Pharmacological profile of a novel cyclic AMP-linked P2 receptor on undifferentiated HL-60 leukemia 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.

Thymidine 5'-O-monophosphorothioate induces HeLa cell migration by activation of the P2Y6 receptor

ATP, ADP, UTP, and UDP acting as ligands of specific P2Y receptors activate intracellular signaling cascades to regulate a variety of cellular processes, including proliferation, migration, differentiation, and cell death. Contrary to a widely held opinion, we show here that nucleoside 5'-O-monophosphorothioate analogs, containing a sulfur atom in a place of one nonbridging oxygen atom in a phosphate group, act as ligands for selected P2Y subtypes. We pay particular attention to the unique activity of thymidine 5'-O-monophosphorothioate (TMPS) which acts as a specific partial agonist of the P2Y6 receptor (P2Y6R). We also collected evidence for the involvement of the P2Y6 receptor in human epithelial adenocarcinoma cell line (HeLa) cell migration induced by thymidine 5'-O-monophosphorothioate analog. The stimulatory effect of TMPS was abolished by siRNA-mediated P2Y6 knockdown and diisothiocyanate derivative MRS 2578, a selective antagonist of the P2Y6R. Our results indicate for the first time that increased stability of thymidine 5'-O-monophosphorothioate as well as its affinity toward the P2Y6R may be responsible for some long-term effects mediated by this receptor.

Spinal astrocytes produce and secrete dynorphin neuropeptides

Dynorphin peptide neurotransmitters (neuropeptides) have been implicated in spinal pain processing based on the observations that intrathecal delivery of dynorphin results in proalgesic effects and disruption of extracellular dynorphin activity (by antisera) prevents injury evoked hyperalgesia. However, the cellular source of secreted spinal dynorphin has been unknown. For this reason, this study investigated the expression and secretion of dynorphin-related neuropeptides from spinal astrocytes (rat) in primary culture. Dynorphin A (1-17), dynorphin B, and α-neoendorphin were found to be present in the astrocytes, illustrated by immunofluorescence confocal microscopy, in a discrete punctate pattern of cellular localization. Measurement of astrocyte cellular levels of these dynorphins by radioimmunoassays confirmed the expression of these three dynorphin-related neuropeptides. Notably, BzATP (3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate) and KLA (di[3-deoxy-D-manno-octulosonyl]-lipid A) activation of purinergic and toll-like receptors, respectively, resulted in stimulated secretion of dynorphins A and B. However, α-neoendorphin secretion was not affected by BzATP or KLA. These findings suggest that dynorphins A and B undergo regulated secretion from spinal astrocytes. These findings also suggest that spinal astrocytes may provide secreted dynorphins that participate in spinal pain processing.

Involvement of P2Y1 and P2Y11 purinoceptors in parasympathetic inhibition of colonic smooth muscle

Purinergic signaling was first recognized in the guinea pig (Cavia porcellus) taenia coli, where relaxation of smooth muscle by nerve-released ATP may involve the activation of P2Y(1) and P2Y(11) receptors, and where transcripts for both genes have been found. A partial sequence for P2Y(11) protein was identified; the full-length P2Y(1) sequence has already been described. P2Y(1) and P2Y(11) proteins were localized by immunohistochemistry in smooth muscle cells. P2X(2) and P2X(3) proteins were also localized in motoneurons of the myenteric plexus. alphabeta-Methylene-ATP (alphabetameATP) and dibenzoyl-ATP (BzATP) evoked fast relaxations in the taenia, and they were inhibited by the P2Y(1) receptor antagonist 2'-deoxy-N(6)-methyladenosine 3',5'-bisphosphate (MRS2179). However, alphabetameATP and BzATP may stimulate neuronal P2X receptors to release ATP, which then acts on P2Y(1) receptors. In accordance, fast relaxations evoked by alphabetameATP and BzATP were inhibited by the P2X(3) and P2X(2/3) receptor antagonist 5-({[3-phenoxybenzyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl] amino} carbonyl)-1,2,4-benzene-tricarboxylic acid (A317491). When P2Y(1), P2X(3), and P2X(2/3) receptors were blocked and adenosine was removed enzymatically, alphabetameATP and BzATP evoked slow relaxations that were inhibited by Reactive Red. Fast and slow relaxations involve small and large conductance calcium-activated potassium channels; the latter are dependent on intracellular cyclic AMP levels, which altered the duration and amplitude of relaxations. alphabetameATP and BzATP were confirmed as agonists, and Reactive Red as an antagonist, of human P2Y(11) receptors. In summary, G(q)-coupled P2Y(1) receptors are involved mainly in fast relaxations, whereas G(q)and G(s)-coupled P2Y(11) receptors are involved in both fast and slow relaxations. These P2Y receptor subtypes, plus neuronal P2X receptors, may explain the phenomenon of parasympathetic inhibition first described by Langley (1898).

