Zhao Wei, Liu Haiyan, Liu Wei, Wu Yinwei, Chen Wei, Jiang Bin, Zhou Yue, Xue Rong, Luo Chan, Wang Lan, Jiang Jian-Dong, Liu Jingwen
Second Hospital of Nanjing City, Nanjing, PR China.
Int J Oncol. 2006 May;28(5):1081-8.
Liver cancer is the fifth most common neoplastic disease and the fourth leading cause of cancer-related death. Identification of the key molecular targets involved in hepatocarcinogenesis has significant therapeutic implications. In this study, by conducting immunohistochemistry, we show that the neuronal protein, synuclein-gamma (SNCG), is abnormally expressed in a high percentage of liver cancer (46/70, 65.7%). The expression of SNCG in liver cancer exhibits a clear stage-specific pattern of low expression in stage I (1/19, 5.3%) and high expression in stages III to IV (44/50, 88%). Importantly, all patients with metastatic diseases expressed SNCG in their primary tumors (15/15, 100%). Consistent with the IHC results, RT-PCR assays demonstrate that SNCG mRNA is highly expressed in the tumor tissue of advanced hepatocellular carcinomas. Analyses of the methylation status of the CpG island of the SNCG gene by methylation-specific PCR confirmed that all tumor samples contained the demethylated gene. To determine whether demethylation of SNCG is an early event of genetic abnormality in the process of hepatocarcinogenesis, we examined the methylation status of SNCG in 70 non-malignant cirrhotic liver samples and showed that 64.3% cirrhotic liver samples contained the partially or completely demethylated gene. We further show that SNCG expression in liver cancer is not restricted to HBV- and HCV-infected tumors, implying the involvement of other hepatocarcinogenic risk factors in SNCG gene reactivation. Utilizing human hepatoma-derived cell line HepG2 as an in vitro model, we demonstrate that hepatic carcinogens aflatoxin B1 and N-nitrosodimethylamine (DMN) are strong inducers of SNCG expression. Collectively, these new findings suggest that SNCG protein expression in primary tumors is a strong indicator of distant metastasis and demethylation of SNCG CpG island is an early sign of genetic abnormality in liver cirrhosis preceding hepatocarcinogenesis. Our studies also suggest that inducing demethylation of SNCG by hepatocarcinogens may represent one underlying mechanism for the aberrant expression of SNCG in HCC.
肝癌是第五大常见肿瘤性疾病，也是癌症相关死亡的第四大主要原因。鉴定参与肝癌发生的关键分子靶点具有重要的治疗意义。在本研究中，通过进行免疫组织化学，我们发现神经元蛋白γ-突触核蛋白（SNCG）在高比例的肝癌中异常表达（46/70，65.7%）。SNCG在肝癌中的表达呈现出明显的阶段特异性模式，在I期低表达（1/19，5.3%），在III至IV期高表达（44/50，88%）。重要的是，所有转移性疾病患者的原发肿瘤均表达SNCG（15/15，100%）。与免疫组织化学结果一致，逆转录-聚合酶链反应（RT-PCR）分析表明SNCG mRNA在晚期肝细胞癌的肿瘤组织中高表达。通过甲基化特异性PCR分析SNCG基因启动子区域CpG岛的甲基化状态，证实所有肿瘤样本中该基因均为去甲基化状态。为了确定SNCG的去甲基化是否是肝癌发生过程中基因异常的早期事件，我们检测了70例非恶性肝硬化肝组织样本中SNCG的甲基化状态，结果显示64.3%的肝硬化肝组织样本中该基因部分或完全去甲基化。我们进一步表明，SNCG在肝癌中的表达并不局限于乙肝病毒（HBV）和丙肝病毒（HCV）感染的肿瘤，这意味着其他肝癌致癌风险因素参与了SNCG基因的重新激活。利用人肝癌细胞系HepG2作为体外模型，我们证明肝癌致癌物黄曲霉毒素B1和N-亚硝基二甲胺（DMN）是SNCG表达的强诱导剂。总的来说，这些新发现表明原发肿瘤中SNCG蛋白表达是远处转移的有力指标，SNCG基因启动子区域CpG岛的去甲基化是肝癌发生前肝硬化基因异常的早期迹象。我们的研究还表明，肝癌致癌物诱导SNCG去甲基化可能是肝癌中SNCG异常表达的一种潜在机制。
