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.
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.
Mesh Terms:
Antigens, CD95, Apoptosis, Caspase 3, Caspases, Cell Line, Transformed, Cysteine Endopeptidases, Enzyme Activation, Gene Expression Regulation, Enzymologic, Humans, Ligases, Multienzyme Complexes, Proteasome Endopeptidase Complex, Proteins, Recombinant Fusion Proteins, Ubiquitin-Conjugating Enzymes, Ubiquitin-Protein Ligases, X-Linked Inhibitor of Apoptosis Protein
Antigens, CD95, Apoptosis, Caspase 3, Caspases, Cell Line, Transformed, Cysteine Endopeptidases, Enzyme Activation, Gene Expression Regulation, Enzymologic, Humans, Ligases, Multienzyme Complexes, Proteasome Endopeptidase Complex, Proteins, Recombinant Fusion Proteins, Ubiquitin-Conjugating Enzymes, Ubiquitin-Protein Ligases, X-Linked Inhibitor of Apoptosis Protein
Proc. Natl. Acad. Sci. U.S.A.
Date: Jul. 17, 2001
PubMed ID: 11447297
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