Clinical implications of the LINE-1 methylation levels in patients with gastrointestinal cancer.

Epigenetic alterations, such as DNA methylation, histone modification and the loss of genome imprinting, are important indicators of human carcinogenesis. DNA methylation is a fundamental epigenetic process that modulates the gene expression levels. In cancer cells, DNA methylation may be altered in two principle ways: global DNA hypomethylation and site-specific CpG island promoter hypermethylation. Long interspersed element-1 (LINE-1 or L1) is a repetitive DNA retrotransposon that duplicates via a copy-and-paste genetic mechanism. Since LINE-1 constitutes a substantial portion (approximately 17 %) of the human genome, the extent of LINE-1 methylation is regarded to be a surrogate marker of global DNA methylation. Measuring the level of LINE-1 methylation using pyrosequencing technology has emerged as a cost-effective and high-throughput method for assessing the global DNA methylation status. In some types of gastrointestinal (GI) cancers, LINE-1 hypomethylation is strongly associated with a poor prognosis, supporting its potential role as a prognostic marker. In addition, the LINE-1 methylation level may prove to be a useful clinical biomarker for assessing the risk of cancer or predicting the chemotherapeutic efficacy of treatment in patients with GI cancers. In this article, we summarize current knowledge regarding LINE-1 methylation and its clinical implications in GI cancers, including colorectal cancer, gastric cancer and esophageal cancer.