Cell killing by viruses: III. The interferon system and inhibition of cell killing by vesicular stomatitis virus

Abstract

The dose response of cell killing particle (CKP) activity of vesicular stomatitis virus (VSV) in GMK Vero cells treated with interferon or mouse L cells treated with poly(rI)·poly(rC) was determined from single-cell survival curves, and compared with dose-response curves for infectivity and viral transcript accumulation. “Pulse-infection” with temperature-sensitive (ts) mutants of VSV was used to confine formation of putative cell killing factor or its precursors to the time equivalent of a single cycle of growth. Cells which through interferon or poly(rI)·poly(rC) action survived a pulse-infection with ts-mutant virus at permissive temperature produced colonies normal in both appearance and growth rate. Cells treated with interferon or poly(rI)·poly(rC) and challenged with VSV generated a family of survival curves for CKP activity whose slopes decreased as the dose of the interferon-interference inducer increased. These survival curves revealed that the capacity to express CKP activity or accumulate transcripts in interferon-treated Vero cells were both lost initially at an exponential rate about four to five times slower than that observed for the loss of plaque or yield reducing capacity, demonstrating that it required four to five times more interferon to prevent cell killing or transcript accumulation by VSV than was needed to reduce infectivity by an equivalent amount. A marked tailing of the survival curves was observed as the interferon dose was increased, resulting in surviving activity for CKP and transcript accumulation far in excess of that expected by extrapolation from low-dose regions of the curve. These results are discussed in light of our previous hypothesis which stated that viral transcription was a requisite, though insufficient reaction to produce cell killing by VSV and that integrity of about one-fifth of the viral genome sufficed to provide these transcripts (Marcus, P. I., and Sekellick, M. J. (1974). Virology 57, 321–338; (1975). Virology 63, 176–190). We extend this hypothesis and propose that the lethal action of VSV on cells requires: (i) functional virion transcriptase, (ii) transcription of a special one-fifth of the genome, most likely that coding for proteins N and NS, (iii) translation of these transcripts into minimally functional polypeptides which lead to (iv) formation and subsequent action by a putative cell killing factor.