Department of Biochemistry and Molecular Biology, School of Biological Sciences, Central University of Kerala, Tejaswini Hills, Periye, Kasargod 671316, Kerala, India.
Department of Zoology, School of Biological Sciences, Central University of Kerala, Tejaswini Hills, Periye, Kasargod 671316, Kerala, India.
Sci Total Environ. 2021 Mar 25;762:143175. doi: 10.1016/j.scitotenv.2020.143175. Epub 2020 Oct 22.
The potent environmental toxicant aflatoxin B (AFB), is a group I carcinogen reported to induce the expression of many cancer associated proteins. Epigenetic alterations such as DNA methylation and histone modifications play vital role in AFB-mediated carcinogenesis. These epigenetic modifications may result in the recruitment of specific proteins and transcription factors to the promoter region and regulate gene expression. Here we show that AFB, at lower concentrations (100 and 1000 nM) induced proliferation in L-132 and HaCaT cells with activation of the Akt pathway, which ultimately steered abnormal proliferation and transmission of survival signals. We demonstrated a significant reduction in the expression of p21 with a remarkable increase in the expression of cyclin D1 that correlated with increased methylation of CpG dinucleotides in p21 proximal promoter, while cyclin D1 promoter remained unmethylated. The chromatin immunoprecipitation results revealed the enrichment of DNMT3a and H3K27me3 repressive marks on the p21 proximal promoter where EZH2 mediated H3K27me3 mark enhanced the binding of DNMT3a at the promoter and further contributed to the transcriptional inactivation. The overall study provided the novel information on the impact of AFB on p21 inactivation via EZH2 and promoter methylation which is known to be a vital process in proliferation. Furthermore, AFB induced the expression of EZH2 analogue protein E(z), cyclin D1 analogue cyclin D and decreased the expression of p21 analogue Dacapo in Drosophila melanogaster. Interestingly, the aggressiveness in their expression upon re-exposure in successive generations suggested first hand perspectives on multigenerational epigenetic memory.
强环境毒物黄曲霉毒素 B（AFB）是一种 I 类致癌物质，据报道可诱导许多癌症相关蛋白的表达。表观遗传改变，如 DNA 甲基化和组蛋白修饰，在 AFB 介导的致癌作用中起着至关重要的作用。这些表观遗传修饰可能导致特定蛋白质和转录因子募集到启动子区域，并调节基因表达。在这里，我们表明 AFB 在较低浓度（100 和 1000 nM）下诱导 L-132 和 HaCaT 细胞增殖，激活 Akt 途径，最终导致异常增殖和存活信号的传递。我们发现 p21 的表达显著降低，cyclin D1 的表达显著增加，这与 p21 近端启动子中 CpG 二核苷酸的甲基化显著增加相关，而 cyclin D1 启动子保持未甲基化。染色质免疫沉淀结果显示，DNMT3a 和 H3K27me3 抑制标记在 p21 近端启动子上富集，其中 EZH2 介导的 H3K27me3 标记增强了 DNMT3a 在启动子上的结合，并进一步导致转录失活。总的来说，该研究提供了关于 AFB 通过 EZH2 和启动子甲基化对 p21 失活的影响的新信息，这是增殖过程中的一个重要过程。此外，AFB 诱导果蝇黑腹果蝇中 EZH2 类似蛋白 E(z)、cyclin D1 类似蛋白 cyclin D 的表达，并降低 p21 类似蛋白 Dacapo 的表达。有趣的是，在连续几代重新暴露时它们表达的增强表明了多代表观遗传记忆的第一手观点。