International Union of Pharmacology LVIII: update on the P2Y G protein-coupled nucleotide receptors: from molecular mechanisms and pathophysiology to therapy

There have been many advances in our knowledge about different aspects of P2Y receptor signaling since the last review published by our International Union of Pharmacology subcommittee. More receptor subtypes have been cloned and characterized and most orphan receptors de-orphanized, so that it is now possible to provide a basis for a future subdivision of P2Y receptor subtypes. More is known about the functional elements of the P2Y receptor molecules and the signaling pathways involved, including interactions with ion channels. There have been substantial developments in the design of selective agonists and antagonists to some of the P2Y receptor subtypes. There are new findings about the mechanisms underlying nucleotide release and ectoenzymatic nucleotide breakdown. Interactions between P2Y receptors and receptors to other signaling molecules have been explored as well as P2Y-mediated control of gene transcription. The distribution and roles of P2Y receptor subtypes in many different cell types are better understood and P2Y receptor-related compounds are being explored for therapeutic purposes. These and other advances are discussed in the present review.

ATP stimulates Na+-glucose cotransporter activity via cAMP and p38 MAPK in renal proximal tubule cells

Extracellular ATP plays an important role in the regulation of renal function. However, the effect of ATP on the Na(+)-glucose cotransporters (SGLTs) has not been elucidated in proximal tubule cells (PTCs). Therefore, this study was performed to examine the action of ATP on SGLTs and their related signal pathways in primary cultured rabbit renal PTCs. ATP increased [(14)C]-alpha-methyl-d-glucopyranoside (alpha-MG) uptake in a time-dependent (>1 h) and dose-dependent (>10(-6) M) manner. ATP stimulated alpha-MG uptake by increasing in V(max) without affecting K(m). ATP-induced increase of alpha-MG uptake was correlated with the increase in both SGLT1 and SGLT2 protein expression levels. ATP-induced stimulation of alpha-MG uptake was blocked by suramin (nonspecific P2 receptor antagonist), RB-2 (P2Y receptor antagonist), and MRS-2179 (P2Y(1) receptor antagonist), suggesting a role for the P2Y receptor. ATP-induced stimulation of alpha-MG uptake was blocked by pertussis toxin (PTX, a G(i) protein inhibitor), SQ-22536 (an adenylate cyclase inhibitor), and PKA inhibitor amide 14-22 (PKI). ATP also increased cAMP formation, which was blocked by PTX and RB-2. However, pretreatment of adenosine deaminase did not block ATP-induced cAMP formation. In addition, ATP-induced stimulation of alpha-MG uptake was blocked by SB-203580 (p38 MAPK inhibitor), but not by PD-98059 (p44/42 MAPK inhibitor) or SP-600125 (JNK inhibitor). Indeed, ATP induced phosphorylation of p38 MAPK. In conclusion, ATP increases alpha-MG uptake via cAMP and p38 MAPK in renal PTCs.

