title: Bax membrane insertion during Fas(CD95)-induced apoptosis precedes cytochrome c release and is inhibited by Bcl-2.
abstract: Ligation of the Fas cell surface receptor leads to activation of caspases and subsequent apoptosis. Members of the Bcl-2 family of proteins control the cellular commitment to apoptosis, although their role in Fas-induced apoptosis is ill-defined. In this report we demonstrate that the pro-apoptotic protein, Bax, translocates from the cytosol specifically to the mitochondria following Fas ligation in MCF10A1 breast epithelial cells. Bax translocation was dependent on caspase activation, and preceded the release of cytochrome c and loss of mitochondrial respiratory activity. Bax translocation occurred in concert with activation of downstream caspases as determined by cleavage of a synthetic substrate, proteolysis of poly(ADP-ribose) polymerase, and processing of procaspase-3 and -7. Overexpression of the anti-apoptotic protein, Bcl-2, prevented Bax insertion, cytochrome c release, complete processing of caspase-3 and -7, and full activation of DEVD-specific cleavage activity. These data establish a role for Bax mitochondrial insertion during Fas-mediated apoptosis, and support a model in which Bax insertion amplifies the Fas apoptotic cascade through cytochrome c release and complete processing of caspases-3 and -7. In addition, our findings indicate that prevention of Bax insertion into the mitochondria represents a novel mechanism by which Bcl-2 inhibits Fas-induced apoptosis.
authors.affiliation: Department of Microbiology and Immunology, University of Louisville, Louisville, Kentucky, KY 40292, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Murphy
authors.forename: U N
authors.initials: UN
authors.lastname: Streips
authors.forename: R B
authors.initials: RB
authors.lastname: Lock
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D001692:Biological Transport; D001940:Breast / Q000166:cytology; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D019069:Cell Respiration; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D000590:Amino Acid Chloromethyl Ketones; C494826:BAX protein, human; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D003574:Cytochrome c Group; 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; D011065:Poly(ADP-ribose) Polymerases; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases