Neutrophil elastase induces MUC5AC messenger RNA expression by an oxidant-dependent mechanism

Airway diseases such as cystic fibrosis, chronic bronchitis, and viral- or pollution-triggered asthma have two common pathologic features: mucus obstruction of the airways, and neutrophil-predominant airway inflammation. Neutrophils release high concentrations of elastase (neutrophil elastase [NE]), a serine protease, into the airways; exposure to elastase results in secretory metaplasia and increased production/secretion of mucin glycoproteins. We have previously shown that NE increases gene expression of a respiratory mucin, MUC5AC, in both A549, a lung adenocarcinoma cell line, and cultured normal human bronchial epithelial cells. In this study, we explored the intracellular signaling mechanisms required for NE-regulated MUC5AC gene expression. A549 cells were treated with dimethylthiourea (DMTU; 4 mM and 40 mM), a scavenger of hydroxyl radical, peroxynitrite, and other hydroxylated products, prior to and during NE stimulation. DMTU inhibited NE-induced MUC5AC expression. Furthermore, using dichlorodihydrofluorescein, an intracellular redox indicator, we showed that in both A549 cells and cultured normal human bronchial epithelial cells, NE treatment induced oxidative stress. These results support the role of reactive oxygen species mediating NE-induced MUC5AC gene expression.