Synergy between Interleukin-1 β , Interferon- γ , and Glucocorticoids to Induce TLR2 Expression Involves NF- κ B, STAT1, and the Glucocorticoid Receptor

Glucocorticoids act via the glucocorticoid receptor (GR; NR3C1) to downregulate inflammatory gene expression and are effective treatments for mild to moderate asthma. However, in severe asthma and virus-induced exacerbations, glucocorticoid therapies are less efficacious, possibly due to reduced repressive ability and/or the increased expression of proinflammatory genes. In human A549 epithelial and primary human bronchial epithelial cells, toll-like receptor (TLR)-2 mRNA and protein were -additively induced by interleukin-1 (IL-1 ) plus dexamethasone (IL-1 +Dex), interferon- (IFN- ) plus dexamethasone (IFN- +Dex), and IL-1 plus IFN- plus dexamethasone (IL-1 +IFN- +Dex). Indeed, ∼34- to 2100-fold increases were apparent at 24 hours for IL-1 +IFN- +Dex, and this was greater than for any single or dual treatment. Using the A549 cell model, TLR2 induction by IL-1 +IFN- +Dex was antagonized by Org34517, a competitive GR antagonist. Further, when combined with IL-1 , IFN- , or IL-1 +IFN- , the enhancements by dexamethasone on TLR2 expression required GR. Likewise, inhibitor of B kinase 2 inhibitors reduced IL-1 +IFN- +Dex-induced TLR2 expression, and TLR2 expression induced by IL-1 +Dex, with or without IFN- , required the nuclear factor (NF)- B subunit, p65. Similarly, signal transducer and activator of transcription (STAT)-1 phosphorylation and -interferon-activated sequence-dependent transcription were induced by IFN- These, along with IL-1 +IFN- +Dex-induced TLR2 expression, were inhibited by Janus kinase (JAK) inhibitors. As IL-1 +IFN- +Dex-induced TLR2 expression also required STAT1, this study reveals cooperation between JAK-STAT1, NF- B, and GR to upregulate TLR2 expression. Since TLR2 agonism elicits inflammatory responses, we propose that synergies involving TLR2 may occur within the cytokine milieu present in the immunopathology of glucocorticoid-resistant disease, and this could promote glucocorticoid resistance. SIGNIFICANCE STATEMENT: This study highlights that in human pulmonary epithelial cells, glucocorticoids, when combined with the inflammatory cytokines interleukin-1 (IL-1 ) and interferon- (IFN- ), can synergistically induce the expression of inflammatory genes, such as TLR2. This effect involved positive combinatorial interactions between NF- B/p65, glucocorticoid receptor, and JAK-STAT1 signaling to synergistically upregulate TLR2 expression. Thus, synergies involving glucocorticoid enhancement of TLR2 expression may occur in the immunopa