Genetic and epigenetic factors in regulation of microRNA in colorectal cancers.

Studies on miRNA profiling revealed that a large number of them are significantly deregulated in human cancers. The molecular mechanisms of this deregulation are not totally clarified, even if genetics and epigenetics are frequently involved. Single nucleotide polymorphisms (SNPs) are the most common type of genetic variation in the human genome. A SNP into miRNA gene might affect the transcription of primary miRNA, its processing and miRNA–mRNA interaction. We investigated the distribution of sequence variants of miR-146a, miR-196a2, miR-499 and miR-149 in colorectal cancer (CRC) and their effect on miRNA expression. Each variant was identified with HRM. For miR-499 we demonstrated a significant reduction of its expression in CRC connected to a specific genotype. To evaluate the epigenetic effects on miRNA genes in CRC, we investigated the influence of DNA methylation on miR-34b, miR-34c and miR-9-1 expression. We aimed to verify the relationship between the methylation status of these miRNA genes and their relative expression in tumor samples. For the quantification of DNA methylation we adopted a method based on Differential High Resolution Melting (D-HRM).