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

Abstract

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 supra-additively induced by interleukin-1b (IL-1b) plus dexamethasone (IL-1b1Dex), interferon-c (IFN-c) plus dexamethasone (IFN-c1Dex), and IL-1b plus IFN-c plus dexamethasone (IL-1b1IFN-c1Dex). Indeed, ~34- to 2100-fold increases were apparent at 24 hours for IL-1b1IFN-c1Dex, and this was greater than for any single or dual treatment. Using the A549 cell model, TLR2 induction by IL-1b1IFN-c1Dex was antagonized by Org34517, a competitive GR antagonist. Further, when combined with IL-1b, IFN-c, or IL-1b1IFN-c, the enhancements by dexamethasone on TLR2 expression required GR. Likewise, inhibitor of jB kinase 2 inhibitors reduced IL-1b1IFN-c1 Dex–induced TLR2 expression, and TLR2 expression induced by IL-1b1Dex, with or without IFN-c, required the nuclear factor (NF)-jB subunit, p65. Similarly, signal transducer and activator of transcription (STAT)-1 phosphorylation and c-interferon-activated sequence-dependent transcription were induced by IFN-c. These, along with IL-1b1IFN-c1Dex–induced TLR2 expression, were inhibited by Janus kinase (JAK) inhibitors. As IL-1b1IFN-c1Dex–induced TLR2 expression also required STAT1, this study reveals cooperation between JAK-STAT1, NF-jB, 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.