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Glucocorticoids regulate calcineurin-dependent trans-activating pathways for interleukin-2 gene transcription in
1Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Disease, National Institutes of Health, Bethesda, Maryland 20892-1268, USA.
Abstract:
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.
Insights
Glucocorticoids inhibit T cell activation by blocking the IL-2 gene. This study shows they also inhibit calcineurin, a key phosphatase in T cell signaling pathways.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Glucocorticoids (GC) are known to inhibit IL-2 gene transcription by affecting activator protein-1.
- Calcineurin, a Ca2+/calmodulin-dependent phosphatase, is crucial for T cell receptor signaling and IL-2 gene transcription.
Purpose of the Study:
- To investigate whether glucocorticoids regulate calcineurin activity.
- To elucidate the role of calcineurin in glucocorticoid-mediated inhibition of T cell activation.
Main Methods:
- Jurkat T cells were cotransfected with IL-2 promoter constructs and a constitutively active calcineurin mutant (delta CaM-AI).
- Dexamethasone (Dex) treatment was used to assess inhibition of IL-2 promoter activation.
- Specificity of Dex effect was confirmed using an unrelated promoter and estradiol, and by using the glucocorticoid antagonist RU 486.
Main Results:
- Constitutive calcineurin activity (delta CaM-AI) partially rescued IL-2 promoter activation in the presence of phorbol ester.
- Dexamethasone inhibited IL-2 promoter activation by 50-60% under these conditions, an effect reversed by RU 486.
- Overexpression of calcineurin reduced Jurkat cells' sensitivity to dexamethasone, increasing the IC50 by approximately 5-fold.
Conclusions:
- Glucocorticoids inhibit T cell activation not only via activator protein-1 but also by suppressing calcineurin-dependent pathways.
- These findings reveal a novel mechanism of glucocorticoid action in T cell regulation.