Modulation of glucocorticoid receptor expression in human bronchial epithelial cell lines by IL-1β, TNF-α and LPS

Abstract

Bronchial epithelium plays a major role in the regulation of inflammatory reactions in the airways. It is thought to be a possible target for glucocorticoid therapy. Glucocorticoid responsiveness requires the presence of specific glucocorticoid receptors (GR). Until now, little was known about the presence of such receptors in the human bronchial epithelium. In this study we demonstrated the expression of GR messenger ribonucleic acid (mRNA) in two simian virus (SV)-40/adenovirus-transformed human bronchial epithelial cell lines, BEAS S6 and BEAS 2B. In a whole cell dexamethasone binding assay, BEAS S6 and BEAS 2B cells were found to possess (mean ± SEM) 28.9 ± 4.4 x 103 and 32.1 ± 5.7 x 103 binding sites per cell, respectively, with dissociation constant (Kd) values of 8.2 ± 1.5 and 8.6 ± 2.4 nM, respectively. Using electrophoretic mobility shift assays we demonstrated the binding of nuclear translocated GR to specific sites on deoxyribonucleic acid (DNA), named glucocorticoid responsive elements (GRE). Lipopolysaccharide (LPS) and interleukin-1β (IL-1β) significantly increased the number of GR per cell (median = 312% and 171% of control, respectively; p < 0.05), but significantly reduced the ligand affinity of these receptors, i.e. increased the Kd (median = 410% and 145% of control, respectively; p < 0.05) in BEAS 2B cells. These results indicate that the bronchial epithelium may be an actual target for glucocorticoid therapy. Inflammatory mediators, such as IL-1β and LPS, modulate the number and ligand affinity of these GR. Therefore, the response of bronchial epithelium to glucocorticoid therapy may be modulated by airway diseases associated with inflammation.