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

项目 总结/摘要 太阳紫外线（UV）是我们自然环境中最普遍的致癌物质。跨损伤 DNA合成（TLS）是一种DNA损伤耐受机制，其利用专门的DNA聚合酶来绕过 紫外线和其他复制阻断病变，往往导致诱变。TLS导致的体细胞突变 不可修复的紫外线损伤是基本上所有皮肤癌，特别是黑色素瘤的主要原因。的确， 黑素瘤 建筑 与紫外线照射相关的肿瘤中，每个肿瘤的体细胞突变数量最多。基本 核小体是真核生物染色质的一部分，它由DNA包裹组蛋白组成 八聚体由一个（H3-H4）2四聚体和两个H2 A-H2 B二聚体组成。PCNA是一种中枢蛋白， DNA复制、复制偶联核小体组装和TLS。LRS伊萨核小体结构域组成的 的 突变的S.啤酒。的 组蛋白H3和H4的某些残基。 H4 LRS突变大部分或完全嵌入核小体，但不是那些 我们鉴定了多种UV敏感或抗性组蛋白H4 LRS， 在核小体表面，减弱TLS和UV诱变。全球TLS缺陷型H4 LRS突变 使染色质结构不稳定，但不影响PCNA泛素化，这是一种已知的 TLS，表明它们影响PCNA修饰下游的TLS步骤。到目前为止，研究如何 染色质结构调节TLS和诱变已经很少，如果不是不存在。人们普遍 假设染色质组织被动地抑制TLS。我们的发现挑战了假设， 表明LRS中的染色质特征是高效TLS所必需的。我们的发现提供了一条重要线索 揭开了染色质结构如何调节TLS和诱变的长期谜团。的目标 本项目旨在阐明组蛋白H4 LRS突变如何减弱TLS和UV诱变。我们 假设TLS缺陷型H4 LRS突变损害了复制偶联核小体组装 以及DNA损伤上游的组装后核小体稳定性，从而减弱PCNA的保留 和TLS聚合酶的募集。我们将确定TLS缺陷型组蛋白H4 LRS突变1） 影响UV损伤上游的核小体，2）影响PCNA的保留和 TLS聚合酶，和3）与组蛋白H3-H4分子伴侣在功能上相互作用，其作用于TLS聚合酶的不同步骤。 复制偶联核小体组装过程，影响TLS和UV诱变。项目结果 将为将来阐明核小体特征如何与组蛋白伴侣和局部分子发生串扰奠定基础。 基因组特征来调节TLS和诱变的基因组景观。此外，这项研究可能是 本发明提供了用于鉴定治疗和/或预防癌症，特别是黑素瘤的新靶标的信息。

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.