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An ATP-site on-off switch that restricts phosphatase accessibility of Akt

Kui Lin1, Jie Lin, Wen-I Wu

  • 1Genentech Inc., South San Francisco, CA 94080, USA. klin@gene.com

Science Signaling
|May 10, 2012
PubMed

Insights

Akt inhibitors paradoxically increase Akt phosphorylation by stabilizing a protective conformation. Nucleotides like ATP and ADP, not allosteric inhibitors, regulate Akt accessibility, revealing a new kinase regulation model.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Signaling

Background:

  • The protein kinase Akt is crucial for cell survival and growth.
  • Akt activation involves phosphorylation at threonine 308 and serine 473.
  • ATP-competitive inhibitors paradoxically increase Akt phosphorylation.

Purpose of the Study:

  • To investigate the mechanism behind increased Akt phosphorylation upon treatment with ATP-competitive inhibitors.
  • To elucidate the role of nucleotides (ATP, ADP) and allosteric inhibitors in regulating Akt conformation and accessibility.

Main Methods:

  • Conformational analysis of Akt in the presence of ATP, ADP, ATP-competitive inhibitors, and allosteric inhibitors.
  • Phosphatase accessibility assays to determine the impact of nucleotide binding and inhibitors on phosphorylated Akt residues.

Main Results:

  • ATP-competitive inhibitors stabilize a conformation where phosphorylated Akt sites (Thr308, Ser473) are protected from phosphatases.
  • ATP binding also protects these sites, while ADP and allosteric inhibitors increase their accessibility.
  • Oncogenic or myristoylated Akt forms are more potently inhibited by ATP-competitive inhibitors.

Conclusions:

  • Nucleotides act as an on-off switch for Akt via conformational changes.
  • ATP-competitive inhibitors disrupt this nucleotide-mediated regulation by locking Akt in a protected, active-like conformation.
  • A new model for Akt kinase regulation involving nucleotide-dependent conformational modulation is proposed.

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