BACKGROUND: Clinical studies demonstrate synergistic liver damage by alcohol and hepatitis C virus (HCV); however, the mechanisms by which alcohol promotes HCV infection remain obscure. The liver-specific microRNA-122 (miR-122) regulates HCV replication and expression of host genes, including Cyclin G1. Here, we hypothesized that alcohol regulates miR-122 expression and thereby modulates HCV RNA replication.

METHODS: The J6/JFH/Huh-7.5 model of HCV infection was used in this study. Real-time quantitative polymerase chain reaction, Western blotting, electrophoretic mobility shift assay, and confocal microscopy were used for experimental analysis.

RESULTS: We found that acute alcohol exposure (25 mM) significantly increased intracellular HCV RNA as well as miR-122 levels in Huh-7.5 and Huh-7.5/CYP2E1 expressing cells in the presence and absence of J6/JFH-HCV infection. Expression of the miR-122 target, Cyclin G1, was inhibited by alcohol both in J6/JFH-infected and uninfected Huh-7.5 cells. The use of a miR-122 inhibitor increased Cyclin G1 expression and prevented the alcohol-induced increase in HCV RNA and protein levels, suggesting a mechanistic role for alcohol-induced miR122 in HCV replication. We discovered that siRNA-mediated silencing of Cyclin G1 significantly increased intracellular HCV RNA levels compared with controls, suggesting a mechanistic role for Cyclin G1 in HCV replication. Alcohol-induced increase in miR-122 was associated with increased nuclear translocation and DNA binding of the nuclear regulatory factor-kappaB and could be prevented by NF-kappaB inhibition.

CONCLUSIONS: Our novel data indicate a miR-122-mediated mechanism for alcohol increasing HCV RNA replication. We show for the first time that Cyclin G1, a miR-122 target gene, has regulatory effects on HCV replication and that alcohol increases HCV replication by regulating miR-122 and Cyclin G1.