Normal airways homeostatically regulate the volume of airway surface liquid (ASL) through both cAMP-and Ca 2+ -dependent regulation of ion and water transport. In cystic fibrosis (CF), a genetic defect causes a lack of cAMP-regulated CFTR activity, leading to diminished Cl -and water secretion from airway epithelial cells and subsequent mucus plugging, which serves as the focus for infections. Females with CF exhibit reduced survival compared with males with CF, although the mechanisms underlying this sex-related disadvantage are unknown. Despite the lack of CFTR, CF airways retain a limited capability to regulate ASL volume, as breathing-induced ATP release activates salvage purinergic pathways that raise intracellular Ca 2+ concentration to stimulate an alternate pathway to Cl -secretion. We hypothesized that estrogen might affect this pathway by reducing the ability of airway epithelia to respond appropriately to nucleotides. We found that uridine triphosphate-mediated (UTP-mediated) Cl -secretion was reduced during the periovulatory estrogen maxima in both women with CF and normal, healthy women. Estrogen also inhibited Ca 2+ signaling and ASL volume homeostasis in non-CF and CF airway epithelia by attenuating Ca 2+ influx. This inhibition of Ca 2+ signaling was prevented and even potentiated by estrogen antagonists such as tamoxifen, suggesting that antiestrogens may be beneficial in the treatment of CF lung disease because they increase Cl -secretion in the airways.

The P2Y 14 receptor was initially identified as a G protein-coupled receptor activated by UDP-glucose and other nucleotide sugars. We have developed several cell lines that stably express the human P2Y 14 receptor, allowing facile examination of its coupling to native G i family G proteins and their associated downstream signaling pathways (J Pharmacol Exp Ther 330: [162][163][164][165][166][167][168] 2009). In the current study, we examined P2Y 14 receptor-dependent inhibition of cyclic AMP accumulation in human embryonic kidney (HEK) 293, C6 glioma, and Chinese hamster ovary (CHO) cells stably expressing this receptor. Not only was the human P2Y 14 receptor activated by UDP-glucose, but it also was activated by UDP. The apparent efficacies of UDP and UDP-glucose were similar, and the EC 50 values (74, 33, and 29 nM) for UDP-dependent activation of the P2Y 14 receptor in HEK293, CHO, and C6 glioma cells, respectively, were similar to the EC 50 values (323, 132, and 72 nM) observed for UDP-glucose. UDP and UDP-glucose also stimulated extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in P2Y 14 receptor-expressing HEK293 cells but not in wild-type HEK293 cells. A series of analogs of UDP were potent P2Y 14 receptor agonists, but the naturally occurring nucleoside diphosphates, CDP, GDP, and ADP exhibited agonist potencies over 100-fold less than that observed with UDP. Two UDP analogs were identified that selectively activate the P2Y 14 receptor over the UDP-activated P2Y 6 receptor, and these molecules stimulated phosphorylation of ERK1/2 in differentiated human HL-60 promyeloleukemia cells, which natively express the P2Y 14 receptor but had no effect in wild-type HL-60 cells, which do not express the receptor. We conclude that UDP is an important cognate agonist of the human P2Y 14 receptor.The metabotropic P2Y receptors include a subgroup of five receptors, the P2Y 1 , P2Y 2 , P2Y 4 , P2Y 6 , and P2Y 11 receptors, that primarily signal through G q -activated signaling pathways and a subgroup of three receptors, the P2Y 12 , P2Y 13 , and P2Y 14 receptors, that primarily signal by activating heterotrimeric G proteins of the G i family (Abbracchio et al., 2006;Burnstock, 2007). The human P2Y 1 , P2Y 11 , P2Y 12 , and P2Y 13 receptors are activated by adenine nucleotides. The human P2Y 4 and P2Y 6 receptors are activated by uridine nucleotides, and the P2Y 2 receptor is activated by both ATP and UTP.

We previously synthesized a series of potent and selective A 3 adenosine receptor (AR) agonists (North-methanocarba nucleoside 5′-uronamides) containing dialkyne groups on extended adenine C2 substituents. We coupled the distal alkyne of a 2-octadiynyl nucleoside by Cu(I)-catalyzed "click" chemistry to azide-derivatized G4 (fourth-generation) PAMAM dendrimers to form triazoles. A 3 AR activation was preserved in these multivalent conjugates, which bound with apparent K i 0.1-0.3 nM. They were substituted with nucleoside moieties, solely or in combination with water-solubilizing carboxylic acid groups derived from hexynoic acid. A comparison with various amide-linked dendrimers showed that triazole-linked conjugates displayed selectivity and enhanced A 3 AR affinity. We prepared a PAMAM dendrimer containing equiproportioned peripheral azido and amino groups for conjugation of multiple ligands. A bifunctional conjugate activated both A 3 and P2Y 14 receptors (via amide-linked uridine-5′-diphosphoglucuronic acid), with selectivity in comparison to other ARs and P2Y receptors. This is the first example of targeting two different GPCRs with the same dendrimer conjugate, which is intended for activation of heteromeric GPCR aggregates. Synergistic effects of activating multiple GPCRs with a single dendrimer conjugate might be useful in disease treatment.

