Enforced dimerization of BAX results in its translocation, mitochondrial dysfunction and apoptosis.
Expression of the pro-apoptotic molecule BAX has been shown to induce cell death. While BAX forms both homo- and heterodimers, questions remain concerning its native conformation in vivo and which moiety is functionally active. Here we demonstrate that a physiologic death stimulus, the withdrawal of interleukin-3 (IL-3), resulted in the translocation of monomeric BAX from the cytosol to the mitochondria where it could be cross-linked as a BAX homodimer. In contrast, cells protected by BCL-2 demonstrated a block in this process in that BAX did not redistribute or homodimerize in response to a death signal. To test the functional consequence of BAX dimerization, we expressed a chimeric FKBP-BAX molecule. Enforced dimerization of FKBP-BAX by the bivalent ligand FK1012 resulted in its translocation to mitochondria and induced apoptosis. Caspases were activated yet caspase inhibitors did not block death; cytochrome c was not released detectably despite the induction of mitochondrial dysfunction. Moreover, enforced dimerization of BAX overrode the protection by BCL-XL and IL-3 to kill cells. These data support a model in which a death signal results in the activation of BAX. This conformational change in BAX manifests in its translocation, mitochondrial membrane insertion and homodimerization, and a program of mitochondrial dysfunction that results in cell death.
Gross
A
A
Division of Molecular Oncology, Departments of Medicine and Pathology, Howard Hughes Medical Institute, Washington University School of Medicine, St Louis, MO 63110, USA.
Jockel
J
J
Wei
M C
MC
Korsmeyer
S J
SJ
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D006801:Humans; D007377:Interleukin-3 / Q000502:physiology; D008024:Ligands; D008564:Membrane Potentials; D051379:Mice; D008928:Mitochondria / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D051381:Rats; D011993:Recombinant Fusion Proteins; D016559:Tacrolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D000590:Amino Acid Chloromethyl Ketones; C494826:BAX protein, human; C494811:BCL2L1 protein, human; C494827:Bax protein, mouse; C494828:Bax protein, rat; C494812:Bcl2l1 protein, mouse; C494813:Bcl2l1 protein, rat; D015853:Cysteine Proteinase Inhibitors; C084260:FK 1012; D007377:Interleukin-3; D008024:Ligands; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; C506434:Casp9 protein, mouse; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D003546:Cysteine Endopeptidases; D016559:Tacrolimus