Protein kinase R is increased and is functional in hepatitis C virus-related hepatocellular carcinoma.

Abstract

Protein kinase R (PKR) interacts with dsRNA and phosphorylates eukaryotic initiation factor-2 (eIF2alpha), which in turn inhibits host translation initiation as well as hepatitis C virus (HCV) translation. Because PKR inhibits host cell growth and proliferation, it has also been proposed to act as a eukaryotic tumor suppressor. To evaluate the role of PKR in HCV-related hepatocellular carcinoma (HCC), we compared PKR and related protein expression in paired tumor (T) and surrounding nontumor (NT) tissue. Tissue samples were obtained from 12 HCV-infected HCCs. To determine PKR and related protein expression, Western blotting and semiquantitative reverse transcriptase-polymerase chain reaction were performed. PKR protein levels were consistently increased in HCV-related HCC compared with NT (p=0.001); similar increases were seen in total eIF2alpha and the PKR inhibitor p58IPK in T compared with NT (p=0.022, p=0.048, respectively). Relative increases in phosphorylated eIF2alpha (peIF2alpha) were also seen, and the ratio of peIF2alpha/total eIF2alpha did not change in T compared with NT, suggesting that PKR remains functional within T. Cytoplasmic levels of HCV RNA within T were decreased compared with NT. These findings indicate that PKR has increased activity in human HCC compared with LC, and suggest that PKR acts as a growth inducer in HCC.