Extracellular ATP couples to cAMP generation and granulocytic differentiation in human NB4 promyelocytic leukaemia cells

Noradrenaline and ATP regulate adiponectin exocytosis in white adipocytes: Disturbed adrenergic and purinergic signalling in obese and insulin-resistant mice

White adipocyte adiponectin exocytosis is triggered by cAMP and a concomitant increase of cytosolic Ca²⁺ potentiates its release. White adipose tissue is richly innervated by sympathetic nerves co-releasing noradrenaline (NA) and ATP, which may act on receptors in the adipocyte plasma membrane to increase cAMP via adrenergic receptors and Ca²⁺ via purinergic receptors. Here we determine the importance of NA and ATP for the regulation of white adipocyte adiponectin exocytosis, at the cellular and molecular level, and we specifically detail the ATP signalling pathway. We demonstrate that tyrosine hydroxylase (enzyme involved in catecholamine synthesis) is dramatically reduced in inguinal white adipose tissue (IWAT) isolated from mice with diet-induced obesity; this is associated with diminished levels of NA in IWAT and with a reduced ratio of high-molecular-weight (HMW) to total adiponectin in serum. Adiponectin exocytosis (measured as an increase in plasma membrane capacitance and as secreted product) is triggered by NA or ATP alone in cultured and primary mouse IWAT adipocytes, and enhanced by a combination of the two secretagogues. The ATP-induced adiponectin exocytosis is largely Ca²⁺-dependent and activated via purinergic P2Y2 receptors (P2Y2Rs) and the Gq11/PLC pathway. Adiponectin release induced by the nucleotide is abrogated in adipocytes isolated from obese and insulin-resistant mice, and this is associated with ∼70% reduced abundance of P2Y2Rs. The NA-triggered adiponectin exocytosis is likewise abolished in "obese adipocytes", concomitant with a 50% lower gene expression of beta 3 adrenergic receptors (β₃ARs). An increase in intracellular Ca²⁺ is not required for the NA-stimulated adiponectin secretion. Collectively, our data suggest that sympathetic innervation is a principal regulator of adiponectin exocytosis and that disruptions of this control are associated with the obesity-associated reduction of circulating levels of HMW/total adiponectin.

Bone marrow niche ATP levels determine leukemia-initiating cell activity via P2X7 in leukemic models

How particular bone marrow niche factors contribute to the leukemogenic activities of leukemia-initiating cells (LICs) remains largely unknown. Here, we showed that ATP levels were markedly increased in the bone marrow niches of mice with acute myeloid leukemia (AML), and LICs preferentially localized to the endosteal niche with relatively high ATP levels, as indicated by a sensitive ATP indicator. ATP could efficiently induce the influx of ions into LICs in an MLL-AF9-induced murine AML model via the ligand-gated ion channel P2X7. P2x7 deletion led to notably impaired homing and self-renewal capacities of LICs and contributed to an approximately 5-fold decrease in the number of functional LICs but had no effect on normal hematopoiesis. ATP/P2X7 signaling enhanced the calcium flux-mediated phosphorylation of CREB, which further transactivated phosphoglycerate dehydrogenase (Phgdh) expression to maintain serine metabolism and LIC fates. P2X7 knockdown resulted in a markedly extended survival of recipients transplanted with either human AML cell lines or primary leukemia cells. Blockade of ATP/P2X7 signaling could efficiently inhibit leukemogenesis. Here, we provide a perspective for understanding how ATP/P2X7 signaling sustains LIC activities, which may benefit the development of specific strategies for targeting LICs or other types of cancer stem cells.

A critical look at the function of the P2Y11 receptor

The P2Y11 receptor is a member of the purinergic receptor family. It has been overlooked, somewhat due to the lack of a P2ry11 gene orthologue in the murine genome, which prevents the generation of knockout mice, which have been so helpful for defining the roles of other P2Y receptors. Furthermore, some of the studies reported to date have methodological shortcomings, making it difficult to determine the function of P2Y11 with certainty. In this review, we discuss the lack of a murine "P2Y11-like receptor" and highlight the limitations of the currently available methods used to investigate the P2Y11 receptor. These methods include protein recognition with antibodies that show very little specificity, gene expression studies that completely overlook the existence of a fusion transcript between the adjacent PPAN gene and P2RY11, and agonists/antagonists reported to be specific for the P2Y11 receptor but which have not been tested for activity on numerous other adenosine 5'-triphosphate (ATP)-binding receptors. We suggest a set of criteria for evaluating whether a dataset describes effects mediated by the P2Y11 receptor. Following these criteria, we conclude that the current evidence suggests a role for P2Y11 in immune activation with cell type-specific effects.

