Transforming growth factor‐β impairs glucocorticoid activity in the A549 lung adenocarcinoma cell line

BACKGROUND AND PURPOSE The lung adenocarcinoma cell line, A549, undergoes epithelial‐mesenchymal cell transition (EMT) in response to TGF‐β. Glucocorticoids do not prevent the EMT response, but TGF‐β induced resistance to the cytokine‐regulatory action of glucocorticoids. We sought to characterize the impairment of glucocorticoid response in A549 cells. EXPERIMENTAL APPROACH A549 cells were exposed to TGF‐β for up to 96 h before glucocorticoid treatment and challenge with IL‐1α to assess glucocorticoid regulation of IL‐6 and CXCL8 production. Nuclear localization of the glucocorticoid receptor α (GRα) was ascertained by immunofluorescence and Western blotting. Transactivation of the glucocorticoid response element (GRE) was measured with a transfected GRE‐secreted human placental alkaline phosphatase reporter. KEY RESULTS TGF‐β (40–400 pM) reduced the maximum inhibitory effect of dexamethasone on IL‐1α‐induced IL‐6 and CXCL8 production. The impaired glucocorticoid response was detected with 4 h of TGF‐β (40 pM) exposure (and 4 h IL‐1α to induce CXCL8 expression) and therefore was not secondary to EMT, a process that requires longer incubation periods and higher concentrations of TGF‐β. TGF‐β also impaired dexamethasone regulation of granulocyte‐macrophage colony‐stimulating factor in thrombin‐stimulated BEAS‐2B epithelial cells. Impaired regulation of CXCL8 was associated with markedly reduced GRE transactivation and reduced induction of mRNA for IκBα, the glucocorticoid‐inducible leucine zipper and the epithelial sodium channel (SCNN1A). The expression, cellular levels and nuclear localization of GRα were reduced by TGF‐β. CONCLUSIONS AND IMPLICATIONS We have identified mechanisms underlying the impairment of responses to glucocorticoids by TGF‐β in the A549 and BEAS‐2B cell lines.