肝癌中mTOR信号通路对DNA甲基化的调控机制及其临床意义

Liver is one of the key organs for metabolism in our bodies. Liver cells are in a complex microenvironment. How the extracellular signal changes the epigenetics of the cells to adapt the external microenvironment is unknown. Its molecular mechanism also remains unclear. mTOR pathway can sense extracellular nutrition signals and regulate cell metabolism. Our team found in previous study that mTOR is localized in the nucleus and the change of its activity will affect genome DNA methylation, which is associated with sensitivity of rapamycin in cancer cells. Accordingly, we hypothesized that mTOR signaling pathway sense extracellular stimuli, affect DNA methylation and change the physiological state of cancer cells. We would like to carry out the following three aspects in liver cancer: 1) To explore the role of mTOR signaling pathway activated or suppressed by extracellular signals in the DNA methylation and its biological significance; 2) To clarify the molecular mechanism of DNA methylation regulated by mTOR signaling pathways and its role in cancer development; 3) To identify biomarkers to guide mTOR-targeted therapy, by detecting change of key molecular in cancer cell lines and animal models. Successful implementation of these objectives should lead to new insights into the role of epigenetics in liver cancer, and help to develop new strategies for liver cancer treatment.

肝是人体代谢的重要器官，肝细胞面临复杂多变的微环境。胞外信号如何改变细胞的表观遗传以适应外界微环境，其分子机制仍不明确。mTOR通路可以感受胞外营养信号，调控细胞代谢。本团队在前期研究中发现，mTOR可定位于细胞核内，其活性的改变会影响肝癌细胞基因组DNA甲基化水平，并且相关变化与肝癌细胞的雷帕霉素敏感性相关。据此我们提出假设，mTOR信号通路感受胞外刺激，影响DNA甲基化水平，进而改变肿瘤细胞的生理状态。我们拟以肝癌为对象，开展以下三方面研究：①探索肿瘤胞外微环境中的各类信号激活或抑制mTOR信号通路对DNA甲基化调控的作用及其生物学意义；②阐明mTOR通路调控DNA甲基化变化的关键分子及其在肿瘤发生发展中的分子机制；③通过检测肿瘤细胞中的关键分子，结合动物模型，筛选和鉴定mTOR抑制剂用药标志物。本项目的实施，将有助于阐明肝癌的表观遗传调控机制，并为改进肝癌的临床治疗策略提供理论依据。

肝脏是人体最重要的代谢器官之一。肝脏代谢异常对于肝脏疾病，尤其是肝细胞癌(HCC)的发展至关重要。雷帕霉素的机制靶点 (mTOR)是环境代谢信号的关键传感器，在HCC中mTOR级联失调是最常见的，此外，表观遗传修饰的紊乱，如DNA甲基化修饰的异常，在癌变过程中也起着重要作用。. 在本研究中，我们发现mTOR信号的激活与51对HCC组织及其癌旁组织中的DNA甲基化谱呈正相关。体外研究表明，由于mTOR信号抑制，营养缺乏的环境和mTOR抑制剂雷帕霉素的治疗使细胞DNA甲基化水平下调。我们筛选了甲基化相关酶，发现mTOR信号的激活增加了DNA甲基转移酶1 (DNMT1)的表达和活性。mTOR可以以依赖4E-BP1的方式促进DNMT1的翻译效率。此外，4E-BP1的磷酸化缺陷突变体可以增强其对DNMT1的抑制作用。富含嘧啶的翻译元件 (PRTE)的突变或缺失可以消除雷帕霉素对DNMT1的抑制作用。mTOR和表观遗传抑制剂的联合在体外和体内对抑制HCC均显示出协同作用。因此，mTOR可以通过影响DNMT1的翻译效率来调节DNA甲基化谱，从而促进HCC的发展。mTOR和DNMT1协同靶向是一种有潜力的HCC治疗策略。