Epigenetics and miRNAs in human cancer.

Epigenetic factors and microRNAs (miRNAs) are regulators of gene expression. Their regulatory function is frequently aberrant in cancer. In this chapter, we show that a tight connection occurs between miRNAs and epigenetics. Epigenetic factors can be responsible for the aberrancies of the miRNome (defined as the full spectrum of miRNAs for a specific genome) observed in cancer. Indeed, miRNAs undergo the same epigenetic regulatory laws like any other protein-coding gene. Moreover, a specific group of miRNAs (defined as epi-miRNAs) can directly target effectors of the epigenetic machinery (such as DNA methyltransferases, histone deacetylases, and polycomb repressive complex genes) and indirectly affect the expression of tumor suppressor genes, whose expression is controlled by epigenetic factors. The result of this epigenetic-miRNA interaction is a new layer of complexity in gene regulation, whose comprehension opens new avenues to understand human cancerogenesis and to achieve new cancer treatments.