Epigenetic silencing of SFRP1 and SFRP5 by hepatitis B virus X protein enhances hepatoma cell tumorigenicity through Wnt signaling pathway
Epigenetic silencing of SFRP1 and SFRP5 by hepatitis B virus X protein enhances hepatoma cell tumorigenicity through Wnt signaling pathway
复制标题
乙型肝炎病毒X蛋白表观遗传沉默SFRP1和SFRP5通过Wnt信号通路增强肝癌细胞致瘤性
DOI：
10.1002/ijc.28697
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发表时间：
2014-08-01
影响因子：
6.4
通讯作者：
Tang, Ni
中科院分区：
文献类型：
--
作者：
Xie, Qing;Chen, Linlin;Tang, Ni
分泌卷曲相关蛋白（SFRPs）是Wnt信号通路的拮抗剂，其表观遗传下调已被证明参与肝癌的发生。然而，乙型肝炎病毒（HBV） X蛋白（HBx）诱导的SFRPs失调在HBV相关的肝细胞癌（HBV- hcc）中从未被研究过。在本研究中，我们试图确定肝癌细胞和HBV-HCC患者中hbx诱导的SFRPs失调的临床意义和潜在机制。我们的研究结果表明，HBx显著降低了肝癌细胞中SFRP1和SFRP5的表达。肝癌细胞中被抑制的表达被DNA甲基化抑制剂部分拯救，并通过与组蛋白去乙酰转移酶抑制剂联合治疗协同增加。此外，我们发现SFRP1和SFRP5启动子在表达hbx的肝癌细胞和HBV-HCC组织中都是高甲基化的。HBV-HCC组织中SFRP1和SFRP5下调与DNA甲基转移酶1 （DNMT1）过表达和肿瘤分化不良显著相关。HBx促进DNMT1和DNMT3A与SFRP1和SFRP5启动子的结合，导致SFRP1和SFRP5的表观遗传沉默。此外，SFRP1、SFRP5过表达或RNA干扰介导的DNMT1沉默使Wnt信号通路失活，降低Wnt靶基因c-Myc和CyclinD1的表达水平，从而在体外和体内阻碍HCC生长，逆转hbx诱导的上皮-间质转化（EMT）。我们的研究结果强烈表明，HBx对SFRP1和SFRP5的表观遗传沉默允许Wnt信号通路的组成性激活，从而有助于肝癌的发生。
Secreted frizzled-related proteins (SFRPs) are antagonists of the Wnt signaling pathway whose epigenetic downregulation have been shown to be involved in hepatocarcinogenesis. However, dysregulation of SFRPs induced by hepatitis B virus (HBV) X protein (HBx) has never been studied in HBV-related hepatocellular carcinoma (HBV-HCC). In this study, we sought to determine the clinical significance and underlying mechanism of HBx-induced SFRPs dysregulation in hepatoma cells and HBV-HCC patients. Our results showed that SFRP1 and SFRP5 expression were dramatically decreased by HBx in hepatoma cells. The repressed expression in hepatoma cells was partially rescued by a DNA methylation inhibitor and synergistically increased by a combination treatment with a histone deacetyltransferases inhibitor. In addition, we identified that SFRP1 and SFRP5 promoters were hypermethylated in both HBx-expressing hepatoma cells and HBV-HCC tissues. Downregulation of SFRP1 and SFRP5 in HBV-HCC tissues was significantly correlated with overexpression of DNA methyltransferase 1 (DNMT1) and poor tumor differentiation. HBx facilitated the binding of DNMT1 and DNMT3A to SFRP1 and SFRP5 promoters, and resulted in epigenetic silencing of SFRP1 and SFRP5. Moreover, overexpression of SFRP1, SFRP5 or RNA interference mediated silencing of DNMT1 inactivated the Wnt signaling pathway and decreased the expression levels of Wnt target genes c-Myc and CyclinD1, thus impeding HCC growth in vitro and in vivo, and regressing HBx-induced epithelial-mesenchymal transition (EMT). Our findings strongly suggest that epigenetic silencing of SFRP1 and SFRP5 by HBx allows constitutive activation of Wnt signaling pathway and hence contributes to hepatocarcinogenesis.