Mechanisms for chromatin modification during transcription elongation

描述（由申请人提供）：染色质的结构受到多个元件精心设计的作用的严格调控。染色质正常模式的破坏通常导致基因表达的错误调节，这是癌症和其他人类疾病的共同特征。因此，了解染色质动力学调控的详细机制非常重要。这项提议的长期目标是了解染色质相关复合物如何帮助转录机制克服核小体障碍，同时仍然保持基因组的完整性。最近，我们和其他人发现了一种新的信号通路，通过该通路RNA聚合酶II（Pol II）在通过核小体模板转录的同时保持染色质的完整性。组蛋白甲基转移酶Set 2结合延伸Pol II的磷酸化CTD并共转录甲基化组蛋白H3 K36，然后由组蛋白脱乙酰酶复合物Rpd 3S识别。一旦被靶向，Rpd 3S使转录区域脱乙酰基以保持转录起始的准确性，从而将转录限制于真正的启动子而不是隐蔽的转录起始位点。该提案旨在通过三个具体目标剖析推动这一关键途径的详细机制。(1)Rpd 3S与K36甲基化核小体结合的分析及其在转录延伸中的意义。我们将测试Rpd 3S内的多个结构域如何协调以实现协同结合。(2)剖析Pol II利用K36甲基化作为短期转录记忆标记的分子机制。我们将研究延长Pol II是否可以控制转录叉周围相关组蛋白修饰的方向性。(3)在转录延伸过程中K36甲基化的时间控制机制的鉴定。我们将探讨组蛋白去甲基化酶的作用和去除这种可逆的组蛋白修饰的信号。重要的是，人类Set 2已被证明与亨廷顿蛋白（亨廷顿病蛋白）相互作用;组蛋白脱乙酰酶抑制剂的治疗可以阻止模型系统中的神经变性。因此，我们对Set 2-Rpd 3S通路的理解也可能有助于设计潜在的治疗药物来治疗神经退行性疾病。 公共卫生相关性：这些研究的结果有望促进我们对组蛋白代码识别的理解。许多疾病，如癌症和神经退行性变，都与组蛋白修饰缺陷或蛋白质靶向修饰组蛋白有关。因此，我们的工作将为治疗各种人类疾病的药物提供重要的潜在靶点。

DESCRIPTION (provided by applicant): The structure of chromatin is tightly regulated by the well choreographed actions of multiple elements. Disruption of the normal pattern of chromatin often leads to mis-regulation of gene expression, a common feature of cancer and other human diseases. Therefore, it is important to understand the detailed mechanism regulating chromatin dynamics. The long-term objective of this proposal is to understand how chromatin- related complexes help the transcription machinery overcome the nucleosomal barriers while still maintaining genome integrity. Recently, we and others discovered a novel signaling pathway through which RNA polymerase II (Pol II) maintains chromatin integrity while transcribing through nucleosomal templates. A histone methyltransferase Set2 binds the phosphorylated CTD of elongating Pol II and co-transcriptionally methylates histone H3K36, which is then recognized by a histone deacetylase complex, Rpd3S. Once targeted, Rpd3S deacetylates transcribed regions to preserve the accuracy of transcription initiation, thus restricting transcription to bonafide promoters but not cryptic transcription start sites. This proposal is intended to dissect the detailed mechanisms driving this crucial pathway via three specific aims. (1) Analysis of Rpd3S binding to K36 methylated nucleosomes and its implication in transcription elongation. We will test how multiple domains within Rpd3S coordinate to achieve synergistic binding. (2) Dissecting the molecular mechanism by which Pol II exploits K36 methylation as a marker for short term transcription memory. We will examine if elongating Pol II can control the directionality of relevant histone modifications around the transcription fork. (3) Identification of the temporal control mechanism of K36 methylation during transcription elongation. We will explore the roles of histone demethylases and the signals for removal of this reversible histone modification. Importantly, human Set2 has been shown to interact with Huntingtin, the Huntington disease protein; and the treatment of histone deacetylase inhibitors can arrest neurodegeneration in a model system. Therefore, our understanding on the Set2- Rpd3S pathway may also help design potential therapeutic agents to treat neurodegenerative diseases. PUBLIC HEALTH RELEVANCE: The results from these studies are expected to advance our understanding of histone code recognition. Many diseases such as cancer and neurodegeneration have been linked to defects in histone modification or the targeting of proteins to modified histones. Thus, our work will provide important potential targets for drugs that treat a variety of human diseases.