miRNAs in Melanoma: Tumor Suppressors and Oncogenes with Prognostic Potential

MicroRNAs (miRNAs), which are small non-coding RNA molecules that post-transcriptionally regulate the expression of target genes, control the vast majority of cellular events, including proliferation, differentiation, survival, senescence, autophagy, metabolism and genome stability. Even slight alterations in miRNA expression levels may induce the development of pathological states, including cancer. Several studies have already demonstrated the importance of miRNAs in the regulation of melanocytes. Upregulation of oncogenic miRNAs (oncomiRs), mainly by amplification and translocation of miRNA genes, and downregulation of oncosuppressor miRNAs (anti-oncomiRs) by deletion and other mutations, promoter methylation and abnormal processing contributes to melanoma initiation and progression. At each phase of melanoma progression, tumor cells exhibit distinct profiles of miRNA expression, as compared with normal melanocytes. Moreover, as miRNAs are stable molecules that can be identified in bodily fluids, such as blood and saliva, they can serve as potent non-invasive prognostic markers of disease progression and response to therapy. This review summarizes recent findings regarding miRNA-mediated control of melanocytes and melanoma development, and presents miRNAs as prognostic markers for this disease.