Bax-induced cytochrome C release from mitochondria is independent of the permeability transition pore but highly dependent on Mg2+ ions.
Bcl-2 family members either promote or repress programmed cell death. Bax, a death-promoting member, is a pore-forming, mitochondria-associated protein whose mechanism of action is still unknown. During apoptosis, cytochrome C is released from the mitochondria into the cytosol where it binds to APAF-1, a mammalian homologue of Ced-4, and participates in the activation of caspases. The release of cytochrome C has been postulated to be a consequence of the opening of the mitochondrial permeability transition pore (PTP). We now report that Bax is sufficient to trigger the release of cytochrome C from isolated mitochondria. This pathway is distinct from the previously described calcium-inducible, cyclosporin A-sensitive PTP. Rather, the cytochrome C release induced by Bax is facilitated by Mg2+ and cannot be blocked by PTP inhibitors. These results strongly suggest the existence of two distinct mechanisms leading to cytochrome C release: one stimulated by calcium and inhibited by cyclosporin A, the other Bax dependent, Mg2+ sensitive but cyclosporin insensitive.
Eskes
R
R
Serono Pharmaceutical Research Institute, 1228 Plan-les-Ouates, Geneva, Switzerland.
Antonsson
B
B
Osen-Sand
A
A
Montessuit
S
S
Richter
C
C
Sadoul
R
R
Mazzei
G
G
Nichols
A
A
Martinou
J C
JC
D000818:Animals; D001865:Bongkrekic Acid / Q000494:pharmacology; D019556:COS Cells; D016572:Cyclosporine / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007425:Intracellular Membranes / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D051379:Mice; D008815:Mice, Inbred Strains; D008930:Mitochondria, Liver / Q000187:drug effects / Q000502:physiology*; D010539:Permeability; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C494827:Bax protein, mouse; D003574:Cytochrome c Group; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein; D001865:Bongkrekic Acid; D016572:Cyclosporine; D008274:Magnesium