Inducible gene expression of IκB-kinase ε (IKKε) is dependent on nuclear factor-κB (NF-κB) in human pulmonary epithelial cells.

While IkB-kinase-ε (IKKε) induces immunomodulatory genes following viral stimuli, its upregulation by inflammatory cytokines remains under-explored. Since airway epithelial cells respond to airborne insults and potentiate inflammation, IKKε expression was characterized in pulmonary epithelial cell lines (A549, BEAS-2B) and primary human bronchial epithelial cells (pHBECs) grown as submersion or differentiated air-liquid interface (ALI) cultures. IKKε expression was upregulated by the pro-inflammatory cytokines, IL-1ß and TNF⍺. Thus, mechanistic interrogations in A549 cells were used to demonstrate the NF-κB dependence of cytokine-induced IKKε. Furthermore, chromatin immunoprecipitation in A549 and BEAS-2B cells revealed robust recruitment of the NF-κB subunit, p65, to one 5' and two intronic regions within the IKKε locus (IKBKE). In addition, IL-1ß and TNFα induced strong RNA polymerase 2 recruitment to the 5' region, the first intron, and the transcription start site. Stable transfection of the p65-binding regions into A549 cells revealed IL-1ß- and TNFα-inducible reporter activity that required NF-κB, but was not repressed by glucocorticoid. While critical NF-κB motifs were identified in the 5' and downstream intronic regions, the first intronic region did not contain functional NF-κB motifs. Thus, IL-1ß- and TNFα-induced IKKε expression involves three NF-κB-binding regions, containing multiple functional NF-κB motifs, and potentially other mechanisms of p65 binding through non-classical NF-κB binding motifs. By enhancing IKKε expression, IL-1ß may prime, or potentiate, responses to alternative stimuli, as modeled by IKKε phosphorylation induced by phorbol 12-myristate 13-acetate. However, since IKKε expression was only partially repressed by glucocorticoid, IKKε-dependent responses could contribute to glucocorticoid-resistant disease.

Synergy between Interleukin-1ß, Interferon-γ, and Glucocorticoids to Induce TLR2 Expression Involves NF-κB, 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 supra-additively induced by interleukin-1ß (IL-1ß) plus dexamethasone (IL-1ß+Dex), interferon-γ (IFN-γ) plus dexamethasone (IFN-γ+Dex), and IL-1ß plus IFN-γ plus dexamethasone (IL-1ß+IFN-γ+Dex). Indeed, ∼34- to 2100-fold increases were apparent at 24 hours for IL-1ß+IFN-γ+Dex, and this was greater than for any single or dual treatment. Using the A549 cell model, TLR2 induction by IL-1ß+IFN-γ+Dex was antagonized by Org34517, a competitive GR antagonist. Further, when combined with IL-1ß, IFN-γ, or IL-1ß+IFN-γ, the enhancements by dexamethasone on TLR2 expression required GR. Likewise, inhibitor of κB kinase 2 inhibitors reduced IL-1ß+IFN-γ+Dex-induced TLR2 expression, and TLR2 expression induced by IL-1ß+Dex, with or without IFN-γ, required the nuclear factor (NF)-κB subunit, p65. Similarly, signal transducer and activator of transcription (STAT)-1 phosphorylation and γ-interferon-activated sequence-dependent transcription were induced by IFN-γ These, along with IL-1ß+IFN-γ+Dex-induced TLR2 expression, were inhibited by Janus kinase (JAK) inhibitors. As IL-1ß+IFN-γ+Dex-induced TLR2 expression also required STAT1, this study reveals cooperation between JAK-STAT1, NF-κB, 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-1ß (IL-1ß) and interferon-γ (IFN-γ), can synergistically induce the expression of inflammatory genes, such as TLR2. This effect involved positive combinatorial interactions between NF-κB/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.