Expression and function of P2 receptors in hematopoietic stem and progenitor cells

Nucleotides have unambiguously emerged as a family of mediators of intercellular communication, which bind to a class of plasma membrane receptors, P2 receptors, to trigger intercellular signaling. P2 receptors can be further divided into P2X and P2Y subfamilies based on structure and function. Different hematopoietic cells express diverse spectrums of P2 receptors at different levels, including hematopoietic stem and progenitor cells (HSPCs). Extracellular adenosine triphosphate (ATP) exerts different effects on HSPCs, regulating cell proliferation, differentiation, migration, and chemotaxis, release of cytokines or lysosomal constituents, and generation of reactive oxygen or nitrogen species. The relationship between abnormal P2 receptor function and human diseases attracts more and more attention. This review summarizes the expression and function of P2 receptors in HSPCs and the relationship to hematopoietic diseases.

Purinergic signalling and cancer

Receptors for extracellular nucleotides are widely expressed by mammalian cells. They mediate a large array of responses ranging from growth stimulation to apoptosis, from chemotaxis to cell differentiation and from nociception to cytokine release, as well as neurotransmission. Pharma industry is involved in the development and clinical testing of drugs selectively targeting the different P1 nucleoside and P2 nucleotide receptor subtypes. As described in detail in the present review, P2 receptors are expressed by all tumours, in some cases to a very high level. Activation or inhibition of selected P2 receptor subtypes brings about cancer cell death or growth inhibition. The field has been largely neglected by current research in oncology, yet the evidence presented in this review, most of which is based on in vitro studies, although with a limited amount from in vivo experiments and human studies, warrants further efforts to explore the therapeutic potential of purinoceptor targeting in cancer.

Highly potent and selective ectonucleotide pyrophosphatase/phosphodiesterase I inhibitors based on an adenosine 5'-(α or γ)-thio-(α,β- or β,γ)-methylenetriphosphate scaffold

Aberrant nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) activity is associated with chondrocalcinosis, osteoarthritis, and type 2 diabetes. The potential of NPP1 inhibitors as therapeutic agents, and the scarceness of their structure-activity relationship, encouraged us to develop new NPP1 inhibitors. Specifically, we synthesized ATP-α-thio-β,γ-CH2 (1), ATP-α-thio-β,γ-CCl2 (2), ATP-α-CH2-γ-thio (3), and 8-SH-ATP (4) and established their resistance to hydrolysis by NPP1,3 and NTPDase1,2,3,8 (<5% hydrolysis) (NTPDase = ectonucleoside triphosphate diphosphohydrolase). Analogues 1-3 at 100 μM inhibited thymidine 5'-monophosphate p-nitrophenyl ester hydrolysis by NPP1 and NPP3 by >90% and 23-43%, respectively, and only slightly affected (0-40%) hydrolysis of ATP by NTPDase1,2,3,8. Analogue 3 is the most potent NPP1 inhibitor currently known, Ki = 20 nM and IC50 = 0.39 μM. Analogue 2a is a selective NPP1 inhibitor with Ki = 685 nM and IC50 = 0.57 μM. Analogues 1-3 were found mostly to be nonagonists of P2Y1/P2Y2/P2Y11 receptors. Docking analogues 1-3 into the NPP1 model suggested that activity correlates with the number of H-bonds with binding site residues. In conclusion, we propose analogues 2a and 3 as highly promising NPP1 inhibitors.

Development of selective agonists and antagonists of P2Y receptors

Although elucidation of the medicinal chemistry of agonists and antagonists of the P2Y receptors has lagged behind that of many other members of group A G protein-coupled receptors, detailed qualitative and quantitative structure–activity relationships (SARs) were recently constructed for several of the subtypes. Agonists selective for P2Y₁, P2Y₂, and P2Y₆ receptors and nucleotide antagonists selective for P2Y₁ and P2Y₁₂ receptors are now known. Selective nonnucleotide antagonists were reported for P2Y₁, P2Y₂, P2Y₆, P2Y₁₁, P2Y₁₂, and P2Y₁₃ receptors. At the P2Y₁ and P2Y₁₂ receptors, nucleotide agonists (5′-diphosphate derivatives) were converted into antagonists of nanomolar affinity by altering the phosphate moieties, with a focus particularly on the ribose conformation and substitution pattern. Nucleotide analogues with conformationally constrained ribose-like rings were introduced as selective receptor probes for P2Y₁ and P2Y₆ receptors. Screening chemically diverse compound libraries has begun to yield new lead compounds for the development of P2Y receptor antagonists, such as competitive P2Y₁₂ receptor antagonists with antithrombotic activity. Selective agonists for the P2Y₄, P2Y₁₁, and P2Y₁₃ receptors and selective antagonists for P2Y₄ and P2Y₁₄ receptors have not yet been identified. The P2Y₁₄ receptor appears to be the most restrictive of the class with respect to modification of the nucleobase, ribose, and phosphate moieties. The continuing process of ligand design for the P2Y receptors will aid in the identification of new clinical targets.

