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Nitrogen source activates TOR (target of rapamycin) complex 1 via glutamine and independently of Gtr/Rag proteins

Daniele Stracka1, Szymon Jozefczuk2, Florian Rudroff2

  • 1From the Biozentrum, University of Basel, 4056 Basel, Switzerland and.

The Journal of Biological Chemistry
|July 27, 2014
PubMed

Insights

Yeast nutrient sensing involves TORC1 activation by nitrogen sources. Glutamine production is key for sustained TORC1 activity, which operates independently of Gtr/Rag GTPases.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The evolutionarily conserved Target Of Rapamycin Complex 1 (TORC1) is a central regulator of cell growth, responding to nutrient availability.
  • In yeast, the precise mechanism by which nitrogen sources activate TORC1 remains incompletely understood.
  • Amino acids, such as leucine, activate TORC1 through small GTPases Gtr1 and Gtr2, which are homologs of mammalian Rag GTPases.

Purpose of the Study:

  • To investigate the activation of TORC1 by different nitrogen sources in yeast.
  • To elucidate the relationship between nitrogen source-mediated TORC1 activation and activation by Gtr/Rag GTPases.

Main Methods:

  • Assessed TORC1 activity by measuring Sch9 phosphorylation in response to various nitrogen sources.
  • Quantified glutamine accumulation within yeast cells.
  • Investigated the role of glutamine synthesis inhibition on TORC1 activity and growth.
  • Examined TORC1 activation in yeast strains deficient in Gtr1.

Main Results:

  • The quality of the nitrogen source, indicated by growth promotion and glutamine accumulation, directly correlates with TORC1 activation (Sch9 phosphorylation).
  • Preferred nitrogen sources induce rapid, sustained Sch9 phosphorylation and glutamine accumulation, while poor sources cause rapid but transient phosphorylation.
  • Inhibition of glutamine synthesis impairs TORC1 activity and cell growth.
  • A Gtr1 deficiency abolishes transient TORC1 stimulation but does not impact sustained activation by favorable nitrogen sources.

Conclusions:

  • Sustained TORC1 activation by nitrogen sources requires the conversion of the nitrogen source into glutamine, the preferred nitrogen source in yeast.
  • The nitrogen source and Gtr/Rag GTPases activate TORC1 through distinct mechanisms.
  • Sustained TORC1 activity in response to nutrient quality is independent of the Gtr/Rag GTPase pathway.
Keywords:
Amino AcidKineticsNitrogen MetabolismTarget of Rapamycin (TOR)Yeast

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