Lian Zhaorui, Liu Jie, Li Li, Li Xianxing, Clayton Marcy, Wu Meng-Chao, Wang Hong-Yang, Arbuthnot Patrick, Kew Michael, Fan Daiming, Feitelson Mark A
Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Hepatology. 2006 Mar;43(3):415-24. doi: 10.1002/hep.21053.
Intrahepatic expression of hepatitis B x antigen (HBxAg) is associated with the development of hepatocellular carcinoma (HCC), perhaps through trans-activation of selected cellular genes. When this was examined by PowerBlot analysis, upregulated levels of beta-catenin and several known beta-catenin effectors were observed in HBxAg-positive compared with HBxAg-negative HepG2 cells. When HBxAg was introduced into Hep3B cells, upregulated expression of wild-type beta-catenin was observed. This was also observed in Hep3B cells overexpressing the HBxAg upregulated gene, URG11. Upregulated expression of URG11 and beta-catenin correlated with HBxAg trans-activation function. Transient transfection assays with fragments of the beta-catenin promoter showed that it was activated by both HBxAg and URG11 and inhibited by URG11-specific small inhibitory RNA. The latter also inhibited the growth of Hep3BX cells in a serum-free medium, which correlated with depressed levels of beta-catenin. Activation of beta-catenin effector genes was observed in cells stably expressing HBxAg or overexpressing URG11 compared with control cells transfected with the pTOPFLASH reporter plasmid. Extensive costaining between HBxAg, URG11, and beta-catenin was observed in infected liver and HCC nodules, suggesting a close relationship in vivo. In conclusion, wild-type beta-catenin is activated by HBxAg, in part, through the upregulated expression of the HBxAg effector URG11. URG11 stimulates the beta-catenin promoter and hepatocellular growth and survival. These observations also suggest that URG11 may be a regulatory element in the beta-catenin signaling pathway and may be a target for chemoprevention of HCC.
乙型肝炎X抗原（HBxAg）的肝内表达与肝细胞癌（HCC）的发生发展相关，可能是通过对特定细胞基因的反式激活作用。当通过免疫印迹分析对此进行检测时，与HBxAg阴性的HepG2细胞相比，在HBxAg阳性细胞中观察到β-连环蛋白及几种已知的β-连环蛋白效应分子的水平上调。当将HBxAg导入Hep3B细胞时，观察到野生型β-连环蛋白的表达上调。在过表达HBxAg上调基因URG11的Hep3B细胞中也观察到了这种现象。URG11和β-连环蛋白的表达上调与HBxAg的反式激活功能相关。用β-连环蛋白启动子片段进行的瞬时转染试验表明，它可被HBxAg和URG11激活，并被URG11特异性小干扰RNA抑制。后者还在无血清培养基中抑制了Hep3BX细胞的生长，这与β-连环蛋白水平降低相关。与用pTOPFLASH报告质粒转染的对照细胞相比，在稳定表达HBxAg或过表达URG11的细胞中观察到了β-连环蛋白效应基因的激活。在受感染的肝脏和HCC结节中观察到HBxAg、URG11和β-连环蛋白之间广泛的共染色，提示它们在体内关系密切。总之，野生型β-连环蛋白部分地通过HBxAg效应分子URG11的表达上调而被激活。URG11刺激β-连环蛋白启动子及肝细胞的生长和存活。这些观察结果还提示，URG11可能是β-连环蛋白信号通路中的一个调节元件，可能是HCC化学预防的一个靶点。