Inhibition of neutrophil apoptosis by ATP is mediated by the P2Y11 receptor

Neutrophils undergo rapid constitutive apoptosis that is delayed by a range of pathogen- and host-derived inflammatory mediators. We have investigated the ability of the nucleotide ATP, to which neutrophils are exposed both in the circulation and at sites of inflammation, to modulate the lifespan of human neutrophils. We found that physiologically relevant concentrations of ATP cause a concentration-dependent delay of neutrophil apoptosis (assessed by morphology, annexin V/To-Pro3 staining, and mitochondrial membrane permeabilization). We found that even brief exposure to ATP (10 min) was sufficient to cause a long-lasting delay of apoptosis and showed that the effects were not mediated by ATP breakdown to adenosine. The P2 receptor mediating the antiapoptotic actions of ATP was identified using a combination of more selective ATP analogs, receptor expression studies, and study of downstream signaling pathways. Neutrophils were shown to express the P2Y11 receptor and inhibition of P2Y11 signaling using the antagonist NF157 abrogated the ATP-mediated delay of neutrophil apoptosis, as did inhibition of type I cAMP-dependent protein kinases activated downstream of P2Y11, without effects on constitutive apoptosis. Specific targeting of P2Y11 could retain key immune functions of neutrophils but reduce the injurious effects of increased neutrophil longevity during inflammation.

The metabotropic P2Y4 receptor participates in the commitment to differentiation and cell death of human neuroblastoma SH-SY5Y cells

Extracellular nucleotides exert a variety of biological actions through different subtypes of P2 receptors. Here we characterized in the human neuroblastoma SH-SY5Y cells the simultaneous presence of various P2 receptors, belonging to the P2X ionotropic and P2Y metabotropic families. Western blot analysis detected the P2X1,2,4,5,6,7 and P2Y1,2,4,6, but not the P2X3 and P2Y12 receptors. We then investigated which biological effects were mediated by the P2Y4 subtype and its physiological pyrimidine agonist UTP. We found that neuronal differentiation of the SH-SY5Y cells with dibutiryl-cAMP increased the expression of the P2Y4 protein and that UTP itself was able to positively interfere with neuritogenesis. Moreover, transient transfection and activation of P2Y4 also facilitated neuritogenesis in SH-SY5Y cells, as detected by morphological phase contrast analysis and confocal examination of neurofilament proteins NFL. This was concurrent with increased transcription of immediate-early genes linked to differentiation such as cdk-5 and NeuroD6, and activity of AP-1 transcription family members such as c-fos, fos-B, and jun-D. Nevertheless, a prolonged activation of the P2Y4 receptor by UTP also induced cell death, both in naive, differentiated, and P2Y4-transfected SH-SY5Y cells, as measured by direct count of intact nuclei and cytofluorimetric analysis of damaged DNA. Taken together, our data indicate that the high expression and activation of the P2Y4 receptor participates in the neuronal differentiation and commitment to death of SH-SY5Y cells.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

3-Deazauridine triggers dose-dependent apoptosis in myeloid leukemia cells and enhances retinoic acid-induced granulocytic differentiation of HL-60 cells

Therapeutic nucleoside analogue 3-deazauridine (DU) exerts cytotoxic activity against cancer cells by disruption of DNA synthesis resulting in cell death. The present study evaluates whether DU alone at doses 2.5-15 microM or in combination with all trans retinoic acid (RA) or dibutyryl cAMP (dbcAMP) is effective against myelogenous leukemia. The data of this study indicate that DU induces dose-dependent cell death by apoptosis in myeloid leukemia cell lines HL-60, NB4, HEL and K562 as demonstrated by cell staining or flow cytometry and agarose gel electrophoresis. 24h-treatment with DU produced dose-dependent HL-60 cell growth inhibition and dose-independent S phase arrest that was not reversed upon removal of higher doses of DU (10-15 microM). Exposition to nontoxic dose of DU (2.5 microM) for 24h followed by RA or dbcAMP and 96 h-cotreatment with DU significantly enhanced RA- but not dbcAMP-mediated granulocytic differentiation. Cell maturation was paralleled with an increase in the proportion of cells in G1 or G2+M phase. We conclude that, depending on the dose or the sequence of administration with RA, an inhibitor of DNA replication, DU triggers a process of either differentiation or apoptosis in myeloid leukemia cells.

