title: SMAC/Diablo mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events.
abstract: p53-upregulated modulator of apoptosis (PUMA) is a BH3-only Bcl-2 family protein and an essential mediator of DNA damage-induced apoptosis. PUMA is localized in the mitochondria and induces apoptosis through the mitochondrial pathway. However, the mechanisms of PUMA-induced apoptosis remain unclear. In this study, we found that second mitochondria-derived activator of caspase (SMAC)/Diablo, a mitochondrial apoptogenic protein, mediates the proapoptotic function of PUMA by regulating PUMA-induced mitochondrial events. SMAC is consistently released into the cytosol in colon cancer cells undergoing PUMA-induced apoptosis. In SMAC-deficient cells, execution of PUMA-induced apoptosis is abrogated, in company with decreases in caspase activation, cytosolic release of cytochrome c and collapse of mitochondrial membrane potential. Reconstituting SMAC expression restored these events in the SMAC-deficient cells. Furthermore, SMAC and agents that mimic the inhibitor of apoptosis proteins (IAPs) inhibition function of SMAC significantly sensitize cells to PUMA-induced apoptosis. These results demonstrate an important role of SMAC in executing DNA damage-induced and PUMA-mediated apoptosis and suggest that SMAC participates in a feedback amplification loop to promote cytochrome c release and other mitochondrial events in apoptosis.
authors.affiliation: Department of Pharmacology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: J
authors.initials: J
authors.lastname: Yu
authors.forename: P
authors.initials: P
authors.lastname: Wang
authors.forename: L
authors.initials: L
authors.lastname: Ming
authors.forename: M A
authors.initials: MA
authors.lastname: Wood
authors.forename: L
authors.initials: L
authors.lastname: Zhang
mesh_terms: D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism* / Q000502:physiology; D053453:Caspase 9 / Q000378:metabolism; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000037:antagonists & inhibitors / Q000378:metabolism; D045325:HCT116 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism* / Q000502:physiology
chemical_list: D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; D061945:Caspase Inhibitors; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D045304:Cytochromes c; D053453:Caspase 9