CHEMOKINES REGULATE CELLULAR-POLARIZATION AND ADHESION RECEPTOR REDISTRIBUTION DURING LYMPHOCYTE INTERACTION WITH ENDOTHELIUM AND EXTRACELLULAR-MATRIX - INVOLVEMENT OF CAMP SIGNALING PATHWAY

Leukocyte recruitment is a key step in the inflammatory reaction. Seve ral changes in the cell morphology take place during lymphocyte activa tion and migration: spheric-shaped resting T cells become polarized du ring activation, developing a well defined cytoplasmic projection desi gnated as cellular uropod. We found that the chemotactic and proinflam matory chemokines RANTES, MCP-1, and, to a lower extent, MIP-1 alpha, MTP-1 beta, and IL-8, were able to induce uropod formation and ICAM3 r edistribution in T lymphoblasts adhered to ICAM-1 or VCAM-1. A similar chemokine-mediated effect was observed during T cells binding to the fibronectin fragments of 38- and 80-kD, that contain the binding sites for the integrins VLA-4 and VLA-5, respectively. The uropod structure concentrated the ICAM-3 adhesion molecule (a ligand for LFA-1), and e merged to the outer milieu from the area of contact between lymphocyte and protein ligands. In addition, we found that other adhesion molecu les such as ICAM-1, CD43, and CD44, also redistributed to the lymphocy te uropod upon RANTES stimulation, whereas a wide number of other cell surface receptors did not redistribute. Chemokines displayed a select ive effect among different T cell subsets; MIP-1 beta had more potent action on CD8+ T cells and tumor infiltrating lymphocytes (TIL), where as RANTES and MIP-1 alpha targeted selectively CD4(+) T cells. We have also examined the involvement of cAMP signaling pathway in uropod for mation. Interestingly, several cAMP agonists were able to induce uropo d formation and ICAM-3 redistribution, whereas H-89, a specific inhibi tor of the cAMP-dependent protein kinase, abrogated the chemokine-medi ated uropod formation, thus pointing out a role for cAMP-dependent sig naling in the development of this cytoplasmic projection. Since the ly mphocyte uropod induced by chemokines was completely abrogated by Bord etella pertussis toxin, the formation of this membrane projection appe ars to be dependent on G proteins signaling pathways. In addition, the involvement of myosin-based cytoskeleton in uropod formation and ICAM -3 redistribution in response to chemokines was suggested by the preve ntion of this phenomenon with the myosin-disrupting agent butanedione monoxime. Interestingly, this agent also inhibited the ICAM-3-mediated cell aggregation, but not the cell adhesion to substrata. Altogether, these results demonstrate that uropod formation and adhesion receptor redistribution is a novel function mediated by chemokines; this pheno menon may represent a mechanism that significantly contributes to the recruitment of circulating leukocytes to inflammatory foci.