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The DNA damage-induced decrease of Bcl-2 is secondary to the activation of apoptotic effector caspases

Javorina Milosevic1, Sandra Hoffarth, Claudia Huber

  • 1Gene Therapy Laboratory, Johannes Gutenberg University, 55101 Mainz, Germany.

Oncogene
|October 10, 2003
PubMed

Insights

DNA damage triggers apoptosis via mitochondrial pathways. This study reveals that proapoptotic Bcl-2 family proteins, not decreased antiapoptotic Bcl-2, initiate the release of cytochrome c, activating caspases.

Area of Science:

  • Cellular biology
  • Molecular biology
  • Biochemistry

Background:

  • Apoptosis is crucial for development and disease.
  • DNA damage and radiation induce apoptosis through intrinsic and extrinsic pathways.
  • The mitochondrial pathway involves caspase activation and Bcl-2 family proteins.

Purpose of the Study:

  • To investigate the role of Bcl-2 family proteins in DNA damage-induced apoptosis.
  • To determine whether downregulation of antiapoptotic Bcl-2 or activation of proapoptotic proteins initiates mitochondrial apoptosis.
  • To elucidate the mechanism of cytochrome c release in response to DNA damage.

Main Methods:

  • Utilized murine embryonic fibroblasts (MEF) proficient and deficient in Apaf1.
  • Assessed DNA damage response using Western blotting for Bcl-2 and Noxa.
  • Measured Bax activation, cytochrome c release, and mitochondrial membrane potential (Deltapsim).
  • Investigated the effect of caspase inhibition on Bcl-2 levels.

Main Results:

  • DNA damage induced proapoptotic Noxa and Bax activation in both wt and apaf1(-/-) MEF.
  • Cytochrome c release and mitochondrial depolarization occurred irrespective of Apaf1 status.
  • Bcl-2 downregulation was observed only in wt MEF and was prevented by caspase inhibition.
  • Apaf1(-/-) MEF showed defective effector caspase activation and apoptosis despite mitochondrial events.

Conclusions:

  • Activation of proapoptotic Bcl-2 family proteins, not Bcl-2 downregulation, is the primary signal for mitochondrial apoptogenic protein release.
  • Caspase activation downstream of cytochrome c release is essential for apoptosis following DNA damage.
  • Apaf1 is critical for effector caspase activation and subsequent apoptosis, but not for the initial mitochondrial permeabilization signal.

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