DNA hypermethylation encroachment at CpG island borders in cancer is predisposed by H3K4 monomethylation [TAB-Seq]

DNA methylation plays a key role in demarcation of regulatory regions, including promoter-associated CpG islands. While CpG islands are typically maintained in an unmethylated state in normal cells, a proportion of CpG islands are subject to hypermethylation in cancer cells. It still remains elusive how the exquisite demarcation of the bimodal methylation state is established and maintained at the CpG island flanks and conversely what triggers the erosion of CpG island DNA methylation in tumorigenesis. Here, we applied whole-genome bisulphite sequencing to study the comprehensive methylation patterns of prostate normal and cancer tissues. Alongside we performed TET-assisted bisulphite sequencing to study genome-wide DNA hydroxymethylation patterns of normal prostate and prostate cancer tissues. Overall design: To investigate DNA hydroxymethylation patterns at CpG islands in normal prostate and prostate cancer, TET-assisted bisulphite treatment of 3 pairs of clinical benign-tumor samples was performed using the 5hmC TAB-seq Kit (WiseGene, USA, cat no K001).