UDP-glucose (UDPG) and derivatives are naturally occurring agonists of the Gi protein-coupled P2Y14 receptor, which occurs in the immune system. We synthesized and characterized pharmacologically novel analogues of UDPG modified on the nucleobase, ribose, and glucose moieties, as the basis for designing novel ligands in conjunction with modeling. The recombinant human P2Y14 receptor expressed in COS-7 cells was coupled to phospholipase C through an engineered Galpha-q/i protein. Most modifications of the uracil or ribose moieties abolished activity; this is among the least permissive P2Y receptors. However, a 2-thiouracil modification in 15 (EC50 49 +/- 2 nM) enhanced the potency of UDPG (but not UDP-glucuronic acid) by 7-fold. 4-Thio analogue 13 was equipotent to UDPG, but S-alkylation was detrimental. Compound 15 was docked in a rhodposin-based receptor homology model, which correctly predicted potent agonism of UDP-fructose, UDP-mannose, and UDP-inositol. The hexose moiety of UDPG interacts with multiple H-bonding and charged residues and provides a fertile region for agonist modification.

The P2Y14 receptor is a relatively broadly expressed G protein-coupled receptor that is prominently associated with immune and inflammatory cells as well as with many epithelia. This receptor historically was thought to be activated selectively by UDP-glucose and other UDP-sugars. However, UDP is also a very potent agonist of this receptor, and may prove to be one of its most important cognate activators.

The P2Y 14 receptor, a nucleotide signaling protein, is activated by uridine-5′-diphosphoglucose 1 and other uracil nucleotides. We have determined that the glucose moiety of 1 is the most structurally permissive region for designing analogues of this P2Y 14 agonist. For example, the carboxylate group of uridine-5′-diphosphoglucuronic acid proved to be suitable for flexible substitution by chain extension through an amide linkage. Functionalized congeners containing terminal 2-acylaminoethylamides prepared by this stratgegy retained P2Y 14 activity, and molecular modeling predicted close proximity of this chain to the 2nd extracellular loop of the receptor. In addition, replacement of glucose with other sugars did not diminish P2Y 14 potency. For example, the [5″] ribose derivative had an EC 50 of 0.24 μM. Selective monofluorination of the glucose moiety indicated a role for the 2″-and 6″-hydroxyl groups of 1 in receptor recognition. The β-glucoside was 2-fold less potent than the native α-isomer, but methylene replacement of the 1″-oxygen abolished activity. Replacement of the ribose ring system with cyclopentyl or rigid bicyclo[3.1.0]hexane groups abolished activity. Uridine-5′-diphosphoglucose also activates the P2Y 2 receptor, but the 2-thio analogue and several of the potent modified-glucose analogues were P2Y 14 -selective.

Eight G protein-coupled receptors comprise the P2Y receptor family of cell signaling proteins.

G protein-coupled P2Y receptors (P2Y-R) are activated by adenine and uracil nucleotides. The P2Y 14 receptor (P2Y 14 -R) is activated by at least four naturally occurring UDP sugars, with UDPglucose (UDP-Glc) being the most potent agonist. With the goal of identifying a competitive antagonist for the P2Y 14 -R, UDP was examined for antagonist activity in COS-7 cells transiently expressing the human P2Y 14 -R and a chimeric G␣ protein that couples Gi-coupled receptors to stimulation of phosphoinositide hydrolysis. UDP antagonized the agonist action of UDP-Glc, and Schild analysis confirmed that the antagonism was competitive (pK B ϭ 7.28). Uridine 5Ј-O-thiodiphosphate also antagonized the human P2Y 14 -R (hP2Y 14 -R) with an apparent affinity similar to that of UDP. In contrast, no antagonist activity was observed with ADP, CDP, or GDP, and other uracil analogs also failed to exhibit antagonist activity. The antagonist activity of UDP was not observed at other hP2Y-R. In contrast to its antagonist action at the hP2Y 14 -R, UDP was a potent agonist (EC 50 ϭ 0.35 M) at the rat P2Y 14 -R. These results identify the first competitive antagonist of the P2Y 14 -R and demonstrate pharmacological differences between receptor orthologs.