IFN-γ-induced JAK/STAT, but not NF-κB, signaling pathway is insensitive to glucocorticoid in airway epithelial cells

Abstract

Although the majority of patients with asthma are well controlled by inhaled glucocorticoids (GCs), patients with severe asthma are poorly responsive to GCs. This latter group is responsible for a disproportionate share of health care costs associated with asthma. Recent studies in immune cells have incriminated interferon-γ (IFN-γ) as a possible trigger of GC insensitivity in severe asthma; however, little is known about the role of IFN-γ in modulating GC effects in other clinically relevant nonimmune cells, such as airway epithelial cells. We hypothesized that IFN-γ-induced JAK/STAT-associated signaling pathways in airway epithelial cells are insensitive to GCs and that strategies aimed at inhibiting JAK/STAT pathways can restore steroid responsiveness. Using Western blot analysis we found that all steps of the IFN-γ-induced JAK/STAT signaling pathway were indeed GC insensitive. Transfection of cells with reporter plasmid showed IFN-γ-induced STAT1-dependent gene transcription to be also GC insensitive. Interestingly, real-time PCR analysis showed that IFN-γ-inducible genes (IIGs) were differentially affected by GC, with CXCL10 being GC sensitive and CXCL11 and IFIT2 being GC insensitive. Further investigation showed that the differential sensitivity of IIGs to GC was due to their variable dependency to JAK/STAT vs. NF-κB signaling pathways with GC-sensitive IIGs being more NF-κB dependent and GC-insensitive IIGs being more JAK/STAT dependent. Importantly, transfection of cells with siRNA-STAT1 was able to restore steroid responsiveness of GC-insensitive IIGs. Taken together, our results show the insensitivity of IFN-γ-induced JAK/STAT signaling pathways to GC effects in epithelial cells and also suggest that targeting STAT1 could restore GC responsiveness in patients with severe asthma.

Severe asthma in humans and mouse model suggests a CXCL10 signature underlies corticosteroid-resistant Th1 bias

“…Based on ChIP data, once established, this pathway may actually be perpetuated by chronic steroid therapy through interactions between GR and STAT1 on target sites in the CXCL10 promoter. As observed in our study using monocytic cells, in a previous study of air-way epithelial cells derived from patients with chronic obstructive pulmonary disease, CS did not inhibit IFN-γ-induced STAT1 phosphorylation (57). This inability of CS to inhibit STAT1 phosphorylation can be expected to facilitate GR-STAT1 collaboration, as observed in our ChIP assay.…”

DUSP1 Maintains IRF1 and Leads to Increased Expression of IRF1-dependent Genes

“…Likewise data from DUSP1 knock-out mouse models directly support these findings, and taken together this emphasizes the in vivo relevance of the current findings (12,46). Additionally, IRF1 is activated by interferons (IFNs) via the STAT1 transcription factor, and IFN-and STAT1-mediated inflammatory responses are also insensitive to glucocorticoids (12,65). However, because the deficiency of DUSP1 attenuates IFN␥-and IRF1-dependent IL12 expression, a wider relevance to these data is anticipated (12,66).…”

Cytokine-induced STAT1 activation is increased in patients with primary Sjögren's syndrome

“…It seems thus that the medications did not significantly affect our results. Likewise, a recent study on asthma patients showed insensitivity of IFN-γ-induced JAK/STAT signaling pathways to corticosteroid effects in epithelial cells [34].…”