The MUC6 gene encodes gastric mucin, a secreted glycoprotein that plays an essential role in epithelial cytoprotection from acid, proteases, pathogenic microorganisms, and mechanical trauma in the gastrointestinal tract. May provide a mechanism for modulation of the composition of the protective mucus layer related to acid secretion or the presence of bacteria and noxious agents in the lumen. Plays an important role in the cytoprotection of epithelial surfaces and are used as tumor markers in a variety of cancers. May play a role in epithelial organogenesis.