丙型肝炎病毒核心蛋白表观调控DKK在肝癌发生中的作用及分子机制研究

Aberrant activation of the Wnt/β-catenin signaling pathway contributes to 50% of hepatocellular carcinogenesis. As a structural component of HCV, the 21 kDa Core protein has been strongly implicated in HCC pathogenesis by virtue of its role in transcriptional regulation of cellular proto-oncogenes through interaction with cytoplasmic proteins and signal transduction pathways, including Wnt/β-catenin signaling pathway. Mounting data suggest that regulatory mechanisms other than genetic mutations play important roles in carcinogenesis. However, whether HCV Core protein plays a direct role in epigenetic regulation of Wnt antagonist Dickkopf (DKK) remains unclear. DKK can bind to the extracellular domain of Lrp5/6 complex and prevent the formation of the FZD-Wnt-Lrp5/6 in response to Wnt, thereby attenuating Wnt activity. DKK has been shown to be transcriptionally inactivated through CpG methylation in the development of various cancers, such as breast cancer, prostatic cancer, and liver cancer. The previous research showed that HCV Core protein triggers epigenetic silencing of SFRP1 gene which can hinder Wnt-receptor interactions and block Wnt signaling.Therefore, in this project, we will investigate whether the HCV Core protein epigenetically regulates DKK expression and hence determine if it is involved in HCV-related hepatocellular carcinoma （HCC）development. To this end, firstly we will observe whether HCV Core protein suppresses the expression levels of DKK in HCC cell lines and tumor tissues of HCC patients. To further determine molecular mechanisms through which HCV Core regulates DKK expression, the levels of epigenetic modification enzyme bound to the DKK promoter region in Core-expressing cells will be detected. Finally, the change of tumor biological behavior induced by HCV Core in a xenograft HCC model and HCC cell lines will be evaluated. This study will provide new information regarding epigenetical regulation of HCV Core induced HCC development through activation of the Wnt/β-catenin pathway.

50%以上肝癌发生与Wnt/β-catenin信号异常活化有关。HCVCore蛋白可能通过激活Wnt/ β-catenin通路介导肝癌的发生、发展，但具体机制尚未明确。Wnt/β-catenin拮抗分子DKK 通过与Lrp5/6结合，抑制Wnt信号通路活化。研究发现，DKK启动子区高甲基化所导致的表达沉 默与乳腺癌、前列腺癌、肝癌等多种肿瘤发生密切相关。我们前期研究提示HCVCore通过甲基 化修饰阻遏另一种拮抗分子SFRP1的表达。据此推测HCV Core可能通过甲基化等表观遗传修饰 抑制DKK的表达，活化Wnt信号通路。本课题选择肝癌细胞系和HCV相关肝癌组织，观察HCVCore对DKK的表达调控；采用表观遗传学方法探索HCVCore调控DKK基因启动子区甲基化修饰的分 子机制；体外及体内验证HCVCore诱导肝癌的发生提供新的理论依据。