Platelet/endothelial cell adhesion molecule-1 (PECAM-1) is localized over the entire plasma membrane of endothelial cells.
The subcellular localization of PECAM-1 in endothelial cells was examined by using advanced morphological techniques, such as confocal scanning microscopy and immunolabeling procedures for electron microscopy. The localization of PECAM-1 was studied immunohistochemically with five specific monoclonal antibodies and one polyclonal antibody (all anti-human) in human and rabbit myocardium and in isolated endothelial cells. In vivo, PECAM-1 was localized uniformly on the plasma membrane of all vascular endothelial cells, predominantly on the luminal side of vessels. No specific increase in labeling was found at sites of cell-to-cell contact. In vitro, primary isolated cells (human umbilical vein endothelial cells) showed continuous labeling of the entire cell membrane. Cells of higher passages were labeled in a manner similar to freshly isolated cells. Our findings refute the commonly accepted hypothesis that PECAM-1 is localized only at cell-to-cell contacts. Further, we have not been able to confirm the hypothesis regarding the important mechanical role of PECAM-1 in stabilizing the endothelial monolayer. Since PECAM-1 is also expressed on platelets and is known to bind to itself, the way in which PECAM-1-positive endothelial cells are protected against binding of PECAM-1-positive platelets remains unclear. In view of these findings, the role of PECAM-1 in the leukocyte migration cascade needs to be re-evaluated.
Scholz
D
D
Max Planck Institute, Department of Experimental Cardiology, Benekestrasse 2, D-61231 Bad Nauheim, Germany. dscholz@kerckhoff.mpg.de
Schaper
J
J
D000818:Animals; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure*; D006801:Humans; D018613:Microscopy, Confocal; D016253:Microscopy, Immunoelectron; D009206:Myocardium / Q000276:immunology / Q000378:metabolism / Q000648:ultrastructure; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism*; D011817:Rabbits
D019408:Platelet Endothelial Cell Adhesion Molecule-1