MST4激酶通过调控DNA双链断裂修复抑制胃癌发生的功能机制

Gastric adenocarcinoma, ranking second out of top five cancers in China, is a leading threat to human health. Genome instability is highly associated with gastric tumorigenesis, however, the underlying molecular mechanisms remain elusive. Dysregulation of DNA damage responses (DDR) is a key driver to the genome instability and tumorigenesis. Previously, the applicant systemically characterized functions of the E3 ubiquitin ligase RNF169 in DNA double-strand breaks (DSBs) signaling and repair control, and further investigated the association between its dysregulation and breast cancer (PNAS 2017; JBC 2017; PNAS 2018). Here we identified serine/threonine kinase MST4 as a novel regulator of DNA DSB signaling and repair. Importantly, we found MST4 mRNA is significantly decreased in gastric carcinoma via database analysis, suggesting that it may play key roles in maintaining genome integrity and suppressing gastric tumorigenesis. In this proposal, we will extensively characterize the regulatory effects of MST4 in genome stability and DSB repair. Then, we will employ multiple techniques including molecular, biochemistry, structural and cell biology to establish MST4 interaction network and to elucidate the underlying molecular mechanisms. In the end, by analyzing how MST4-associated DNA damage responses contribute to tumorigenesis in mouse stomach models, we will establish the interrelationship between genomic instability and gastric adenocarcinoma. Our study will not only shed light on new regulatory axis in DNA damage responses, but provide clues for targeting DNA damage machinery as new anti-gastric strategies.

胃癌是我国的高发恶性肿瘤。基因组不稳定性与胃癌发生密切相关，但对其诱发癌变的分子机制有待阐明。DNA损伤应答失调是基因组不稳定性的重要诱因。申请人前期发现了DNA双链断裂损伤信号转导及修复调控的新机制，并就相关的DNA损伤应答紊乱与肿瘤发生展开探索（PNAS 2017; JBC 2017; PNAS 2018）；近期新发现丝/苏氨酸激酶MST4参与调控DNA双链断裂损伤应答，在胃癌组织中呈下调趋势，提示其可能通过维持基因组稳定性抑制胃癌发生。据此，申请人将深入探讨MST4激酶对DNA双链断裂损伤应答修复及基因组稳定性的调控效应，阐明其蛋白作用网络及分子机制；以小鼠胃癌模型为研究体系，系统分析MST4介导的DNA损伤应答与胃癌早发之间的分子信号联系。本项目将建立新的蛋白分子、DNA损伤应答与胃癌之间的信号轴，在推动DNA损伤应答理论创新的同时为新型胃癌诊疗标志物的研发提供科学依据。

胃癌是我国高发恶性肿瘤，DNA损伤修复失调与基因组不稳定是驱动肿瘤发生的重要因素，Hippo信号通路紊乱与肿瘤恶性增殖密切相关。申请人早期发现Hippo通路上游STRIPAK复合物核心组分丝/苏氨酸激酶MST4可抑制癌基因YAP活性，在胃癌中呈下调趋势；并且其所在STRIPAK复合物参与调控DNA双链断裂损伤（DSB）应答。在本项目资助下，申请人先后探索了MST4组分对YAP活性以及其所在复合物调控DNA损伤应答的功能机制。首先，申请人发现MST4可通过直接磷酸化YAP Thr83位点使其滞留在细胞质，进而抑制其入核活化。重要的是，MST4激酶可与经典Hippo通路LATS1/2激酶相互独立磷酸化YAP不同位点，两者协同抑制其转录活性。在此基础上，申请人结合原位成瘤模型及临床样本建立了MST4的低表达、YAP激活及胃癌发生的病理联系。总体上，我们揭示了一条非经典的MST4-YAP信号轴，有助于理解YAP在病理条件下过度活化与多重调控的复杂性，同时为胃癌的诊疗提供了新思路（J Exp Med, 2020）。另一方面，申请人系统解析了包括MST4在内的多个组分对DSB修复的调控效应及信号转导机制，发现该复合物组装紊乱可通过提高DNA修复能力诱导胃癌细胞对放化疗产生耐药性，并针对性研发了靶向STRIPAK组装的多肽抑制剂用于逆转胃癌耐药性（J Clin Invest, 2020）。此外，在本项目资助下，申请人以共同第一作者身份在Cell Res和Cancer Res发表2篇合作论文，并获得包括基金委面上项目和上海市青年启明星等课题资助。