A monoclonal antibody identifies a novel GPI-anchored glycoprotein involved in epithelial intercellular adhesion

BD31 mAb, raised against a line of gastric carcinoma cells, reacts with intercellular boundaries of human transformed cells originating from carcinomas or sarcomas growing in epithelial-like clusters as well as in primary cultures of epithelial and endothelial cells. BD31 also reacts with intercellular rims of normal and transformed epithelial tissues and is particularly abundant in glands and fast-growing epithelia but absent in nervous and muscle tissues as well as in blood and in mesenchyme-derived cells. Confocal analysis indicates that BD31 is located in dots at cell-cell contacts but not in basal and apical domains of cultured and in situ epithelial cells. mAb BD31 precipitates a 100 kDa protein from cells labeled with [³⁵S]methionine or [³H]glucosamine as well as from ¹²⁵I-surface-labeled cells. This glycoprotein resists to trypsin in the presence of Ca²⁺, releases an 80 kDa fragment in the medium and does not react with antibodies to the conserved cytodomain of known cadherins or, specifically, to the ectodomain of E-cadherin in western blotting; moreover, the lack of cadherin cytodomain and protein removal by phosphoinositide-specific phospkolipase indicate its membrane anchoring by a glycosyl-phosphatidylinositol (GPI) moiety. BD31 IgGs do not impair cell-matrix adhesion but induce inhibition of Ca²⁺-dependent aggregation, loss of cell-cell adhesion, scattering of confluent cells and appearance of migratory cell phenotypes in a dose- and time-dependent manner. This novel GPI-anchored glycoprotein may regulate intercellular adhesion by a mechanism involving membrane-associated phospholipases.