Tumor Suppressor Roles of E2F7 & E2F8 in Hepatocellular Carcinoma (HCC)

描述（由申请人提供）：E2F转录因子家族由8个不同的基因编码，基于结构-功能研究和氨基酸序列分析，可分为两个主要亚类，激活因子E2F （E2F1-3）和由典型抑制因子（E2F4-6）和非典型抑制因子（E2F7-8）组成的抑制因子E2F。与其他E2F家族成员不同，E2F7和E2F8与DP1/DP2蛋白独立结合DNA，缺乏通常用于与rb相关蛋白相互作用的氨基酸序列，因此这些非典型E2F可能在典型的CDK-Rb-E2F途径之外发挥作用。随着最近关键遗传工具的发展，在小鼠中有条件地破坏或表达E2f7和E2f8，敲除有条件地表达内源性野生型和突变型E2f8蛋白的小鼠和敲除含有两个关键E2F应答靶基因（Cdc6和Cyclin A2）的改变启动子的小鼠，我们期望在机制理解E2F家族的这一重要分支如何有助于控制转录、细胞周期、和体内肿瘤抑制。关键的初步数据显示，E2F8在小鼠肝脏的内环和肿瘤抑制中发挥着关键作用，其活性似乎是通过与E2F7及相关大分子复合物的物理相互作用来调节Cdk-Rb通路影响之外的基因表达。该建议的总体假设是E2F8作为转录抑制因子控制细胞周期，基因组倍性水平，并在HCC中作为肿瘤抑制因子。利用遗传、生化和全局分析方法的三个具体目标将直接检验这一假设。这些研究的长期目标是了解“非典型（E2F8）臂”如何在控制细胞周期和肿瘤抑制的整个E2F转录程序中发挥作用。

DESCRIPTION (provided by applicant): The E2F family of transcription factors are encoded by eight distinct genes that based on structure-function studies and amino acid sequence analysis, fall into two main subclasses, activator E2Fs (E2F1-3) and repressor E2Fs composed of canonical repressors (E2F4-6) and atypical repressors (E2F7-8). Unlike other E2F family members, E2F7 and E2F8 bind DNA independent of dimerization with DP1/DP2 proteins and lack amino acid sequences typically used to interact with Rb-related proteins, and thus these atypical E2Fs may function outside the canonical CDK-Rb-E2F pathway. With the recent development of key genetic tools to conditionally disrupt or express E2f7 and E2f8 in mice, knocking mice that conditionally express endogenous wild type and mutant forms of E2F8 protein and knockin mice containing altered promoters of two key E2F-responsive target genes (Cdc6 and Cyclin A2) we expect to make significant strides towards a mechanistic understanding of how this important arm of the E2F family contribute to the control of transcription, cell cycle, and tumor suppression in vivo. Key preliminary data shows that E2F8 plays a critical role in endocycles and tumor suppression in the mouse liver and that its activity appears to be mediated by physical interactions with E2F7 and associated macro-molecular complexes to regulate gene expression outside the influence of the Cdk-Rb pathway. The overarching hypothesis of this proposal is that E2F8 functions as a transcriptional repressor to control cell cycles, genome ploidy levels and acts as a tumor suppressor in HCC. Three specific aims utilizing genetic, biochemical, and global profiling approaches will directly test this hypothesis. The long-term goal of these studies is to understand how the "atypical (E2F8) arm" contributes to the overall E2F transcriptional program in controlling cell cycles and tumor suppression.