Summary

Extracellular nucleotides bind to type-2 purinergic/pyrimidinergic(P2) receptors that mediate various responses, such as cellactivation, proliferation and apoptosis, implicated in inflammatoryprocesses. The role of P2 receptors and their associatedsignal transduction pathways in endothelial cell responses hasnot been fully investigated. Here, it is shown that stimulation ofhuman umbilical vein endothelial cells (HUVEC) with extracellularATP or UTP increased intracellular free calcium ion concentrations([Ca2+] i ), induced phosphorylation of focal adhesion kinase(FAK), p130^cas and paxillin, and caused cytoskeletal rearrangementswith consequent cell migration. Furthermore, UTPincreased migration of HUVEC in a phosphatidylinositol 3-kinase(PI3-K)-dependent manner. BAPTA or thapsigargin inhibited the extracellular nucleotide-induced increase in [Ca2+]_i ,a response crucial for both FAK phosphorylation and cell migration.Furthermore, long-term exposure of HUVEC to ATPand UTP, agonists of the G protein-coupled P2Y2 and P2Y4 receptorsubtypes, caused upregulation of a v integrin expression,a cell adhesion molecule known to directly interact with P2Y2receptors. Our results suggest that extracellular nucleotidesmodulate signaling pathways in HUVEC influencing cell functions,such as cytoskeletal changes, cellular adhesion and motility,typically associated with integrin-activation and the action ofgrowth factors.We propose that P2Y2 and possibly P2Y4 receptorsmediate those responses that are important in vascular inflammation,atherosclerosis and angiogenesis.