Analysis of intercellular adhesion molecules in endothelial cells

Abstract Intercellular adhesion between endothelial cells (ECs) is mediated by members of the cadherin, immunoglobulin, integrin, and proteoglycan families of cell adhesion molecules. Some of these molecules are concentrated at intercellular structures known as adherens junctions and tight junctions. Other molecules, such as platelet–endothelial cell adhesion molecule-1 (PECAM-1), are localized at cell–cell contacts, but outside of the junctional complexes. Although the morphological and molecular organization of these complexes are similar in ECs and in other cell types, some components are more specific for the endothelium. For instance, vascular endothelial-cadherin (VE-cadherin) is expressed exclusively in ECs at the adherens junctions, while claudin-5 and the alpha minus isoform of zonula occludens-1 (ZO-1), two tight junction components, are expressed preferentially in the endothelium (1, 2). By interacting (either homophilically or heterophilically) with their receptors, junctional adhesive molecules provide physical links that hold ECs together and regulate the paracellular passage of ions, solutes, and transmigrating leukocytes. Also, by interacting with intracellular partners, the adhesive receptors may strengthen their own linkage with the cytoskeleton. Finally, besides providing attachment for neighbouring cells and the cytoskeleton, junctional molecules may also impinge upon cell signalling and trigger responses that are translated into changes in cell morphology and eventually in the organization of three-dimensional networks of patent tubes (3).