Context-dependent Cooperation between Nuclear Factor κB (NF-κB) and the Glucocorticoid Receptor at a TNFAIP3 Intronic Enhancer

Abstract

Background: The effects of glucocorticoids on the expression of negative feedback regulators of NF-kB are not well understood Results: A novel intronic enhancer for TNFAIP3 was synergistically induced by the glucocorticoid receptor and NF-kB Conclusion: The glucocorticoid receptor can cooperate with NF-kB to enhance the expression of anti-inflammatory genes such as TNFAIP3 Significance: These results establish a novel mechanism for anti-inflammatory effects of glucocorticoids ABSTRACT TNF expression is elevated in asthma and other inflammatory airway diseases that are commonly treated with glucocorticoid-based therapies, but the impact of glucocorticoids on negative feedback control of TNF is not well understood. We analyzed the effect of dexamethasone, a potent synthetic glucocorticoid, on TNF-regulated gene expression in cultured airway epithelial cells. While dexamethasone-mediated activation of the glucocorticoid receptor (GR) potently repressed expression of IL1β, IL8, and several other pro-inflammatory TNF targets, the expression of anti-inflammatory TNF targets such as TNFAIP3 and NFKBIA was selectively spared or augmented by dexamethasone treatment. Despite divergent effects on gene expression, GR and NF-kB occupancy at the TNFAIP3 locus and GR-repressed targets was similar. A co-occupied intronic TNFAIP3 regulatory element mediated cooperative enhancement of transcription by GR and NF-kB that required the presence of a functional GR binding site (GBS). GBS exchanges between reporters for TNFAIP3 and FKBP5, a canonical GR-induced target, revealed substantial latitude in the GBS sequence requirements for GR/NF-kB cooperation, suggesting that the TNFAIP3 GBS acts primarily as a docking site in this context. Supporting this notion, a selective GR ligand with only weak agonist activity for induction of FKBP5 enabled robust GR/NF-kB cooperative induction of a mutant TNFAIP3 reporter harboring the FKBP5 GBS. Taken together, our data support a model in which the expression of anti-inflammatory targets of TNF is maintained during treatment with glucocorticoids through context dependent cooperation between GR and NF-kB.