The Ca-MOv18 molecule, a cell-surface marker of human ovarian carcinomas, is anchored to the cell membrane by phosphatidylinositol

The struture of the 38 kD cell surface glycoprotein identified by the monoclonal antibody MOv18 and specifically expressed by human ovarian carcinomas has been investigated at a molecular level. The ovarian carcinoma cell line IGROV-1, which expresses high levels of Ca-MOv18, was treated with the phosphatidylinositol-specific phospholipase C from B. thuringiensis. The phospholipase C specifically released most of the Ca-MOv18 molecules as shown by flow cytometric analysis of the treated cells and by radioimmunometric assays of the corresponding supernatants. Consistent with the known structure of other phosphatidylinositol-linked molecules, Ca-MOv18 was biosynthetically labeled by [³H]ethanolamine and the labeled molecules were immunoprecipitated from the supernatant of the phospholipase C treated cells. Evidence that Ca-MOv18 is anchored to the cell membrane via phosphatidylinositol may prove to be relevant in current investigations regarding the biological and clinical significance of this tumor marker.