Nucleotide receptor P2u partially mediates ATP-induced cell cycle progression of aortic smooth muscle cells

Abstract

mRNA of the P2u purinoceptor (or nucleotide receptor) is detected both by polymerase chain reaction or Northern blot analyses in cultured aortic smooth muscle cells. When added to the culture medium of these cells, UTP, a specific ligand of the P2u receptor, induces an increased expression of both immediate-early and delayed-early cell cycle-dependent genes. This induction demonstrates similar features (kinetics, concentration dependence) to those obtained after stimulation of aortic smooth cells by exogenous ATP, a common ligand for most P2 purinoceptors. In contrast, 2-methylthioATP, a preferential ligand for P2y purinoceptors, induces only a significant increase of immediate-early genes but not of delayed-early genes. Moreover, the 2-methylthioATP-induced responses (c-fos mRNA increase, free intracellular calcium transient) are lower than those induced by ATP or UTP and are complementary to those of UTP. These results demonstrate that functional P2u receptors are present on cultured aortic smooth muscle cells and suggest that the bulk of responses induced by extracellular ATP on cell cycle progression are mediated via P2u purinoceptors, a hypothesis confirmed by cytofluorometric studies. Since some ATP- or UTP-induced genes code for chemotactic proteins (monocyte chemoattractant protein-1 and osteopontin), this study suggests that these nucleotides may contribute to vascular or blood cell migration and proliferation and consequently to the genesis of arterial diseases.

P2 receptors in atherosclerosis and postangioplasty restenosis

“…The majority of the cells in intact blood vessels are SMC, which occupy most of the media, and are involved in vasoconstriction and vasorelaxation of the vessel. P2Y 2 Rs in SMC mediate the induction of immediate-early and delayed-early cell cycle-dependent genes, consistent with a role for P2Y 2 Rs in vascular proliferation of SMC [20, 21]. A recent study demonstrated that P2Y 2 is the predominant functional receptor that responds to ATP and UTP in rat aortic SMC [22].…”

“…Taken together, it seems that the principal receptor mediating UTP/UDP-induced contractile responses in blood vessels might be the P2Y 6 subtype. Other studies have reported the presence of both P2Y 4 and P2Y 6 receptors in rat aortic SMC [21, 28, 29]. P2Y 1 receptors are expressed in SMC of a number of blood vessel types and like their EC counterparts mediate vasodilatation most likely through the activation of K + channels (see [18] for review).…”

“…Nucleotides can also modulate rat aortic smooth muscle cell adhesion and migration by increasing the expression of osteopontin [51, 57], a protein involved in both processes. Moreover, extracellular nucleotides may play a role in intra-arterial attraction of monocytes by inducing an increased expression of monocyte-chemoattractant protein-1 by arterial SMC [21]. Stimulation of P2 receptors is coupled to the release of the proinflammatory cytokines interleukin (IL)-1β, IL-1α, IL-8, and tumor necrosis factor (TNF)-α (see [4] for review) that are of obvious relevance to inflammation in atherosclerosis.…”

“…The dramatic increase in P2Y 2 mRNA expression observed in balloon angioplasty-induced intimal lesions would suggest increased activity of extracellular nucleotides with consequent enhancement of cell proliferation and vasoreactivity. Indeed, extracellular nucleotides, particularly ATP and UTP, have been shown to induce cell cycle progression and proliferation of cultured arterial SMC [21, 49, 50, 51] and vasoconstriction in the absence of endothelial cells [17, 108, 109]. Since both neointimal hyperplasia and vasoconstrictive remodeling have been found to be involved in postangioplasty restenosis [1, 5, 107, 110], these findings suggest that extracellular nucleotides may play a significant role in this process, at least as long as functional endothelial cells, which regulate intimal thickening [111, 112] and nucleotide-induced vasorelaxation [113, 114], are not regenerated.…”

“…Although the expression of other P2 receptors has been described in arterial SMC [21, 29, 115], the P2Y 2 receptor seems to be more specifically involved in the response of SMC to ATP and UTP [116], particularly in the potentiation of proliferation [21, 50]. The effects of extracellular nucleotides are not only dependent on the nature and number of P2 receptors present on target cells, but also on the local concentrations of nucleotide agonists.…”