MicroRNAs and Epigenetics.

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression mainly at the posttranscriptional level. Similar to protein-coding genes, their expression is also controlled by genetic and epigenetic mechanisms. Disruption of these control processes leads to abnormal expression of miRNAs in cancer. In this chapter, we discuss the supportive links between miRNAs and epigenetics in the context of carcinogenesis. miRNAs can be epigenetically regulated by DNA methylation and/or specific histone modifications. However, they can themselves (epi-miRNAs) repress key enzymes that drive epigenetic remodeling and also bind to complementary sequences in gene promoters, recruiting specific protein complexes that modulate chromatin structure and gene expression. All these issues affect the transcriptional landscape of cells. Most important, in the cancer clinical scenario, knowledge about miRNAs epigenetic dysregulation can not only be beneficial as a prognostic biomarker, but can also help in the design of new therapeutic approaches.