Ligand-independent activation of the glucocorticoid receptor by beta(2)-adrenergic receptor agonists in primary human lung fibroblasts and vascular smooth muscle cells

The glucocorticoid receptor (GR) is a ubiquitously expressed transcription factor present in most cell types. Upon ligand binding, the GR is activated and translocates into the nucleus where it transmits the anti-inflammatory actions of glucocorticoids. Here, we describe the ligand-independent activ ation of GR by the beta(2)-adrenergic receptor (beta(2)-AR) agonists, salbu tamol and salmeterol, in primary human lung fibroblasts and vascular smooth muscle cells. Immunohistochemistry demonstrated expression of GR and the b eta(2)-AR by fibroblasts and vascular smooth muscle cells. Treatment of the cells with the beta(2)-AR agonists, salbutamol or salmeterol, resulted in translocation of GR into the nucleus beginning at 30 min, as shown by immun ohistochemistry and Western blotting of cytosolic and nuclear cell extracts . In comparison, activation of GR induced by the corticosteroids dexamethas one and fluticasone occurred at the same time after treatment (30 min) but resulted in a more complete depletion of GR from the cytosolic compartment. Electrophoretic mobility shift assays confirmed that nuclear GR, activated by both beta(2)-AR agonists and glucocorticoids, actively bound to the GR consensus sequence (GR element). Functional activation of the GR was confir med by a Luciferase reporter gene assay, using a GR driven promoter fragmen t from the p21((WAF1/CIP1)) gene. The effects of the beta(2)-AR agonists, s albutamol and salmeterol, were dependent upon binding to the beta(2)-AR, be cause blocking of beta(2)-AR with propranolol abrogated GR activation. GR a ctivation appeared to involve cAMP, In summary, these data show that beta(2 )-AR agonists are potent activators of GR, Ligand-independent activation of GR by beta(2)-AR agonists may substantially mediate the anti-inflammatory actions of these drugs observed in vitro and in vivo.