In a Calu3 cell line deficient for CFTR expression, lack of channel function caused increased secretion and concentration of both MUC5AC and MUC5B proteins, while no increase in mucin gene expression was detected, suggesting that the abnormal properties of CF mucus stimulate the release of mucin granules independently of MUC gene upregulation [119]. Here, MUC5AC is linked to cystic fibrosis.