NON-POLARIZED EXPRESSION OF BASAL-CELL ADHESION MOLECULE B-CAM IN EPITHELIAL OVARIAN CANCERS

The basal cell adhesion molecule (B-CAM) is a M(r) 90,000 cell surface glycoprotein identified by two monoclonal antibodies (mAbs), F8 and G253, raised against human tumor cells. Cloning and sequence analysis of a B-CAM cDNA has revealed a characteristic immunoglobulin domain structure of the B-CAM polypeptide, most closely related to MUC18, a cell surface protein of invasive human melanomas. The pattern of B-CAM expression in cultured cells suggests that the molecule is associated with a substrate-adherent growth pattern in some lineages. Moreover, B-CAM expression is upregulated following malignant transformation in some cell types. In the present study, we have used immunohistochemical methods to examine S-CAM expression in normal and neoplastic tissues, including over 200 tumors of diverse histological type. B-CAM was detected in several normal tissues, including polarized expression in several epithelia and expression in vascular endothelium and smooth muscle. Among the tumors tested, B-CAM was found most uniformly and with a non-polarized pattern in epithelial cancers of the ovary (27 of 31 tumors B-CAM-positive), By contrast, only small subsets of epithelial cancers of other organs, including some neuroendocrine, breast, and lung carcinomas, showed uniform or polarized B-CAM expression. Most non-ovarian carcinomas, lymphomas, sarcomas, and neuroectodermal tumors tested were B-CAM-negative. Immunoprecipitation studies with ovarian carcinoma cell lines showed that B-CAM in these cells is a M, 90,000 glycoprotein, composed of M(r) 65,000-75,000 polypeptides with abundant, N-linked carbohydrate side chains. These findings identify B-CAM as a characteristic cell surface protein of epithelial ovarian cancers. The availability of B-CAM-specific mAbs and cDNAs may help identify the role of B-CAM in normal endothelial and epithelial cells and ovarian cancers.