title: Apical topography and modulation of ICAM-1 expression on activated endothelium.
abstract: Leukocyte-endothelium interactions and general inflammatory responses are contributed by the regulated expression of intercellular adhesion molecule-1 (ICAM-1) on endothelium. It is now shown by confocal fluorescence microscopy and immunogold transmission electron microscopy that ICAM-1 was exclusively localized on the apical (luminal) membrane of cytokine-activated human umbilical vein endothelial cells. In contrast, other cell adhesion-promoting molecules, including beta 1 integrins, were expressed exclusively on the basolateral endothelial cell membrane, under the same experimental conditions. Kinetic binding studies of a 125I-labeled monoclonal antibody to ICAM-1 revealed that approximately 8% of membrane ICAM-1 on cytokine-activated endothelium was internalized in both coated and non-coated vesicles at 37 degrees C, with a t1/2 of approximately 18 min and a rate of approximately 3200 molecules/minute. This internalization pathway was directly dependent upon the level of ICAM-1 expression on the cell surface. Genetically engineered ICAM-1 transfectants, expressing a 10-fold higher receptor density than activated endothelium, internalized approximately 18% of membrane ICAM-1 at a rate of 75,000 molecules/minute with a t1/2 of approximately 22 min. These findings suggest that a combined pathway of polarized membrane topography and receptor trafficking may regulate ICAM-1-dependent adhesion at the site of vascular injury and endothelial cell activation.
mesh_terms: D002448:Cell Adhesion; D002454:Cell Differentiation; D016207:Cytokines / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000737:chemistry* / Q000187:drug effects / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000187:drug effects / Q000648:ultrastructure*; D018613:Microscopy, Confocal; D014162:Transfection; D014470:Umbilical Cord / Q000737:chemistry
chemical_list: D016207:Cytokines; D018799:Intercellular Adhesion Molecule-1