Cell-cell contacts in the human cell line ECV304 exhibit both endothelial and epithelial characteristics

Endothelial cells separate the intra- and extravascular space and regulate transport processes between these compartments. Since intercellular junctio ns are required for these specific cell functions, the cell-cell contacts i n the permanent cell line ECV304 were systematically analyzed and compared with human umbilical vein endothelial cells (HUVECs) in primary culture and with the epithelial Madin Darby Canine Kidney (MDCK) cell line. Filter-gro wn ECV304 cells generate a distinct electrical resistance and a permeabilit y barrier between cell culture compartments. Electron microscopy of ECV304 cells revealed lateral membrane interdigitations, typically found in endoth elial cells in vivo, with direct membrane contact sites, which prevented th e diffusion of lanthanum. By immunoblot and immunofluorescence analysis, th e expression and cellular localization of the tight junction and adherens-t ype junction proteins occludin, ZO-1, symplekin, beta-catenin, and plakoglo bin were analyzed. ECV304 cells display further characteristics of endothel ial cells, including the expresssion of thrombomodulin and of the vitronect in receptor CD51, as well as the secretion of plasminogen activator inhibit or 1 (PAI-1) and endothelin. However, ECV304 cells also express proteins ch aracteristically found in epithelial cells, including E-cadherin and the de smosomal proteins desmoplakin, desmocollin, and desmoglein; occasionally de smosomal structures can be identified by electron microscopy. In conclusion , ECV304 cells express many endothelial markers and form specialized interc ellular junctions that display some epithelial features. Thus this reported ly endothelial-derived permanent human cell line may be dedifferentiated to ward an epithelial phenotype.