XIAP inhibition of caspase-3 preserves its association with the Apaf-1 apoptosome and prevents CD95- and Bax-induced apoptosis

• Published in: Cell death and differentiation Vol. 9; no. 9; pp. 881 - 892
• Main Authors: Bratton, S B, Lewis, J, Butterworth, M, Duckett, C S, Cohen, G M
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01.09.2002
• Subjects: Adapter proteins; Apoptosis; Apoptosis - drug effects; Apoptosis - physiology; Apoptotic Protease-Activating Factor 1; bcl-2-Associated X Protein; Binding Sites - genetics; Caenorhabditis elegans Proteins - metabolism; Carrier Proteins - metabolism; Caspase 3; Caspase 9; Caspases - metabolism; Cell death; Cells, Cultured; Cysteine Endopeptidases - genetics; Cysteine Endopeptidases - metabolism; Cytochrome; Enzyme Inhibitors - pharmacology; Eukaryotic Cells - cytology; Eukaryotic Cells - drug effects; Eukaryotic Cells - enzymology; fas Receptor - metabolism; Humans; Intracellular Signaling Peptides and Proteins; Medical research; Mitochondrial Proteins - metabolism; Models, Biological; Multienzyme Complexes - genetics; Multienzyme Complexes - metabolism; Mutation - genetics; Proteasome Endopeptidase Complex; Proteins - genetics; Proteins - metabolism; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2; Signal transduction; Signal Transduction - genetics; X-Linked Inhibitor of Apoptosis Protein; Ann Arbor Michigan; United States > US; Michigan
• ISSN: 1350-9047; 1476-5403
• DOI: 10.1038/sj.cdd.4401069

Ligation of death receptors or formation of the Apaf-1 apoptosome results in the activation of caspases and execution of apoptosis. We recently demonstrated that X-linked inhibitor-of-apoptosis protein (XIAP) associates with the apoptosome in vitro. By utilizing XIAP mutants, we now report that XIAP binds to the 'native' apoptosome complex via a specific interaction with the small p12 subunit of processed caspase-9. Indeed, we provide the first direct evidence that XIAP can simultaneously bind active caspases-9 and -3 within the same complex and that inhibition of caspase-3 by the Linker-BIR2 domain prevents disruption of BIR3-caspase-9 interactions. Recent studies suggest that inhibition of caspase-3 is dispensable for its anti-apoptotic effects. However, we clearly demonstrate that inhibition of caspase-3 is required to inhibit CD95 (Fas/Apo-1)-mediated apoptosis, whereas inhibition of either caspase-9 or caspase-3 prevents Bax-induced cell death. Finally, we illustrate for the first time that XIAP mutants, which are incapable of binding to caspases-9 and -3 are completely devoid of anti-apoptotic activity. Thus, XIAP's capacity to maintain inhibition of caspase-9 within the Apaf-1 apoptosome is influenced by its ability to simultaneously inhibit active caspase-3, and depending upon the apoptotic stimulus, inhibition of caspase-9 or 3 is essential for XIAP's anti-apoptotic activity.