DNA甲基化在低剂量镉诱导肝脏肿瘤发生的作用机制研究

Cadmium (Cd) has been classified as a human carcinogen, with the rise of world-wide industrialization, the level of environmental Cd has been raised and the Cd-caused human diseases, including cancer, have become public health concerns. Waisberg et al. proposed multiple mechanisms for Cd-associated carcinogenesis, among these possible mechanisms induction of aberrant DNA methylation may be predominant in Cd carcinogenesis at the molecular level. An epigenetic mechanism of proto-oncogene gene activation by Cd involves inhibition of DNA methylation, a cellular tool for the regulation of gene repression. In our recent study, we found a persistent increase of hepatic cell proliferation in rats at 48th weeks after 4-week exposure to low-dose Cd. The present study extends it to show that chronic Cd exposure causes 5-methyl-cytidine expression markedly decreased in the liver of rats. Perhaps one of the most intriguing findings in the present study is the appearance of hepatic preneoplasia in Cd-treated mice with the newly-established novel marker CK8/18. Thus Cd-induced aberrant DNA methylation could be an early molecular lesion responsible for the inhibition of cell death pathway and stimulation of cell proliferation, and preneoplasia, which may be a possible underlying carcinogenic mechanism of Cd at the late stage. Giving that Cd has a long biological half life, considered to be somewhere between 15 and 25 years, it is more important to understand the late, persistent effects of Cd in the individuals who were previously exposed to Cd at low levels.

镉是一种半衰期很长的有毒重金属和环境污染物，镉暴露与多种肿瘤相关，但致癌机理不明。我们前期工作已证实，低剂量镉暴露大鼠模型在远期检测到肝脏组织蛋白组学改变，其中抗氧化相关蛋白表达水平降低；肝脏细胞增殖增多，凋亡减少；共聚焦显微镜观察到DNA双链断裂及甲基化水平下降；并观察到了肝脏组织出现癌前病变。本项目在前期工作基础上，建立肝毒性敏感的小鼠模型，采用分子生物学、组织病理学、DNA甲基化芯片等技术对低剂量镉染毒后不同时间点引起肝脏基因组DNA的CpG岛甲基化水平变化进行检测，然后通过生物信息学方法，Gene ontology (GO) 注释和功能分析后得到与肿瘤发生相关通路，明确镉对肝脏基因组DNA甲基化的影响；并对其中肿瘤发生相关基因进行筛选、验证。期望从DNA甲基化角度阐明镉对基因组影响的分子机理，揭示基因甲基化在肝脏肿瘤的发生发展中的作用，为人们减少从环境中摄入镉提供科学理论和实验依据

镉是一种半衰期很长的有毒重金属和环境污染物，镉暴露与多种肿瘤相关，但致癌机理不明。 本项目在前期工作基础上，我们应用FL83B细胞系来验证是否DNA甲基化参与了镉对细胞增殖的影响。结果显示，当FL83B细胞暴露于低剂量Cd(0.085μM)14天时，细胞增殖和DNMT甲基转移酶表达和活动增加，而肿瘤基因的mRNA和蛋白质caspase-8显著减少，细胞凋亡显著降低，细胞浸润和转移增加。此外，caspase-8基因启动子Cd暴露的Fl83B细胞高甲基化与前期动物实验一致。DNA甲基化抑制剂，5-aza-2脱氧胞苷(5-aza-dC)能够防止Cd诱导的细胞增殖、侵袭和转移与恢复caspase-8表达式。这些结果表明低剂量的Cd可能诱发caspase-8基因启动子甲基化，导致下调表达，从而促进细胞增殖、侵袭和转移，减少细胞凋亡，将增加Cd诱导的致癌作用。本项目期望从DNA甲基化角度阐明镉对基因组影响的分子机理，揭示基因甲基.化在肝脏肿瘤的发生发展中的作用，为人们减少从环境中摄入镉提供科学理论和实验依据。