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

Am J Physiol Lung Cell Mol Physiol. 2015 Aug 15;309(4):L348-59. doi: 10.1152/ajplung.00099.2015. Epub 2015 Jun 19.

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.

Keywords: airway remodeling; asthma; epithelial cell; glucocorticoid insensitivity; inflammation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Active Transport, Cell Nucleus
  • Aged
  • Androstadienes / pharmacology*
  • Asthma / drug therapy
  • Asthma / metabolism
  • Asthma / pathology
  • Cell Line, Tumor
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism*
  • Female
  • Fluticasone
  • Glucocorticoids / pharmacology*
  • Humans
  • Interferon-gamma / physiology*
  • Janus Kinases / metabolism
  • Male
  • Middle Aged
  • NF-kappa B / metabolism
  • Phosphorylation
  • Protein Processing, Post-Translational
  • Respiratory Mucosa / pathology
  • STAT1 Transcription Factor / metabolism*
  • Signal Transduction
  • Transcription, Genetic

Substances

  • Androstadienes
  • Glucocorticoids
  • NF-kappa B
  • STAT1 Transcription Factor
  • STAT1 protein, human
  • Interferon-gamma
  • Fluticasone
  • Janus Kinases