Novel function of the cell adhesion molecule uvomorulin as an inducer of cell surface polarity

Na⁺,K⁺-ATPase has distinctly different distributions in mesenchymal cells, where it has an unrestricted distribution over the entire cell surface, compared with polarized epithelial cells, where it is restricted to the basal-lateral membrane domain. The generation of this restricted distribution is important in mesenchyme to epithelia conversion in development and the function of transporting epithelia, but the mechanisms involved are unknown. Here we show that expression of the epithelial CAM uvomorulin in transfected fibroblasts is sufficient to induce a redistribution of Na⁺,K⁺-ATPase to sites of uvomorulin-mediated cell-cell contacts, similar to that in polarized epithelial cells. This restricted distribution of Na⁺,K⁺-ATPase occurs in the absence of tight junctions but coincides with the reorganization of the membrane cytoskeleton. The results indicate a direct role for CAMs as inducers of cell surface polarity of selective cytoplasmic and membrane proteins.