Interferon-χ but not -β Genes Require De Novo Protein Synthesis for Efficient Expression in Human Monocytes.

Monocytes produce interferon-α (IFN-α) and -β when human peripheral blood mononuclear cells (PBMCs) are stimulated in vitro by Sendai virus (SV). We found that about 70% of the IFN-producing cells (IPCs) expressed both IFN-α and -β mRNA; the rest expressed only IFN-β mRNA. In the presence of the protein synthesis inhibitor cycloheximide(CMX), the frequency of IFN-α mRNA-containing cells, measured after 6h, was decreased by 85-90%. Results of nuclear run-on transcription assays showed that CHX inhibited IFN-α gene expression. The frequency of IFN-α mRNA-containing cells was not reduced by CHX. Actually, a threefold increase was observed at the lower CHX concentrations. Studies on the kinetics of IFN-α/β mRNA induction showed that CHX accelerated the appearance of IFN-β mRNA-containing cells, increased IFN-β mRNA levels, and delayed the normally occurring post-inductional decrease of IFN-β mRNA. Unexpectedly, an initially normal or even accelerated IFN-α mRNA response was seen in the presence of CHX during the first 3-4 h after SV stimulation. This occurred in a small proportion of the potential IPCs. However. CHX prevented the subsequent marked increase of IFN-α mRNA levels. Preincubation of PBMCs for 6 h in conditioned medium (CM) containing IFN and other cytokines prevented the CHX-mediated inhibition of IFN-α mRNA. Without preincubation this was not seen. The preincubation in CM caused an accelerated appearance of IFN-α mRNA. resembling that of IFN-β mRNA. The results suggest that IFN-α and -β genes are differentially regulated in the same monocytes, the former requiring de novo synthesis of intracellular protein(s) for efficient expression. [ABSTRACT FROM AUTHOR]