Ribavirin up-regulates the activity of double-stranded RNA-activated protein kinase and enhances the action of interferon-alpha against hepatitis C virus.

Background: Ribavirin's mechanism of action in the treatment of chronic hepatitis C remains to be clarified. Double-stranded RNA-activated protein kinase (PKR) plays a role in cell defense against virus infection. This study investigated whether PKR is a mediator of the effectiveness of ribavirin, used either alone or in combination with interferon (IFN)- alpha , against hepatitis C virus (HCV) infection.

Methods: Primary human hepatocytes and HCV-replicon cells were treated with ribavirin and/or IFN- alpha . PKR activity was assayed by immunoblotting. A pulse-chase assay of the half-life of PKR protein was performed to study whether ribavirin decreases PKR degradation. We used small-interference RNA (siRNA) to knock down PKR to assess its importance in the suppression of HCV-RNA replication in the replicon system.

Results: Ribavirin was able to up-regulate the levels of phosphorylated PKR and phosphorylated eIF2 alpha , leading to suppression of HCV-RNA replication. The effects that treatment with ribavirin plus IFN- alpha had on PKR activity were greater than those observed for treatment with either ribavirin alone or IFN- alpha alone. Knockdown of PKR increased HCV-RNA replication, supporting the importance of PKR in the control of HCV-RNA replication. The pulse-chase experiment showed that ribavirin can reduce the degradation rate of PKR protein.

Conclusions: These results suggest that the anti-HCV action of ribavirin is partly attributable to its ability to up-regulate PKR activity.