ABSTRACT
Cigarette smoking is strongly implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). Mucus hypersecretion is the key manifestation in patients with COPD and mucin 5AC (MUC5AC) is a major component of airway mucus. Hypoxia inducible factor‐1 (HIF‐1) is a transcriptional factor which can be stimulated to bind to the MUC5AC promoter and induce MUC5AC promoter activation. Previous studies have reported that activation of HIF‐1__α__ pathways by cigarette smoke contributes to the development of COPD. We hypothesize that cigarette smoke up‐regulates HIF‐1__α__ production and HIF‐1 activity through epidermal growth factor receptor (EGFR)‐activated signal cascades pathways, leading to mucin production in human airway epithelial cells (16HBE). We show that cigarette smoke increases HIF‐1__α__ production, HIF‐1 activity and MUC5AC expression. These effects are prevented by small interfering RNA (siRNA) for HIF‐1__α__, indicating that cigarette smoke‐induced mucin production is HIF‐1__α__‐dependent. Cigarette smoke activates extracellular signal‐regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3‐kinase (PI3K) signal pathways, both of which are inhibited by gefitinib (an inhibitor of EGFR), suggesting that cigarette smoke‐activated signal pathways are mediated by EGFR in 16HBE cells. Furthermore, pretreatment with gefitinib and the pharmacological inhibitors of PI3K (LY294002) and ERK1/2 (PD98059) prevented cigarette smoke‐mediated Akt and ERK1/2 phosphorylation responses, HIF‐1__α__ production, HIF‐1 activity and MUC5AC expression. These observations demonstrate an important role for EGFR‐mediated signaling pathways in regulating cigarette smoke‐induced HIF‐1 activation and MUC5AC expression. Our results suggest that cigarette smoke activates EGFR‐mediated signaling pathways, leading to HIF‐1__α__ production and HIF‐1 activation, resulting in mucin expression in human airway epithelial cells. Copyright © 2011 John Wiley & Sons, Ltd.