ABSTRACT
Background: Cancer cells are frequently characterized by hypomethylation of the genome including repetitive sequences. This epigenetic process is believed to be associated with several biological causes and consequences in cancer. Therefore, LINE-1 repetitive sequences demethylation in cancer should result in different clinical outcomes. Objective: Recently, we have developed an improved quantitative combined bisulfite restriction analysis PCR protocol that efficiently evaluates the methylation status of LINE-1s; the method is referred to as PCR “COBRALINE-1”. This article reviewed what have been learned by applying this technique to study methylation level of repetitive sequences from several sources of genomic DNA. Results: We have found that LINE-1 methylation patterns among normal tissues are distinct. Therefore, this epigenetic event may be continuously altered in adult tissues by the process of cellular differentiation. Moreover, we confirmed that global hypomethylation is an ongoing process that develops during tumor progression, in addition to previous evidence of genomic and LINE-1 hypomethylation occurring as an early event in carcinogenesis. COBRALINE-1 is a highly effective technique for evaluating the genome-wide level of methylation, in particular from tissue samples with minute amounts of low quality DNA. The technique has been applied to study samples from micro-dissected archived paraffin-embedded tissues and sera of several types of cancer. Conclusion: The COBRALINE-1 technique demonstrated its potential to be a tumor marker and a great tool to explore the biology of global hypomethylation.