Oxidative stress causes mucin synthesis via transactivation of epidermal growth factor receptor: Role of neutrophils

Oxidative stress has been implicated in the pathogenesis of inflammatory di seases of airways. Here we show that oxidative stress causes ligand-indepen dent activation of epidermal growth factor receptors (EGFR) and subsequent activation of mitogen-activated protein kinase kinase (MEK)-p44/42 mitogen- activated protein kinase (p44/42(mapk)). resulting in mucin synthesis in NC I-H292 cells. Exogenous hydrogen peroxide and neutrophils activated by IL-8 , FMLP, or TNF-alpha increased EGFR tyrosine phosphorylation and subsequent activation of p44/42(mapk) and up-regulated the expression of MUC5AC at bo th mRNA and protein levels in NCI-H292 cells. These effects were blocked by selective EGFR tyrosine kinase inhibitors (AG1478, BIBX1522) and by a sele ctive MEK inhibitor (PD98059), whereas a selective platelet-derived growth factor receptor tyrosine kinase inhibitor (AG1295), a selective p38 MAPK in hibitor (SB203580), and a negative compound of tyrosine kinase inhibitors ( Al) mere without effect. Neutrophil supernatant-induced EGFR tyrosine phosp horylation, activation of p44/42(mapk), and MUC5AC synthesis were inhibited by antioxidants (N-acetyl-L-cysteine, DMSO, dimethyl thiourea, or superoxi de dismutase); neutralizing Abs to EGFR ligands (EGF and TGF-alpha) were wi thout effect, and no TGF-alpha protein was found in the neutrophil supernat ant, In contrast, the EGFR ligand, TGF-alpha, increased EGFR tyrosine phosp horylation, activation of p44/42(mapk), and subsequent MUC5AC synthesis, bu t these effects were not inhibited by antioxidants. These results implicate oxidative stress in stimulating mucin synthesis in airways and provide new therapeutic approaches in airway hypersecretory diseases.