Mesothelin is a 40kD glycosylphosphatidylinositol-anchored glycoprotein that is expressed on mesothelial cells in the pleura, pericardium and peritoneum and overexpressed in mesotheliomas and ovarian or pancreatic adenocarcinoma.
Mesothelin is a product of the CAK-1 gene, which also encodes megakaryocyte-potentiating factor (MPF).
Mature human mesothelin shares 60% amino acid identity with either mouse or rat mesothelin.
Two variant forms exist; variant 1 has an eight amino acid (1kD) insertion and is rarely expressed, while variant 2 is a truncated form secreted in the majority of ovarian cancers but rarely found in normal individuals.