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. CONCLUSION: These results suggest that the anti-HCV action of ribavirin is partly attributable to its ability to up-regulate PKR activity.
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. CONCLUSION: These results suggest that the anti-HCV action of ribavirin is partly attributable to its ability to up-regulate PKR activity.
Authors: Jordan J Feld; Glen A Lutchman; Theo Heller; Koji Hara; Julie K Pfeiffer; Richard D Leff; Claudia Meek; Maria Rivera; Myung Ko; Christopher Koh; Yaron Rotman; Marc G Ghany; Vanessa Haynes-Williams; Avidan U Neumann; T Jake Liang; Jay H Hoofnagle Journal: Gastroenterology Date: 2010-03-17 Impact factor: 22.682
Authors: Nigel J Stevenson; Alison G Murphy; Nollaig M Bourke; Catherine A Keogh; John E Hegarty; Cliona O'Farrelly Journal: PLoS One Date: 2011-11-16 Impact factor: 3.240