The BH3 domain is required for caspase-independent cell death induced by Bax and oligomycin

Bar causes apoptosis by associating with mitochondria and triggering cytoch rome c release, which activates the caspase cascade. Bar can also kill some cells independently of caspases, but the requirements for such killing are poorly understood. Here we describe an inducible fibroblast line that expr esses Bar when tetracycline is withdrawn; the resulting apoptosis can be bl ocked by the caspase inhibitor zVAD-fmk, Even when caspases are inhibited, however, treating the Bax-expressing cells with the mitochondrial toxin oli gomycin efficiently triggers death with features resembling apoptosis, Bar mutants lacking the BH3 domain remain able to cause cytochrome c release an d caspase-mediated death, but cannot support this caspase-independent killi ng. Mutating specific BH3 residues needed for binding Bcl2 does not prevent synergy with oligomycin, implying that no such binding is required. These findings illuminate a caspase-independent pathway of death that depends on the Bar BH3 domain and on effecters emanating from mitochondria.