BAX translocation is a critical event in neuronal apoptosis: Regulation byneuroprotectants, BCL-2, and caspases

Members of the BCL-2 family of proteins either promote or repress programme d cell death. Here we report that neonatal sympathetic neurons undergoing a poptosis after nerve growth factor (NGF) deprivation exhibited a protein sy nthesis-dependent, caspase-independent subcellular redistribution of BAX fr om cytosol to mitochondria, followed by a loss of mitochondrial cytochrome c and cell death. Treatment with elevated concentrations of the neuroprotec tants KCl or cAMP at the time of deprivation prevented BAX translocation an d cytochrome c release. However, administration of KCl or cAMP 12 hr after NGF withdrawal acutely prevented loss of mitochondrial cytochrome c, but no t redistribution of BAX; rescue with NGF acutely prevented both events. Ove rexpression of Bcl-2 neither altered the normal subcellular localization of BAX nor prevented its redistribution with deprivation but did inhibit the subsequent release of cytochrome c, caspase activation, and cell death. Bcl -2 overexpression did not prevent cell death induced by cytoplasmic microin jection of cytochrome c into NGF-deprived competent-to-die neurons. These o bservations suggest that the subcellular redistribution of BAX is a critica l event in neuronal apoptosis induced by trophic factor deprivation. BCL-2 acts primarily, if not exclusively, at the level of mitochondria to prevent BAX-mediated cytochrome c release, whereas NGF, KCl, or cAMP may abort the apoptotic program at multiple checkpoints.