Abstract
In some cell types long-acting β2-agonists (LABA) exert anti-inflammatory effects via ligand-independent activation of the glucocorticoid receptor (GR). This event was studied in human bronchial epithelial cells. Methods: Cells (NHBE) were treated with the LABA formoterol (FM) or salmeterol (SM) and/or the glucocorticoid budesonide (BUD) for 15min-24h (10-12-10-6M). GR translocation was evaluated by Western Blot on nuclear and cytoplasmic extracts whilst GRE-reporter gene assays established GR activity. The role of the GR (using siRNA) was studied in a TRE-reporter gene system and by measuring TNFα induced GM-CSF release. Results: A dose-dependent GR nuclear translocation was observed by BUD at 15min, with reversal at 6h. This correlated to a dose-dependent increase in GRE- and decrease in TRE-activity and GM-CSF levels. Neither FM nor SM translocated the GR into the nucleus and FM (SM not tested) did not affect BUD-induced GR translocation or activation. FM (SM not tested) did not activate GRE yet was able to inhibit TRE-activity and GM-CSF levels. Both anti-inflammatory activities occurred in the absence of the GR. Conclusions: Neither FM nor SM translocated the GR into the nucleus in bronchial epithelial cells. FM could not activate the GR nor affect BUD-induced GR nuclear translocation and activation. FM reduced PMA-stimulated TRE-activity and TNFα-induced GM-CSF release in absence of the GR. This suggests that the transrepressive anti-inflammatory effects of LABA in bronchial epithelial cells are mediated through GR-independent pathways.