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PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase

Yasemin Sancak1, Carson C Thoreen, Timothy R Peterson

  • 1Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Nine Cambridge Center, Cambridge, MA 02142, USA.

Molecular Cell
|March 28, 2007
PubMed

Insights

Researchers identified PRAS40 as a key regulator of the mTORC1 pathway. Insulin signaling phosphorylates PRAS40, relieving its inhibition on mTORC1 and promoting cell growth.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Biochemistry

Background:

  • The mechanistic target of rapamycin complex 1 (mTORC1) pathway is crucial for cell growth and is dysregulated in various cancers.
  • Insulin signaling activates mTORC1, but the precise regulatory mechanisms remain incompletely understood.
  • TSC1/TSC2 tumor suppressors normally inhibit mTORC1; their loss leads to constitutive pathway activation.

Purpose of the Study:

  • To elucidate the regulatory mechanisms controlling mTORC1 kinase activity in response to insulin.
  • To identify novel proteins interacting with and modulating mTORC1 function.
  • To understand how PRAS40 integrates with the mTORC1 pathway.

Main Methods:

  • Co-immunoprecipitation assays to identify mTORC1-interacting proteins.
  • In vitro kinase assays to measure mTORC1 activity.
  • Cell-based assays to assess cell growth and S6K1 phosphorylation.
  • Site-directed mutagenesis and Akt/PKB-mediated phosphorylation studies.

Main Results:

  • PRAS40 was identified as a raptor-interacting protein that inhibits mTORC1 activity and S6K1 phosphorylation.
  • PRAS40 binding to mTORC1 is regulated by salt concentration and disrupted by GTP-bound Rheb.
  • Insulin signaling, via Akt/PKB, phosphorylates PRAS40, thereby relieving its inhibitory effect on mTORC1.
  • Insulin-induced PRAS40 phosphorylation is essential for pathway activation in cells.

Conclusions:

  • PRAS40 acts as a critical inhibitor of mTORC1 signaling.
  • Insulin activates mTORC1 through coordinated regulation of Rheb and PRAS40.
  • The interplay between Rheb and PRAS40 determines overall mTORC1 pathway activity, impacting cell growth and proliferation.

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