2′-5′ oligoadenylate synthetase plays a critical role in interferon-γ inhibition of respiratory syncytial virus infection of human epithelial cells

Abstract

Respiratory syncytial virus (RSV), associated with bronchiolitis and asthma, is resistant to the antiviral effects of type-I interferons (IFN), but not IFN-γ. However, the antiviral mechanism of IFN-γ action against RSV infection is unknown. The molecular mechanism of IFN-γ-induced antiviral activity was examined in this study using human epithelial cell lines HEp-2 and A549. Exposure of these cells to 100-1000 units/ml of IFN-γ, either before or after RSV infection, results in a significant decrease in RSV infection. After 1 h of exposure, IFN-γ induces protein expression of IFN regulatory factor-1 (IRF-1) but not IRF-2, double-stranded RNA-activated protein kinase, and inducible nitric-oxide synthase in these cells. The mRNA for IRF-1, p40, and p69 isoforms of 2′-5′ oligoadenylate synthetase (2-5 AS) are detectable, respectively, at 1 and 4 h of IFN-γ exposure. Studies using cycloheximide and antisense oligonucleotides to IRF-1 indicate a direct role of IRF-1 in activating 2-5 AS. Cells transfected with 2-5 AS antisense oligonucleotides inhibit the antiviral effect of IFN-γ. A stable cell line of HEp-2 overexpressing RNase L inhibitor, RLI-14, which exhibits an IFN-γ-induced gene expression pattern similar to that of the parent cell line, shows a significant reduction in RNase L activity and IFN-γ-mediated antiviral effect, compared with HEp-2 cells. These results provide direct evidence of the involvement of 2-5 AS in IFN-γ-mediated antiviral activity in these cells.