Mahoney D J, Cheung H H, Mrad R Lejmi, Plenchette S, Simard C, Enwere E, Arora V, Mak T W, Lacasse E C, Waring J, Korneluk R G
Apoptosis Research Centre, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada K1H 8L1.
Proc Natl Acad Sci U S A. 2008 Aug 19;105(33):11778-83. doi: 10.1073/pnas.0711122105. Epub 2008 Aug 12.
The cellular inhibitor of apoptosis 1 and 2 (cIAP1 and cIAP2) proteins have been implicated in the activation of NF-kappaB by TNFalpha; however, genetic deletion of either cIAP1 or 2 did not support a physiologically relevant role, perhaps because of functional redundancy. To address this, we used combined genetic and siRNA knockdown approaches and report that cIAP1 and 2 are indeed critical, yet redundant, regulators of NF-kappaB activation upon TNFalpha treatment. Whereas NF-kappaB was properly activated by TNFalpha in cultured and primary cells deficient in either cIAP1 or 2, removal of both cIAPs severely blunted its activation. After treatment with TNFalpha, cIAP1 and 2 were rapidly recruited to the TNF receptor 1, along with the adapter protein TNF receptor associated factor 2. Importantly, either cIAP1 or 2 was required for proper TNF receptor 1 signalosome function. In their combined absence, polyubiquitination of receptor interacting protein 1, an upstream event necessary for NF-kappaB signaling, was attenuated. As a result, phosphorylation of the inhibitor of kappaB kinase beta was diminished, and signal transduction was severely blunted. Consequently, cells missing both cIAP1 and 2 were sensitized to TNFalpha-mediated apoptosis. Collectively, these data demonstrate that either cIAP1 or 2 is required for proper Rip1 polyubiquitination and NF-kappaB activation upon TNFalpha treatment.
细胞凋亡抑制蛋白1和2（cIAP1和cIAP2）已被证实参与肿瘤坏死因子α（TNFα）介导的核因子κB（NF-κB）激活过程；然而，单独敲除cIAP1或cIAP2的基因并不能支持其在生理功能方面的作用，这可能是由于功能冗余所致。为了解决这一问题，我们采用了基因编辑和小干扰RNA（siRNA）敲低相结合的方法，并报告称cIAP1和cIAP2确实是TNFα处理后NF-κB激活的关键但冗余的调节因子。虽然在缺乏cIAP1或cIAP2的培养细胞和原代细胞中，TNFα能够正常激活NF-κB，但同时去除这两种蛋白则会严重削弱其激活作用。用TNFα处理后，cIAP1和cIAP2会与衔接蛋白肿瘤坏死因子受体相关因子2（TRAF2）一起迅速募集到肿瘤坏死因子受体1（TNFR1）上。重要的是，cIAP1或cIAP2对于TNFR1信号小体的正常功能是必需的。在它们共同缺失的情况下，受体相互作用蛋白1（RIP1）的多聚泛素化（NF-κB信号传导的上游必要事件）会减弱。结果，κB激酶β（IKKβ）的磷酸化减少，信号转导严重受阻。因此，同时缺失cIAP1和cIAP2的细胞对TNFα介导的细胞凋亡更加敏感。总的来说，这些数据表明，在TNFα处理后，cIAP1或cIAP2对于RIP1的正常多聚泛素化和NF-κB激活是必需的。
