p48 Overexpression enhances interferon-mediated expression and activity of double-stranded RNA-dependent protein kinase in human hepatoma cells.
OBJECTIVE
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.
Tamada
Yoko
Y
Department of Clinical Pharmacology, Nagasaki University, 1-7-1 Sakamoto, Nagasaki 852-8501, Japan.
Nakao
Kazuhiko
K
Nagayama
Yuji
Y
Nakata
Keisuke
K
Ichikawa
Tatsuki
T
Kawamata
Yosei
Y
Ishikawa
Hiroki
H
Hamasaki
Keisuke
K
Eguchi
Katsumi
K
Ishii
Nobuko
N
D000998:Antiviral Agents / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular; D004268:DNA-Binding Proteins / Q000235:genetics*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D019698:Hepatitis C, Chronic / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha / Q000494:pharmacology*; D008113:Liver Neoplasms; D012330:RNA, Double-Stranded / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured; D019892:eIF-2 Kinase / Q000235:genetics* / Q000378:metabolism
D000998:Antiviral Agents; D004268:DNA-Binding Proteins; D015852:Eukaryotic Initiation Factor-2; C494227:IRF9 protein, human; D050832:Interferon-Stimulated Gene Factor 3; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D016898:Interferon-alpha; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D014157:Transcription Factors; D019892:eIF-2 Kinase