Mechanisms for chromatin modification during transcription elongation

描述(申请人提供)：染色质的结构受到多种元素精心设计的动作的严格调控。染色质正常模式的破坏经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，了解染色质动力学的详细调控机制是非常重要的。这项建议的长期目标是了解与染色质相关的复合体如何帮助转录机制克服核小体障碍，同时仍保持基因组的完整性。最近，我们和其他人发现了一条新的信号通路，通过它，RNA聚合酶II(POL II)在通过核小体模板转录时保持染色质的完整性。组蛋白甲基转移酶Set2与延长的Pol II的磷酸化CTD和共转录甲基化的组蛋白H3K36结合，然后被组蛋白去乙酰酶复合体Rpd3S识别。一旦被靶向，Rpd3S就会去乙酰化转录区域以保持转录起始的准确性，从而将转录限制在真正的启动子上，而不是神秘的转录起始部位。这项提议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)Rpd3S与K36甲基化核小体的结合分析及其在转录延伸中的意义。我们将测试RPD3S中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甲基化作为短时转录记忆标记的分子机制。我们将检查延长POL II是否可以控制转录分叉周围相关组蛋白修饰的方向性。(3)K36甲基化在转录延伸过程中的时间调控机制。我们将探索组蛋白去甲基酶的作用以及去除这种可逆的组蛋白修饰的信号。重要的是，人类Set2已被证明与亨廷顿病蛋白质Huntingtin相互作用；在模型系统中，组蛋白脱乙酰酶抑制剂的治疗可以阻止神经退化。因此，我们对Set2-Rpd3S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密码识别的理解。许多疾病，如癌症和神经退行性变，都与组蛋白修饰的缺陷或将蛋白质靶向修饰的组蛋白有关。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.