Abstract
Dual oxidase 2 enzyme is a member of the reactive oxygen species-generating cell membrane NADPH oxidases involved in mucosal innate immunity. It is not known if the biological activity of dual oxidase 2 is mediated by direct bacterial killing by reactive oxygen species produced by the enzyme or by the same reactive oxygen species acting as second messengers that stimulate novel gene expression. To uncover the role of reactive oxygen species and dual oxidases as signaling molecules, we have dissected the pathway triggered by epidermal growth factor to induce mucins, the principal protective components of gastrointestinal mucus. We show that dual oxidase 2 is essential for selective epidermal growth factor induction of the transmembrane MUC3 and the secreted gel-forming MUC5AC mucins. Reactive oxygen species generated by dual oxidase 2 stabilize tyrosine phosphorylation of epidermal growth factor receptor and induce MUC3 and MUC5AC through persistent activation of extracellular signal-regulated kinases 1/2-protein kinase C. Knocking down dual oxidase 2 by selective RNA targeting (siRNA) reduced epidermal growth factor receptor phosphorylation, and MUC3 and MUC5AC gene expression. Extracellular reactive oxygen species produced by dual oxidase 2, upon stimulation by epidermal growth factor, stabilize epidermal growth factor receptor phosphorylation and activate extracellular signal-regulated kinases 1/2-protein kinase C which induce MUC5AC and MUC3. Extracellular reactive oxygen species produced by dual oxidase 2 that are known to directly kill bacteria, also contribute to the maintenance of the epidermal growth factor-amplification loop, which induces mucins. These data suggest a new function of dual oxidase 2 protein in the luminal protection of the gastrointestinal tract through the induction of mucin expression by growth factors.