Abstract
miRNAs have recently been implicated in hepatocarcinogenesis, although the actions and mechanisms of individual miRNAs remain incompletely understood. We examined the biological functions and molecular mechanisms of miR-185 in hepatocellular carcinoma (HCC). The expression of miR-185 is decreased in human HCC tissues compared with the nonneoplastic liver parenchyma. Quantitative RT-PCR showed a reduction of miR-185 in human HCC cells compared with primary hepatocytes. miR-185 overexpression in human HCC cells inhibited cell proliferation and invasion in vitro and prevented tumor growth in SCID mice. miR-185 overexpression inhibited DNMT1 3' untranslated region luciferase reporter activity in HCC cells; this effect was abolished when the miR-185 binding site was mutated. miR-185 mimic or overexpression decreased the level of DNMT1 protein in HCC cells. These findings establish DNMT1 as a bona fide target of miR-185 in HCC cells. The role of DNMT1 in miR-185-induced inhibition of HCC growth was further supported by the fact that DNMT1 overexpression prevented miR-185-induced inhibition of HCC cell proliferation/invasion. miR-185 mimic or overexpression reduced PTEN promoter DNA methylation and enhanced PTEN expression, leading to the inhibition of Akt phosphorylation; these effects were partially reversed by DNMT1 overexpression. These results provide novel evidence that miR-185 inhibits HCC cell growth by targeting DNMT1, leading to PTEN induction and Akt inhibition. Thus, reactivation or induction of miR-185 may represent a novel therapeutic strategy for HCC treatment.