25-Hydroxyvitamin D Inhibits Hepatitis C Virus Production in Hepatocellular Carcinoma Cell Line by a Vitamin D Receptor-Independent Mechanism.

Previously, we have reported that the active vitamin D metabolite, calcitriol and vitamin D-3 (cholecalciferol), both remarkably inhibit hepatitis C virus production. The mechanism by which vitamin D-3 exerts its effect is puzzling due to the low levels of calcitriol produced in vitamin D-3-treated Huh7.5 cells. In this study, we aimed to explore the mechanism of vitamin D-3 anti-hepatitis C virus effect. We show that vitamin D-3 activity is not mediated by its metabolic conversion to calcitriol, but may be due to its primary metabolic product 25(OH)D-3. This is inferred from the findings that 25(OH)D-3 could inhibit hepatitis C virus production in our system, and that adequate concentrations needed to exert this effect are produced in Huh7.5 cells treated with vitamin D-3. Using the CRISPR-Cas9 editing technology to knockout the vitamin D receptor, we found that the antiviral activity of vitamin D-3 and 25(OH)D-3 was not impaired in the vitamin D receptor knockout cells. This result indicates that 25(OH)D-3 anti-hepatitis C virus effect is exerted by a vitamin D receptor-independent mode of action. The possibility that vitamin D-3 and 25(OH)D-3, being 3-hydroxysteroids, affect hepatitis C virus production by direct inhibition of the Hedgehog pathway in a vitamin D receptor-independent manner was ruled out. Taken together, this study proposes a novel mode of action for the anti-hepatitis C virus activity of vitamin D-3 that is mediated by 25(OH)D-3 in a vitamin D receptor-independent mechanism.