Identification and Characterization of a Cell-Surface Receptor, P2Y15, for AMP and Adenosine

Abstract

AMP and adenosine are found in all cell types and can be released by cells or created extracellularly from the breakdown of ATP and ADP. We have identified an orphan G protein-coupled receptor with homology to the P2Y family of nucleotide receptors that can respond to both AMP and adenosine. Based on its ability to functionally bind the nucleotide AMP, we have named it P2Y15. Upon stimulation, P2Y15 induces both Ca 2؉ mobilization and cyclic AMP generation, suggesting coupling to at least two different G proteins. It is highly expressed in mast cells and is found predominantly in the tissues of the respiratory tract and kidneys, which are known to be affected by AMP, adenosine, and adenosine antagonists. Until now, the effects of AMP have been thought to depend on its dephosphorylation to adenosine but we demonstrate here that P2Y15 is a bona fide AMP receptor by showing that it binds [ 32 P]AMP. Because AMP and adenosine have bronchoconstrictive effects that can be inhibited by theophylline, we tested whether theophylline and other adenosine receptor antagonists can block P2Y15. We found inhibition at a theophylline concentration well within the therapeutic dose range, indicating that P2Y15 may be a clinically important target of this drug.Adenosine can mediate diverse physiological effects including bronchoconstriction, inhibition of platelet aggregation, inhibition of lipolysis, induction of sedation, vasodilation, suppression of cardiac rate and contractility, and stimulation of gluconeogenesis. To date, five cell-surface receptors have been identified for adenosine, namely adenosine receptors A1, A2A, A2B, and A3 (collectively referred to as P1 receptors) and the growth hormone secretagogue receptor (1, 2). AMP has a similarly diverse repertoire of effects (3-6) including bronchoconstriction, stimulation of DNA synthesis, mitogenesis, and stimulation of chloride secretion, but no receptor for AMP has previously been reported. Numerous cell types can release adenosine including mast cells (7), kidney brush border cells (8), and cardiac cells (9), whereas AMP can be released by such cell types as activated platelets (10), neutrophils (4), and eosinophils (11). AMP can also be generated extracellularly from the hydrolysis of ATP and ADP by ecto-ATPases (12) and ecto-ATP diphosphohydrolases (13) and can be further dephosphorylated by ecto-5Ј-nucleotidases to produce adenosine (14).

Identification of GPR99 Protein as a Potential Third Cysteinyl Leukotriene Receptor with a Preference for Leukotriene E4 Ligand

“…By a quantitative RT-PCR, human GPR99 mRNA is predominantly expressed in trachea, salivary glands, kidney, fetal brain, and lung and highly expressed in umbilical cord blood-derived mast cells (27). A quantitative RT-PCR analysis in the mouse revealed that GPR99 mRNA is highly expressed in kidney, testis, and smooth muscle (23).…”

Agonists and Antagonists for P2 Receptors

“…We ought to mention that recently a P2Y 15 receptor was proposed (Inbe et al 2004), which was said to be activated by adenosine and AMP. Papers were published subsequently that negated this claim (e.g.…”

Neuroprotective roles of the P2Y2 receptor

“…Activation of the G q -coupled P2Y 2 R by ATP or UTP (EC 50 ∼1-6 μM) [7,74] is linked to the stimulation of PLC leading to an increase in the production of inositol 1,4,5 trisphosphate (IP 3 ) and diacylglycerol that elevates the intracellular Ca 2+ concentration, [Ca 2+ ] i , and activates protein kinase C (PKC), respectively [73,87]. Recent studies have demonstrated that the P2Y 2 R can activate signaling pathways independent of coupling to G q protein.…”

“…It has become apparent that P2 receptors for extracellular nucleotides are ubiquitously expressed in a wide variety of tissues, and the complexity of responses to nucleotides is due in large part to the presence of multiple subtypes of P2X receptor ligand-gated ion channels and G protein-coupled P2Y receptors [1][2][3][4][5][6][7]. This functional complexity is well manifested in the central nervous system (CNS) where 7 P2X and 8 P2Y receptor subtypes are expressed under a range of conditions in several different interacting cell types [6,[8][9][10][11][12].…”