Anti-interferon activity of adenovirus-2-encoded VAI and VAII RNAs in translation in cultured human cells

Abstract

The mode of anti-interferon action of VAI and VAII RNAs of adenovirus type 2 (Ad2) was studied by transfecting interferon-α (IFN-α)-treated KB cells in culture with a plasmid construct containing the VAI or VAII RNA gene and an SV40 promoter-chloramphenicol acetyltransferase (CAT) gene construct as reporter (pSV2-CAT). The longer the treatment of KB cells with IFN-α (2000 IU/ml) lasted, the higher was the inhibition of CAT expression. A maximum of 76% inhibition was attained without pronounced cytotoxicity during 48 h of treatment. The earlier the VAI RNA gene was transfected, the higher was the enhancement of CAT expression. CAT activity increased from 113 to 157% in normal cells and 200–400% in IFN-α treated cells, as compared with the corresponding controls without VAI RNA transfection. The level of CAT mRNA was neither appreciably decreased by IFN-α treatment, nor detectably increased by VAI or VAII RNA. The effect of VA RNA thus appeared to be on translation rather than on transcription. The relative constancy of the level of CAT mRNA indicated that IFN-α inhibition of CAT expression was not due to the activation of RNase L, but due mainly to translational repression. The level of VAII RNA expressed was only 9–13% of that of VAI RNA. Nevertheless, VAII RNA gene transfection stimulated CAT activity to 112% of the control in non-IFN-α-treated cells, and 126–182% in IFN-α-inhibited cells. When IFN-α treatment was started late after VAI RNA cotransfection, CAT expression increased to 169% which was higher than the expression in cotransfected control cells without IFN-α treatment. The enhanced level of CAT activity was in remarkable contrast to the IFN-α inhibited level of 25% without VA RNA co-transfection when IFN-α was added upon seeding. The enhanced CAT activity in cells treated late with IFN-α could be ascribed to higher levels of VA RNAs.