Epigenetic regulation of microRNA expression in cancer

Epigenetic gene regulation is important in human cancer. Both functional and observational data implicate alterations of histone modifications, DNA promoter methylation, and non-coding RNA expression in carcinogenic roles. We sought to explore the role of aberrant DNA hypermethylation in the regulation of microRNA (miR) expression in human cancer. From human genome databases we calculated that 13 and 28% of human miR genes are located within 3 and 10 kb of a CpG island, respectively. To identify miRs that are regulated by epigenetic mechanisms in cancer, we performed expression profiling prior to and following treatment of cell lines with 5-azacytidine. We used oligonucleotide microarrays to determine miR expression. For miRs whose expression changed following 5-azacytidine treatment, we sequenced the adjacent CpG island and promoter using bisulphite-treated DNA. Here, we describe these methods to enable other researchers to use this approach.