Gastrointestinal Cancer Research Laboratory, Division of Gastroenterology, Baylor Research Institute, Baylor University Medical Center, Dallas, Texas, United States of America.
PLoS One. 2013;8(2):e57709. doi: 10.1371/journal.pone.0057709. Epub 2013 Feb 27.
Recent evidence suggests that several dietary polyphenols may exert their chemopreventive effect through epigenetic modifications. Curcumin is one of the most widely studied dietary chemopreventive agents for colon cancer prevention, however, its effects on epigenetic alterations, particularly DNA methylation, remain unclear. Using systematic genome-wide approaches, we aimed to elucidate the effect of curcumin on DNA methylation alterations in colorectal cancer cells.
To evaluate the effect of curcumin on DNA methylation, three CRC cell lines, HCT116, HT29 and RKO, were treated with curcumin. 5-aza-2'-deoxycytidine (5-aza-CdR) and trichostatin A treated cells were used as positive and negative controls for DNA methylation changes, respectively. Methylation status of LINE-1 repeat elements, DNA promoter methylation microarrays and gene expression arrays were used to assess global methylation and gene expression changes. Validation was performed using independent microarrays, quantitative bisulfite pyrosequencing, and qPCR.
As expected, genome-wide methylation microarrays revealed significant DNA hypomethylation in 5-aza-CdR-treated cells (mean β-values of 0.12), however, non-significant changes in mean β-values were observed in curcumin-treated cells. In comparison to mock-treated cells, curcumin-induced DNA methylation alterations occurred in a time-dependent manner. In contrast to the generalized, non-specific global hypomethylation observed with 5-aza-CdR, curcumin treatment resulted in methylation changes at selected, partially-methylated loci, instead of fully-methylated CpG sites. DNA methylation alterations were supported by corresponding changes in gene expression at both up- and down-regulated genes in various CRC cell lines.
Our data provide previously unrecognized evidence for curcumin-mediated DNA methylation alterations as a potential mechanism of colon cancer chemoprevention. In contrast to non-specific global hypomethylation induced by 5-aza-CdR, curcumin-induced methylation changes occurred only in a subset of partially-methylated genes, which provides additional mechanistic insights into the potent chemopreventive effect of this dietary nutraceutical.
最近的证据表明，几种膳食多酚可能通过表观遗传修饰发挥其化学预防作用。姜黄素是研究最多的用于预防结肠癌的膳食化学预防剂之一，但其对表观遗传改变（特别是 DNA 甲基化）的影响尚不清楚。本研究采用系统的全基因组方法，旨在阐明姜黄素对结直肠癌细胞中 DNA 甲基化改变的影响。
为了评估姜黄素对 DNA 甲基化的影响，用姜黄素处理三种 CRC 细胞系 HCT116、HT29 和 RKO。5-氮杂-2'-脱氧胞苷（5-aza-CdR）和曲古抑菌素 A 处理的细胞分别作为 DNA 甲基化变化的阳性和阴性对照。使用 LINE-1 重复元件的甲基化状态、DNA 启动子甲基化微阵列和基因表达阵列来评估整体甲基化和基因表达变化。通过独立的微阵列、定量亚硫酸氢盐焦磷酸测序和 qPCR 进行验证。
正如预期的那样，基因组范围的甲基化微阵列显示 5-aza-CdR 处理的细胞中存在显著的 DNA 低甲基化（平均β值为 0.12），但姜黄素处理的细胞中平均β值没有显著变化。与对照细胞相比，姜黄素诱导的 DNA 甲基化改变呈时间依赖性。与 5-aza-CdR 引起的普遍非特异性全基因组低甲基化不同，姜黄素处理导致了选定的、部分甲基化基因座而非完全甲基化 CpG 位点的甲基化改变。在各种 CRC 细胞系中，DNA 甲基化改变与上调和下调基因的相应基因表达变化相吻合。
本研究数据提供了以前未被认识到的证据，表明姜黄素介导的 DNA 甲基化改变可能是结肠癌化学预防的潜在机制。与 5-aza-CdR 诱导的非特异性全基因组低甲基化不同，姜黄素诱导的甲基化改变仅发生在一部分部分甲基化基因中，这为这种膳食营养补充剂的强效化学预防作用提供了额外的机制见解。
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