Bax interacts with the permeability transition pore to induce permeability transition and cytochrome<i>c</i>release in isolated mitochondria

TLDR

Cytochrome c release and mitochondrial permeability transition, marked by loss of Δψ, are key events in apoptosis. Recombinant Bax and Bak trigger Ca²⁺‑dependent mitochondrial permeability transition, swelling, and cytochrome c release in isolated mitochondria, an effect blocked by cyclosporin A, bongkrekic acid, anti‑apoptotic Bcl‑2 proteins, and oligomycin, and mediated through interaction with VDAC, showing that Bax/Bak induce PT and cytochrome c release via PT pores.

Abstract

Cytochrome c release and the mitochondrial permeability transition (PT), including loss of the transmembrane potential (Δψ), play an important role in apoptosis. Using isolated mitochondria, we found that recombinant Bax and Bak, proapoptotic members of the Bcl-2 family, induced mitochondrial Δψ loss, swelling, and cytochrome c release. All of these changes were dependent on Ca 2+ and were prevented by cyclosporin A (CsA) and bongkrekic acid, both of which close the PT pores (megachannels), indicating that Bax- and Bak-induced mitochondrial changes were mediated through the opening of these pores. Bax-induced mitochondrial changes were inhibited by recombinant Bcl-x L and transgene-derived Bcl-2, antiapoptotic members of the Bcl-2 family, as well as by oligomycin, suggesting a possible regulatory effect of F 0 F 1 -ATPase on Bax-induced mitochondrial changes. Proapoptotic Bax- and Bak-BH3 (Bcl-2 homology) peptides, but not a mutant BH3 peptide nor a mutant Bak lacking BH3, induced the mitochondrial changes, indicating an essential role of the BH3 region. A coimmunoprecipitation study revealed that Bax and Bak interacted with the voltage-dependent anion channel, which is a component of PT pores. Taken together, these findings suggest that proapoptotic Bcl-2 family proteins, including Bax and Bak, induce the mitochondrial PT and cytochrome c release by interacting with the PT pores.