Alpha/beta interferons fail to induce antiviral activity from within the nucleus.

Electrophoretically pure murine alpha/beta interferons (IFN-alpha/beta) were microinjected directly into the nuclei of mouse L cells, each nucleus receiving 10 fl containing about 20,000 (IFN) molecules, an amount sufficient to induce the antiviral state when added to the culture medium of control cells. Three, six or 24 h after intranuclear delivery, the cells were challenged with vesicular stomatitis virus or Semliki Forest virus and the appearance of cytopathic effects was scored for each individual cell. The scoring of more than 1,000 intranuclearly injected cells in nine different experiments showed unambiguously that the intranuclear delivery of IFN-alpha/beta did not induce the antiviral state. The results argue strongly against the physiological importance of high-affinity nuclear binding sites for native IFN that have been recently described (V. M. Kushnaryov, H. S. MacDonald, G. P. Lemense, J. Debruin, J. J. Sedmak, and S. E. Grossberg, Cytobios 53:185-197, 1988). Together with earlier results of other groups describing the lack of IFN activity after intracytoplasmic injection (Y. Higashi and Y. Sokawa, J. Biochem. 91:2021-2028, 1982; G. Huez, M. Silhol, and B. Lebleu, Biochem. Biophys. Res. Commun. 110:155-160, 1983), these results lend weight to the hypothesis that the binding of IFN-alpha/beta to the plasma membrane receptor is sufficient to set into motion the complex mechanism of transmembrane signalling without requiring internalization of the bound IFN molecules.