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.
Liu
Wei-Liang
WL
Graduate Institute of Molecular Medicine, National Taiwan University College of Medicine, Taipei, Taiwan.
Su
Wen-Cheng
WC
Cheng
Ching-Wei
CW
Hwang
Lih-Hwa
LH
Wang
Chih-Chiang
CC
Chen
Hui-Ling
HL
Chen
Ding-Shinn
DS
Lai
Ming-Yang
MY
D000998:Antiviral Agents / Q000494:pharmacology; D002478:Cells, Cultured; D004359:Drug Therapy, Combination; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D016174:Hepacivirus / Q000187:drug effects*; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D012367:RNA, Viral / Q000378:metabolism; D012254:Ribavirin / Q000494:pharmacology*; D015854:Up-Regulation; D014779:Virus Replication; D019892:eIF-2 Kinase / Q000378:metabolism*
D000998:Antiviral Agents; D016898:Interferon-alpha; D012367:RNA, Viral; D012254:Ribavirin; D019892:eIF-2 Kinase