Epigenetic regulation of miR-196b expression in gastric cancer

MicroRNAs (miRNAs) are short noncoding RNAs that play important roles in cellular processes and disease pathogenesis via the control of specific targeted gene expression. The miR-196s miRNA is encoded at three paralogous loci in three HOX clusters and acts as an oncogenic miRNA in cancer progression. Recent studies have demonstrated that the expression of miR-196b increases cell proliferation and survival in leukemic cells. Here, we used a sequential methylation analysis to reveal that the methylation status correlated well with miR-196b expression in different cell lines. Treatment with the demethylating drug 5-Aza-dC reactivated miR-196b transcription in methylation-silenced cells. Using in vitro methylation approach, we further provide evidences that promoter hypermethylation represses miR-196b transcriptional activation tightly in human cancer cell lines. We also demonstrate that the expression of miR-196b is significantly elevated in gastric cancer and that hypomethylation status of miR-196b CpG islands frequently is observed in primary gastric tumors. Our results provide important information on miR-196s regulation and demonstrate that abnormal DNA hypomethylation induces overexpression of miR-196b in gastric cancer.