Abundant and dynamic expression of G protein-coupled P2Y receptors in mammalian development

Extracellular ATP mediates diverse biological effects by activating two families of receptors, the P2X and P2Y receptors. There is growing evidence to show that activation of G protein-coupled P2Y receptors can produce trophic effects in many cell types. Yet the expression and function of the P2Y receptors in development has rarely been studied and has never been investigated in mammalian development. This study used the reverse transcription-polymerase chain reaction and immunohistochemistry to demonstrate the abundant and dynamic expression of P2Y receptors in rat development. These receptors were expressed in a wide range of embryonic structures, notably somites, skeletal muscle, the central and peripheral nervous system, the heart, lung, and liver. All the P2Y receptors studied were expressed as early as embryonic day 11, when most embryonic organs were far from being functional and still in the process of being formed. P2Y receptor proteins were strongly expressed in temporary, developmental structures that do not have a correlate in the adult animal, including the somites (P2Y1, P2Y2, and P2Y4) and the floor plate of the neural tube (P2Y1). P2Y receptors were also dynamically expressed, with receptor mRNA and protein being both up- and down-regulated at different developmental stages. The down-regulation of the P2Y1, 2, and 4 receptor proteins in skeletal muscle and heart, and the disappearance of the P2Y4 receptor from the brainstem and ventral white matter of the spinal cord postnatally, demonstrated that many P2Y receptors were likely to be involved in functions specific to embryonic life. Thus, these findings strongly suggest that P2Y receptors play an important role in the development of many tissues, and pioneer further studies into the role of purinergic signalling in development.

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.

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.

The mononucleotide-dependent, nonantisense mechanism of action of phosphodiester and phosphorothioate oligonucleotides depends upon the activity of an ecto-5'-nucleotidase

Many reports indicate different nonantisense yet sequence-specific effects of antisense phosphorothioate oligonucleotides. Products of enzymatic degradation of the oligonucleotides can also influence cell proliferation. The cytotoxic effects of deoxyribonucleoside-5'-phosphates (dNMPs) and their 5'-phosphorothioate analogs, deoxyribonucleoside-5'-monophosphorothioates (dNMPSs) on 4 human cell types (HeLa, HL-60, K-562, and endothelial cells) were examined, and the effects were correlated with the catabolism of these compounds. The results indicate that differences in cytotoxicity of dNMPs or dNMPSs in these cells depend upon different activity of an ecto-5'-nucleotidase. It has also been found that dNMPSs stimulate proliferation of human umbilical vein endothelial cells and HL-60 cells in a concentration-dependent manner. This stimulation might be caused by the binding of deoxynucleoside-5'-phosphorothioates to as-yet unidentified nucleotide receptor(s) at the cell surface. (Blood. 2001;98:995-1002)

Cotranscription and intergenic splicing of human P2Y11 and SSF1 genes

The P2Y(11) receptor is an ATP receptor positively coupled to the cAMP and phosphoinositide pathways. Ssf1 is a Saccharomyces cerevisiae nuclear protein, which plays an important role in mating. The gene encoding the human orthologue of SSF1 is adjacent to the P2Y(11) gene on chromosome 19. During the screening of placenta cDNA libraries, we isolated a chimeric clone resulting from the intergenic splicing between the P2Y(11) and SSF1 genes. The fusion protein was stably expressed in CHO-K1 cells where it generated a cAMP response to ATP qualitatively indistinguishable from that of the P2Y(11) receptor. According to both Western blotting and cAMP response, the expression of the fusion protein in the transfected cells was clearly lower than that of the P2Y(11) receptor. Both P2Y(11) and SSF1 probes detected a 5.6-kb messenger RNA with a similar pattern of intensity in each of 11 human tissues. The ubiquitous presence of chimeric transcripts and their up-regulation during granulocytic differentiation indicate that the transgenic splicing between the P2Y(11) and the SSF1 genes is a common and regulated phenomenon. There are very few examples of intergenic splicing in mammalian cells, and this is the first case involving a G-protein-coupled receptor.

P2Y(11), a purinergic receptor acting via cAMP, mediates secretion by pancreatic duct epithelial cells

