Effect Of Inhibitors Of Methylation On Early And Late Interferon Synthesis In Bovine Kidney-Cell-Cultures

In virus infected bovine kidney cell cultures mainly late interferon is produced starting at about 4 hr after infection. Poly rI:poly rC induced cells as well as interferon pretreated virus infected cells produce early interferon starting immediately after induction. In infected cells the proportion of early interferon increases with time of interferon pretreatment, while late interferon is decreasing. Production of late interferon is selectively inhibited by cycloleucine, an inhibitor of S-adenosylmethionine (SAM) biosynthesis, whereas early interferon synthesis is not affected by the drug. Likewise, late interferon production is reduced much stronger than early interferon production by a combination of adenosine, L-homocysteine thiolactone, and erythro-9[3-(2-hydroxynonyl)]-adenine (EHNA) inducing in cells an accumulation of S-adenosylhomocysteine which inhibits SAM mediated methylation reactions. Inhibition of late interferon synthesis by cycloleucine is time and dose dependent and partially reversible. Cycloheximide equally blocks both early and late interferon production. Inhibition of incorporation of methyl groups into cellular RNA by the methylation inhibitors used is demonstrated by labeling with [methyl-3H] methionine and 3H-uridine. The results indicate that the synthesis of functional mRNA for early and late interferon is differentially sensitive to inhibition of methylation. The data suggest that, if early and late interferon is coded by the same structural gene, two different pathways are available for the cell to synthesize one species of mRNA.