Distinct patterns of IFN sensitivity observed in cells infected with vaccinia K3L- and E3L- mutant viruses

Recent results have implicated a role for both the VV K3L- and E3L-encoded gene products in conferring VV with an IFN-resistant phenotype (Beattie et al., Virology 183, 419-422, 1991; Beattie et al., J. Virol. 69, 499-505, 1995). As a means of further establishing the mechanisms by which these functions mediate this process in VV-infected cells, we have further assessed the IFN phenotype in K3L- (vP872) and E3L- (vP1080) virus-infected cells. Biochemical and molecular biological analyses were performed comparing the effects of IFN on wild-type as well as K3L- and E3L- virus-infected cells. Expression analyses of the K3L and E3L gene products revealed that both are evidenced in virus-infected cells as early as 0.5 hr postinfection. E3L expression, however, appears more prolonged, in that it was detectable between 3 to 4 hr postinfection while K3L was undetectable after 3 hr postinfection. Despite having similar expression profiles at early times postinfection, a pronounced sensitivity of protein synthesis to IFN was observed by 30 min postinfection in VV K3L- virus-infected cells, whereas IFN sensitivity was not observed in VV E3L(-)-infected cells until 2 hr postinfection. Subsequent analyses of the IFN-induced antiviral pathways in VV-infected cells demonstrated that the K3L gene product does not contribute to the previously identified specific kinase inhibitory factor (SKIF) activity but does reduce the level of phosphorylated eIF-2 alpha in VV-infected cells. Interestingly, the IFN-induced 2',5'-oligoadenylate synthetase-mediated antiviral pathway was active in VV K3L(-)-infected cells and not in wild-type virus-infected cells. Collectively these results suggest that the K3L(-)- and E3L(-)-encoded products abrogate the antiviral effect of IFN at distinct levels.