Cytokines induce an early steroid resistance in airway smooth muscle cells: novel role of interferon regulatory factor-1

Authors:
Tliba O, Damera G, Banerjee A, Gu S, Baidouri H, Keslacy S, Amrani Y
In:
Source: Am J Respir Cell Mol Biol
Publication Date: (2008)
Issue: 38(4): 463-72
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
SMC, airway (HASM), human
Species: human
Tissue Origin: lung
Platform:
Nucleofector® I/II/2b
Abstract
We have previously shown that long-term treatment of airway smooth muscle (ASM) cells with a combination of TNFalpha and IFNgamma impaired steroid anti-inflammatory action through the upregulation of glucocorticoid receptor beta isoform (GRbeta) (Mol Pharmacol. 2006 Feb;69(2):588-96). We here found that steroid actions could also be suppressed by short-term exposure of ASM cells to TNFalpha and IFNgamma (6 h) as evidenced by the abrogated glucocorticoid responsive element (GRE)-dependent gene transcription; surprisingly neither GRalpha nuclear translocation nor GRbeta expression was affected by cytokine mixture. The earlier induction of CD38, a molecule recently involved in asthma, seen with TNFalpha and IFNgamma 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 TNFalpha-induced IRF-1 expression, IRF-1 DNA binding, and transactivation activities, was completely lost in cells exposed to TNFalpha and IFNgamma 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 GRbeta-independent mechanism mediating steroid dysfunction induced by pro-asthmatic cytokines, in part via the suppression of GRalpha activities.