MTHFR表达下调导致的DNA低甲基化在肝细胞癌发生发展中的作用及机制研究

Aberrant DNA methylation (including whole hypomethylation and hypermethylation of promoter region) plays an important role in hepatocellular carcinoma (HCC). Previous studies more concentrated on the investigation of promoter region hypermethylation. Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in DNA methylation process. It has been described that there is relationship between gene polymorphism and epidemiology for MTHFR in stroke, heart disease and many types of cancer, however, expression, function, and related mechanism have not been reported in HCC. Our preliminary studies showed that MTHFR was down-regulated in HCC. In this project, we attempt to explore possibility of transcript factor and microRNA in regulation of MTHFR expression, role of MTHFR downregulation, DNA methylation profile caused by MTHFR downregulation, and gene regulation driven by DNA hypomethylation which is caused by MTHFR downregulation in HCC. We expect to elucidate that molecular mechanism of DNA hypomethylation caused by MTHFR in HCC and provide experimental evidence for treatment of HCC.

DNA甲基化异常(包括大范围低甲基化及局部启动子区域高甲基化)在肝癌等肿瘤发生发展中起着重要作用，以往多集中于对启动子区域高甲基化的研究。亚甲基四氢叶酸还原酶（Methylene tetrahydrofolate reductase, MTHFR）是DNA甲基化过程提供甲基的关键酶，以往研究集中在基因多态性与脑卒中、肿瘤等多种疾病流行病学关系上，对其在肝癌中表达情况及作用机制未见报导。申请人前期工作发现MTHFR在肝癌中表达下调，本课题将围绕：1、肝癌中MTHFR表达下调诱导因子；2、MTHFR表达下调在肝癌演进中执行的肿瘤生物学作用；3、MTHFR表达下调诱导DNA低甲基化谱式；4、MTHFR表达下调诱导DNA低甲基化可能释放哪些肝癌相关基因来执行这些肿瘤生物学作用等四个方面进行深入研究，期望以MTHFR为线索说明DNA低甲基化在肝癌发生发展中的作用及机制，为肝癌临床治疗提供实验依据。

DNA甲基化异常在肝癌等肿瘤发生发展中起着重要作用，以往多集中于对启动子区域高甲基化的研究，本项目主要研究DNA低甲基化在肝细胞癌中的相关情况。经过本项目的研究，我们发现在肝细胞癌中DNA呈低甲基化状态，这种DNA整体低甲基化与肝细胞癌预后及生存期的长短有关，另外我们也发现在纤维化肝组织中相较于对照组织，DNA也呈低甲基化状态；进而，我们发现DNA甲基化相关的基因DNA甲基化转移酶DNMTs、四羟叶酸还原酶MTHFR在肝细胞癌组织和肝纤维化组织中也呈低表达状态；第三，我们发现miR-103、miR-29b和miR-142-5p可以调控DNMTs和MTHFR；最后，我们发现microRNAs可以通过调控DNA甲基化相关基因降低DNA甲基化水平，促进IFN-γ表达，从而促进病变肝组织纤维化。通过本项目的研究，我们对肝脏病变中DNA甲基化状况有了进一步理解，了解表观遗传学因素肝细胞纤维化的影响，为肝细胞癌的理解、治疗提供进一步信息。