Dissimilar mechanisms of cytochrome c release induced by octyl glucoside-activated BAX and by BAX activated with truncated BID

In the present study, we compared alkali-resistant BAX insertion into the outer mitochondrial membrane, mitochondrial remodeling, mitochondrial membrane potential changes, and cytochrome c (Cyt c) release from isolated brain mitochondria triggered by recombinant BAX oligomerized with 1% octyl glucoside (BAXoligo) and by a combination of monomeric BAX (BAXmono) and caspase 8-cleaved C-terminal fragment of recombinant BID (truncated BID, tcBID). We also examined whether the effects induced by BAXoligo or by BAXmono activated with tcBID depended on induction of the mitochondrial permeability transition. The results obtained in this study revealed that tcBID plus BAXmono produced BAX insertion and Cyt c release without overt changes in mitochondrial morphology. On the contrary, treatment of mitochondria with BAXoligo resulted in BAX insertion and Cyt c release, which were accompanied by gross distortion of mitochondrial morphology. The effects of BAXoligo could be at least partially suppressed by mitochondrial depolarization. The effects of tcBID plus BAXmono were insensitive to depolarization. BAXoligo produced similar BAX insertion, mitochondrial remodeling, and Cyt c release in KCl- and in N-methyl-d-glucamine-based incubation media indicating a non-essential role for K+ influx into mitochondria in these processes. A combination of cyclosporin A and ADP, inhibitors of the mitochondrial permeability transition, attenuated Cyt c release, mitochondrial remodeling, and depolarization induced by BAXoligo, but failed to influence the effects produced by tcBID plus BAXmono. Thus, our results suggest a significant difference in the mechanisms of the outer mitochondrial membrane permeabilization and Cyt c release induced by detergent-oligomerized BAXoligo and by BAX activated with tcBID.