Thought to provide a protective, lubricating barrier against particles and infectious agents at mucosal surfaces. Binds to MSLN. Binding to MSLN mediates heterotypic cell adhesion. This may contribute to the metastasis of ovarian cancer to the peritoneum by initiating cell attachment to the mesothelial epithelium via binding to MSLN. May be liberated into the extracellular space following the phosphorylation of the intracellular C-terminus which induces the proteolytic cleavage and liberation of the extracellular domain. Expressed in corneal and conjunctival epithelia (at protein level). Overexpressed in ovarian carcinomas and ovarian low malignant potential (LMP) tumors as compared to the expression in normal ovarian tissue and ovarian adenomas. Up-regulated in ovarian cancer cells. Composed of three domains, a Ser-, Thr-rich N-terminal domain, a repeated domain containing between 12 and 60 partially conserved tandem repeats of 156 amino acids and a C-terminal transmembrane contain domain with a short cytoplasmic tail. Heavily O-glycosylated; expresses both type 1 and type 2 core glycans. Heavily N-glycosylated; expresses primarily high mannose and complex bisecting type N-linked glycans. May be phosphorylated. Phosphorylation of the intracellular C-terminal domain may induce proteolytic cleavage and the liberation of the extracellular domain into the extracellular space. May contain numerous disulfide bridges. Association of several molecules of the secreted form may occur through interchain disulfide bridges providing an extraordinarily large gel-like matrix in the extracellular space or in the lumen of secretory ducts. The number of repeats is highly polymorphic and can be composed between 12 and 60 extracellular mucin repeats. Antigen that is the basis for a widely used serum assay for the monitoring of patients with ovarian epithelial cancer. Due to lack of sensitivity for stage I disease and lack of specificity, it is of little value in the detection of early ovarian cancer. Due to its similarly elevated levels in some nonmalignant conditions, it is not specific enough to be used for population screening. Truncated N-terminus.