SIGNAL REQUIREMENTS FOR INTERLEUKIN-4 PROMOTER ACTIVATION IN HUMAN T-CELLS

We have studied the signal requirements for human IL-4 promoter activa tion in Jurkat T cells by the use of DNA transfection assays with vect ors carrying the IL-4 promoter linked to a reporter gene, Stimulation with calcium (Ca2+) ionophores (ionomycin), but not with phorbol ester s (phorbol myristate acetate, PMA) or cyclic AMP elevating agents (pro staglandin Ea(2) PGE(2)), induced the transcriptional activity of the IL-4 promoter by similar to 3-fold. Costimulation with ionomycin and P GE(2) resulted in the same level of IL-4 promoter activity as the stim ulation with ionomycin alone. In contrast, costimulation with ionomyci n and PMA decreased the activity of the IL-4 promoter by similar to 40 % compared to stimulation with ionomycin alone. Induction of IL-4 prom oter by ionomycin was partially inhibited (similar to 50% inhibition) in the presence of as high as 2 mu g/ml cyclosporin A (CsA), an inhibi tor of the Ca+/calmodulin-dependent phosphatase calcineurin. Under the same conditions, only 0.1 mu g/ml of CsA inhibited by >95% the transa ctivation of the IL-2 promoter in response to ionomycin and PMA. Trans fection of a deletion mutant of the calcineurin catalytic subunit (Del ta CaM-AI) known to have Ca2+-independent, constitutive phosphatase ac tivity increased IL-4 promoter activity by similar to 14-fold. Stimula tion with ionomycin of cells transfected with low doses of Delta CaM-A I, further induced IL-4 promoter activity by similar to 2-fold, These results identify the Ca2+-signaling system as a key component of the s ignal transduction pathway leading to IL-4 promoter activation in Jurk at T cells and suggest a major role of calcineurin in its regulation. (C) 1996 Academic Press, Inc.