组蛋白去甲基化酶KDM5B在DNA损伤修复和维持基因组稳定性中的作用

The ability of cells to maintain genome stability is critical for homeostasis, and defects in the maintenance of genome stability underlie a number of developmental disorders and human diseases including cancer and premature aging. DNA double strand breaks (DSBs) repair has been considered as a crucial barrier to keep eukarytic cell genome integrity, as DSBs and a failure to repair that damage in an appropriate manner would result in aberration of chromosome structure including translocations, deletions, inversions, and duplications. Emerging evidence suggests that DNA repair occurs in the context of highly structured chromatin and the ability of repair factors to detect DNA lesions and function properly at breaks is determined by histone modifications around the DSBs, as well as chromatin-remodelling events. Histone demethylase KDM5B has been tightly linked to the progression of breast cancer and prostate cancer. However, the role of KDM5B in tumor development and progression is not fully understood. Our preliminary data suggested that loss of function of KDM5B profoundly inhibits the efficiency of DNA DSBs repair. By combining cellular protein fractionation and Western blot analysis, we demonstrated that chromatin binding ability of KDM5B increased in response to irradiation (IR). Furthermore, chromatin immunoprecipitation (ChIP) experiment revealed that KDM5B could be directly recruited to the DSBs sites. In addition, we examined the impact of KDM5B on cellular fitness and observed that knockdown of KDM5B reduced survival ability of cells exposed to IR. Moreover, we observed that reduction of cellular levels of KDM5B is accompanied by enhenced spontaneous DNA damage, marked by H2AX phosphorylation (gammaH2AX) and p53 phosphorylation. These preliminary results indicated that KDM5B plays a role of importance in DSBs repair and maintenance of genome stability. But the underlying mechanism of how KDM5B regulate and influence on DSBs repair need to be further elucidated. We will focus on this issue in our future research. We envision that the further understanding of the molecular mechanisms through which KDM5B operates in DSBs repair, in combination with the elucidation of the physiological interactions between chromatin micro-environment and different DSBs repair pathways, will aid new approaches development to maintain genome stability and will benefit the therapeutic pursuits for many human diseases including cancer and premature aging.

DNA双链损伤修复作为保护基因组稳定性的重要屏障，其应答过程障碍可以引起染色体结构异常进而导致肿瘤、早老症等疾病的发生。越来越多的证据表明DNA双链损伤修复是在染色质水平发生的，组蛋白修饰以及染色质重塑蛋白在这一过程中发挥着重要作用。组蛋白去甲基化酶KDM5B，与乳腺癌和前列腺癌等癌症的发生发展密切相关，但是其作用机制尚未完全阐明。我们的初步研究表明，KDM5B可以被直接招募到DNA损伤区域；其功能缺失显著的抑制了细胞DNA双链损伤修复的能力，在增强自发DNA损伤的同时增加了细胞对损伤处理的敏感性。这些结果初步提示KDM5B在DNA损伤修复以及维持基因组稳定性的过程中起着重要的作用。我们将在今后的研究中进一步探索KDM5B在这一过程中的作用以及相关分子机制。该研究将对认识以染色质为平台的损伤修复过程、如何有效的维持基因组稳定性以及肿瘤、早老症等疾病的治疗和临床药物研发提供一定的指导。

基因组稳定性对于维持正常组织发育和预防癌症等疾病至关重要。经过多年的研究表明，基因组信息包裹在染色质中，染色质环境在DNA损伤应答方面扮演了重要角色。然而，关于表观遗传机制如何调控DNA损伤应答，至今还并不十分清楚。我们的工作表明，组蛋白去甲基化酶KDM5B在人体细胞DNA双链断裂应答过程的多个方面都扮演了重要角色。研究发现在经过电离辐射（ironizing radiation）或者核酸内切酶处理后，KDM5B会依赖于其自身的多聚核糖化和组蛋白变异体的识别在DNA损伤位点附近募集，通过其去甲基化酶活性改变损伤区域的染色质结构和状态，进而招募非同源末端连接和同源重组的必要因子Ku70和BRCA1，达到调节DNA双链损伤修复的目的。进一步研究发现，KDM5B缺失会阻滞DNA修复的正常进程，使细胞处于对损伤刺激的敏感化状态；同时其缺失会阻碍自发性DNA损伤的修复，激活p53信号通路并抑制细胞周期的进程。这些研究成果指出，KDM5B是调控DNA损伤应答的一个至关重要的蛋白，而且也是维持基因组稳定性的一个必要的守护者和关键调控因子，该研究有助于解析维持遗传保真性的表观遗传作用，对认识基因组不稳定性相关疾病如癌症等具有重要的意义。关于该研究的论文于2014年4月28日在线发表在国际著名综合性科学杂志PNAS，论文题目为“Histone demethylase KDM5B is a key regulator of genome stability”.此外，在该基金的资助下，我们在乳腺癌和干细胞分化的表观遗传机制方面，还取得了以下成果：1. 揭示了蛋白质去泛素化酶USP7和组蛋白去甲基化酶PHF8在乳腺癌发生发展中的作用以及分子机制。该工作于2016年6月发表在The Journal of Clinical Investigation杂志，并入选JCI当期的Editor's picks。2. 发现多聚ADP核糖聚合酶1 (PARP1) 通过组蛋白H1的募集协同调节GATA3的转录活性。该工作已于2013年5月被Oncogene杂志接收，2014年正式发表。3. 发现组蛋白去甲基化酶LSD1通过其酶活性促进人脂肪基质干细胞成骨分化,该研究于2014年在生物材料学顶尖杂志Biomaterials发表。