Kinetics of decay in the expression of interferon-dependent mRNAs responsible for resistance to virus

We used 5,6-dichloro-beta D-ribofuranosyl-benzimidazole (DRB), a selective and reversible inhibitor of mRNA production, to investigate the regulation of the pathway leading to resistance to viruses in cells treated with interferon (IF). DRB allows initiation of transcription but promotes premature termination of the nucleotide chains, so that it abolishes interferon-dependent protection against viruses. When the DRB is removed, synthesis of complete mRNAs can resume. Mouse L-929 cells were exposed to 100 microM DRB before and during a 1-hr pulse of IF followed by treatment with antibody to IF to prevent cell-to-cell spread of IF after that time. At different intervals thereafter the cells were washed and the DRB was replaced by medium; after further incubation, the cells were infected with vesicular stomatitis virus. Resistance to virus was inversely proportional to the duration of the block imposed by DRB. When the DRB was removed soon after the IF pulse, substantial protection from virus ensued, but none developed when removal of the DRB was deferred for 5-6 hr. Cells exposed to DRB for 5 hr, then pulsed with IF for 1 hr, still mounted a strong antiviral response. The data show that the ability of cells to resist viral infection decays within 5-6 hr after treatment with IF. Whether the decay is due to shutoff of transcription of mRNAs, or to their destruction or degradation, or whether regulation takes place at one or more subsequent steps in the antiviral pathway, remains to be determined.