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Resistance of Akt kinases to dephosphorylation through ATP-dependent conformational plasticity

Tung O Chan1, Jin Zhang, Ulrich Rodeck

  • 1Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, Philadelphia, PA 19107, USA. tung.chan@KimmelCancerCenter.org

Proceedings of the National Academy of Sciences of the United States of America
|October 28, 2011
PubMed

Insights

Targeting Akt kinase to the cell membrane reduces its sensitivity to dephosphorylation. Nucleotide binding pocket occupancy shields the activation loop, sustaining Akt phosphorylation and explaining inhibitor-induced hyperphosphorylation.

Area of Science:

  • Molecular Biology
  • Cell Signaling
  • Biochemistry

Background:

  • Akt kinase phosphorylation is crucial for its activity and often deregulated in cancer.
  • Akt phosphorylation is regulated by a balance between kinases and phosphatases in vivo.

Purpose of the Study:

  • To investigate the mechanisms regulating Akt phosphorylation and dephosphorylation.
  • To understand how Akt localization and nucleotide binding affect its phosphatase sensitivity.

Main Methods:

  • Studied Akt kinase localization to the cell membrane.
  • Investigated the effect of ATP and ATP-competitive inhibitors on Akt phosphorylation.
  • Performed mutational analysis of key Akt residues (R273/R274).

Main Results:

  • Targeting Akt to the cell membrane reduced its sensitivity to protein phosphatase 2A-mediated dephosphorylation.
  • Nucleotide binding pocket occupancy, by ATP or inhibitors, amplified this effect.
  • Residues R273/R274 are essential for shielding the T308 activation loop from dephosphorylation.
  • This mechanism explains paradoxical Akt hyperphosphorylation induced by ATP-competitive inhibitors.

Conclusions:

  • Akt kinase localization and nucleotide binding pocket occupancy create a phosphatase-resistant state.
  • This shielding mechanism sustains Akt phosphorylation and has implications for cancer and diabetes mellitus.

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