THE LOCALIZATION OF PLATELET GpIIb-IIIa RELATED PROTEINS IN ENDOTHELIAL CELL ADHESION STRUCTURE

Abstract

Different laboratories bave reported that human endothelial cells (EC) synthesize and express surface proteins biochemically and immunologically related to platelet GpIIb-IIIa. However the functional role of this glycoprotein complex in EC has not yet been elucidated. In this study we investigated whether these molecules are involved in the process of EC adhesion to different substrata. Cultured human umbilical vein ECs ,seeded on purified fibrinogen(fg), or vitronectin(VN) coated coverslips, adhered ,underwent spreading, organization of thick microfilament bundles and formation of focal contacts as shown by immunofluorescence and interference reflection microscopy.Polyclonal antibodies raised against human platelet GpIIb-IIIa and cross reacting with the EC form, showed by immunofluorescence a discrete and well organized distribution at cell adhesion structures, Indeed they distributed at vinculin rich focal contacts at the membrane insertion of microfilament bundles of stress fiber type.They were also found at cell to cell contacts and in a diffuse pattern at the dorsal surface of EC.GpIIb-IIIa antibodies added to EC suspensions prior to plating inhibited EC adhesion and spreading in a concentration dependent way. This effect was present at different degrees when EC were seeded on fg or VN being clearly more evident on VN and somehow less apparent on fg.In addition when the antibodies were added to confluent EC monolayers for 24 h they disrupted cell to cell contacts and caused cell rounding and detachment Preimmune serum or control antibodies able to bind to EC external membrane but which did not recognized GpIIb-IIIa proteins were unable to inhibit EC attachment and spreading. These results indicate that EC GpIIb-IIIa complex is involved in the adhesion mechanism of these cells to extracellular matrix proteins.