Inhibitory effect of interferon on cellular DNA synthesis: modulation by pure mitogenic factors

Quiescent Swiss 3T3 cells can be stimulated to synthesize DNA by combinations of polypeptide hormones, retinoids and tubulin-disrupting agents. Low doses of mouse interferon are effective in inhibiting DNA synthesis induced by one, two or three factors. When more growth factors are added DNA synthesis is not further stimulated, although the dose response curve for interferon is shifted dramatically to the right. Even when added before the mitogenic stimulus, up to 2000 units of interferon have no effect on DNA synthesis stimulated by five factors. A change in the dose-response curve for interferon as an antiviral agent is also observed when the mitogenic stimulation is increased, but the effect is less dramatic than that observed on its function as an inhibitor or DNA synthesis.