Regulation of P2Y₁ Receptor-Mediated Signaling by the Ectonucleoside Triphosphate Diphosphohydrolase Isozymes NTPDase1 and NTPDase2

Abstract

Ectonucleoside triphosphate diphosphohydrolases (NTPDases) control the concentration of released extracellular nucleotides, but the precise physiological roles played by these isozymes in modulation of P2 receptor signaling remain unclear. Activation of the human P2Y 1 receptor was studied in the presence of NTPDase1 or NTPDase2 expressed either in the same cell as the receptor or in P2Y 1 receptor-expressing cells cocultured with NTPDaseexpressing cells. Coexpression of NTPDase1 with the P2Y 1 receptor resulted in increases in the EC 50 for 2Ј-methylthioadenosine 5Ј-diphosphate (2MeSADP; 12-fold), ADP (50-fold), and ATP (10-fold) for activation of phospholipase C. Similar effects were observed when the P2Y 1 receptor and NTPDase1 were expressed on different cells. These results are explained by the capacity of NTPDase1 to hydrolyze both nucleoside triphosphates and diphosphates. NTPDase2 preferentially hydrolyzes nucleoside triphosphates, and the presence of NTPDase2 under either coexpression or coculture conditions did not change the EC 50 of 2MeSADP, ADP, or adenosine 5Ј-O-(2-thiodiphosphate) for activation of the P2Y 1 receptor. However, the EC 50 for ATP was 15-fold lower in the presence of NTPDase2 than in cells expressing the P2Y 1 receptor alone. Whereas expression of NTPDase1 decreased basal activity of the P2Y 1 receptor, the presence of the NTPDase2 resulted in P2Y 1 receptor-dependent increases in basal activity. These results suggest that basal activity of the P2Y 1 receptor is maintained by paracrine or autocrine release of receptor agonists and that the biological and/or pharmacological response mediated by P2Y receptors in target tissues is highly dependent on the types of ectonucleotidases expressed in the vicinity of the receptor.

ADP mediates inhibition of insulin secretion by activation of P2Y13 receptors in mice

“…Effects of glucose on insulin and glucagon secretion in the presence of apyrase Apyrase rapidly eliminates ATP and ADP by degradation to AMP [28], which in turn may then be degraded to adenosine by CD73 [7]. Addition of 1 U/ml apyrase (Sigma) to pancreatic islets in the presence of 1 mmol/l glucose stimulated an increase in insulin release from 0.27±0.04 to 0.59±0.06 ng islet −1 h −1 (p<0.001).…”

“…The net pharmacological effects of extracellular ATP are difficult to predict since ATP by itself can stimulate P2Y 2 , P2Y 4 (in rodents), P2Y 11 and P2X 1 -P2X 7 receptors present on the cell surface [6]. Furthermore, ATP is rapidly degraded by ectonucleotidases to ADP [7], which can act on P2Y 1 , P2Y 12 and P2Y 13 receptors. ADP is then further degraded by ecto-5′-nucleotidase to adenosine, which in turn can activate four different adenosine receptors [8].…”

Cellular function and molecular structure of ecto-nucleotidases

“…These cells do not express P2 receptors and reveal low ecto-nucleotidase activity [169]. Ecto-nucleotidases selectively modulated the effective agonist concentration at P2Y 1 receptors on identical or also neighboring cells, either by degrading ATP or by generating ADP from ATP.…”

Extracellular nucleotide signaling in adult neural stem cells: synergism with growth factor-mediated cellular proliferation

“…Furthermore, nucleotides may play a significant role in the activation of neural progenitors following central lesions, including stroke, that result in the release of cellular nucleotides (Zhang et al, 2004). Ecto-nucleotidases can selectively modulate the effective agonist concentration at P2Y receptors on identical or also on neighboring cells, either by degrading ATP/UTP or by generating ADP/UDP (Alvarado-Castillo et al, 2005;Jhandier et al, 2005). The strong expression of NTPDase2 in type B cells in situ suggests that the effective concentration of ATP/UTP is reduced, whereas that of ADP/UDP is increased in the immediate environment of these progenitors.…”