Description: Some miRNA genes harboring CpG-islands undergo methylation-mediated silencing, a characteristic of many tumor-suppressor genes. To identify such miRNAs in hepatocellular carcinoma (HCC), we first examined the methylation status of 43 loci containing CpG-islands around 39 mature miRNA genes in a panel of HCC cell lines and non-cancerous liver tissues as controls. Among 11 miRNA genes frequently methylated in HCC cell lines but not in non-cancerous liver tissues, 3 miRNA genes, i.e. miR-124, miR-203, and miR-375, were selected as silenced miRNAs through CpG-island methylation by comparing methylation and expression status and evaluating restored expression after treatment with 5-aza-2'-deoxycytidine. In primary tumors of HCC with paired non-tumorous liver tissues, only miR-124 and miR-203 showed frequent tumor-specific methylation, and their expression status was inversely correlated with methylation status. Ectopic expression of miR-124 or miR-203 in HCC cells lacking their expression inhibited cell growth, with direct down-regulation of possible targets, cyclin-dependent kinase 6 (CDK6), vimentin (VIM), SET and MYND domain containing 3 (SMYD3), and IQ motif containing GTPase activating protein 1 (IQGAP1) or ATP-binding cassette, sub-family E, member 1 (ABCE1), respectively. Our results suggest that miR-124 and miR-203 are novel tumor-suppressive miRNAs for HCC epigenetically silenced and activating multiple targets during hepatocarcinogenesis. |
