
  • To elucidate the mechanism by which Ryh1 GTPase interacts with and activates TORC2.
  • To investigate the functional significance of the TORC2-Ryh1 pathway in cellular processes.

Main Methods:

  • Genetic screening in Schizosaccharomyces pombe to identify Ryh1 as a TORC2 activator.
  • Site-directed mutagenesis to analyze the function of Ryh1 domains and GTP-binding.
  • Biochemical assays to assess protein-protein interactions between Ryh1, TORC2, and Gad8.
  • Phenotypic analysis of mutant strains to evaluate vacuolar integrity and stress sensitivity.

Main Results:

  • Ryh1 GTPase, a homolog of human Rab6, was identified as an activator of TORC2 signaling in S. pombe.
  • Mutations in Ryh1 or its guanine nucleotide exchange factor impaired TORC2-dependent Gad8 phosphorylation.
  • The effector domain of Ryh1 is essential for its interaction with TORC2 and activation of signaling.
  • GTP-bound Ryh1 directly stimulates TORC2-Gad8 signaling, promoting Gad8 hyperphosphorylation.
  • Loss of Ryh1, TORC2, or Gad8 function resulted in similar vacuolar fragmentation and stress sensitivity phenotypes.
  • Human Rab6 functionally substituted for Ryh1 in S. pombe.

Conclusions:

  • GTP-bound Ryh1 activates TORC2 signaling towards the AGC kinase Gad8.
  • The Ryh1 GTPase and the TORC2-Gad8 pathway are essential for maintaining vacuolar integrity and cellular stress resistance in S. pombe.
  • Human Rab6 represents a potential mammalian TORC2 activator, suggesting conserved regulatory mechanisms.

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