Aurora-A过表达通过Ku70/Ku80异常调节DNA双链断裂修复促进胃癌放疗抵抗的作用机理研究

Radioresistance is a thorny problem in the treatment of gastric cancer. DNA damage repair is the major cause of radioresistance. Double-strand-breaks (DSBs) is the most lethal kind of DNA damage induced by radiotherapy. DSBs were mainly repaired through homologous recombination (HR) and non-homology end joining (NHEJ), which competes with each other. The overexpression of Aurora-A was related with radioresistance, but overexpression of Aurora-A was reported to inhibit HR. Ku70/Ku80 is the sensor of NHEJ. Aurora-A promotes the expression of NF-kB and the downstream IL-6, while NF-kB and IL-6 facilitate the expression and activity of Ku70/Ku80. Thus we suppose that overexpression of Aurora-A may promote NHEJ and radioresistance through NF-kB and IL-6-induced Ku70/Ku80. On the other hand, NF-kB promotes HR in the presence of BRCA1/2, but Aurora-A decreases the expression of BRCA1/2. Thus, Aurora-A-mediated expression of BRCA1/2 may play a role in Aurora-A-induced NHEJ and radioresistance. This project aims to illustrate the mechanism of Aurora-A-induced radioresistance, and explore the new target to overcome radioresistance. The results will be of great significance in improving the effect of treatments for gastric cancer.

放疗抵抗是胃癌治疗中的棘手问题。放疗抵抗的主要原因是DNA损伤修复。放疗致DNA损伤最严重的形式是DNA双链断裂，主要由同源重组（HR）和非同源末端连接（NHEJ）修复，且HR和NHEJ存在一定的竞争关系。Aurora-A过表达与放疗抵抗相关，但过表达的Aurora-A抑制HR。Ku70/Ku80是NHEJ的感应分子。过表达的Aurora-A上调NF-kB和IL-6，而NF-kB和IL-6上调Ku70/Ku80。因此Aurora-A过表达可能通过NF-kB和IL-6上调Ku70/80而促进NHEJ并介导放疗抵抗。NF-kB在BRCA1/2存在时促进HR。但Aurora-A抑制BRCA1/2，因此Aurora-A抑制的BRCA1/2可能参与了Aurora-A促进的NHEJ和放疗抵抗。本研究旨在研究Aurora-A引起放疗抵抗的机制，探索逆转放疗抵抗的新靶点，对提高胃癌放疗疗效有重大意义。

极光（Aurora）激酶是一个丝氨酸/苏氨酸蛋白激酶家族，有Aurora-A、-B、-C三个成员。在线数据库分析提示，在胃癌中，Aurora-A，-B和-C基因的改变基本是相互排斥的，而Aurora-A的改变最常见。因此，本研究终点研究Aurora-A的功能。公共数据库和本院病理标本均显示肿瘤组织中Aurora-A mRNA和蛋白水平显著高于相邻正常组织。肿瘤组织中高水平的Aurora-A mRNA和较差的首次进展和总生存相关。在经过DNA毒性方式（铂类化疗和放疗）治疗的胃癌患者中，肿瘤组织中的较高的Aurora-A水平和与较差的首次进展时间在统计学上显着相关，并提示较差的总生存。所以，胃癌组织中Aurora-A高表达与患者的较差的预后相关。过表达Aurora-A增加细胞对顺铂的IC50，增加且经X-照射后的克隆形成能力；减少细胞凋亡；过表达Aurora-A的肿瘤在顺铂处理后仍能较快生长，并能形成较重的肿瘤。这些结果表明，过表达Aurora-A在体内和体外均增加肿瘤对DNA损伤的耐受，Aurora-A可能在DNA损伤修复中起作用。已知DNA双链断裂（DSBs）是DNA损伤中最致命的一种类型，主要通过同源重组修复（HR）和非同源末端连接（NHEJ）通路修复；过表达Aurora-A抑制HR通路。所以我们检测了NHEJ通路中的关键蛋白。过表达Aurora-A增加细胞内Ku70和Ku80的蛋白水平；而其他相关蛋白变化不明显。无论是X-射线辐照或顺铂处理后，过表达Aurora-A的细胞的核内均遗留较少的γ-H2AX灶点，提示Aurora-A促进DNA双链断裂修复。这些结果提示，过表达Aurora-A会通过增加Ku70和Ku80的水平，进而增加DNA双链断裂修复效率。总的来说，本研究结果提示，胃癌组织中Aurora-A过表达和患者预后相关，Aurora-A可能通过Ku70和Ku80增加DNA双链断裂修复，在Aurora-A过表达的患者中同时应用DNA损伤手段和靶向NHEJ的治疗可能会提高治疗效率。