Rhinovirus (RV) infections are the major cause of asthma exacerbations, the major cause of morbidity and mortality in asthma. MUC5AC is the major mucin produced by bronchial epithelial cells. Whether RV infection upregulates MUC5ACin vivois unknown and the molecular mechanisms involved are incompletely understood.We investigated RV induction of MUC5ACin vivoandin vitroto identify targets for development of new therapies for asthma exacerbations.RV infection increased MUC5AC release in normal and asthmatic volunteers experimentally infected with RV-16, and in asthmatic, but not normal, subjects, this was related to virus load. Bronchial epithelial cells were confirmed a source of MUC5ACin vivo. RV induction of MUC5AC in bronchial epithelial cellsin vitrooccurredvianuclear factor-κB-dependent induction of matrix metalloproteinase-mediated transforming growth factor-α release, thereby activating an epidermal growth factor receptor-dependent cascade culminating,viamitogen-activated protein kinase activation, in specificity protein-1 transactivation of the MUC5AC promoter.RV induction of MUC5AC may be an important mechanism in RV-induced asthma exacerbationsin vivo. Revealing the complex serial signalling cascade involved identifies targets for development of pharmacologic intervention to treat mucus hypersecretion in RV-induced illness.