Cytokines Induce an Early Steroid Resistance in Airway Smooth Muscle Cells

Abstract

We have previously shown that long-term treatment of airway smooth muscle (ASM) cells with a combination of TNF-a and IFN-g impaired steroid anti-inflammatory action through the up-regulation of glucocorticoid receptor beta isoform (GRb) (Mol Pharmacol 2006;69:588-596). We here found that steroid actions could also be suppressed by short-term exposure of ASM cells to TNF-a and IFN-g (6 h) as shown by the abrogated glucocorticoid responsive element (GRE)-dependent gene transcription; surprisingly, neither GRa nuclear translocation nor GRb expression was affected by cytokine mixture. The earlier induction of CD38, a molecule recently involved in asthma, seen with TNF-a and IFN-g combination but not with cytokine alone, was also completely insensitive to steroid pretreatment. Chromatin-immunoprecipitation (IP) and siRNA strategies revealed not only increased binding of interferon regulatory factor 1 (IRF-1) transcription factor to CD38 promoter, but also its implication in regulating CD38 gene transcription. Interestingly, the capacity of fluticasone to completely inhibit TNF-a-induced IRF-1 expression, IRF-1 DNA binding, and transactivation activities was completely lost in cells exposed to TNF-a and IFN-g in combination. This early steroid dysfunction seen with cytokine combination could be reproduced by enhancing IRF-1 cellular levels using constitutively active IRF-1, which dose-dependently inhibited GRE-dependent gene transcription. Consistently, reducing IRF-1 cellular levels using siRNA approach significantly restored steroid transactivation activities. Collectively, our findings demonstrate for the first time that IRF-1 is a novel alternative GRb-independent mechanism mediating steroid dysfunction induced by pro-asthmatic cytokines, in part via the suppression of GRa activities.

TNF and IFN Synergistically Enhance Transcriptional Activation of CXCL10 in Human Airway Smooth Muscle Cells via STAT-1, NF- B, and the Transcriptional Coactivator CREB-binding Protein

“…2B). In keeping with data published previously (28,39,40), TNF␣ and IFN␥, when used in combination, induced additional steroid insensitivity, with the highest concentration of fluticasone (10 Ϫ6 M) inhibiting CXCL10 release by 19.2 Ϯ 3.4% (from 17,070.7 Ϯ 4642.9 pg/ml to 14,095 Ϯ 4428.2 pg/ml; Fig. 2C).…”

Cytokines Alter Glucocorticoid Receptor Phosphorylation in Airway Cells

“…The expression of these GC-insensitive proasthmatic proteins by ASM correlated with the severity of asthma. We and others replicated this finding in vitro using cultured human ASM cells (ASMCs) exposed to a combination of TNF-a and IFN-g (8)(9)(10). We showed that the induction of a variety of proasthmatic genes, namely CD38, CXCL10, CX3CL1, and CCL5, by TNF-a and IFN-g was surprisingly insensitive to the inhibition by GC (9,11).…”

“…We showed that the induction of a variety of proasthmatic genes, namely CD38, CXCL10, CX3CL1, and CCL5, by TNF-a and IFN-g was surprisingly insensitive to the inhibition by GC (9,11). This "corticosteroidinsensitive" state induced by TNF-a and IFN-g was associated with a marked suppression of GC receptor (GR)-mediated transactivation activities (8)(9)(10). These findings showing that the responsiveness of ASMCs to GC therapy could be dramatically affected by proasthmatic cytokines led us to suggest that the reduced sensitivity of "airway structural" cells to GC during inflammatory condition may contribute to the overall CSI seen in patients with severe asthma.…”

Current view on a role of CD38 for pathogenesis of bronchial asthma

“…TNF α -другой важный воспалительный цитокин, регулирующий экспрес сию CD38 в дыхательных путях. Патофизиологичес кую роль TNF α доказывает наличие его в высоких концентрациях в бронхоальвеолярной жидкости и мокроте пациентов с астмой [43]. TNF α -важный фактор в изменении сопротивления дыхательных путей и формировании обструкции при БА [20,44].…”