NHP2通过调控DNA损伤的非同源末端连接（NHEJ）修复促进结直肠癌放疗耐受的机制研究

放疗是结直肠癌的主要治疗手段之一，放疗耐受往往使治疗效果不佳，阐明其机制十分必要。我们前期利用全基因组shRNA文库对CRC细胞进行筛选，在两个细胞中取交集得到6种新的候选CRC放疗耐受基因。经细胞水平的实验，证实候选基因之一NHP2能通过正向调控DNA损伤的非同源末端连接（NHEJ）修复促进结直肠癌放疗耐受。进一步探究机制发现，NHP2能与Ku70/Ku80互作，在放射诱导下，NHP2可能作为连接蛋白受到组蛋白H2B的招募，形成Ku70/Ku80-NHP2-H2B复合体，促进H2B单泛素化，加快Ku70/Ku80结合到染色质松弛区域的DNA断端，完成修复。本项目拟在分子水平明晰NHP2调控NHEJ的作用机制；在细胞与动物水平（细胞系与临床组织来源）明确NHP2促进CRC放疗耐受的功能；并且利用临床样本回顾性分析NHP2的临床意义，为将其作为CRC放疗疗效预测和预后判断的标志物提供依据。

Radiation therapy is one of the main therapeutic methods for colorectal cancer. However, radioresistance still occurs in a proportion of patients having poor clinical outcome. It’s urgent to clarify its mechanism. In our previous study, a genome-wide shRNA library was used to screen candidate radioresistant genes, and 6 genes were found. Cell-based experiments have confirmed that NHP2, one of the candidate genes, promotes radioresistance by facilitating nonhomologous end joining (NHEJ) mediated DNA repair. Mechanistically, NHP2 interacts with Ku70/Ku80 in CRC, after radiation, NHP2 may be recruited by histone H2B to form a Ku70/Ku80-NHP2-H2B complex, which promotes mono-ubiquitination of H2B, accelerates the binding of Ku70/Ku80 to DNA double strand breaks in the chromatin fiber decompaction region and then completes repair. In this proposal, we intend to clarify the mechanism of NHP2 regulating NHEJ detailly at the molecular level, and the role of NHP2 in promoting radioresistance in CRC by performing functional experiments in vitro and vivo (cell lines and clinical tissue sources). Moreover, clinical significance of NHP2 was retrospectively analyzed in extensive clinical samples, which will provide a basis for its application as a predictive marker for radiosensitivity and prognosis of CRC.