MUC5AC and Barrett esophagus: Proposed interactions include an increased reactive oxygen species concentration in the esophageal mucosa,[17] pH-dependent induction of calcium ion-dependent intracellular signaling pathways,[18,19] induction of the expression of cellular receptors (e.g., TGR 5),[20,21] promotion of genomic instability through double-strand DNA breaks (DNA-SB),[22] and overexpression of the mucin family of matrix proteins: MUC1, MUC4, MUC-5AC, with the latter one expressed only in Barrett esophagus cells.[23–25]