Scherer Paul C, Ding Yan, Liu Zhiqing, Xu Jing, Mao Haibin, Barrow James C, Wei Ning, Zheng Ning, Snyder Solomon H, Rao Feng
The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205;
National Institute of Biological Sciences, Beijing 102206, China;
Proc Natl Acad Sci U S A. 2016 Mar 29;113(13):3503-8. doi: 10.1073/pnas.1525580113. Epub 2016 Mar 14.
The family of cullin-RING E3 Ligases (CRLs) and the constitutive photomorphogenesis 9 (COP9) signalosome (CSN) form dynamic complexes that mediate ubiquitylation of 20% of the proteome, yet regulation of their assembly/disassembly remains poorly understood. Inositol polyphosphates are highly conserved signaling molecules implicated in diverse cellular processes. We now report that inositol hexakisphosphate (IP6) is a major physiologic determinant of the CRL-CSN interface, which includes a hitherto unidentified electrostatic interaction between the N-terminal acidic tail of CSN subunit 2 (CSN2) and a conserved basic canyon on cullins. IP6, with an EC50 of 20 nM, acts as an intermolecular "glue," increasing cullin-CSN2 binding affinity by 30-fold, thereby promoting assembly of the inactive CRL-CSN complexes. The IP6 synthase, Ins(1,3,4,5,6)P5 2-kinase (IPPK/IP5K) binds to cullins. Depleting IP5K increases the percentage of neddylated, active Cul1 and Cul4A, and decreases levels of the Cul1/4A substrates p27 and p21. Besides dysregulating CRL-mediated cell proliferation and UV-induced apoptosis, IP5K depletion potentiates by 28-fold the cytotoxic effect of the neddylation inhibitor MLN4924. Thus, IP5K and IP6 are evolutionarily conserved components of the CRL-CSN system and are potential targets for cancer therapy in conjunction with MLN4924.
泛素连接酶E3家族（CRLs）和组成型光形态建成9（COP9）信号体（CSN）形成动态复合物，介导20%的蛋白质组的泛素化，但对其组装/拆卸的调控仍知之甚少。肌醇多磷酸是高度保守的信号分子，参与多种细胞过程。我们现在报告，肌醇六磷酸（IP6）是CRL-CSN界面的主要生理决定因素，其中包括CSN亚基2（CSN2）的N端酸性尾巴与泛素连接酶上一个保守的碱性峡谷之间迄今未被识别的静电相互作用。IP6的半数有效浓度（EC50）为20 nM，作为分子间的“胶水”，使泛素连接酶与CSN2的结合亲和力提高30倍，从而促进无活性的CRL-CSN复合物的组装。IP6合酶，即肌醇（1,3,4,5,6）五磷酸2-激酶（IPPK/IP5K）与泛素连接酶结合。耗尽IP5K会增加经NEDD化修饰的、有活性的Cul1和Cul4A的比例，并降低Cul1/4A底物p27和p21的水平。除了失调CRL介导的细胞增殖和紫外线诱导的细胞凋亡外，耗尽IP5K还会使NEDD化抑制剂MLN4924的细胞毒性作用增强28倍。因此，IP5K和IP6是CRL-CSN系统中进化上保守的成分，是与MLN4924联合用于癌症治疗的潜在靶点。
