Abstract
BACKGROUND AND AIMS: Hepatitis C virus (HCV) infection promotes hepatocyte growth and progress to hepatocellular carcinoma. We previously observed that HCV infection of hepatocytes transcriptionally down-regulates miR-181c expression through CCAAT/enhancer binding protein β (C/EBP-β). Here, we examined the role of miR-181c in the regulation of cell cycle progression in relation to HCV infection. In silico analysis suggested that ataxia-telangiectasia mutated (ATM) protein, a protein kinase, is a direct target of miR-181c. ATM is a central mediator of response for cellular DNA double-strand break. APPROACH AND RESULTS: Our results demonstrated that ATM expression is higher in HCV-infected hepatocytes and chronic HCV-infected liver biopsy specimens. We have shown a direct interaction of miR-181c with the 3' untranslated region of ATM, and the presence of ATM in miR-181c-associated RNA-induced silencing complex. Exogenous expression of miR-181c inhibited ATM expression and activation of its downstream molecules, Chk2 and Akt. On the other hand, introduction of anti-miR-181c restored ATM and phosphorylated Akt. Furthermore, introduction of miR-181c significantly inhibited phospho-cyclin-dependent kinase 2 (CDK2) and cyclin-A expression, arresting cell cycle progression, whereas overexpression of miR-181c promoted apoptosis of HCV-infected hepatocytes and can be inhibited by overexpression of ATM from a clone lacking miR-181c binding sites. In addition, miR-181c significantly regressed tumor growth in the xenograft human hepatocellular carcinoma mouse model. CONCLUSIONS: Together, our results suggest that HCV infection suppresses miR-181c in hepatocytes, resulting in ATM activation and apoptosis inhibition for promotion of cell cycle progression. The results provide mechanistic insight into understanding the role of miR-181c in HCV-associated hepatocyte growth promotion, and may have the potential for therapeutic intervention.