Methylation of microRNA Genes and Oncogenesis (review)
The interaction of miRNA with messenger RNA of target genes at posttranscriptional level realizes fine and dynamic regulation of cell signaling pathways. Each miRNA can participate in regulation of hundreds of genes coding proteins; and vice versa, a structural gene usually presents a target for a set of miRNAs. Epigenetic inactivation associated with methylation of promoter CpG-islands is typical both of protein-coding genes and that of miRNA genes. In the present review, data concerning miRNA functions in tumor cell phenotype development are given. Information is presented on genome the organization of promoter CpG-islands of miRNA genes located in intergenic and intragenic regions. The literature as well as our own data on miRNA gene methylation frequency in tumors is summarized. Data on relationship of this modification with alteration of miRNA gene activity and, as a consequence, with that of target protein-coding genes are reported. In addition, data on the influence of miRNA gene methylation on key processes of carcinogenesis and the cell signaling pathways involved are discussed.