DNA甲基化/去甲基化重编程在泌尿系统上皮细胞分化、恶性转化、侵袭转移中的作用机理研究

Mammalian development required cytosine methylation (5mC) which is a heritable epigenetic mark of cellular memory believed to maintain a cell’s identity. It plays roles in cell differentiation and physiological processes, such as embryogenesis and tumorigenesis. It has been showed that tumor cells show features of dedifferentiation and deregulation of DNA methylation reprogramming. Tumor cells showed global reduction of DNA methylation and gain of methylation in promoters of individual genes. Although, it still remains limited known that the mechanisms and functional significance of DNA methylation reprogramming in tissue-specific cell differentiation and tumorigenesis. For example, whether 5mC oxidative products, such as 5-hydroxymethylcytosine (5hmC), mediates the DNA methylation/demethylation reprogramming during tissue-specific cell differentiation and tumorigenesis? The previous studies in our lab showed that there are 5hmC-independent DNA demethylation pathways in both mouse (Cell, 2014) and zebrafish (Cell, 2013). On the contrary, 5hmC reprogramming is associated with DNA hypermethylation during kidney tumorigenesis (Cell research, under revision). Herein, we will elucidate the pattern and molecular mechanisms of DNA methylation reprogramming during urological epithelial cells differentiation, tumorigenesis and metastasis. Firstly, we will map base-resolution of 5mC and 5hmC patterns of epithelial cells and corresponding tumor cells. We will focus on the most prevalent tumors in urological cancer, kidney cancer and bladder cancer which are originated from the tubular epithelial cells and transitional cells, respectively. We anticipate to identify the urological tumor-specific 5mC/5hmC biomarkers from this part of study. Secondly, we will use renal cell carcinoma as model to explore the extent and functional roles of DNA methylation/demethylation reprograming during tumor metastasis. We will track the genomic and epigenetic variations (5mC and 5hmC) during tumor cell microevolution (normal cell, tumor cells and metastasis tumor cells in different targeted organs). Population genetics methods will be applied to discover the driver variations from background variations. Further integrating the data from cell differentiation and tumorigenesis, the ultimate goal of my laboratory is to define the epigenetic changes that occur in cancers especially renal cell carcinomas, to discover the molecular causes of these changes, and to translate that newly gained knowledge into the clinical in the form of novel, epigenetic-based therapies.

实验室前期研究发现：在斑马鱼(Cell，2013)和小鼠（Cell，2014）早期胚胎发育过程中都存在不依赖于5mC氧化为5羟甲基胞嘧啶（5hmC）的DNA去甲基化机制；但5hmC重编程参与肾癌发生过程中的DNA甲基化重编程（Cell Research，under revision）。本课题拟深入探索泌尿系统器官组织特异的上皮细胞恶性转化、侵袭转移过程DNA甲基化/去甲基化重编程规律和作用机制。首先，比较肾小管上皮细胞和移行上皮细胞及其恶性转化过程DNA甲基化/去甲基化重编程的规律和作用机制，预期阐明泌尿系统肿瘤特异的5mC/5hmC表观标记物。其次，探索同一肾癌患者肿瘤细胞侵袭转移演化过程中基因组和表观遗传变异规律。以进化理论为指导，预期将在表观遗传变异和基因组变异如何协同驱动肿瘤不同器官转移方面取得突破进展。整合以上研究结果，鉴定泌尿系统肿瘤特异的早诊和复发动态监测表观遗传标记物。

表观遗传改变可能驱动肿瘤的发生和转移，但是目前表观遗传变异在原发肿瘤及肿瘤转移中的重编程规律还不甚清楚。本研究先从肾癌原发灶入手，获得了单碱基分辨率的全基因组5hmC和5mC图谱，并根据该图谱找到了5mC和5hmC在透明肾细胞癌（ccRCC）中的重编程模式和规律，更新了现有肿瘤甲基化重编程的认识，同时发现5hmC可以作为肾癌预后监测的潜在新型表观遗传标记物和靶向治疗的靶点（Cell Research，2016）。基于此，再结合DNA修饰的可逆性，本研究还发现了一种化合物，它能够逆转5hmC水平，所以有可能可以作为一个5hmC重塑化合物用于治疗肾癌（专利申报阶段）。此外，本研究还收集了多例泌尿系统肿瘤的转移灶和原发灶样品，继续探索同一肾癌患者肿瘤细胞侵袭转移演化过程中基因组和表观遗传变异规律，预期将在表观遗传变异和基因组变异如何协同驱动肿瘤不同器官转移方面取得突破进展，鉴定泌尿系统肿瘤特异的早诊和复发动态监测表观遗传标记物。