Glucocorticoids regulate calcineurin-dependent trans-activating pathways for interleukin-2 gene transcription in human T lymphocytes.

Glucocorticoids (GC) inhibit IL-2 gene transcription by interfering with the binding of the nuclear factor activator protein-1 on the IL-2 promoter. Calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, is an essential component of the T cell antigen receptor signal transduction pathway leading to IL-2 gene transcription. Therefore, we have asked whether this phosphatase may also be regulated by GC. Jurkat T cells were cotransfected with plasmids containing the intact IL-2 promoter or its NF-AT and Oct-1 motifs, and a deletion mutant (delta CaM-AI) of calcineurin known to have Ca(2+)-independent constitutive phosphatase activity. Cotransfection of IL-2 promoter with delta CaM-AI allowed the activation of IL-2 promoter in the presence of phorbol ester alone. Under these conditions dexamethasone (Dex; 10(-6) M) inhibited IL-2 promoter activation by 50-60%. The inhibitory effect of Dex was specific, as demonstrated by experiments using an unrelated promoter (simian virus 40) and estradiol. Furthermore, it was completely reversed in the presence of excess amounts of the glucocorticoid antagonist RU 486, which suggests that it is mediated through the glucocorticoid receptor. Overexpression of calcineurin via delta CaM-AI in Jurkat cells decreased their apparent sensitivity to Dex (approximately 5-fold increase in IC50). Similar results were obtained with the NF-AT and Oct-1 constructs, which are also known to be activated by calcineurin. Thus, in addition to their known inhibitory effects on activator protein-1, GC also inhibit calcineurin-dependent pathways for T cell activation.