Overexpression of manganese superoxide dismutase protects against mitochondrial-initiated poly(ADP-ribose) polymerase-mediated cell death

Mitochondria have recently been shown to serve a central role in programmed cell death. In addition, reactive oxygen species (ROS) have been implicated in cell death pathways upon treatment with a variety of agents; however, the specific cellular source of the ROS generation is unknown. We hypothesize that mitochondria-derived free radicals play a critical role in apoptotic cell death. To directly test this hypothesis, we treated murine fibrosarcoma cell lines, which expressed a range of mitochondrial manganese superoxide dismutase (MnSOD) activities, with respiratory chain inhibitors. Apoptosis was confirmed by DNA fragmentation analysis and electron microscopy. MnSOD overexpression specifically protected against cell death upon treatment with rotenone or antimycin. We examined bcl-xL, p53 and poly(ADP-ribose) polymerase (PARP) to identify specific cellular pathways that might contribute to the mitochondrial-initiated ROS-mediated cell death. Cells overexpressing MnSOD contained less bcl-xL within the mi...