title: Apoptosis-associated release of Smac/DIABLO from mitochondria requires active caspases and is blocked by Bcl-2.
abstract: Smac/DIABLO is a mitochondrial protein that potentiates some forms of apoptosis, possibly by neutralizing one or more members of the IAP family of apoptosis inhibitory proteins. Smac has been shown to exit mitochondria and enter the cytosol during apoptosis triggered by UV- or gamma-irradiation. Here, we report that Smac/DIABLO export from mitochondria into the cytosol is provoked by cytotoxic drugs and DNA damage, as well as by ligation of the CD95 death receptor. Mitochondrial efflux of Smac/DIABLO, in response to a variety of pro-apoptotic agents, was profoundly inhibited in Bcl-2-overexpressing cells. Thus, in addition to modulating apoptosis-associated mitochondrial cytochrome c release, Bcl-2 also regulates Smac release, suggesting that both molecules may escape via the same route. However, whereas cell stress-associated mitochondrial cytochrome c release was largely caspase independent, release of Smac/DIABLO in response to the same stimuli was blocked by a broad-spectrum caspase inhibitor. This suggests that apoptosis-associated cytochrome c and Smac/DIABLO release from mitochondria do not occur via the same mechanism. Rather, Smac/DIABLO efflux from mitochondria is a caspase-catalysed event that occurs downstream of cytochrome c release.
authors.affiliation: Molecular Cell Biology Laboratory, Department of Genetics, The Smurfit Institute, Trinity College, Dublin 2, Ireland.
authors.forename: C
authors.initials: C
authors.lastname: Adrain
authors.forename: E M
authors.initials: EM
authors.lastname: Creagh
authors.forename: S J
authors.initials: SJ
authors.lastname: Martin
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000096:biosynthesis*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004249:DNA Damage; D003609:Dactinomycin / Q000494:pharmacology; D003630:Daunorubicin / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005720:Gamma Rays; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000096:biosynthesis*; D008954:Models, Biological; D011485:Protein Binding; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D014466:Ultraviolet Rays; D019014:fas Receptor / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; C412403:DIABLO protein, human; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D019014:fas Receptor; D003609:Dactinomycin; D020169:Caspases; D019311:Staurosporine; D003630:Daunorubicin