Prostaglandins posttranscriptionally inhibit monocyte expression of interleukin 1 activity by increasing intracellular cyclic adenosine monophosphate.

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Abstract
The effect of prostaglandins and cyclic 3',5'-adenosine monophosphate (cAMP) on expression of human interleukin 1 (IL 1) activity was investigated in the promonocytic tumor cell line U937 and peripheral blood monocytes. After in vitro stimulation by bacteriotoxins, monocytes express IL 1 activity, as measured by the thymocyte costimulation assay. Although high doses of bacteriotoxins impaired expression of IL 1, this effect was reversed by indomethacin. When stimulated monocytes were cultured with exogenous prostaglandins, including PGE2 and PGI2, expression of IL 1 was reversibly inhibited. Interaction of U937 cells with PGE2 resulted in a transient increase in cellular cAMP concentration during the first hour of exposure. Other agents that cause an increase in levels of cellular cAMP, including theophylline, isobutylmethylxanthine, dibutyryl cAMP, or cholera toxin, also reversibly reduced expression of IL 1 by stimulated monocytes. The effect of these agents on levels of IL 1 mRNA was analyzed. TSS-stimulated increase in levels of IL 1-encoding mRNA was studied both by DNA-RNA hybridization analysis performed with an IL 1-beta cDNA probe and by injecting U937 polyadenylated mRNA into frog oocytes and then measuring expression of IL 1 activity in the oocyte supernatant. Agents that increased levels of cellular cAMP did not alter levels of IL 1 mRNA accumulation or global protein synthesis in TSS-stimulated U937 cells. IL 1 stimulates synthesis of prostaglandins that reach high levels during immune and inflammatory reactions. Our data suggest that prostaglandins participate in an autoregulatory pathway that posttranscriptionally reduces expression of IL 1 activity.