DISTINCT GLYCOFORMS OF A TUMOR-SPECIFIC GLYCOPROTEIN, GP200, IN HUMANTESTIS AND TESTICULAR-TUMORS

We recently purified a 200 kD peanut agglutinin-binding glycoprotein f rom the embryonal carcinoma cell line HT-E (833K) that is expressed se lectively in nonseminomatous germ cell tumors. We now further characte rize gp200 using Western blot analysis to compare normal and malignant testicular germ cells for reactivity to peanut agglutinin, a plant le ctin that recognizes terminal D-galactosyl residues, and GCTM-2, a mon oclonal antibody that recognizes a 200 kD keratan-sulfate proteoglycan on human embryonal carcinoma. The results indicate that normal germ c ells express gp200 as a membrane-bound 230 kD glycoform that expresses terminal galactose residues. This 230 kD glycoprotein is absent on sp ermatozoa but present on seminomatous germ cell tumors and somatic tis sue and does not express terminal galactose on its carbohydrate side c hains. In contrast, nonseminomatous germ cell tumors express a heavily sialylated glycoform of gp200 that does express terminal galactose re sidues. These results describe a glycoprotein that exists in several g lycoforms in normal and malignant testicular germ cells. The different ial expression of these glycoforms may help in understanding the ontog eny of germ cell tumors.