Increased glucocorticoid receptor β alters steroid response in glucocorticoid-insensitive asthma

Rationale: Glucocorticoids (GCs) are highly effective in the treatment of asthma. However, some individuals have GC-insensitive asthma. Objectives: To evaluate the functional response to steroids of bronchoalveolar lavage (BAL) cells from sites of airway inflammation from patients with GC-insensitive versus GC-sensitive asthma. As well, to attempt to define the functional role of glucocorticoid receptor (GCR)beta (a splicing variant, and dominant negative inhibitor of, the classic GCR alpha) in controlling GCR alpha nuclear translocation and transactivation at a molecular level. Methods and Measurements: Fiberoptic bronchoscopy with collection of BAL fluid was performed on seven patients with GC-sensitive asthma and eight patients with GC-insensitive asthma. GCR alpha cellular shuttling in response to 10(-6) M dexamethasone treatment and GCR beta expression were analyzed in BAL cells by immunofluorescence staining. The effects of overexpression and silencing of GCR beta mRNA on GCR alpha function were assessed. Main Results: Significantly reduced nuclear translocation of GCR alpha in response to steroids was found in BAL cells from patients with GC-insensitive asthma. BAL macrophages from patients with GC-insensitive asthma had significantly increased levels of cytoplasmic and nuclear GCR beta. It was demonstrated that GCR alpha nuclear translocation and its transactivation properties were proportionately reduced by level of viral transcluction of the GCR beta gene into the DO-11.10 cell line. RNA silencing of GCR beta mRNA in human BAL macrophages from patients with GC-insensitive asthma resulted in enhanced dexamethasone-induced GCR alpha transactivation. Conclusions: GC insensitivity is associated with loss of GCR alpha nuclear translocation in BAL cells and elevated GCR beta, which may inhibit GCR alpha transactivation in response to steroids.