AN ANTIGLYCOLIPID ANTIBODY INHIBITS MADIN-DARBY CANINE KIDNEY-CELL ADHESION TO LAMININ AND INTERFERES WITH BASOLATERAL POLARIZATION AND TIGHT JUNCTION FORMATION

Epithelial cells polarize not only in response to cell-cell contacts, but also to contacts with a substratum composed of extracellular matri x molecules. To probe the role of specific matrix constituents in epit helial cell polarization, we investigated the effects of an adhesion-b locking mAb, 12B12, on initial polarization of MDCK cells. The 12B12 a ntibody, raised against whole MDCK cells, blocks adhesion to laminin b y 65% but has no effect on adhesion of cells to collagen type I. Takin g advantage of this antibody's function-blocking activity, as well as the fact that MDCK cells secrete laminin, the role of endogenous lamin in in polarization was examined by plating cells on collagen-coated su bstrata in the presence of the antibody. Under these conditions, cell spreading was reduced 1.5 h after plating, and cells were flatter and had fewer microvilli after 24 h. Even though lateral cell membranes we re closely apposed, transepithelial resistance in the presence of the antibody was significantly reduced relative to controls. When the pola rization of specific apical and basolateral markers was examined both biochemically and immunocytochemically in the presence of the antibody , we observed that the apical marker polarized at normal rates while b asolateral markers did not. Surprisingly, the 12B12 antibody was not d irected against any known cell adhesion protein but reacted specifical ly with Forssman antigen, a glycosphingolipid. These results suggest t hat glycolipids may play a significant role in cell adhesion via lamin in and in epithelial cell polarization.