ENDOTHELIAL-DEPENDENT MECHANISMS REGULATE LEUKOCYTE TRANSMIGRATION - A PROCESS INVOLVING THE PROTEASOME AND DISRUPTION OF THE VASCULAR ENDOTHELIAL-CADHERIN COMPLEX AT ENDOTHELIAL CELL-TO-CELL JUNCTIONS

Although several adhesion molecules expressed on leukocytes (beta 1 an d beta 2 integrins, platelet endothelial cell adhesion molecule 1 [PEC AM-1], and CD47) and on endothelium (intercellular adhesion molecule 1 , PECAM-1) have been implicated in leukocyte transendothelial migratio n, less is known about the role od endothelial lateral junctions durin g this process. We have shown previously (Read, M.A., A.S. Neish, F.W. Luscinskas, V.J. Palambella, T. Maniatis, and T. Collins. 1995. Immun ity. 2:493-506) that inhibitors of the proteasome reduce lymphocyte an d neutrophil adhesion and transmigration across TNF-alpha-activated hu man umbilical vein endothelial cell (EC) monolayers in an in vitro flo w model. The current study examined EC lateral junction proteins, prin cipally the vascular endothelial (VE)-cadherin complex and the effects of proteasome inhibitor; (MG132 and lactacystin) on lateral junctions during leukocyte adhesion, to gain a better understanding of the role of EC junctions in leukocyte transmigration. Both biochemical and ind irect immunofluorescence analyses of the adherens junction zone of EC monolayers revealed that neutrophil adhesion, not transmigration, indu ced disruption of the VE-cadherin complex and loss of its lateral junc tion localization. In contrast, PECAM-1, which is located at lateral j unctions and is implicated in neutrophil transmigration, was not alter ed. These findings identify new and interrelated endothelial-dependent mechanisms for leukocyte transmigration that involve alterations in l ateral junction structure and a proteasome-dependent event(s).