title: TRAIL-induced apoptosis requires Bax-dependent mitochondrial release of Smac/DIABLO.
abstract: Recent reports suggest that a cross-talk exists between apoptosis pathways mediated by mitochondria and cell death receptors. In the present study, we report that mitochondrial events are required for apoptosis induced by the cell death ligand TRAIL (TNF-related apoptosis-inducing ligand) in human cancer cells. We show that the Bax null cancer cells are resistant to TRAIL-induced apoptosis. Bax deficiency has no effect on TRAIL-induced caspase-8 activation and subsequent cleavage of Bid; however, it results in an incomplete caspase-3 processing because of inhibition by XIAP. Release of Smac/DIABLO from mitochondria through the TRAIL-caspase-8-tBid-Bax cascade is required to remove the inhibitory effect of XIAP and allow apoptosis to proceed. Inhibition of caspase-9 activity has no effect on TRAIL-induced caspase-3 activation and cell death, whereas expression of the active form of Smac/DIABLO in the cytosol is sufficient to reconstitute TRAIL sensitivity in Bax-deficient cells. Our results show for the first time that Bax-dependent release of Smac/DIABLO, not cytochrome c, from mitochondria mediates the contribution of the mitochondrial pathway to death receptor-mediated apoptosis.
authors.affiliation: Huffington Center on Aging and Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Yibin
authors.initials: Y
authors.lastname: Deng
authors.forename: Yahong
authors.initials: Y
authors.lastname: Lin
authors.forename: Xiangwei
authors.initials: X
authors.lastname: Wu
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D020239:Receptor Cross-Talk; D018124:Receptors, Tumor Necrosis Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; D020169:Caspases