Glucocorticoids Inhibit MUC5AC Production Induced by Transforming Growth Factor-α in Human Respiratory Cells

Background: Mucus hypersecretion from airway epithelium is a characteristic feature of severe asthma. Glucocorticoids (GCs) may suppress mucus production and diminish the harmful airway obstruction. We investigated the ability of GCs to suppress mRNA expression and protein synthesis of a gene encoding mucin, MUC5AC, induced by transforming growth factor (TGF)-alpha in human mucoepidermoid carcinoma (NCI-H292) cells and the molecular mechanisms underlying the suppression. Methods: We determined if GCs such as dexamethasone (DEX), budesonide (BUD), and fluticasone (FP) could suppress MUC5AC production induced by a combination of TGF-alpha and double-strand RNA, polyinosinic-polycytidylic acid (polyl:C). MUC5AC mRNA expression and MUC5AC protein production were evaluated. The signaling pathways activated by TGF-alpha and their inhibition by GCs were tested using a phosphoprotein assay and MUC5AC promoter assay. Results: DEX significantly suppressed the expression of MUC5AC mRNA and MUC5AC protein induced by TGF-alpha. The activation of the MUC5AC promoter by TGF-alpha was significantly inhibited by DEX. DEX did not affect activation of downstream pathways of the EGF receptor or mRNA stability of MUC5AC transcripts. DEX, BUD, and FP suppressed MUC5AC protein expression induced by a combination of TGF-alpha and polyl:C in a dose-dependent manner. Conclusions: GCs inhibited MUC5AC production induced by TGF-alpha alone or a combination of TGF-alpha and polyl:C; the repression may be mediated at the transcriptional but not post-transcriptional level.