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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
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Published on: March 9, 2012

Regulation of the small GTPase Rheb by amino acids

M Roccio1, J L Bos, F J T Zwartkruis

  • 1Department of Physiological Chemistry and Centre for Biomedical Genetics, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG, Utrecht, The Netherlands.

Oncogene
|September 20, 2005
PubMed

Insights

Nutrient sensing by the mTOR pathway involves two levels. Amino acid levels regulate Rheb activation and also impact mTOR signaling independently of Rheb.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Metabolic regulation

Background:

  • The mechanistic target of rapamycin (mTOR)/S6K/4E-BP1 pathway integrates growth factor and nutrient signals.
  • Activation of mTOR requires TSC1/2 complex inhibition, which regulates Rheb GTP loading.
  • The precise mechanism of amino acid sensing within this pathway remains unclear.

Purpose of the Study:

  • To investigate the level at which amino acid availability is sensed in the mTOR pathway.
  • To determine if amino acid sensing occurs upstream or downstream of Rheb GTP loading.
  • To elucidate the mechanism of mTOR regulation by amino acids in a Rheb-independent manner.

Main Methods:

  • Utilized insulin and TPA stimulation in cell culture models.
  • Assessed Rheb activation and GTP loading under varying amino acid conditions.
  • Examined mTOR/S6 kinase signaling in TSC2-deficient fibroblasts.

Main Results:

  • Amino acid depletion abolished insulin- and TPA-induced Rheb activation, indicating upstream sensing.
  • mTOR/S6 kinase signaling was inhibited by amino acid depletion even when Rheb-GTP levels remained high.
  • This demonstrates a second, Rheb-independent amino acid sensing mechanism affecting mTOR.

Conclusions:

  • Amino acid sensing occurs at least at two distinct levels within the mTOR pathway.
  • One level involves regulation upstream of Rheb activation.
  • A second, Rheb-independent mechanism directly influences mTOR activity based on amino acid availability.

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