IAP Family Proteins and Cancer

描述（由申请人提供）：IAPs （Inhibitor of Apoptosis Proteins）在癌症中普遍过表达，通过多种机制抑制细胞凋亡。相反，某些内源性IAPs抑制剂，特别是编码ARTS （Septin4）的基因，似乎作为肿瘤抑制因子起作用，其表达在某些恶性肿瘤中丢失。IAP家族成员XIAP、c-IAP1和c-IAP2是E3连接酶，催化在底物上形成多泛素链，涉及赖氨酸48 （K48）或K63键，其中K48靶向蛋白酶体介导的降解蛋白，而K63是与信号复合物形成相关的翻译后修饰。IAPs与K48-或k63特异性ubc结合的生物学后果是深远的，对理解癌症细胞凋亡抵抗机制具有重要意义。例如，c-IAP1和c-IAP2与肿瘤坏死因子（TNF）受体复合物结合，促进k63连接的Rip1泛素化，这是一种翻译后修饰，可抑制Rip1介导的细胞毒性，并刺激NF-κB活化，从而帮助细胞存活、细胞增殖和细胞迁移。本研究旨在探讨IAPs的调控机制及其在肿瘤细胞凋亡抑制和信号转导中的作用。要验证的中心假设是，控制IAPs的各种E3连接酶活性的机制在调节这些蛋白质的水平及其细胞活性方面起着关键作用。具体目的包括：(1)确定IAPs的化学拮抗剂（基于模拟SMAC）如何刺激其自我导向的k48连接的多泛素化和蛋白酶体依赖性降解；(2)探索IAP与Rip1激酶相互作用对其k63定向E3连接酶活性的影响，并验证Rip1结合是K48向k63特异性连接酶活性转化的关键假设；(3)阐明c-IAP1和c-IAP2与去泛素酶CYLD拮抗作用调控Rip1的K63泛素化的机制，从而决定TNFR1信号复合物的组装，从而促进或抑制tnf α诱导的细胞凋亡；(4)探讨内源性XIAP拮抗剂ARTS的抑瘤作用机制。总之，所提出的研究将揭示IAPs作为细胞死亡和信号转导调节剂的多功能性质的生化和细胞机制，为癌症治疗的治疗应用提供新的策略。

DESCRIPTION (provided by applicant): Inhibitor of Apoptosis Proteins (IAPs) are commonly over-expressed in cancers, suppressing apoptosis through diverse mechanisms. Conversely, certain endogenous inhibitors of IAPs, particularly the gene encoding ARTS (Septin4), appear to operate as tumor suppressors whose expression becomes lost in certain malignancies. IAP family members XIAP, c-IAP1, and c-IAP2 are E3 ligases, catalyzing formation of polyubiquitin chains on substrates involving either lysine 48 (K48) or K63 linkages, where K48 targets proteins for proteasome- mediated degradation while K63 is a post-translational modification associated with formation of signaling complexes. The biological consequences of partnering of IAPs with K48- versus K63-specific UBCs are profound, having important implications for understanding mechanisms of apoptosis resistance of cancers. For example, c-IAP1 and c-IAP2 associate with Tumor Necrosis Factor (TNF) Receptor complexes to promote K63-linked ubiquitinylation of Rip1, a post-translational modification that suppresses Rip1-mediated cytotoxicity and that stimulates NF-κB activation, thereby aiding cell survival, cell proliferation and cell migration. This proposal addresses the mechanisms that control the IAPs and their roles in apoptosis suppression and signal transduction in cancer. The central hypothesis to be tested is that mechanisms controlling the diverse E3 ligase activities of IAPs play a critical role in regulating both the levels of these proteins and their cellular activities. Specific Aims include: (1) Determining how chemical antagonists of IAPs (based on mimicking SMAC) stimulate their self-directed K48-linked polyubiquitination and proteasome-dependent degradation; (2) Exploring the influence of IAP interactions with the kinase Rip1 on their K63-directed E3 ligase activity and testing the hypothesis that Rip1 binding is key to conversion from K48 to K63-specific ligase activity; (3) Addressing the mechanisms by which c-IAP1 and c-IAP2 operate antagonistically with Deubiquitinase CYLD to modulate K63 ubiquitination of Rip1, thereby dictating the assembly of TNFR1 signaling complexes that either promote or suppress TNFα-induced apoptosis; and (4) Investigating the mechanisms by which ARTS, an endogenous antagonist of XIAP, exerts its tumor suppressor effect. Altogether, the proposed studies will reveal the biochemical and cellular mechanisms underlying the multi-functional nature of IAPs as regulators of cell death and signal transduction, suggesting novel strategies for therapeutic applications to cancer treatment.