Mechanisms of RING1B and PRC1 complexes in transcriptional activation

项目总结 聚梳族(PcG)复合体是一种多蛋白质、进化上保守的表观遗传机制 调控干细胞的命运决定和早期发育。Polycomb基因的突变和异常表达 抑制复合体1(PRC1)亚单位也与人类疾病有关。Prc1是一种蛋白质复合体， 被经典地认为是调节基因转录抑制的。我们和其他人最近表明 特定的PRC1复合体，由六个哺乳动物PCGF类似物之一的存在定义，也可以 促进干细胞和癌细胞中的基因转录，以调节细胞命运决定和癌基因。PRC1如何 被招募到染色质并介导转录激活的机制还知之甚少。我们最近展示了 Prc1和雌激素受体α(ER)共同占据转录活性基因和增强子 调控乳腺癌细胞增殖。ER在功能上被类固醇激素雌激素激活。一次 激活后，ER与染色质结合并招募共激活剂来调节基本的生物过程 如发育、生殖、新陈代谢和癌症。我们新的初步数据显示，雌激素可以诱导 快速和动态地募集到所有PRC1复合体的核心亚单位Ring1b的染色质以激活 基因转录在Prc1-独立的方式。此外，我们还发现R环的形成和ER可能是 Ring1b对染色质募集很重要，这表明Ring1b通过不同的方式与染色质捆绑在一起 机械装置。重要的是，Ring1b也是ER招募、基因和增强子转录所必需的 激活以及染色质的组织。我们初步的3D染色质结构数据也显示 含有Ring1b/ER的增强子在物理上与雌激素反应基因相互作用。这些结果揭示了 雌激素注射时Ring1b介导转录激活的潜在新机制。 最后，我们发现Ring1b在转移性内分泌抵抗型乳腺癌中过度表达，并且 内分泌抵抗细胞对Ring1b上瘾。我们推测Ring1b是一种新的表观遗传调控因子 雌激素介导的基因调控和染色质结构，以及Ring1b的耗尽和化学 抑制会减少转移性内分泌抵抗型乳腺癌。在这里，我们建议：确定如何 Ring1b被招募到雌激素反应基因(Aim 1)，Ring1b在增强子-启动子中的作用 雌激素使用过程中的相互作用(目标2)，以及Ring1b在内分泌抵抗中的作用(目标3)。嗨- C实验，结合全基因组研究(包括基因表达谱、染色质可获得性 分析)、蛋白质组学、异种移植和PDX模型将用于解决这些中心问题。 从根本上说，这些发现将扩大我们对雌激素反应和Polycomb牵连的理解 在广泛的生物学过程中，包括发育、细胞代谢和癌症。

Project summary Polycomb group (PcG) complexes are multi-protein, evolutionarily conserved epigenetic machineries that regulate stem cell fate decisions and early development. Mutation and abnormal expression of Polycomb Repressive Complex 1 (PRC1) subunits are also implicated in human disease. PRC1 is a protein complex that was classically thought to mediate transcriptional repression of genes. We and others recently showed that specific PRC1 complexes, defined by the presence of one of the six mammalian PCGF paralogs, can also facilitate gene transcription in stem and cancer cells to regulate cell fate decisions and oncogenes. How PRC1 is recruited to chromatin and mediates transcriptional activation is poorly understood. We recently demonstrated that PRC1 and the estrogen receptor alpha (ER) co-occupy transcriptionally active genes and enhancers to regulate proliferation of breast cancer cells. ER is functionally activated by the steroid hormone estrogen. Once activated, ER binds to chromatin and recruits co-activators to regulate fundamental biological processes such as development, reproduction, metabolism, and cancer. Our new preliminary data show that estrogen induces rapid and dynamic recruitment to chromatin of RING1B, the core subunit of all PRC1 complexes, to activate gene transcription in a PRC1-indepenent fashion. Moreover, we found that R-loop formation and ER might be important for RING1B recruitment to chromatin, suggesting that RING1B is tethered to chromatin by different mechanisms. Importantly, RING1B is also required for ER recruitment, gene and enhancer transcriptional activation as well as chromatin organization. Our preliminary 3D chromatin architecture data also revealed that RING1B/ER-containing enhancers physically interact with estrogen-responsive genes. These results uncover potential new mechanisms for transcriptional activation mediated by RING1B upon estrogen administration. Finally, we found that RING1B is overexpressed in metastatic endocrine resistant breast cancer and that endocrine resistant cells are addicted to RING1B. We hypothesize that RING1B is a novel epigenetic regulator of estrogen-mediated gene regulation and chromatin architecture, and that RING1B depletion and chemical inhibition will decrease metastatic endocrine-resistant breast cancer. Here, we propose: to determine how RING1B is recruited to estrogen-responsive genes (Aim 1), the role of RING1B in enhancer-promoter interactions during estrogen administration (Aim 2), and the role of RING1B in endocrine resistance (Aim 3). Hi- C experiments, coupled to genome-wide studies (including gene expression profiles, chromatin accessibility assays), proteomics, and xenografts and PDX models will be used to address these central questions. Fundamentally, these findings will expand our understanding of the estrogen response and Polycomb implicated in broad biological processes including development, cellular metabolism and cancer.