Mechanism of interferon action. Interferon alpha inhibits vesicular stomatitis virus primary transcript accumulation in P1/eIF-2 alpha protein kinase-deficient human fibroblast cells.

The molecular basis of the inhibition of vesicular stomatitis virus (VSV) replication by purified recombinant alpha interferon (IFN-alpha A/D) in human fibroblast GM2767A cells was examined. A saturating concentration of IFN-alpha A/D inhibited infectious VSV yield by about four to five log10. By use of the VSV mutant tsG41, which is competent in RNA transcription but defective in RNA replication at 40 degrees C, it was shown that IFN-alpha A/D treatment significantly inhibited primary viral protein synthesis. However, the apparent IFN-induced inhibition of VSV protein synthesis was due primarily to a reduction in the accumulation of VSV primary transcripts in IFN-alpha A/D treated GM2767A cells rather than to a direct effect on translation per se. The IFN-induced reduction in VSV primary genome expression was detectable after only 1 hour of IFN treatment; actinomycin D treatment of GM2767A cells prior to IFN-alpha A/D treatment blocked the establishment of the IFN-induced inhibition of VSV. In contrast to the results obtained with GM2767A cells, IFN-alpha A/D produced no detectable effect on the accumulation of VSV primary transcripts in human amnion U cells even though VSV primary protein synthesis and infectious virus yield were significantly reduced. In summary, the principal cause of the IFN-alpha induced inhibition of VSV replication in protein P1/eIF-2 alpha kinase-deficient human fibroblast GM2767A cells appears to be at or prior to primary transcript accumulation; thus, the antiviral mechanisms of IFN-alpha in GM2767A cells is fundamentally different from the IFN-alpha induced translation inhibition observed in kinase-sufficient human amnion U cells.