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. Multimer; disulfide-linked. Expressed in the regenerative zone of gastric antrum, gastric body mucosa and gastric incisura mucosa. Expressed in the deeper mucous glands of gastric antrum. Overexpressed in Helicobacter pylori infected gastric epithelium. Highly expressed in duodenal Brunner's glands, gall bladder, seminal vesicle, pancreatic centroacinar cells and ducts, and periductal glands of the common bile duct. Early expressed in fetal development and was observed in Brunner's glands and pancreatic ducts at 18-19 weeks and in gastric glands at 20 weeks of gestation. Expressed transiently in the nephrogenic zone of the kidney in the early mid-trimester of development. Detected in the epithelium of ureteric buds at 13 weeks and at lower levels from 17 to 23 weeks of gestation. Up-regulated by NFKB1. Repressed by mithramycin A which is an inhibitor of binding of transcription factors. O-glycosylated. The number of repeats is highly polymorphic and varies among different alleles. These repeats are very similar but not identical. Truncated C-terminus. Truncated N-terminus.