Role of MicroRNAs in cancer epigenetics

MicroRNAs (miRNAs) are small non-coding RNAs (ncRNAs) with gene expression regulatory functions. Increasing evidence shows that, despite not translated, miRNAs undergo the same regulatory mechanisms of any other protein coding gene (PCG). In particular, they undergo epigenetic regulation. Intriguingly, cancer cells are able to epigenetically regulate the expression of selected miRNAs, therefore granting an overall shift of the transcriptome towards an oncogenic phenotype. In parallel, miRNAs also directly target the expression of key effectors of the epigenetic machinery, therefore indirectly modulating the expression of epigenetically controlled PCGs. This intertwined relationship between the miRNome and the epigenome is further complicated by the existence of other categories of ncRNAs, also modulated by miRNAs and their epigenetic interactions. Overall, the complex layers of reciprocal regulation between ncRNAs and epigenetics are discussed in this chapter and represent a fundamental aspect of the biology of cancer cells.