BID-dependent and BID-independent pathways for BAX insertion into mitochondria.
In the absence of an apoptotic signal, BAX adopts a conformation that constrains the protein from integrating into mitochondrial membranes. Here, we show that caspases, including caspase-8, can initiate BAX insertion into mitochondria in vivo and in vitro. The cleavage product of caspase-8, tBID, induced insertion of BAX into mitochondria in vivo, and reconstitution in vitro showed that tBID, either directly or indirectly, relieved inhibition of the BAX transmembrane signal-anchor by the NH2-terminal domain, resulting in integration of BAX into mitochondrial membrane. In contrast to these findings, however, Bid-null mouse embryo fibroblasts supported Bax insertion into mitochondria in response to death signaling by either TNFalpha or E1A, despite the fact that cytochrome c release from the organelle was inhibited. We conclude, therefore, that a parallel Bid-independent pathway exists in these cells for mitochondrial insertion of Bax and that, in the absence of Bid, cytochrome c release can be uncoupled from Bax membrane insertion.
Ruffolo
S C
SC
Department of Biochemistry, McIntyre Medical Sciences Building, McGill University, Montreal, Quebec, Canada H3G 1Y6.
Breckenridge
D G
DG
Nguyen
M
M
Goping
I S
IS
Gross
A
A
Korsmeyer
S J
SJ
Li
H
H
Yuan
J
J
Shore
G C
GC
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells; D005347:Fibroblasts / Q000502:physiology; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D051379:Mice; D018613:Microscopy, Confocal; D008929:Mitochondria, Heart / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000378:metabolism
D000590:Amino Acid Chloromethyl Ketones; C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494827:Bax protein, mouse; C494828:Bax protein, rat; C494815:Bid protein, mouse; C494816:Bid protein, rat; D002352:Carrier Proteins; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D003576:Electron Transport Complex IV; D020169:Caspases