Enhancement of human interferon production by neutral red and chloroquine: analysis of inhibition of protein degradation and macromolecular synthesis

Two lysosomotrophic drugs, neutral red and chloroquine, enhance polyinosinic:polycytidylic acid-induced interferon production by a strain of diploid human fibroblasts (FS-4). Treatment of cells with neutral red or chloroquine between 2.5 and 3.5 h after induction increases interferon yields 16- to 64- and 4- to 16-fold, respectively, in the subsequent 20.5 h. The two drugs inhibit the rates of protein degradation and of RNA and protein synthesis. In addition, neutral red is a very potent inhibitor of uridine transport into cells. Normalized dose-effect curves show that interferon superinduction is correlated with the inhibition of macromolecular synthesis, but not with that of protein degradation. Treatment of cells with chloroquine at low concentration (25 mug/ml) for a prolonged period of time (24 h) caused approximately 40% reduction in the rate of protein degradation. The usual rapid shutoff of interferon production and the effectiveness of effectiveness of actinomycin D superinduction are not altered by this treatment. This strongly suggests that inhibition of intralysosomal protein degradation does not significantly contribute to interferon superinduction. Degradation of the rapidly and the slowly turning over proteins was unaffected by actinomycin D under conditions of treatment known to enhance interferon production. Treatment with cycloheximide (5 or 50 mug/ml for 5 h) inhibited the rate of degradation of the rapidly turning over component by 10% and the slow component by 30-40%, which suggests that the two components turn over by distinct cellular mechanisms.