title: Ubiquitin-protein ligase activity of X-linked inhibitor of apoptosis protein promotes proteasomal degradation of caspase-3 and enhances its anti-apoptotic effect in Fas-induced cell death.
abstract: The inhibitor of apoptosis (IAP) family of anti-apoptotic proteins regulate programmed cell death and/or apoptosis. One such protein, X-linked IAP (XIAP), inhibits the activity of the cell death proteases, caspase-3, -7, and -9. In this study, using constitutively active mutants of caspase-3, we found that XIAP promotes the degradation of active-form caspase-3, but not procaspase-3, in living cells. The XIAP mutants, which cannot interact with caspase-3, had little or no activity of promoting the degradation of caspase-3. RING finger mutants of XIAP also could not promote the degradation of caspase-3. A proteasome inhibitor suppressed the degradation of caspase-3 by XIAP, suggesting the involvement of a ubiquitin-proteasome pathway in the degradation. An in vitro ubiquitination assay revealed that XIAP acts as a ubiquitin-protein ligase for caspase-3. Caspase-3 was ubiquitinated in the presence of XIAP in living cells. Both the association of XIAP with caspase-3 and the RING finger domain of XIAP were essential for ubiquitination. Finally, the RING finger mutants of XIAP were less effective than wild-type XIAP at preventing apoptosis induced by overexpression of either active-form caspase-3 or Fas. These results demonstrate that the ubiquitin-protein ligase activity of XIAP promotes the degradation of caspase-3, which enhances its anti-apoptotic effect.
authors.affiliation: Laboratory for Motor System Neurodegeneration, RIKEN Brain Science Institute, Wako City, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Y
authors.initials: Y
authors.lastname: Nakabayashi
authors.forename: R
authors.initials: R
authors.lastname: Takahashi
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000235:genetics / Q000378:metabolism*; D002461:Cell Line, Transformed; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D009097:Multienzyme Complexes; D011506:Proteins; D011993:Recombinant Fusion Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D019014:fas Receptor; C097309:UBE2D2 protein, human; C079437:UBE2L3 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases