RNA编辑调控细胞干性及促进肝癌干细胞形成的机制研究

In order to improve the clinical diagnosis and treatment for hepatocellular carcinoma (HCC), it’s urgently needed to explore the mechanism of HCC carcinogenesis as well as develop effective therapeutic targets. Cancer stem cell (CSC) has recently been considered to be the main culprit for tumor formation, recurrence and metastasis. The origins and self-renewal mechanism for CSC, however, remain unclear. Our previous studies and preliminary data showed that, RNA editing-induced epigenetic changes might promote the malignant transformation from normal liver progenitor cells to liver cancer stem cells. Numerous deregulated RNA editing events were found in HCC tissues. These RNA editing events lead to essential oncogenes/tumor suppressor genes imbalance, and as a result, promote HCC carcinogenesis and development. The expression of RNA editing enzyme ADAR1 was up-regulated in induced pluripotent stem cells (iPS cells) while ADAR2 expression was down-regulated. Moreover, the ADAR1 expression deceased gradually as the cells differentiated from human embryonic stem cells (hESC) into mature hepatocyte-like cells (HPLC), while ADAR2 expression increased. These results indicate that RNA editing might be involved in stemness regulation and hepatic CSC formation. In current project, we intend to perform transcriptome sequencing on cells obtained from different time points during hESC differentiation as well as HCC clinical samples. Via systematic analysis, the differences and similarities between RNA editing events of cancer cells and those of normal stem cells will be compared. The effects of these gene editing events on hepatic CSC formation will be evaluated and its mechanisms will be further elucidates. The results would deepen our knowledge on RNA editing and hepatic CSCs, and hopefully pave the way to specifically eliminate hepatic CSCs.

探究肝癌的发生发展机制，寻找有效治疗靶标是目前肝癌诊治的迫切需要。肿瘤干细胞被认为是肿瘤形成和复发转移的元凶。然而肝癌干细胞的来源及自我更新机制尚未明确。本课题组的前期研究发现RNA编辑所介导的表观遗传变异可能促进了肝脏干/祖细胞恶性转化形成肝癌干细胞。肝癌组织中大量的RNA编辑异常现象通过影响原癌基因/抑癌基因平衡失活，促进了肝癌的发生发展。在诱导多能性干细胞中RNA编辑酶ADAR1表达上调，ADAR2表达下调。在定向诱导分化的细胞中发现ADAR1表达随分化程度升高而逐步降低，ADAR2则升高，提示RNA编辑与细胞干性调控以及肿瘤干细胞形成相关。接下来本项目将以胚胎干细胞定向诱导分化的各个阶段以及肝癌临床样品的全转录组测序为切入点，系统性地比较正常干细胞与肿瘤细胞在RNA编辑方面的异同，探究关键基因的RNA编辑在肝癌干细胞形成中的作用和机理，最终为靶向性抑制肝癌干细胞提供坚实的理论基础。

探究肝癌的发生发展机制，寻找有效治疗靶标是目前肝癌诊治的迫切需要。肿瘤干细胞在肝癌发生、转移及复发过程中扮演者重要角色，但ADAR1介导的RNA编辑事件在肝癌干细胞的来源及自我更新中的作用机制尚需进一步深入研究。本项目研究发现在诱导多能性干细胞中RNA编辑酶ADAR1表达上调，在定向诱导分化的细胞中ADAR1表达随分化程度升高而逐步降低，ADAR1在肝癌组织中的表达水平显著高于相应的癌旁组织，且与肝癌病人的预后呈负相关，在肝癌小鼠模型中，ADAR1的表达水平也随着肝癌演变逐渐升高，提示ADAR1介导的RNA编辑与细胞干性调控、分化及肝癌病理进程密切相关。进一步研究发现，ADAR1的敲降与敲除可以显著抑制肝癌细胞的增殖、迁移与成球能力；ADAR1的过表达可以提高肝癌细胞的迁移和侵袭能力。肝脏特异性过表达ADAR1-p110的小鼠可促进DEN/CCL4化学诱导及Myc转基因鼠的肝癌发生与发展。利用转录组测序对ADAR1调控肝癌增殖、迁移及干性的分子机制进行解析发现，ADAR1在肝癌细胞内的过表达与敲低可以显著影响肝癌细胞的整体RNA编辑水平，且影响细胞内炎症、黏附、细胞间连接等相关通路基因的表达。总括之，RNA编辑所介导的表观遗传变异可能促进了肝脏干/祖细胞恶性转化形成肝癌干细胞。本项目的实施可以探究关键基因的RNA编辑事件在肝癌发生及进展中的作用和机理，最终为肝癌的诊断和临床靶向治疗提供坚实的理论基础。