title: Cellular inhibitor of apoptosis 1 and 2 are ubiquitin ligases for the apoptosis inducer Smac/DIABLO.
abstract: Inhibitors of apoptosis (IAPs) are crucial regulators of programmed cell death. The mechanism by which IAPs prevent apoptosis has previously been attributed to the direct inhibition of caspases. The function of mammalian IAPs is counteracted by cell death inducer second mitochondria-derived activator of caspases (Smac)/DIABLO during apoptosis. Here we show that cIAP1 and cIAP2 are E3 ubiquitin-protein isopeptide ligases (ubiquitin ligases) for Smac. cIAPs stimulate Smac ubiquitination both in vivo and in vitro, leading to Smac degradation. cIAP1 and cIAP2 associate with overlapping but distinct subsets of E2 (ubiquitin carrier protein) ubiquitin-conjugating enzymes. The substrate-dependent E3 activity of cIAPs is mediated by their RING domains and is dependent on the specific interactions between cIAPs and Smac. Similarly, Drosophila IAP1 also possesses ubiquitin ligase activity that mediates the degradation of the Drosophila apoptosis inducers Grim and HID. These results suggest a novel and conserved mechanism by which IAPs block apoptosis through the degradation of death inducers.
authors.affiliation: Abramson Family Cancer Research Institute and Department of Cancer Biology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
authors.forename: Shimin
authors.initials: S
authors.lastname: Hu
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Yang
mesh_terms: D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008025:Ligases / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism; D011506:Proteins / Q000502:physiology*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; C111891:DIAP1 protein, Drosophila; D029721:Drosophila Proteins; C108880:HID protein, Drosophila; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D009479:Neuropeptides; D011506:Proteins; D025801:Ubiquitin; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C108881:grim protein, Drosophila; C494833:BIRC2 protein, human; D044767:Ubiquitin-Protein Ligases; D008025:Ligases