Glucocorticoids inhibit calcium- and calcineurin-dependent activation of the human IL-4 promoter

The mechanism by which glucocorticoids (GC) inhibit IL-4 gene expression is currently unknown. In T lymphocytes, IL-4 gene expression is regulated at the level of transcription by increases in intracellular calcium concentrat ion and by the calcium-activated phosphatase calcineurin, In this paper we report that dexamethasone (Dex) inhibits calcium ionophore-induced activati on of the human IL-4 promoter in transiently transfected Jurkat T cells, In hibition of the promoter by Dex is dependent on expression of the GC recept or (GR), because it does not occur in GR-deficient cells. Dex also represse s activation of the promoter induced by cotransfecting cells with a constit utively active mutant of calcineurin. Using a series of deletion constructs , we show that the proximal 95 bp of the IL-4 promoter contain a Dex-sensit ive regulatory element. This region contains the P1 sequence, a proximal bi nding site for NF-AT. A calcium-induced but Dex-inhibited nuclear complex c ontaining NF-AT binds to the P1 element in EMSA, Using immunoprecipitation under nondenaturing conditions, we found that the GR alpha isoform coprecip itates with NF-ATc in nuclear extracts of calcium ionophore- and Dex-treate d cells. Taken together, our results show that GC inhibit IL-4 gene express ion by interfering with NF-AT-depenaent transactivation of the proximal hum an IL-4 promoter.