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Published on: March 5, 2018

Protein kinase A regulates caspase-9 activation by Apaf-1 downstream of cytochrome c

Morag C Martin1, Lindsey A Allan, Michelle Lickrish

  • 1Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Scotland, United Kingdom.

The Journal of Biological Chemistry
|February 11, 2005
PubMed

Insights

Elevated cyclic AMP activates protein kinase A, which suppresses apoptosis. Protein kinase A inhibits apoptosome formation by preventing procaspase-9 recruitment to Apaf-1, thus blocking caspase-9 and caspase-3 activation.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • The cyclic AMP (cAMP) pathway regulates apoptosis, but the precise mechanisms remain unclear.
  • Caspase-9 activation within the apoptosome is crucial for the intrinsic apoptotic pathway, triggered by cytochrome c release.
  • Apaf-1 and procaspase-9 assemble into the apoptosome, leading to effector caspase activation and cell death.

Purpose of the Study:

  • To elucidate the mechanism by which cAMP signaling influences apoptosis.
  • To investigate the role of protein kinase A (PKA) in regulating caspase activation.
  • To determine how PKA affects apoptosome formation and caspase-9 activation.

Main Methods:

  • Utilized Xenopus egg extracts and a human cell-free system to study apoptosis.
  • Investigated the effect of PKA on caspase-9 and caspase-3 activation downstream of cytochrome c.
  • Performed mutational analysis of caspase-9 phosphorylation sites.
  • Assessed the impact of PKA on procaspase-9 recruitment to Apaf-1.

Main Results:

  • PKA activation inhibits caspase-9 and caspase-3 activation in cell-free systems.
  • PKA directly phosphorylates caspase-9 at specific serine residues (Ser99, Ser183, Ser195).
  • Phosphorylation at these sites is not essential for PKA's inhibitory effect on caspase-9 activation.
  • PKA inhibits cytochrome c-dependent procaspase-9 recruitment to Apaf-1, but not activation of caspase-9 by pre-formed Apaf-1 complexes.

Conclusions:

  • PKA suppresses apoptosis by inhibiting apoptosome assembly, specifically blocking procaspase-9 recruitment to Apaf-1.
  • This inhibition occurs downstream of cytochrome c release, providing a novel regulatory mechanism for apoptosis.
  • Elevated cAMP levels, leading to PKA activation, can serve as a protective signal against apoptosis by preventing apoptosome formation.

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