Distinct stages of cytochrome c release from mitochondria: evidence for a feedback amplification loop linking caspase activation to mitochondrial dysfunction in genotoxic stress induced apoptosis

Cell Death Differ. 2000 Feb;7(2):227-33. doi: 10.1038/sj.cdd.4400629.


Cytochrome c (cyto c) release from mitochondria is a critical event in apoptosis. By investigating the ordering of molecular events during genotoxic stress-induced apoptosis, we found that ionizing radiation (IR) and etoposide induced the release of cyto c from mitochondria in two distinct stages. The early release of low levels of cyto c into the cytosol preceded the activation of caspase 9 and 3, but had no effect on ATP levels or mitochrondrial transmembrane potential (Deltapsim). In contrast, the late stage cyto c release resulted in a drastic loss of mitochondrial cyto c and was associated with reduction of ATP levels and Deltapsim. Moreover, caspases contributed to the late cyto c release since the caspase inhibitor zVAD prevented only the late but not the early-stage cyto c release. Recombinant caspase 3 induced cyto c release from isolated mitochondria in the absence of cytosolic factors. Bcl-2 but not Bid was cleaved during apoptosis after caspase activation. This suggests that Bcl-2 cleavage might contribute to the late cyto c release, which results in mitochondrial dysfunction manifested by the decrease of ATP and Deltapsim. zVAD prevented the reduction of ATP, Deltapsim, and nuclear condensation when added up to 8 h after IR, at the time the caspases were highly activated but when the majority of cyto c was still maintained in the mitochondria. These findings link the feedback loop control of caspase-induced cyto c release with mitochondrial dysfunction manifested by ATP and Deltapsim decline.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Apoptosis*
  • Caspase 3
  • Caspase 9
  • Caspases / metabolism*
  • Cytochrome c Group / metabolism*
  • Enzyme Activation
  • Feedback
  • Humans
  • Mitochondria / enzymology*
  • Mitochondria / pathology*
  • Multiple Myeloma
  • Tumor Cells, Cultured


  • Cytochrome c Group
  • CASP3 protein, human
  • CASP9 protein, human
  • Caspase 3
  • Caspase 9
  • Caspases