Molecular mechanisms and (patho)physiological consequences of PRC2.1-mediated gene regulation

多梳抑制复合体2 （Polycomb suppression Complex 2, PRC2）在胚胎发生和细胞分化等多种生物学过程中起着关键作用。它由多个亚基组成，用于沉积抑制性H3K27me3组蛋白标记。最近的研究结果表明，存在不同组成的PRC2亚复合物，如PRC2.1亚复合物，其特征是存在polycomb-样蛋白（Pcl）， EPOP（也称为C17orf96），但也不存在JARID2亚基。Pcl蛋白（PHF1, MTF2, PHF19）与活性组蛋白标记H3K36me3和未甲基化的CpG岛相互作用，而EPOP与转录延伸因子伸长BC和去泛素酶USP7相关联。这些相互作用表明PRC2.1在活性基因转录过程中发挥作用。到目前为止，Polycomb生物学的这方面的研究还很少。在此，我建议分两部分进行工作计划，第一部分研究我在博士后工作期间描述的EPOP介导的基因调控的分子机制（Liefke et al., 2016; Liefke et al., 2015）。我想揭示EPOP在prc2.1复合体中的调控机制，它与Elongin BC和USP7相互作用的重要性，以及它的翻译后修饰的相关性。第二部分探讨了PRC2.1复合体成员在小鼠早期胚胎发生、体细胞重编程和肺癌中的功能作用。采用功能增益和功能损失的方法研究了EPOP在早期小鼠胚胎中建立多能外胚层（EPI）的功能。EPOP及其子结构域在小鼠胚胎成纤维细胞（mef）体细胞重编程过程中的作用将被剖析。由于在人类癌症中经常观察到EPOP和PHF19短异构体的上调与生存率低相吻合，我们将以肺癌细胞为模型系统，研究它们对信号通路和转录程序的致癌重新连接的贡献。该项目的成功实施将大大扩展我们对PRC2.1及其亚基调控作用的理解，并可能导致治疗干预策略的发现。

The Polycomb Repressive Complex 2 (PRC2) plays pivotal roles in several biological processes including embyrogenesis and cellular differentiation. It is composed of multiple subunits and serves to deposit the repressive H3K27me3 histone mark. Recent results show the existence of differentially composed PRC2 subcomplexes, such as the PRC2.1 subcomplex, which is characterized by the presence of the polycomb-like proteins (Pcl), EPOP (also known as C17orf96), but also by the absence of the JARID2 subunit . The Pcl proteins (PHF1, MTF2, PHF19) interact with the active histone mark H3K36me3 and unmethylated CpG islands, while EPOP associates with the transcription elongation factor Elongin BC and the deubiquitinase USP7. These interactions suggest a role for PRC2.1 during active gene transcription. So far, this aspect of Polycomb biology is only scarcely studied.Here I suggest a bipartite work program that studies in the first part the molecular mechanisms of gene regulation mediated by EPOP, which I have characterized during my postdoctoral work (Liefke et al., 2016; Liefke et al., 2015). I want to unravel the regulatory mechanisms of EPOP within the PRC2.1-complex, the importance of its interaction with Elongin BC and USP7, as well as the relevance of its posttranslational modifications. The second part addresses the functional role of PRC2.1 complex members in early mouse embryogenesis, in somatic reprogramming and in lung cancer. The function of EPOP for the establishment of the pluripotent epiblast (EPI) in early mouse embryos is studied using gain- and loss-of function approaches. The role of EPOP and its subdomains will be dissected during somatic reprogramming from mouse embryonic fibroblasts (MEFs). As the frequently observed upregulation of EPOP and the short isoform of PHF19 in human cancers coincides with a poor survival, we will study their contribution to oncogenic rewiring of signaling pathways and transcription programs taking lung cancer cells as our model system.The successful execution of this project would significantly expand our understanding of the regulatory role of PRC2.1 and its subunits and may lead to the discovery of strategies for therapeutic intervention.