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A MAP4 kinase related to Ste20 is a nutrient-sensitive regulator of mTOR signalling

Greg M Findlay1, Lijun Yan, Julia Procter

  • 1Institute of Cancer Research, Cancer Research U.K. Centre of Cell and Molecular Biology, 237 Fulham Road, London SW3 6JB, U.K.

The Biochemical Journal
|January 27, 2007
PubMed

Insights

Researchers identified MAP4K3, a protein kinase, as a key player in nutrient signaling to the mTOR pathway. This finding helps elucidate how amino acids regulate cell growth.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The mammalian target of rapamycin (mTOR) pathway regulates cell growth and is influenced by growth factors and nutrients.
  • Signaling pathways from growth factors to mTOR are understood, but nutrient-mediated signaling pathways are not well-characterized.

Purpose of the Study:

  • To identify protein kinases involved in nutrient signaling to the mTOR pathway.
  • To elucidate the role of MAP4K3 in nutrient-mediated regulation of cell growth.

Main Methods:

  • Conducted a screen for protein kinases in the mTOR signaling pathway in Drosophila.
  • Investigated the regulation of MAP4K3 activity by amino acids, insulin, and rapamycin.
  • Assessed the impact of MAP4K3 on S6K/4E-BP1 phosphorylation and cell growth.

Main Results:

  • Identified MAP4K3, a Ste20 family member, as essential for maximal S6K/4E-BP1 phosphorylation and cell growth.
  • Demonstrated that MAP4K3 activity is regulated by amino acids but not by insulin or rapamycin.
  • MAP4K3 is a key mediator of amino acid signaling to mTORC1.

Conclusions:

  • MAP4K3 acts as a sensor for amino acids, linking nutrient availability to mTORC1 signaling.
  • This study proposes a model where nutrients signal to mTORC1 through the activation of MAP4K3.
  • Uncovers a novel pathway for nutrient sensing in cell growth regulation.

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