The Carboxy Terminal C-Tail of BNip3 Is Crucial in Induction of Mitochondrial Permeability Transition in Isolated Mitochondria

BNip3 is a member of Bcl-2 family proteins that displays proapoptotic activity. It contains Bcl-2 homology (BH) 3 and single carboxy terminal membrane-anchoring domain (TM), which targets to specific intracellular organelles, especially to mitochondria. Mitochondria play significant roles in apoptosis by releasing apoptogenic factors through large conductance channel known as permeability transition pore (PTP). Although BNip3 associates with mitochondria when overexpressed, apoptotic pathways including mitochondrial cascade and functional domains of BNip3 are still unknown. In this report, we demonstrate that recombinant BNip3 (rBNip3) induces mitochondrial permeability transition (MPT) and cytochrome c release from isolated mitochondria, which are inhibited by the PT inhibitor cyclosporin A (CsA). We further show that carboxy terminal tail of BNip3, but not BH3, is essential for the induction of PT and cytochrome c release on the base of mutational analysis. Moreover, addition of carboxy terminal c-tail to TM substitution mutant, which did not induce the PT and cytochrome c release, restored PT-inducing activity. Taken together, our results suggest that BNip3 exerts proapoptotic activity through PT induction and that carboxy terminal c-tail is crucial for it.