Implication of histone H4 LRS mutations in translesion synthesis and UV mutagenesis

工程 摘要/摘要 太阳紫外线(UV)是自然环境中最普遍的致癌物质。经损伤 合成(TLS)是一种DNA损伤耐受机制，它利用专门的DNA聚合酶绕过 紫外线和其他抑制复制的损伤，通常会导致突变。TLS引起的体细胞突变 未修复的紫外线损伤是几乎所有皮肤癌，特别是黑色素瘤的主要原因。的确， 黑色素瘤 建筑 与紫外线照射相关的每个肿瘤的体细胞突变数量最多。最基本的 真核生物染色质的区块是核小体，它由包裹在组蛋白周围的DNA组成 八聚体由一个(H_3-H_4)_2四聚体和两个H_2A-H_2B二聚体组成。增殖细胞核抗原是一种中枢蛋白，通过调节 DNA复制、复制偶联的核小体组装和TLS。LRS ISA核小体结构域的合成 的 酿酒酵母的突变。这个 组蛋白H3和H4的某些残基。 H4LRS突变主要或完全嵌入核小体，而不是那些 我们发现了多个对紫外线敏感或耐紫外线的组蛋白H4受体 在核小体表面，减弱TLS和紫外线的诱变作用。全球TLS缺陷型H4LRS突变 破坏染色质结构的稳定，但不影响增殖细胞核抗原的泛素化，这是已知需要的一种修饰 TLS，表明它们影响了增殖细胞核抗原修饰下游的TLS步骤。到目前为止，关于如何 染色质结构调节TLS和突变一直很少，如果不是不存在的话。总体上讲， 假设染色质组织被动地抑制TLS。我们的发现挑战了这一假设 表明LRS中的染色质特征是有效的TLS所必需的。我们的发现提供了一条重要线索 揭开染色质结构如何调节TLS和突变的长期谜团。的目标是 本项目旨在阐明组蛋白H4LRS突变如何减弱TLS和UV的诱变作用。我们 假设TLS缺陷的H4LRS突变损害了复制偶联核小体组装 和DNA损伤上游的组装后核小体的稳定性，从而减弱了增殖细胞核抗原的保留 以及TLS聚合酶的募集。我们将确定TLS缺陷组蛋白H4 LRS如何突变1) 影响紫外线损伤上游的核小体占有率，2)影响增殖细胞核抗原的保留和募集 TLS聚合酶，以及3)功能上与组蛋白H3-H4伴侣相互作用，后者作用于 复制偶联的核小体组装过程，影响TLS和紫外线的诱变。该项目的发现 将为进一步阐明核小体如何与组蛋白伴侣蛋白和局部蛋白串扰奠定基础 基因组特征来调节TLS的基因组图景和诱变。此外，这项研究可能是 有助于确定治疗和/或预防癌症，特别是黑色素瘤的新靶点。

PROJECT SUMMARY/ABSTRACT The solar ultraviolet (UV) is the most pervasive carcinogen in our natural environment. Translesion synthesis (TLS) is a DNA damage tolerance mechanism that utilizes specialized DNA polymerases to bypass UV and other replication-blocking lesions, often leading to mutagenesis. Somatic mutations resulting from TLS of unrepaired UV lesions are the major causes for essentially all skin cancers, especially melanoma. Indeed, melanoma building associated with UV exposure has the highest number of somatic mutations per tumor. The basic block of eukaryotic chromatin is the nucleosome, which consists of DNA wrapping around a histone octamer comprised of one (H3-H4)2 tetramer and two H2A-H2B dimers. PCNA is a hub protein that mediates DNA replication, replication-coupled nucleosome assembly, and TLS. LRS isa nucleosome domain composed of mutations in S. cerevisiae. The certain residues of histones H3 and H4. H4 LRS mutations mostly or entirely embedded in the nucleosome, but not those We identified multiple UV sensitive or resistant histone H4 LRS on the nucleosome surface, attenuate TLS and UV mutagenesis. The TLS-deficient H4 LRS mutations globally destabilize chromatin structure, but do not affect PCNA ubiquitination, a modification known to be required for TLS, indicating that they affect a TLS step downstream of the PCNA modification. To date, studies on how chromatin structures modulate TLS and mutagenesis have been scarce, if not nonexistent. It has been generally assumed that chromatin organization passively inhibits TLS. Our finding challenges the assumption and indicates that a chromatin feature in the LRS is required for efficient TLS. Our finding offers an important clue for unraveling the long-standing enigma of how chromatin structures modulate TLS and mutagenesis. The goal of this project is to elucidate how the histone H4 LRS mutations attenuate TLS and UV mutagenesis. We hypothesize that the TLS-deficient H4 LRS mutations compromise replication-coupled nucleosome assembly and post-assembly nucleosome stability upstream of DNA lesions, thereby attenuating the retention of PCNA and the recruitment of TLS polymerases. We will determine how the TLS-deficient histone H4 LRS mutations 1) affect nucleosome occupancies upstream of UV lesions, 2) affect the retention of PCNA and the recruitment of TLS polymerases, and 3) functionally interact with histone H3-H4 chaperones, which act at different steps of the replication-coupled nucleosome assembly process, to affect TLS and UV mutagenesis. Findings from the project will form the basis for future elucidation of how nucleosome features crosstalk with histone chaperones and local genomic features to modulate the genomic landscape of TLS and mutagenesis. Also, the study may be informative for identifying new targets for the treatment and/or prevention of cancers, especially melanoma.