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Re-evaluating AKT regulation: role of TOR complex 2 in tissue growth

Ville Hietakangas1, Stephen M Cohen

  • 1European Molecular Biology Laboratory Meyerhofstrasse 1, D-69117 Heidelberg, Germany.

Genes & Development
|March 21, 2007
PubMed

Insights

Target of rapamycin complex 2 (TORC2) regulates Phosphatidylinositol-3-kinase (PI3K)/AKT signaling. Loss of TORC2 activity in Drosophila inhibits hyperplasia by modulating AKT signaling at high pathway activity levels.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Cancer research

Background:

  • Phosphatidylinositol-3-kinase (PI3K)/AKT signaling is crucial for cell growth, metabolism, and is frequently dysregulated in cancer.
  • AKT activity is regulated by phosphorylation at conserved sites by PDK1 and target of rapamycin (TOR) complex 2 (TORC2).

Purpose of the Study:

  • To investigate the role of TORC2-mediated AKT phosphorylation in Drosophila.
  • To understand how TORC2 modulates AKT signaling, particularly in the context of elevated pathway activity.

Main Methods:

  • Analysis of Drosophila mutants lacking critical TORC2 components (rictor, sin1).
  • Assessment of AKT hydrophobic motif (HM) phosphorylation and AKT activity.
  • Evaluation of hyperplasia in response to altered PI3K/AKT pathway activity.

Main Results:

  • Mutants lacking rictor or sin1 showed reduced AKT HM phosphorylation and activity, with minimal impact on normal growth.
  • A mutant AKT lacking the HM phosphorylation site exhibited comparable activity to wild-type.
  • Loss of TORC2 activity significantly inhibited hyperplasia caused by elevated PI3K/AKT signaling, such as in PTEN mutants.

Conclusions:

  • TORC2 plays a critical role in regulating AKT activity, especially at higher signaling levels.
  • TORC2 functions as a rheostat, expanding the dynamic range of AKT signaling.
  • These findings highlight TORC2's importance in controlling pathway flux and its implications in cancer biology.

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