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Cleavage and inactivation of antiapoptotic Akt/PKB by caspases during apoptosis

S Rokudai1, N Fujita, Y Hashimoto

  • 1Institute of Molecular and Cellular Biosciences, University of Tokyo, Japan.

Journal of Cellular Physiology
|January 7, 2000
PubMed

Insights

The anti-apoptotic protein Akt is cleaved by caspases during apoptosis, inactivating its survival signals. This caspase-mediated cleavage accelerates programmed cell death.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • The Akt (also known as Protein Kinase B or RAC-PK) is a serine/threonine kinase.
  • Akt mediates crucial cell survival signals and protects against apoptosis.
  • Kinase activity of Akt is essential for transmitting survival signals.

Purpose of the Study:

  • To investigate the role of Akt in apoptosis.
  • To determine the mechanism of Akt down-regulation during apoptosis.
  • To elucidate the relationship between caspase activity and Akt function in cell death.

Main Methods:

  • Western blotting to detect Akt protein levels during apoptosis.
  • Treatment with caspase inhibitors to block Akt cleavage.
  • In vitro cleavage assays using purified Akt protein and active caspases.
  • Site-directed mutagenesis to identify Akt cleavage sites.
  • Overexpression of Akt deletion mutants to assess functional consequences.

Main Results:

  • Akt protein levels were significantly down-regulated during apoptosis.
  • Caspase inhibition prevented Akt down-regulation, indicating caspase-mediated cleavage.
  • In vitro assays showed Akt is cleaved by caspases at three specific sites, generating 40- and 44-kDa fragments.
  • Cleavage in the COOH-terminal regulatory domain reduced Akt kinase activity.
  • Overexpression of truncated Akt fragments lacking the NH(2)-terminal or COOH-terminal domains increased sensitivity to apoptosis.

Conclusions:

  • Caspase-dependent cleavage of Akt inactivates its pro-survival function.
  • This cleavage event contributes to the acceleration of apoptotic cell death.
  • Targeting Akt cleavage could be a strategy to modulate apoptosis in disease contexts.

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