Chen Hua, Li ShuanFang, Liu Jie, Diwan Bhalchandra A, Barrett J Carl, Waalkes Michael P
Laboratory of Comparative Carcinogenesis, National Cancer Institute at the National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
Carcinogenesis. 2004 Sep;25(9):1779-86. doi: 10.1093/carcin/bgh161. Epub 2004 Apr 8.
Inorganic arsenic is a human carcinogen that can target the liver, but its carcinogenic mechanisms are still unknown. Global DNA hypomethylation occurs during arsenic-induced malignant transformation in rodent liver cells. DNA hypomethylation can increase gene expression, particularly when occurring in the promoter region CpG sites, and may be a non-genotoxic mechanism of carcinogenesis. Thus, in the present study liver samples of male mice exposed to 0 (control) or 45 p.p.m. arsenic (as NaAsO(2)) in the drinking water for 48 weeks were analyzed for gene expression and DNA methylation. Chronic arsenic exposure caused hepatic steatosis, a lesion also linked to consumption of methyl-deficient diets. Microarray analysis of liver samples showed arsenic induced aberrant gene expression including steroid-related genes, cytokines, apoptosis-related genes and cell cycle-related genes. In particular, the expression of the estrogen receptor-alpha (ER-alpha), and cyclin D1 genes were markedly increased. RT-PCR and immunohistochemistry confirmed arsenic-induced increases in hepatic ER-alpha and cyclin D1 transcription and translation products, respectively. Arsenic induced hepatic global DNA hypomethylation, as evidenced by 5-methylcytosine content of DNA and by the methyl acceptance assay. Arsenic also markedly reduced the methylation within the ER-alpha gene promoter region, as assessed by methylation-specific PCR, and this reduction was statistically significant in 8 of 13 CpG sites within the promoter region. Overall, in controls 28.3% of the ER-alpha promoter region CpG sites were methylated, but only 2.9% were methylated after chronic arsenic exposure. Thus, long-term exposure of mice to arsenic in the drinking water can induce aberrant gene expression, global DNA hypomethylation, and the hypomethylation of the ER-alpha gene promoter, all of which could potentially contribute to arsenic hepatocarcinogenesis.
无机砷是一种可靶向肝脏的人类致癌物，但其致癌机制仍不清楚。在啮齿动物肝细胞砷诱导的恶性转化过程中会发生全基因组DNA低甲基化。DNA低甲基化可增加基因表达，尤其是发生在启动子区域的CpG位点时，可能是一种非遗传毒性致癌机制。因此，在本研究中，分析了饮用含0（对照）或45 ppm砷（以NaAsO₂形式）的饮用水48周的雄性小鼠肝脏样本的基因表达和DNA甲基化情况。慢性砷暴露导致肝脂肪变性，这种病变也与缺乏甲基的饮食摄入有关。肝脏样本的微阵列分析表明，砷诱导了异常基因表达，包括类固醇相关基因、细胞因子、凋亡相关基因和细胞周期相关基因。特别是，雌激素受体α（ER-α）和细胞周期蛋白D1基因的表达显著增加。RT-PCR和免疫组织化学分别证实了砷诱导肝脏中ER-α和细胞周期蛋白D1转录和翻译产物增加。砷诱导肝脏全基因组DNA低甲基化，DNA的5-甲基胞嘧啶含量和甲基接受试验证明了这一点。通过甲基化特异性PCR评估，砷还显著降低了ER-α基因启动子区域内的甲基化，在启动子区域的13个CpG位点中有8个位点的这种降低具有统计学意义。总体而言，在对照组中，ER-α启动子区域28.3%的CpG位点被甲基化，但慢性砷暴露后只有2.9%被甲基化。因此，小鼠长期饮用含砷的水可诱导异常基因表达、全基因组DNA低甲基化以及ER-α基因启动子的低甲基化，所有这些都可能促进砷诱导的肝癌发生。
