Fabian Kiessling

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

Abstract Endothelial cells separate the intra- and extravascular space and regulate transport processes between these compartments. Since intercellular junctions are required for these specific cell functions, the cell-cell contacts in 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-grown ECV304 cells generate a distinct electrical resistance and a permeability barrier between cell culture compartments. Electron microscopy of ECV304 cells revealed lateral membrane interdigitations, typically found in endothelial cells in vivo, with direct membrane contact sites, which prevented the diffusion of lanthanum. By immunoblot and immunofluorescence analysis, the expression and cellular localization of the tight junction and adherens-type junction proteins occludin, ZO-1, symplekin, β-catenin, and plakoglobin were analyzed. ECV304 cells display further characteristics of endothelial cells, including the expresssion of thrombomodulin and of the vitronectin receptor CD51, as well as the secretion of plasminogen activator inhibitor 1 (PAI-1) and endothelin. However, ECV304 cells also express proteins characteristically found in epithelial cells, including E-cadherin and the desmosomal proteins desmoplakin, desmocollin, and desmoglein; occasionally desmosomal structures can be identified by electron microscopy. In conclusion, ECV304 cells express many endothelial markers and form specialized intercellular junctions that display some epithelial features. Thus this reportedly endothelial-derived permanent human cell line may be dedifferentiated toward an epithelial phenotype.

POLARIZED EXPRESSION OF HETEROLOGOUS MEMBRANE PROTEINS TRANSFECTED IN A HUMAN ENDOTHELIAL-DERIVED CELL LINE

The generation and maintenance of cell polarity in endothelial cells is poorly understood, partly because of a lack of a permanent endothelial in vitro model system. Here we evaluated the spontaneously immortalized human endothelial-derived cell line ECV304 as an in vitro model system for the study of the polarized expression of heterologous membrane proteins. Several stable ECV304 clones were generated by calcium phosphate transfection/G418 selection with cDNAs encoding membrane proteins of known cell surface distribution in the epithelial Madin Darby canine kidney (MDCK) cell line: influenza hemagglutinin and uvomorulin/E-cadherin were used as markers for the apical, respectively lateral cell membrane, the human lymphocyte surface marker CD7 served as an example of a circumferentially distributed membrane protein. Analysis of the transfected ECV304 clones using conventional and confocal immunofluorescence microscopy and immunoelectron microscopy revealed the same membrane distribution of the heterologous proteins in ECV304 cells as in MDCK cells. This polarized expression of heterologous membrane proteins in the endothelial-derived ECV304 cell line indicates efficient protein sorting/membrane trafficking mechanisms. The apical, lateral and basal cell membrane domains could be distinguished in ECV304 cells by confocal immunofluorescence microscopy. The permanent endothelial-derived ECV304 cell line may be a useful in vitro model system for the study of endothelial cell polarity.

Influence of intercellular junctions on endothelin secretion of human umbilical vein endothelial cells in vitro.

Abstract The endothelium plays a pivotal role in the theological regulation of blood flow by the secretion of vasoactive factors. The interaction between shear forces and the endothelium is determined by the mechanical properties of the endothelial cell layer which are associated with intercellular junctions. Cell-cell contacts could therefore modulate the secretion of vasocative factors in response to theological stimuli. We investigated the relationship between intercellular junctions and the secretion of the vasoconstrictor peptide endothelin and the coagulation co-factor von Willebrand factor (vWF). Human umbilical vein endothelial cells (HUVECs) were used as in vitro endothelial model system. Intercellular junctions were reversibly disrupted by calcium chelation or hypertonic stress; alternatively, the formation of intercellular junctions was inhibited by culturing the cells in suspension or by plating them in the presence of an inhibitory anti-VE-cadherin antibody. The opening of intercellular junctions was verified by assessing transmonolayer electrical resistance (TMR) and immunofluorescence morphology. The concentration of endothelin and vWF was measured in the cell culture supernatants using specific ELISAs. The secretion of endothelin was inhibited by EGTA (5 mM) and stimulated by incubation with tumor necrosis factor α (TNFα, 40 ng/ml). Treatment with hypertonic medium (glycerol, 1200 mosmol/l) for 10 minutes opened intercellular junctions and markedly reduced the secretion of endothelin. HUVECs in suspension culture did not secrete endothelin and failed to respond to TNFα, but readily resumed these functions upon forming a new monolayer on plastic. The reconstitution of intercellular junctions after suspension culture could be inhibited using a specific anti-VE-cadherin antibody. This antibody, but not a non-specific anti-humanIgG antibody reduced endothelin secretion. The secretion of von Willebrand Factor was less dependent on intercellular junctions. The opening of intercellular junctions did not induce cell death, since the cells continued to exclude trypan blue. The results of this study suggest a novel and potentially pathophysiologically/clinically relevant correlation between intercellular junctions and the secretion of endothelin in endothelial cells.