Interferon induces morphologic reversion with elimination of extrachromosomal viral genomes in bovine papillomavirus-transformed mouse cells.

Abstract

The effect of mouse L-cell interferon on bovine papillomavirus type 1 (BPV-1) transformation of murine cells was examined. Mouse interferon reduced the level of BPV-1-induced transformation of mouse C127 cells by 95%. Long-term treatment of established BPV-1-transformed mouse cell clones with mouse L-cell interferon led to a decrease in the average number of the plasmid viral genomes present in these cells to 1/3-1/8. Although revertants could not be isolated from these lines in the absence of interferon treatment, flat revertants were easily selected from 2 independent clonal transformed lines carried for 60 generations in the continued presence of 200 U of interferon/ml. These flat revetants had the biological characteristics of nontransformed C127 cells and could be retransformed by BPV-1. Southern blot hybridization failed to detect BPV-1 DNA in any of 8 independent revertant lines examined under conditions that could detect 0.2 copies/cell. Evidently, interferon treatment selectively reduced the amount of extrachromosomal BPV-1 DNA in transformed cells and cured some treated cells completely of their viral DNA.