MiRNAs, epigenetics, and cancer.

By virtue of having multiple targets, a microRNA (miRNA) can have variable effects on oncogenesis by acting as tumor suppressor or oncogene in a context-dependent manner. Genome-wide epigenetic changes that occur in various cancers affect the transcription of many genes. Since the transcriptional regulation of miRNAs remains an unexplored field, it is still unknown how epigenetic changes will affect the regulation of miRNAs. Many miRNAs are intron-bound within the body of a protein-coding gene. Any change to the transcription of the "host" gene affects the transcription and genesis of the resident miRNA. It is therefore reasonable to deduce that epigenetic changes brought on by transformation can potentially affect miRNA expression in both direct and indirect ways. We have reviewed the literature pertaining to the epigenetic regulation of miRNA genes in the context of various cancers and have speculated on the potential role of epigenetic modifications on the transcriptional regulation and expression of these genes.