title: 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.
abstract: 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.
authors.affiliation: Department of Cancer Biology, Lerner Research Institute NB40, The Cleveland Clinic Foundation, Cleveland, Ohio, OH 44195, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Chen
authors.forename: B
authors.initials: B
authors.lastname: Gong
authors.forename: A
authors.initials: A
authors.lastname: Almasan
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D003574:Cytochrome c Group / Q000378:metabolism*; D004789:Enzyme Activation; D005246:Feedback; D006801:Humans; D008928:Mitochondria / Q000201:enzymology* / Q000473:pathology*; D009101:Multiple Myeloma; D014407:Tumor Cells, Cultured
chemical_list: D003574:Cytochrome c Group; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases