Glucocorticoids Inhibit Calcium- and Calcineurin-Dependent Activation of the Human IL-4 Promoter

Abstract

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 concentration and by the calcium-activated phosphatase calcineurin. In this paper we report that dexamethasone (Dex) inhibits calcium ionophore-induced activation of the human IL-4 promoter in transiently transfected Jurkat T cells. Inhibition of the promoter by Dex is dependent on expression of the GC receptor (GR), because it does not occur in GR-deficient cells. Dex also represses activation of the promoter induced by cotransfecting cells with a constitutively 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-sensitive regulatory element. This region contains the P1 sequence, a proximal binding site for NF-AT. A calcium-induced but Dex-inhibited nuclear complex containing NF-AT binds to the P1 element in EMSA. Using immunoprecipitation under nondenaturing conditions, we found that the GRα isoform coprecipitates with NF-ATc in nuclear extracts of calcium ionophore- and Dex-treated cells. Taken together, our results show that GC inhibit IL-4 gene expression by interfering with NF-AT-dependent transactivation of the proximal human IL-4 promoter.

Negative regulation of nuclear factor-kappaB activation and function by glucocorticoids

“…In view of the cooperation between transcription factors in driving optimal transcriptional activation, it remains to be determined whether the effect of GCs on antagonizing NF-B is a direct event or, alternatively, a consequence of an earlier antagonism of another factor in the activation cascade (Chen et al 2000). The multitude of conclusions drawn from the literature indicate that GCs most likely affect several transcriptional events, as a single mechanism could not apply to all cell types and stimulation conditions.…”

“…Here, GCs inhibition of AP-1 activity was shown to be the result of proximal inhibition of c-Jun NH2-terminal kinase (JNK), a key mediator of AP-1 activation (Gonzalez et al 2000). It is also plausible that the repression of NF-B binding by GCs was the consequence of earlier antagonism of the binding and/or activation of other transcription factors, described as being required for efficient NF-B binding to its putative DNA site (Casolaro et al 1995, Chen et al 2000.…”

“…This was evidenced by the capacity of hormone-activated GR to repress the nuclear translocation and/or function of the transcription factors AP-1 (a dimer of c-Fos and c-Jun) (Vacca et al 1992, Mori et al 1997, NF-B (De Bosscher et al 1997, 2000b, Heck et al 1997, and NF-AT (Northrop et al 1992, Paliogianni et al 1993, Chen et al 2000. Reduction in transcription factor availability and/or function, in turn, resulted in downstream reduction in, and arrest of, transcriptional activity in target genes.…”

Glucocorticoids upregulate CD40 ligand expression and induce CD40L-dependent immunoglobulin isotype switching

“…Alternatively, GR may directly bind to NF-AT complexes and enhance their activity. This binding could involve the Jun component of AP-1, but also possibly NF-AT, as has been recently shown in the IL-4 promoter (40). Experiments are in progress to test these possibilities.…”

Expression of Activation Markers and Cytokine mRNA by Peripheral Blood CD4 and CD8 T Cells in Atopic and Nonatopic Childhood Asthma: Effect of Inhaled Glucocorticoid Therapy

“…Nevertheless, the data are compatible with the hypothesis that glucocorticoids ameliorate childhood asthma by reducing the production of asthma-relevant cytokines by both CD4 and CD8 T cells. This effect of inhaled glucocorticoids most likely reflects modulation of cytokine mRNA concentrations, 29,30 although a possible effect of glucocorticoids in promoting egress of these cells from the circulation cannot be ruled out.…”