Separation of cytochrome c-dependent caspase activation from thiol- disulfide redox change in cells lacking mitochondrial DNA

Release of mitochondrial cytochrome c (cyt c) is an early and common event during apoptosis. Previous studies showed that the loss of cyt c triggered superoxide production by mitochondria and contributed to the oxidation of cellular thiol-disulfide redox state. In this study, we tested whether loss of the functional electron transport chain due to depleting mitochondrial DNA (mtDNA) would affect this redox-signaling mechanism during apoptosis. Results showed that cyt c release and caspase activation in response to staurosporine treatment were preserved in cells lacking mitochondrial DNA (ρ⁰ cells). However, unlike the case with ρ⁺ cells, in which a dramatic oxidation of intracellular glutathione (GSH) occurred after mitochondrial cyt c release, the thiol-disulfide redox state in apoptotic ρ⁰ cells remained largely unchanged. Thus, mitochondrial signaling of caspase activation can be separated from the bioenergetic function, and mitochondrial respiratory chain is the principal source of ROS generation in staurosporine-induced apoptosis. (C) 2000 Elsevier Science Inc.