Synergy between Interleukin-1, Interferon-, and Glucocorticoids to Induce TLR2 Expression Involves NF-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 immunopathology of glucocorticoid-resistant inflammatory diseases, including severe asthma.