Involvement of P2Y receptors in the differentiation of haematopoietic cells

The effects of extracellular nucleotides are mediated by multiple P2X ionotropic receptors and G protein-coupled P2Y receptors. These receptors are ubiquitous, but few physiological roles have been firmly identified. In this review article, we present a survey of the functional expression of P2Y receptors in the different haematopoietic lineages by analyzing the selectivity of these cells for the various adenine and uracil nucleotides as well as the second messenger signaling pathways involved. The pharmacological profiles of metabotropic nucleotide receptors are different among myeloid, megakaryoid, erythroid, and lymphoid cells and change during differentiation. A role of P2Y receptors in the differentiation and maturation of blood cells has been proposed: In particular the P2Y(11)receptor seems to be involved in the granulocytic differentiation of promyelocytes and in the maturation of monocyte-derived dendritic cells. It is suggested that the role of P2Y receptors in the maturation of blood cells may be more important than believed so far.

ADP-sensitive purinoceptors induce steroidogenesis via adenylyl cyclase activation in bovine adrenocortical fasciculata cells

1. The role of P2Y receptors in the production of cAMP and the activation of protein kinase A (PKA) was studied with respect to the regulation of the steroidogenesis in primary cultures of bovine adrenocortical fasciculata cells (BAFCs). 2. ADP and ATP stimulated cAMP production with EC(50) values of 23.7+/-6.8 microM and 40.1+/-5.5 microM, respectively. In contrast, the EC(50) of BzATP for cAMP production was 153.0+/-37.4 microM. Adenosine and AMP (0.1-1000 microM) were much less effective than ADP and ATP. 2MeSADP and UTP did not exert detectable effects. ADP (10 and 100 microM) significantly stimulated steroidogenesis; the process was blocked by an adenylyl cyclase inhibitor SQ22536 (100 microM) but not by the P2Y(1) receptor antagonist MRS2179 (100 microM). 3. Real-time imaging of the PKA activity with the dye ARII, which became less fluorescent upon phosphorylation, revealed that ADP (100 microM) immediately activated PKA. These effects could be mimicked by forskolin (100 microM) and were blocked by the PKA inhibitor H89 (50 microM). UTP (100 microM) did not activate PKA. 4. The cytoplasm harvested from morphologically and electrophysiologically identified single BAFCs contained mRNA for P2Y(2) but not for P2Y(1), P2Y(4), P2Y(11) or P2Y(12) receptors, as confirmed by single-cell RT-PCR amplification (50 cycles). 5. These results suggest an expression of an ADP-sensitive G(s)-coupled purinoceptor in BAFCs. We propose that this not yet described type of P2Y receptor might mediate the extracellular purine-activated steroidogenesis via cAMP/PKA-mediated pathways, independently from the pathways involving InsP(3) production and consequent intracellular Ca(2+) increase.

P2Y11 receptors activate adenylyl cyclase and contribute to nucleotide-promoted cAMP formation in MDCK-D(1) cells. A mechanism for nucleotide-mediated autocrine-paracrine regulation

Extracellular nucleotides activate P2Y receptors, thereby increasing cAMP formation in Madin-Darby canine kidney (MDCK-D(1)) cells, which express P2Y(1), P2Y(2), and P2Y(11) receptors (Post, S. R., Rump, L. C., Zambon, A., Hughes, R. J., Buda, M. D., Jacobson, J. P., Kao, C. C., and Insel, P. A. (1998) J. Biol. Chem. 273, 23093-23097). The cyclooxygenase inhibitor indomethacin (indo) eliminates UTP-promoted cAMP formation (i.e. via P2Y(2) receptors) but only partially blocks ATP-promoted cAMP formation. The latter response is completely blocked by the nonselective P2Y receptor antagonist suramin. We have sought to identify the mechanism for this P2Y receptor-mediated, indo-resistant cAMP formation. The agonist rank order potencies for cAMP formation were: ADP beta S > or = MT-ADP > 2-MT-ATP > ADP, ATP, ATP gamma S > UTP, AMP, adenosine. We found a similar rank order in MDCK-D(1) cells overexpressing cloned green fluorescent protein-tagged P2Y(11) receptors, but the potency of the agonists was enhanced, consistent with a P2Y(11) receptor-mediated effect. cAMP generation by the P2Y(1) and P2Y(11) receptor agonist ADP beta S was not inhibited by several P2Y(1)-selective antagonists (PPADS, A2P5P, and MRS 2179). Forskolin synergistically enhanced cAMP generation in response to ADP beta S or PGE(2), implying that, like PGE(2), ADP beta S activates adenylyl cyclase via G(s), a conclusion supported by results showing ADP beta S and MT-ADP promoted activation of adenylyl cyclase activity in MDCK-D(1) membranes. We conclude that nucleotide-promoted, indo-resistant cAMP formation in MDCK-D(1) cells occurs via G(s)-linked P2Y(11) receptors. These data describing adenylyl cyclase activity via endogenous P2Y(11) receptors define a mechanism by which released nucleotides can increase cAMP in MDCK-D(1) and other P2Y(11)-containing cells.

