Pro-asthmatic cytokines regulate unliganded and ligand-dependent glucocorticoid receptor signaling in airway smooth muscle

PLoS One. 2013 Apr 4;8(4):e60452. doi: 10.1371/journal.pone.0060452. Print 2013.

Abstract

To elucidate the regulation of glucocorticoid receptor (GR) signaling under pro-asthmatic conditions, cultured human airway smooth muscle (HASM) cells were treated with proinflammatory cytokines or GR ligands alone and in combination, and then examined for induced changes in ligand-dependent and -independent GR activation and downstream signaling events. Ligand stimulation with either cortisone or dexamethsone (DEX) acutely elicited GR translocation to the nucleus and, comparably, ligand-independent stimulation either with the Th2 cytokine, IL-13, or the pleiotropic cytokine combination, IL-1β/TNFα, also acutely evoked GR translocation. The latter response was potentiated by combined exposure of cells to GR ligand and cytokine. Similarly, treatment with either DEX or IL-13 alone induced GR phosphorylation at its serine-211 residue (GR(Ser211)), denoting its activated state, and combined treatment with DEX+IL-13 elicited heightened and sustained GR(Ser211) phosphorylation. Interestingly, the above ligand-independent GR responses to IL-13 alone were not associated with downstream GR binding to its consensus DNA sequence or GR transactivation, whereas both DEX-induced GR:DNA binding and transcriptional activity were significantly heightened in the presence of IL-13, coupled to increased recruitment of the transcriptional co-factor, MED14. The stimulated GR signaling responses to DEX were prevented in IL-13-exposed cells wherein GR(Ser211) phosphorylation was suppressed either by transfection with specific serine phosphorylation-deficient mutant GRs or treatment with inhibitors of the MAPKs, ERK1/2 and JNK. Collectively, these novel data highlight a heretofore-unidentified homeostatic mechanism in HASM cells that involves pro-asthmatic cytokine-driven, MAPK-mediated, non-ligand-dependent GR activation that confers heightened glucocorticoid ligand-stimulated GR signaling. These findings raise the consideration that perturbations in this homeostatic cytokine-driven GR signaling mechanism may be responsible, at least in part, for the insensirtivity to glucocorticoid therapy that is commonly seen in individuals with severe asthma.

Publication types

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

MeSH terms

  • Asthma / genetics
  • Asthma / metabolism
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Cytokines / pharmacology*
  • Enzyme Activation / drug effects
  • Humans
  • Ligands
  • Mitogen-Activated Protein Kinases / metabolism
  • Muscle, Smooth / drug effects*
  • Muscle, Smooth / metabolism*
  • Mutation
  • Phosphorylation / drug effects
  • Protein Binding
  • Protein Transport / drug effects
  • Receptors, Glucocorticoid / genetics
  • Receptors, Glucocorticoid / metabolism*
  • Respiratory System / drug effects*
  • Respiratory System / metabolism*
  • Response Elements
  • Signal Transduction / drug effects*
  • Transcriptional Activation

Substances

  • Cytokines
  • Ligands
  • Receptors, Glucocorticoid
  • Mitogen-Activated Protein Kinases