Chemokine stimulation of lymphocyte alpha 4 integrin avidity but not of leukocyte function-associated antigen-1 avidity to endothelial ligands under shear flow requires cholesterol membrane rafts

Abstract

VLA-4 and LFA-1 are the major vascular integrins expressed on circulating lymphocytes. Previous studies suggested that intact cholesterol rafts are required for integrin adhesiveness in different leukocytes. We found the alpha(4) integrins VLA-4 and alpha(4)beta(7) as well as the LFA-1 integrin to be excluded from rafts of human peripheral blood lymphocytes. Disruption of cholesterol rafts with the chelator methyl-beta-cyclodextrin did not affect the ability of these lymphocyte integrins to generate high avidity to their respective endothelial ligands and to promote lymphocyte rolling and arrest on inflamed endothelium under shear flow. In contrast, cholesterol extraction abrogated rapid chemokine triggering of alpha(4)-integrin-dependent peripheral blood lymphocytes adhesion, a process tightly regulated by G(i)-protein activation of G protein-coupled chemokine receptors (GPCR). Strikingly, stimulation of LFA-1 avidity to intercellular adhesion molecule 1 (ICAM-1) by the same chemokines, although G(i)-dependent, was insensitive to raft disruption. Our results suggest that alpha(4) but not LFA-1 integrin avidity stimulation by chemokines involves rapid chemokine-induced GPCR rearrangement that takes place at cholesterol raft platforms upstream to G(i) signaling. Our results provide the first evidence that a particular chemokine/GPCR pair can activate different integrins on the same cell using distinct G(i) protein-associated machineries segregated within defined membrane compartments.