title: Bcl-2 inhibits apoptosis induced by mitochondrial uncoupling but does not prevent mitochondrial transmembrane depolarization.
abstract: Bcl-2 overexpression protects cells from apoptosis induced by many cytotoxic agents. In this study, we investigated the effects of uncoupling mitochondrial electron transport in both HL60 wild-type and Bcl-2-overexpressing cells using the protonophore carbonyl cyanide m-chlorophenylhydrazone. We found that uncoupling mitochondrial electron transport induced apoptosis in wild-type, but not in Bcl-2-overexpressing cells. To investigate the mechanism of action of Bcl-2-mediated inhibition of cyanide m-chlorophenylhydrazone-induced apoptosis, we measured the mitochondrial transmembrane potential (DeltaPsi(m)) after uncoupling mitochondrial electron transport and found that both HL-60 wild-type and Bcl-2-overexpressing cells similarly depolarize following cyanide m-chlorophenylhydrazone exposure. Western blot analysis demonstrated that Bcl-2 overexpression did not completely block cytochrome c release from mitochondria after uncoupling mitochondrial electron transport. Since Bcl-2 may act as an antioxidant, we studied the effect of altering the cellular redox state prior to uncoupling mitochondrial electron transport in Bcl-2-overexpressing cells. Depletion of mitochondrial (but not cytosolic) glutathione induced apoptosis in Bcl-2-overexpressing cells and negated the protective effect of Bcl-2. Furthermore, following glutathione depletion, Bcl-2-overexpressing cells were sensitized to undergo cyanide m-chlorophenylhydrazone-induced apoptosis. These data suggest that the action of Bcl-2 is dependent, in part, on the cellular and mitochondrial redox state.
authors.affiliation: Department of Radiation Oncology, Stanford University Medical Center, Stanford, California, 94305-5105, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Armstrong
authors.forename: K K
authors.initials: KK
authors.lastname: Steinauer
authors.forename: J
authors.initials: J
authors.lastname: French
authors.forename: P L
authors.initials: PL
authors.lastname: Killoran
authors.forename: J
authors.initials: J
authors.lastname: Walleczek
authors.forename: J
authors.initials: J
authors.lastname: Kochanski
authors.forename: S J
authors.initials: SJ
authors.lastname: Knox
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D003574:Cytochrome c Group / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D003574:Cytochrome c Group; D019253:Proto-Oncogene Proteins c-bcl-2; D014475:Uncoupling Agents; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D005978:Glutathione