Extrajunctional distribution of N-cadherin in cultured human endothelial cells

Human endothelial cells contain prominent Ca(2+)-dependent intercellular adherens-type junctions (AJ), which are associated, at their cytoplasmic surfaces, with actin, vinculin and plakoglobin. The transmembrane adhesion molecules present in these sites are members of the cadherin family, which are recognized by a pancadherin serum, directed against the conserved C terminus of these molecules. Immunoblotting analysis of cultured human endothelial cells using these antibodies revealed three immunoreactive bands with apparent molecular masses of 135, 130 and 120 kDa. Cloning and sequencing of the 135 kDa cadherin from an endothelial cDNA expression library indicated that this molecule is a typical cadherin, essentially identical to N-cadherin. Transfection of cDNA encoding this molecule into CHO cells resulted in the induction of AJ formation and an apparent epithelialization of the cells. Immunofluorescent labeling with antibodies to chicken N-cadherin indicated that the molecule is associated with intercellular junctions in the transfectants. In contrast, cultured human umbilical cord endothelial cells exhibited a largely diffuse N-cadherin labeling over the entire cell surface with only occasional enrichment in cell-cell junctions. Comparison of this pattern with the discrete junctional labeling obtained with the pan-cadherin antibody suggests that different cadherins, co-expressed in the same endothelial cells, may undergo differential surface distribution.