Iacopetta Barry, Grieu Fabienne, Phillips Michael, Ruszkiewicz Andrew, Moore James, Minamoto Toshinari, Kawakami Kazuyuki
School of Surgery and Pathology, WA Institute for Medical Research, University of Western Australia, 35 Stirling Highway, Nedlands 6009, Australia.
Cancer Sci. 2007 Sep;98(9):1454-60. doi: 10.1111/j.1349-7006.2007.00548.x. Epub 2007 Jul 19.
Hypermethylation of CpG island loci within gene promoter regions is a frequent event in colorectal cancer that is often associated with transcriptional silencing and has been referred to as CIMP+. DNA hypomethylation can occur in concert with CIMP+, although these two phenomena appear not to be related in colorectal cancer. The authors investigated here whether the methylation level of LINE-1 repeats, a surrogate marker for genomic methylation, was associated with the level of CpG island methylation in colorectal cancers and in matching normal colonic mucosa from 178 patients. The MethyLight assay was used to quantitate the methylation of CpG islands within the MLH1, P16(INK4A), TIMP3, DAPK, APC, ER and MYOD genes. A real-time, methylation-specific polymerase chain reaction assay was also used to quantitate the methylation of LINE-1 repeats. In colorectal cancer, no associations were seen between methylation levels in LINE-1 repeats and CpG island loci, including a new CpG island panel that was recently proposed for CIMP+. In normal colonic mucosa, however, the methylation level of LINE-1 repeats was inversely correlated with CpG-island methylation of the MLH1, P16, TIMP3, APC, ER and MYOD genes. The methylation level of LINE-1 repeats in normal colonic mucosa also showed significant associations with common polymorphisms in the methylene tetrahydrofolate reductase and methylene tetrahydrofolate dehydrogenase genes involved in methyl group metabolism. Further investigation of genomic and CpG island methylation in normal colonic mucosa and the possible influences of environmental and genetic factors may provide new insights into the development of CIMP+ colorectal cancer.
基因启动子区域内CpG岛位点的高甲基化在结直肠癌中是常见事件，常与转录沉默相关，被称为CIMP+。DNA低甲基化可与CIMP+同时发生，尽管在结直肠癌中这两种现象似乎并无关联。作者在此研究了作为基因组甲基化替代标志物的LINE-1重复序列的甲基化水平，是否与178例患者的结直肠癌及配对的正常结肠黏膜中CpG岛的甲基化水平相关。采用MethyLight分析法对MLH1、P16(INK4A)、TIMP3、DAPK、APC、ER和MYOD基因内CpG岛的甲基化进行定量。还采用实时甲基化特异性聚合酶链反应分析法对LINE-1重复序列的甲基化进行定量。在结直肠癌中，未发现LINE-1重复序列的甲基化水平与CpG岛位点之间存在关联，包括最近为CIMP+提出的一个新的CpG岛组。然而，在正常结肠黏膜中，LINE-1重复序列的甲基化水平与MLH1、P16、TIMP3、APC、ER和MYOD基因的CpG岛甲基化呈负相关。正常结肠黏膜中LINE-1重复序列的甲基化水平还与参与甲基代谢的亚甲基四氢叶酸还原酶和亚甲基四氢叶酸脱氢酶基因的常见多态性存在显著关联。对正常结肠黏膜中的基因组和CpG岛甲基化以及环境和遗传因素可能产生的影响进行进一步研究，可能会为CIMP+结直肠癌的发生发展提供新的见解。
