Lee Jung-Ok, Kwun Hyun Jin, Jung Jin Kyu, Choi Kyung Hee, Min Do Sik, Jang Kyung Lib
Division of Biological Sciences, College of Natural Sciences, Pusan National University, Busan, Korea.
Oncogene. 2005 Oct 6;24(44):6617-25. doi: 10.1038/sj.onc.1208827.
E-cadherin is a key cell adhesion molecule implicated as a tumor suppressor, which is frequently altered in hepatocellular carcinoma, especially in hepatitis B virus (HBV)-related tumors. Here, we report that HBV X protein (HBx) represses E-cadherin expression at the transcription level. Based on the differential effects of HBx natural variants, we determined that Lys-130 in the transactivation domain of HBx is critical for the E-cadherin repression. The repression effect of HBx was abolished after treatment with DNA methyltransferase inhibitor, 5'-Aza-2'dC. In addition, methylation-specific PCR analysis revealed that the CpG island 1 of E-cadherin promoter is hypermethylated by HBx. Furthermore, HBx induces DNA methyltransferase 1 expression by stimulating its transcription. Therefore, we conclude that HBx represses E-cadherin expression by inducing methylation-mediated promoter inactivation. The reduced E-cadherin expression results in dramatic morphological changes of the HBx-expressing cells. In addition, HBx-expressing cells aggregate poorly in suspension culture, reflecting their altered intercellular interactions. The biological significance was further demonstrated by the increased collagen invasion ability of HBx-expressing cells. Therefore, the present study suggests that HBx plays a role during hepatocellular carcinogenesis by favoring cell detachment from the surrounding cells and migration outside of the primary tumor site.
E-钙黏蛋白是一种作为肿瘤抑制因子的关键细胞黏附分子，在肝细胞癌中经常发生改变，尤其是在乙型肝炎病毒（HBV）相关肿瘤中。在此，我们报告HBV X蛋白（HBx）在转录水平上抑制E-钙黏蛋白的表达。基于HBx天然变体的不同作用，我们确定HBx反式激活结构域中的赖氨酸-130对E-钙黏蛋白的抑制至关重要。在用DNA甲基转移酶抑制剂5'-氮杂-2'-脱氧胞苷处理后，HBx的抑制作用被消除。此外，甲基化特异性PCR分析显示，E-钙黏蛋白启动子的CpG岛1被HBx高度甲基化。此外，HBx通过刺激其转录来诱导DNA甲基转移酶1的表达。因此，我们得出结论，HBx通过诱导甲基化介导的启动子失活来抑制E-钙黏蛋白的表达。E-钙黏蛋白表达的降低导致表达HBx的细胞发生显著的形态变化。此外，表达HBx的细胞在悬浮培养中聚集性差，反映出它们细胞间相互作用的改变。表达HBx的细胞胶原侵袭能力增加进一步证明了其生物学意义。因此，本研究表明，HBx通过促进细胞与周围细胞分离并从原发肿瘤部位向外迁移，在肝细胞癌发生过程中发挥作用。
