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Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth

Hugo A Acosta-Jaquez1, Jennifer A Keller, Kathryn G Foster

  • 1Department of Cell and Developmental Biology, University of Michigan Medical School, 109 Zina Pitcher Place, Ann Arbor, MI 48109-2200, USA.

Molecular and Cellular Biology
|June 3, 2009
PubMed

Insights

New research reveals that mammalian target of rapamycin (mTOR) phosphorylation at S1261 is crucial for mTOR complex 1 (mTORC1) signaling, promoting cell growth and substrate phosphorylation.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is a critical regulator of cell growth, responding to environmental cues like growth factors and nutrients.
  • The precise biochemical mechanisms governing mTORC1 signaling and the functional significance of mTOR phosphorylation sites remain incompletely understood.

Purpose of the Study:

  • To identify and functionally characterize novel phosphorylation sites on mTOR.
  • To elucidate the role of mTOR phosphorylation at serine 1261 (S1261) in regulating mTORC1 activity and cellular biosynthesis.

Main Methods:

  • Tandem mass spectrometry was employed to identify new mTOR phosphorylation sites.
  • Experiments involved manipulating insulin-phosphatidylinositol 3-kinase (PI3K) and TSC/Rheb signaling pathways.
  • Western blotting and cell size measurements were used to assess mTORC1 activity and cell growth.

Main Results:

  • A novel mTOR phosphorylation site, S1261, was identified and shown to be regulated by insulin-PI3K and TSC/Rheb signaling in an amino acid-dependent and rapamycin-insensitive manner.
  • Phosphorylation of mTOR at S1261 was demonstrated to be essential for mTORC1-mediated phosphorylation of substrates like S6K1 and 4E-BP1, and for promoting cell growth.
  • mTOR S1261 phosphorylation is required for Rheb-driven mTOR S2481 autophosphorylation and subsequent S6K1 phosphorylation.

Conclusions:

  • Site-specific phosphorylation of mTOR at S1261 is a key regulatory mechanism controlling mTORC1 function.
  • Insulin-stimulated mTOR S1261 phosphorylation enhances mTORC1 autokinase activity, leading to increased substrate phosphorylation and cell growth.

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