UDP acts as a growth factor for vascular smooth muscle cells by activation of P2Y6 receptors

1 Division of Experimental Vascular Research, Department of Medicine, University Hospital, SE-221 85 Lund, Sweden; Departments of 2 Pharmacology and 3 Medicine, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599; 4 Department of Pharmacology, Duke University Medical Center, Durham, North Carolina 27710; 5 Inspire Pharmaceuticals Incorporated, Durham, North Carolina 27700; and Departments of 6 Oncology and 7 Cardiology, University Hospital, SE-221 85 Lund, Sweden Mitogenic effects of the extracellular nucleotides ATP and UTP are mediated by P2Y 1 , P2Y 2 , and P2Y 4 receptors. However, it has not been possible to examine the highly expressed UDP-sensitive P2Y 6 receptor because of the lack of stable, selective agonists. In rat aorta smooth muscle cells (vascular smooth muscle cells; VSMC), UDP and UTP stimulated 3 H-labeled thymidine incorporation with similar pEC 50 values (5.96 and 5.69). Addition of hexokinase did not reduce the mitogenic effect of UDP. In cells transfected with P2Y receptors the stable pyrimidine agonist uridine 5'- O -(2-thiodiphosphate) (UDP S) was specific for P2Y 6 with no effect on P2Y 1 , P2Y 2 , or P2Y 4 receptors. UDP S stimulated [ 3 H]thymidine and [ 3 H]leucine incorporation and increased cell number in VSMC. Flow cytometry demonstrated that UDP stimulated cell cycle progression to both the S and G 2 phases. The intracellular signal pathways were dependent on phospholipase C, possibly protein kinase C- , and a tyrosine kinase pathway but independent of G i proteins, eicosanoids, and protein kinase A. The half-life of P2Y 6 receptor mRNA was