Extracellular
nucleotides bind to type-2 purinergic/pyrimidinergic (P2) receptors that mediate various responses, such as cell activation, proliferation and apoptosis, implicated in inflammatory processes. The role of P2 receptors and their associated signal transduction pathways in endothelial cell responses has not been fully investigated. Here, it is shown that stimulation of human umbilical vein endothelial cells (HUVEC) with extracellular
ATP or
UTP increased intracellular free
calcium ion concentrations ([Ca(2+)](i)), induced phosphorylation of
focal adhesion kinase (FAK), p130(cas) and
paxillin, and caused cytoskeletal rearrangements with consequent cell migration. Furthermore,
UTP increased migration of HUVEC in a
phosphatidylinositol 3-kinase (PI3-K)-dependent manner.
BAPTA or
thapsigargin inhibited the extracellular
nucleotide-induced increase in [Ca(2+)](i), a response crucial for both FAK phosphorylation and cell migration. Furthermore, long-term exposure of HUVEC to
ATP and
UTP, agonists of the
G protein-coupled P2Y2 and
P2Y4 receptor subtypes, caused upregulation of
alpha(v) integrin expression, a
cell adhesion molecule known to directly interact with
P2Y2 receptors. Our results suggest that extracellular
nucleotides modulate signaling pathways in HUVEC influencing cell functions, such as cytoskeletal changes, cellular adhesion and motility, typically associated with
integrin-activation and the action of
growth factors. We propose that P2Y2 and possibly
P2Y4 receptors mediate those responses that are important in vascular
inflammation,
atherosclerosis and angiogenesis.