Submitted on June 14, 2007
Revised on October 16, 2007
Cytokines Induce an Early Steroid Resistance in Airway Smooth Muscle Cells: Novel Role of IRF-1
Omar Tliba1*, Gautam Damera1, Audreesh Banerjee1, Su Gu1, Hasna Baidouri1, Stefan Keslacy1, and Yassine Amrani2
1 University of Pennsylvania School of Medicine, Pulmonary, Allergy and Critical Care Division, Philadelphia, PA, USA,
2 Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, United Kingdom
* To whom correspondence should be addressed. E-mail: omartlib{at}mail.med.upenn.edu.
We have previously shown that long-term treatment of airway smooth muscle (ASM) cells with a combination of TNF
and IFN
impaired steroid anti-inflammatory action through the upregulation of glucocorticoid receptor beta isoform (GR
) (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 TNF
and IFN
(6 h) as evidenced by the abrogated glucocorticoid responsive element (GRE)-dependent gene transcription; surprisingly neither GR
nuclear translocation nor GR
expression was affected by cytokine mixture. The earlier induction of CD38, a molecule recently involved in asthma, seen with TNF
and IFN
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
-induced IRF-1 expression, IRF-1 DNA binding, and transactivation activities, was completely lost in cells exposed to TNF
and IFN
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 GR
-independent mechanism mediating steroid dysfunction induced by pro-asthmatic cytokines, in part via the suppression of GR
activities.