Cigarette smoke induces MUC5AC mucin overproduction via tumor necrosis factor-α-converting enzyme in human airway epithelial (NCI-H292) cells

Abstract
Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death in the U.S. Because cigarette smoking is so importantly implicated in the pathogenesis of COPD and because mucus hypersecretion plays such an important role in COPD, understanding of the mechanisms of smoking-induced mucus hypersecretion could lead to new therapies for COPD. Cigarette smoke causes mucin overproduction via EGF receptor (EGFR) in airway epithelial cells, but the cellular mechanism remains unknown. Airway epithelial cells contain EGFR proligands on their surfaces, which can be cleaved by metalloprotease and subsequently bind to EGFR resulting in mucin production. We hypothesize that TNF-α-converting enzyme (TACE) is activated by cigarette smoke, resulting in increased shedding of EGFR proligand, leading to EGFR phosphorylation and mucin induction in human airway epithelial (NCI-H292) cells. Here we show that cigarette smoke increases MUC5AC production in NCI-H292 cells, an effect that is prevented by an EGFR-neutralizing antibody and by specific knockdown of transforming growth factor-α (TGF-α) using small interfering RNA (siRNA) for TGF-α, implicating TGF-α-dependent EGFR activation in the responses. Cigarette smoke increases TGF-α shedding, EGFR phosphorylation, and mucin production, which are prevented by metalloprotease inhibitors (GM-6001 and TNF-α protease inhibitor-1) and by specific knockdown of TACE with TACE siRNA, implicating TACE in smoking-induced responses. Furthermore, pretreatment with antioxidants prevents smoking-induced TGF-α shedding and mucin production, suggesting that reactive oxygen species is involved in TACE activation. These results implicate TACE in smoking-induced mucin overproduction via the TACE-proligand-EGFR signal pathway in NCI-H292 cells.