School of Medical Sciences, University of NSW, Sydney, Australia.
Mod Pathol. 2009 Dec;22(12):1588-99. doi: 10.1038/modpathol.2009.130. Epub 2009 Sep 4.
O(6)-methylguanine DNA methyltransferase (MGMT) is a DNA repair protein that restores mutagenic O(6)-methylguanine to guanine. MGMT methylation is frequently observed in sporadic colorectal cancer and was recently correlated with the C>T allele at SNP rs16906252, within the transcriptional enhancer element of the promoter. MGMT methylation has also been associated with KRAS mutations, particularly G>A transitions. We studied 1123 colorectal carcinoma to define the molecular and clinicopathological profiles associated with MGMT methylation. Furthermore, we assessed factors contributing to MGMT methylation in the development of colorectal cancer by studying the allelic pattern of MGMT methylation using SNP rs16906252, and the methylation status of neighbouring genes within 10q26 in selected tumours and matched normal colonic mucosa. MGMT methylation was detected by combined bisulphite restriction analysis in 28% of tumours and was associated with a number of characteristics, including CDKN2A methylation, absent lymphovascular space invasion and KRAS mutations (but not specifically with KRAS G>A transitions). In a multivariate analysis adjusted for age and sex, MGMT methylation was associated with the T allele of SNP rs16906252 (P<0.0001, OR 5.5, 95% CI 3.8-7.9). Low-level methylation was detected by quantitative methylation-specific PCR in the normal colonic mucosa of cases, particularly those with a correspondingly methylated tumour, as well as controls without neoplasia, and this was also associated with the C>T SNP. We show that the T allele at SNP rs16906252 is a key determinant in the onset of MGMT methylation in colorectal cancer, whereas the association of methylation at MGMT and CDKN2A suggests that these loci may be targets of a common mechanism of epigenetic dysregulation.
O(6)-甲基鸟嘌呤-DNA 甲基转移酶（MGMT）是一种 DNA 修复蛋白，可将致突变的 O(6)-甲基鸟嘌呤恢复为鸟嘌呤。MGMT 甲基化在散发性结直肠癌中经常观察到，并且最近与 SNP rs16906252 处的 C>T 等位基因相关，该基因位于启动子的转录增强子元件内。MGMT 甲基化也与 KRAS 突变有关，特别是 G>A 转换。我们研究了 1123 例结直肠癌，以确定与 MGMT 甲基化相关的分子和临床病理特征。此外，我们通过研究 SNP rs16906252 处 MGMT 甲基化的等位基因模式以及在选定肿瘤和匹配的正常结肠黏膜中 10q26 内邻近基因的甲基化状态，评估了 MGMT 甲基化在结直肠癌发生中的作用。通过联合亚硫酸氢盐限制分析检测到 28%的肿瘤存在 MGMT 甲基化，并且与多种特征相关，包括 CDKN2A 甲基化、无淋巴血管空间侵犯和 KRAS 突变（但与 KRAS G>A 转换无关）。在调整年龄和性别因素的多变量分析中，MGMT 甲基化与 SNP rs16906252 的 T 等位基因相关（P<0.0001，OR 5.5，95%CI 3.8-7.9）。在病例的正常结肠黏膜中通过定量甲基化特异性 PCR 检测到低水平的甲基化，特别是那些相应甲基化肿瘤的病例，以及无肿瘤的对照，这也与 C>T SNP 相关。我们表明，SNP rs16906252 处的 T 等位基因是结直肠癌中 MGMT 甲基化发生的关键决定因素，而 MGMT 和 CDKN2A 甲基化的相关性表明这些基因座可能是表观遗传失调的共同机制的靶点。
