The inhibitor of apoptosis (IAP) family of proteins enhances cell survival through mechanisms that remain uncertain. In this report, we show that cIAP1 and cIAP2 promote cancer cell survival by functioning as E3 ubiquitin ligases that maintain constitutive ubiquitination of the RIP1 adaptor protein. We demonstrate that AEG40730, a compound modeled on BIR-binding tetrapeptides, binds to cIAP1 and cIAP2, facilitates their autoubiquitination and proteosomal degradation, and causes a dramatic reduction in RIP1 ubiquitination. We show that cIAP1 and cIAP2 directly ubiquitinate RIP1 and induce constitutive RIP1 ubiquitination in cancer cells and demonstrate that constitutively ubiquitinated RIP1 associates with the prosurvival kinase TAK1. When deubiquitinated by AEG40730 treatment, RIP1 binds caspase-8 and induces apoptosis. These findings provide insights into the function of the IAPs and provide new therapeutic opportunities in the treatment of cancer.

The nuclear factor-jB (NF-jB) signalling pathway serves a crucial role in regulating the transcriptional responses of physiological processes that include cell division, cell survival, differentiation, immunity and inflammation. Here we outline studies using mouse models in which the core components of the NF-jB pathway, namely the IjB kinase subunits (IKKa, IKKb and NEMO), the IjB proteins (IjBa, IjBb, IjBe and Bcl-3) and the five NF-jB transcription factors (NF-jB1, NF-jB2, c-Rel, RelA and RelB), have been genetically manipulated using transgenic and knockout technology.

The primary goal of chemotherapy is to cause cancer cell death. However, a side effect of many commonly used chemotherapeutic drugs is the activation of nuclear factor-KB (NF-KB), a potent inducer of antiapoptotic genes, which may blunt the therapeutic efficacy of these compounds. We have assessed the effect of doxorubicin, an anthracycline in widespread clinical use, on NF-KB activation and expression of antiapoptotic genes in breast cancer cells. We show that doxorubicin treatment activates NF-KB signaling and produces NF-KB complexes that are competent for NF-KB binding in vitro. Surprisingly, these NF-KB complexes suppress, rather than activate, constitutiveand cytokine-induced NF-KB-dependent transcription. We show that doxorubicin treatment produces RelA, which is deficient in phosphorylation and acetylation and which blocks NF-KB signaling in a histone deacetylase-independent manner, and we show that NF-KB activated by doxorubicin does not remain stably bound to KB elements in vivo. Together these data show that NF-KB signaling induced by doxorubicin reduces expression of NF-KB-dependent genes in cancer cells.