Guiley Keelan Z, Liban Tyler J, Felthousen Jessica G, Ramanan Parameshwaran, Litovchick Larisa, Rubin Seth M
Department of Chemistry and Biochemistry, University of California at Santa Cruz, Santa Cruz, California 95064, USA;
Division of Hematology, Oncology, and Palliative Care, Richmond, Virginia 23298, USA; Massey Cancer Center, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Genes Dev. 2015 May 1;29(9):961-74. doi: 10.1101/gad.257568.114. Epub 2015 Apr 27.
The DREAM complex represses cell cycle genes during quiescence through scaffolding MuvB proteins with E2F4/5 and the Rb tumor suppressor paralog p107 or p130. Upon cell cycle entry, MuvB dissociates from p107/p130 and recruits B-Myb and FoxM1 for up-regulating mitotic gene expression. To understand the biochemical mechanisms underpinning DREAM function and regulation, we investigated the structural basis for DREAM assembly. We identified a sequence in the MuvB component LIN52 that binds directly to the pocket domains of p107 and p130 when phosphorylated on the DYRK1A kinase site S28. A crystal structure of the LIN52-p107 complex reveals that LIN52 uses a suboptimal LxSxExL sequence together with the phosphate at nearby S28 to bind the LxCxE cleft of the pocket domain with high affinity. The structure explains the specificity for p107/p130 over Rb in the DREAM complex and how the complex is disrupted by viral oncoproteins. Based on insights from the structure, we addressed how DREAM is disassembled upon cell cycle entry. We found that p130 and B-Myb can both bind the core MuvB complex simultaneously but that cyclin-dependent kinase phosphorylation of p130 weakens its association. Together, our data inform a novel target interface for studying MuvB and p130 function and the design of inhibitors that prevent tumor escape in quiescence.
DREAM复合物在静止期通过将MuvB蛋白与E2F4/5以及Rb肿瘤抑制旁系同源物p107或p130进行支架组装来抑制细胞周期基因。细胞周期进入时，MuvB与p107/p130解离，并招募B-Myb和FoxM1以上调有丝分裂基因表达。为了解支撑DREAM功能和调控的生化机制，我们研究了DREAM组装的结构基础。我们在MuvB组分LIN52中鉴定出一个序列，当该序列在DYRK1A激酶位点S28磷酸化时，它能直接结合p107和p130的口袋结构域。LIN52-p107复合物的晶体结构表明，LIN52使用一个次优的LxSxExL序列以及附近S28处的磷酸基团以高亲和力结合口袋结构域的LxCxE裂隙。该结构解释了DREAM复合物中对p107/p130而非Rb的特异性，以及该复合物如何被病毒癌蛋白破坏。基于该结构的见解，我们探讨了细胞周期进入时DREAM如何解体。我们发现p130和B-Myb都能同时结合核心MuvB复合物，但p130的细胞周期蛋白依赖性激酶磷酸化会削弱其结合。总之，我们的数据为研究MuvB和p130功能以及设计防止肿瘤在静止期逃逸的抑制剂提供了一个新的靶点界面。