P2Y(11) receptor expression by human lymphocytes: evidence for two cAMP-linked purinoceptors

The effects of extracellular ATP, ADP, AMP and adenosine on cAMP accumulation have been studied in freshly isolated B-lymphocytes from patients with chronic lymphocytic leukemia. Extracellular ATP and several nucleotide analogs stimulated cAMP accumulation with the following order of potency: ATP (EC(50)=120+/-20 microM)>ADP>>AMP. ADP was less effective than ATP and may be a partial agonist. AMP exhibited variable but generally weak activity. The stable analog of ATP, alpha,beta-methylene ATP (EC(50)=110+/-15 microM) also stimulated cAMP accumulation and exhibited similar efficacy to ATP. The P2Y(2) receptor agonist, UTP had no effect on intracellular cAMP levels. Adenosine and the A(2A)/A(2B) receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) also stimulated cAMP accumulation in CLL lymphocytes. Adenosine deaminase inhibited the cAMP response to adenosine but had no effect on the ATP-induced cAMP response. On the other hand, the AMP analog, adenosine 5'-thiomonophosphate, (AMPS; 1.0 mM) inhibited ATP-induced and alpha,beta-methylene ATP-induced cAMP production but had no effect on adenosine-induced cAMP production. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed the presence of P2Y(11) receptor as well as A(2A) and A(2B) receptor mRNA in chronic lymphocytic leukemia lymphocytes. However, A(2B) receptors would appear to be relatively ineffective because the A(2A) selective agonist, CGS-21680 exhibited comparable efficacy to NECA. Furthermore, the A(2A)-selective antagonist 8-(3-chlorostyryl)-caffeine (CSC) right-shifted the concentration-response curve for NECA. Taken together, the data indicate that ATP induces cAMP accumulation via the activation of P2Y(11) receptors whereas adenosine induces cAMP accumulation via the activation of A(2A) receptors. Coordinate activation of P2Y(11) and A(2A) receptors may influence the developmental fate of normal B-lymphocytes.

Pharmacological characterisation of the P2Y11 receptor in stably transfected haematological cell lines

The recently cloned P2Y11 receptor is unique amongst P2Y receptors with its coupling to the adenylyl cyclase pathway. P2Y11 has previously been shown to be expressed in human acute promyelocytic leukemia (APL) HL-60 and NB4 cell lines, and both cell types elevate cyclic AMP (cAMP) levels upon stimulation with extracellular ATP. Acute erythroleukemic K562 cells and acute monocytic leukemia U937 cells did not elevate cAMP levels upon exposure to 1 mM extracellular ATP. However, K562 and U937 cells stably transfected with P2Y11 (K11 and U11 cells, respectively) were responsive to extracellular ATP, with an EC50 of 31 and 21 microM, respectively. The most potent agonists in both K11 and U11 cells were ATPgammaS (adenosine 5'-O-[3-thiotriphosphate]), ATPalphaS (adenosine 5'-O-[1-thiotriphosphate]), dATP and ADPbetaS (adenosine 5'-O-[2-thiobisphosphate]), which were of similar or greater potency compared to ATP itself. ADP and alpha,beta-methylene ATP were less potent compared to ATP. The order of potency for ATP breakdown products was ATP > ADP > AMP > or = Ado. UTP, a known activator of P2Y2 and P2Y4, was largely ineffective. In the transfected cells, ATP-induced cAMP elevation was inhibited by suramin (0.5 mM), but not XAC (20 microM) nor PPADS (100 microM). AMPS inhibited ATP-induced cAMP elevation in both K11 and U11 cells (EC50 approximately 3 mM) and may be a P2Y11-selective inhibitor. These results are similar to those observed for HL-60 cells and NB4 cells implicating P2Y11 as the receptor responsible for the ATP-induced cAMP elevations in these cells.