Department of Zoology, University of Calcutta, Kolkata 700019, India; Department of Environmental Science, University of Calcutta, Kolkata 700019, India.
Health-Management in Occupational Health, Siemens, India.
Environ Res. 2018 May;163:289-296. doi: 10.1016/j.envres.2018.01.002. Epub 2018 Feb 27.
Arsenic exposure and its adverse health outcome, including the association with cancer risk are well established from several studies across the globe. The present study aims to analyze the epigenetic regulation of key mismatch repair (MMR) genes in the arsenic-exposed population.
A case-control study was conducted involving two hundred twenty four (N=224) arsenic exposed [with skin lesion (WSL=110) and without skin lesion (WOSL=114)] and one hundred and two (N=102) unexposed individuals. The methylation status of key MMR genes i.e. MLH1, MSH2, and PMS2 were analyzed using methylation-specific PCR (MSP). The gene expression was studied by qRTPCR. The expression of H3K36me3, which was earlier reported to be an important regulator of MMR pathway, was assessed using ELISA.
Arsenic-exposed individuals showed significant promoter hypermethylation (p < 0.0001) of MLH1 and MSH2 compared to those unexposed with consequent down-regulation in their gene expression [MLH1 (p=0.001) and MSH2 (p<0.05)]. However, no significant association was found in expression and methylation of PMS2 with arsenic exposure. We found significant down-regulation of H3K36me3 in the arsenic-exposed group, most significantly in the WSL group (p<0.0001). The expression of SETD2, the methyltransferase of an H3K36me3 moiety was found to be unaltered in arsenic exposure, suggesting the involvement of other regulatory factors yet to be identified.
In summary, the epigenetic repression of DNA damage repair genes due to promoter hypermethylation of MLH1 and MSH2 and inefficient recruitment of MMR complex at the site of DNA damage owing to the reduced level of H3K36me3 impairs the mismatch repair pathway that might render the arsenic-exposed individuals more susceptible towards DNA damage and associated cancer risk.
砷暴露及其不良健康后果，包括与癌症风险的关联，已被全球多项研究证实。本研究旨在分析砷暴露人群中关键错配修复（MMR）基因的表观遗传调控。
进行了一项病例对照研究，共纳入 224 名（N=224）砷暴露者（有皮肤损伤[WSL=110]和无皮肤损伤[WOSL=114]）和 102 名（N=102）未暴露者。采用甲基化特异性 PCR（MSP）分析关键 MMR 基因 MLH1、MSH2 和 PMS2 的甲基化状态。通过 qRT-PCR 研究基因表达。使用 ELISA 评估先前报道为 MMR 途径重要调节剂的 H3K36me3 的表达。
与未暴露者相比，砷暴露者的 MLH1 和 MSH2 启动子呈现显著的高甲基化（p<0.0001），导致其基因表达下调[MLH1（p=0.001）和 MSH2（p<0.05）]。然而，PMS2 的表达和甲基化与砷暴露无显著相关性。我们发现砷暴露组的 H3K36me3 表达显著下调，在 WSL 组最为显著（p<0.0001）。砷暴露时 SETD2 的表达，即 H3K36me3 部分的甲基转移酶未发生改变，表明涉及其他尚未确定的调节因子。
总之，由于 MLH1 和 MSH2 启动子的高甲基化导致 DNA 损伤修复基因的表观遗传抑制，以及由于 H3K36me3 水平降低导致 MMR 复合物在 DNA 损伤部位的有效募集受损，从而破坏错配修复途径，使砷暴露个体更容易受到 DNA 损伤和相关癌症风险的影响。
