用DEN诱发ULK1基因敲除小鼠肝癌模型研究自噬在肿瘤发生发展过程中的双向作用

At present the involvement of autophagy in cancer remains a highly controversial and debatable topic. One common understanding is that autophagy suppresses tumorigenesis at the initiation stage, but promotes tumor growth at the promotion and progression stages. We also found autophagy inhibition in early stage of chemical induced carcinogenesis promote tumor initiation. The work in the collaborator (Shen HM)'s lab has provided clear evidence in supporting the pro-survival function of autophagy to protect against necrotic cell death under previous stress conditions, including oxidative stress, DNA damage, and starvation. And ssuppression of autophagy promoted cell death induced by the conventional cancer therapeutic agents. However, so far, most of the evidence supporting such notion is from in vitro cell culture or cancer xenograft models, with very limited information in animal models with primary tumor. There is an urgent need to develop animal models with primary cancer whose entire tumorigenesis process can be assessed. Therefore, the main objective of this study is to investigate the role of autophagy in a diethylnitrosamine (DEN) and Phenobarbital (BP) induced hepatocellular carcinoma (HCC) in ALK1 knockout mice model with the application of autophagy inducer and inhibitor in tumor initiation, promotion and progression stages. The results of this study will provide evidence to better understanding of the role and mechanism of autophagy and a novel cancer preventive and cancer therapeutic strategy by targeting autophagy.

目前关于自噬介导肿瘤的话题仍然争议不断。较普遍的理解是自噬在肿瘤的启动期起抑制作用，而在促长和进展期却起着促进的作用。我们研究也发现化学致癌早期抑制自噬能促进肿瘤，而应激诱导的自噬有促生存作用，抑制肿瘤细胞自噬能增加化疗敏感性，因此强烈支持上述假说。但是，目前支持这种说法的证据几乎都来自体外细胞培养实验或癌细胞异种移植模型，几乎没有来自体内原发肿瘤动物模型的证据却甚少。因此，非常有必要建立一个肿瘤发生、发展全过程都可被检测的原发性肿瘤模型。本项目将建立常见化学致癌物二乙基亚硝胺（DEN）和促癌物苯巴比妥（BP）联合诱发ULK1基因敲除小鼠肝细胞肝癌（HCC）动物模型，在化学致癌的不同阶段，应用自噬诱导剂和抑制剂，全面观察和深入探讨自噬在化学致癌物诱发肿瘤发生、发展全过程中所发挥的作用及其分子机制，研究结果将为进一步利用自噬的调控策略实现肿瘤的化学预防和临床治疗提供科学依据。

自噬与肿瘤的关系十分密切，其在早期抑制肿瘤生长，而在肿瘤晚期促进肿瘤的发展。饮食限制是强有力的自噬诱导因子，研究表明饮食限制能够有效抑制多种肿瘤的发生发展。本课题组研究表明饮食限制能够有效抑制二乙基亚硝胺(diethylnitrosamine, DEN)诱导的C57BL/6小鼠原发性肝细胞癌，抑制肝细胞增殖、促进肝细胞凋亡。通过二代测序，进一步发现饮食限制能够有效逆转DEN对小鼠肝脏转录组的影响，而MAPK信号通路可能是饮食限制发挥抗肿瘤作用的关键。同时，本课题组研究发现ULK1基因敲除使饮食限制及禁食诱导的自噬发生出现障碍，但不影响基础自噬的发生，诱导性自噬缺陷并不能消除饮食限制的抗肿瘤作用，但是敲除ULK1基因能够有效抑制小鼠原发性肿瘤的发生发展，且饮食限制与ULK1基因敲除的抗肿瘤作用之间存在交互效应。