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The c‐IAP‐1 and c‐IAP‐2 proteins are direct inhibitors of specific caspases
Author(s) -
Roy Natalie,
Deveraux Quinn L.,
Takahashi Ryosuke,
Salvesen Guy S.,
Reed John C.
Publication year - 1997
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/16.23.6914
Subject(s) - xiap , caspase , proteases , biology , inhibitor of apoptosis , programmed cell death , cytochrome c , apoptosis , microbiology and biotechnology , inhibitor of apoptosis domain , caspase 2 , intrinsic apoptosis , protease , biochemistry , enzyme
The inhibitor of apoptosis (IAP) family of proteins are highly conserved through evolution. However, the mechanisms by which these proteins interfere with apoptotic cell death have been enigmatic. Recently, we showed that one of the human IAP family proteins, XIAP, can bind to and potently inhibit specific cell death proteases (caspases) that function in the distal portions of the proteolytic cascades involved in apoptosis. In this study, we investigated three of the other known members of the human IAP family, c‐IAP‐1, c‐IAP‐2 and NAIP. Similarly to XIAP, in vitro binding experiments indicated that c‐IAP‐1 and c‐IAP‐2 bound specifically to the terminal effector cell death proteases, caspases‐3 and ‐7, but not to the proximal protease caspase‐8, caspases‐1 or ‐6. In contrast, NAIP failed to bind tightly to any of these proteases. Recombinant c‐IAP‐1 and c‐IAP‐2 also inhibited the activity of caspases‐3 and ‐7 in vitro , with estimated K i s of ≤0.1 μM, whereas NAIP did not. The BIR domain‐containing region of c‐IAP‐1 and c‐IAP‐2 was sufficient for inhibition of these caspases, though proteins that retained the RING domain were somewhat more potent. Utilizing a cell‐free system in which caspases were activated in cytosolic extracts by addition of cytochrome c , c‐IAP‐1 and c‐IAP‐2 inhibited both the generation of caspase activities and proteolytic processing of pro‐caspase‐3. Similar results were obtained in intact cells when c‐IAP‐1 and c‐IAP‐2 were overexpressed by gene transfection, and apoptosis was induced by the anticancer drug, etoposide. Cleavage of c‐IAP‐1 or c‐IAP‐2 was not observed when interacting with the caspases, implying a different mechanism from the baculovirus p35 protein, the broad spectrum suicide inactivator of caspases. Taken together, these findings suggest that c‐IAP‐1 and c‐IAP‐2 function similarly to XIAP by inhibiting the distal cell death proteases, caspases‐3 and ‐7, whereas NAIP presumably inhibits apoptosis via other targets.