Creagh Emma M, Murphy Brona M, Duriez Patrick J, Duckett Colin S, Martin Seamus J
Molecular Cell Biology Laboratory, Department of Genetics, The Smurfit Institute, Trinity College, Dublin 2, Ireland.
J Biol Chem. 2004 Jun 25;279(26):26906-14. doi: 10.1074/jbc.M313859200. Epub 2004 Apr 12.
Inhibitor of apoptosis proteins (IAPs) can block apoptosis through binding to active caspases and antagonizing their function. IAP function can be neutralized by Smac/Diablo, an IAP-binding protein that is released from mitochondria during apoptosis. In addition to their ability to interact with caspases, certain IAPs also display ubiquitin-protein isopeptide ligase activity because of the presence of a RING domain. However, it is not known whether the ubiquitin-protein isopeptide ligase activities of human IAPs contribute to their apoptosis inhibitory activity or whether this IAP property can be modulated through association with Smac/Diablo. Here we demonstrate that the ubiquitin ligase activities of XIAP, and to a lesser extent c-IAP-1 and c-IAP2, are potently repressed through binding to Smac/Diablo. We also show that mutation of the XIAP RING domain rendered this IAP a less effective inhibitor of apoptosis, suggesting that the ubiquitin ligase activity of XIAP contributes to its anti-apoptotic function. These data suggest that Smac/Diablo potentiates apoptosis by simultaneously antagonizing caspase-IAP interactions and repressing IAP ubiquitin ligase activities.
凋亡抑制蛋白（IAPs）可通过与活化的半胱天冬酶结合并拮抗其功能来阻断细胞凋亡。Smac/Diablo是一种在细胞凋亡期间从线粒体释放的IAP结合蛋白，它可中和IAP的功能。除了与半胱天冬酶相互作用的能力外，某些IAPs由于存在RING结构域还具有泛素-蛋白质异肽酶活性。然而，尚不清楚人类IAPs的泛素-蛋白质异肽酶活性是否有助于其凋亡抑制活性，或者这种IAP特性是否可通过与Smac/Diablo结合来调节。在此我们证明，XIAP的泛素连接酶活性，以及程度较轻的c-IAP-1和c-IAP2的泛素连接酶活性，通过与Smac/Diablo结合而被有效抑制。我们还表明，XIAP RING结构域的突变使该IAP成为一种较无效的凋亡抑制剂，这表明XIAP的泛素连接酶活性有助于其抗凋亡功能。这些数据表明，Smac/Diablo通过同时拮抗半胱天冬酶-IAP相互作用和抑制IAP泛素连接酶活性来增强细胞凋亡。
