title: Protein phosphatase 5 mediates corticosteroid insensitivity in airway smooth muscle in patients with severe asthma.
abstract: BACKGROUND
  The mechanisms driving glucocorticoid (GC) insensitivity in patients with severe asthma are still unknown. Recent evidence suggests the existence of GC-insensitive pathways in airway smooth muscle (ASM) caused by a defect in GC receptor (GRα) function. We examined whether other mechanisms could potentially explain the reduced sensitivity of ASM cells to GC in severe asthmatics.
  
  
  METHODS
  Airway smooth muscle cells from healthy and severe asthmatic subjects were treated with TNF-α and responses to corticosteroids in both cohorts were compared by ELISA, immunoblot, immunohistochemistry and real-time PCR. Immunohistochemistry and flow cytometry assays were used to assess the expression of the protein phosphatase PP5 in endobronchial biopsies and ASM cells.
  
  
  RESULTS
  The production of CCL11 and CCL5 by TNF-α was insensitive to both fluticasone and dexamethasone in ASM cells from severe asthmatic compared to that in healthy subjects. Fluticasone-induced GRα nuclear translocation, phosphorylation at serine 211 and expression of GC-induced leucine zipper (GILZ) were significantly reduced in ASM cells from severe asthmatics compared to responses in healthy subjects. Levels of PP5 were increased in ASM cells from severe asthmatics and PP5 knockdown using siRNA restored fluticasone repressive action on chemokine production and its ability to induce GRα nuclear translocation and GRE-dependent GILZ expression. In vivo PP5 expression was also increased in the ASM bundles in endobronchial biopsies in severe asthmatics.
  
  
  CONCLUSIONS
  PP5-dependent impairment of GRα function represents a novel mechanism driving GC insensitivity in ASM in severe asthma.
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: L
authors: L
authors: Chachi
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: M
authors: M
authors: Abbasian
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: A
authors: A
authors: Gavrila
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: A
authors: A
authors: Alzahrani
authors: Department of Pharmaceutical Sciences, Jefferson School of Pharmacy, Thomas Jefferson University, Philadelphia, PA, USA.
authors: O
authors: O
authors: Tliba
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: P
authors: P
authors: Bradding
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: A J
authors: AJ
authors: Wardlaw
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: C
authors: C
authors: Brightling
authors: Department of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK.
authors: Y
authors: Y
authors: Amrani
mesh_terms: D000305:Adrenal Cortex Hormones / Q000494:pharmacology* / Q000627:therapeutic use; D000328:Adult; D018927:Anti-Asthmatic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy / Q000276:immunology* / Q000378:metabolism*; D015415:Biomarkers; D016207:Cytokines / Q000096:biosynthesis; D004361:Drug Tolerance; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008875:Middle Aged; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D012129:Respiratory Function Tests; D020218:Response Elements; D012720:Severity of Illness Index
chemical_list: D000305:Adrenal Cortex Hormones; D018927:Anti-Asthmatic Agents; D015415:Biomarkers; D016207:Cytokines; D009687:Nuclear Proteins; D011965:Receptors, Glucocorticoid; C411470:glucocorticoid receptor alpha; D010749:Phosphoprotein Phosphatases; C089641:protein phosphatase 5
keywords: airway smooth muscle; corticosteroid insensitivity; corticosteroid receptor; protein phosphatase; receptor phosphorylation