p48 Overexpression enhances interferon-mediated expression and activity of double-stranded RNA-dependent protein kinase in human hepatoma cells.

Background/aims: Double-stranded RNA-dependent protein kinase (PKR) is a key factor involved in interferon (IFN)-induced antiviral actions. Since p48, together with signal transducers and activators of transcription 1 and 2 (STAT1 and STAT2), is an indispensable mediator in IFN-alpha signaling pathways, we investigated the effect of p48 gene transduction on PKR expression and its activity in HuH-7 human hepatoma cells.

Methods: HuH-7 cells were infected or transfected with p48 gene expression adenoviral vector or plasmid vector, respectively, and incubated with or without IFN-alpha, then PKR expression and phosphorylation of alpha-subunit of eukaryotic protein synthesis initiation factor-2 (eIF2alpha) in the cells were examined. In addition, PKR activity inhibiting protein translation was determined by the decrease of chloramphenicol acetyltransferase (CAT) gene translation or alpha-fetoprotein secretion.

Results: p48 overexpression itself could not stimulate PKR expression. However, p48 overexpression in combination with interferon-alpha treatment caused a marked increase in PKR expression and augmented the phosphorylation of eIF2alpha, by which the transfected CAT gene translation, as well as the endogenous alpha-fetoprotein synthesis, was blocked without affecting their mRNA levels.

Conclusions: These results suggest that p48 gene transduction may provide a strategy to enhance the IFN-mediated PKR expression and its activity in hepatocytes.