Modified subcellular localization of interferon-induced p68 kinase during encephalomyocarditis virus infection

The double-stranded (ds) RNA-activated protein kinase from human cells is a 68,000 Mr protein (p68 kinase) induced by interferon. When autophosphorylated, p68 kinase catalyzes the phosphorylation of the protein synthesis eukaryotic initiation factor-2, thus mediating inhibition of protein synthesis. The level of p68 kinase is dramatically reduced in nonionic detergent NP-40 extracts, obtained from interferon-treated cells during infection with encephalomyocarditis virus (EMCV) (A. G. Hovanessian, J. Galabru, E. Meurs, C. Buffet-Janvresse, J. Svab and N. Robert, Virology 159, 126-136, 1987). Here we show that such reduction of p68 kinase is in fact due to its reduced NP-40 solubility occurring during EMCV infection. However, p68 kinase can be recovered by extraction with an ionic detergent. Reduced NP-40 extractibility of p68 kinase is dependent on the multiplicity of virus infection and seems to be specific, since other cellular proteins as well as the 100-kDa 2',5'-oligoadenylate synthetase also induced by interferon are not modified. Immunofluorescence studies using specific antibodies demonstrated that p68 kinase which is distributed evenly in the cytoplasm of HeLa cells becomes concentrated around the nuclei after EMCV infection. As a consequence of aggregating around the nuclei, p68 kinase might then resist extraction by NP-40. The aggregated kinase is found to be already activated probably due to binding to the replicative form and/or to replicative intermediates of EMCV RNA. Through this process, the functioning of p68 kinase might be guaranteed by a localized activation in the replication complexes of EMCV.