Pancreatic duct epithelial cells (PDEC) mediate the exocrine secretion of fluid and electrolytes. We previously reported that ATP and UTP interact with P2Y(2) receptors on nontransformed canine PDEC to increase intracellular free Ca2+ concentration ([Ca2+](i)) and stimulate Ca2+-activated Cl- and K+ channels. We now report that ATP interacts with additional purinergic receptors to increase cAMP and activate Cl- channels. ATP, 2-methylthio-ATP, and ATP-gamma-S stimulated a 4- to 10-fold cAMP increase with EC(50) of 10-100 microM. Neither UTP nor adenosine stimulated a cAMP increase, excluding a role for P2Y(2) or P1 receptors. Although UTP stimulated an (125)I(-) efflux that was fully inhibited by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA-AM), ATP stimulated a partially resistant efflux, suggesting activation of additional Cl- conductances through P2Y(2)-independent and Ca2+-independent pathways. In Ussing chambers, increased cAMP stimulated a much larger short-circuit current (I(sc)) increase from basolaterally permeabilized PDEC monolayers than increased [Ca2+](i). Luminal ATP and UTP and serosal UTP stimulated a small Ca2+-type I(sc) increase, whereas serosal ATP stimulated a large cAMP-type I(sc) response. Serosal ATP effect was inhibited by P2 receptor blockers and unaffected by BAPTA-AM, supporting ATP activation of Cl- conductances through P2 receptors and a Ca2+-independent pathway. RT-PCR confirmed the presence of P2Y(11) receptor mRNA, the only P2Y receptor acting via cAMP.

Adenosine triphosphate activates mitogen-activated protein kinase in human granulosa-luteal cells

ATP has been shown to activate the phospholipase C/diacylglycerol/protein kinase C (PKC) pathway. However, little is known about the downstream signaling events. The present study was designed to examine the effect of ATP on activation of the mitogen-activated protein kinase (MAPK) signaling pathway and its physiological role in human granulosa-luteal cells. Western blot analysis, using a monoclonal antibody that detected the phosphorylated forms of extracellular signal-regulated kinase-1 and -2 (p42(mapk) and p44 (mapk), respectively), demonstrated that ATP activated MAPK in a dose- and time-dependent manner. Treatment of the cells with suramin (a P2 purinoceptor antagonist), neomycin (a phospholipase C inhibitor), staurosporin (a PKC inhibitor), or PD98059 (an MAPK/ERK kinase inhibitor) significantly attenuated the ATP-induced activation of MAPK. In contrast, ATP-induced MAPK activation was not significantly affected by pertussis toxin (a G(i) inhibitor). To examine the role of G(s) protein, the intracellular cAMP level was determined after treatment with ATP or hCG. No significant elevation of intracellular cAMP was noted after ATP treatment. To determine the role of MAPK in steroidogenesis, human granulosa-luteal cells were treated with ATP, hCG, or ATP plus hCG in the presence or absence of PD98059. RIA revealed that ATP alone did not significantly affect the basal progesterone concentration. However, hCG-induced progesterone production was reduced by ATP treatment. PD98059 reversed the inhibitory effect of ATP on hCG-induced progesterone production. To our knowledge, this is the first demonstration of ATP-induced activation of the MAPK signaling pathway in the human ovary. These results support the idea that the MAPK signaling pathway is involved in mediating ATP actions in the human ovary.

Serum constituents can affect 2'-& 3'-O-(4-benzoylbenzoyl)-ATP potency at P2X(7) receptors

1. 2'-& 3'-O-(4-benzoylbenzoyl)-ATP (BzATP) is the prototypic agonist for P2X(7) receptors. In this study we demonstrate that bovine serum albumin (BSA) can affect the potency of BzATP at P2X receptors. 2. BzATP potency (pEC(50)) to stimulate ethidium accumulation in cells expressing recombinant P2X7 receptors varied between 6.5 and 4, depending upon the species orthologue studied and ionic conditions employed. BSA (0.1 - 1 mg ml(-1)) and foetal bovine serum (FBS, 1 - 10% v v(-1)) inhibited responses to BzATP but only when the BzATP pEC(50) exceeded 5. 3. BSA did not block ATP-stimulated ethidium accumulation, suggesting its effects were independent of P2X(7) receptor blockade. 4. BSA did not cause breakdown of nucleotides, although FBS (10% v v(-1)) exhibited appreciable nucleotidase activity and caused significant breakdown of ATP. 5. In the presence of BSA, lipids such as 11-((5-dimethylaminonaphthalene-1-sulphonyl)amino)undecanoic acid (DAUDA) and arachidonic acid (AA) markedly increased BzATP potency. Lipids had no affect on ATP potency in the presence of BSA and had little effect on responses to BzATP in the absence of BSA. 6. These results suggested that the reduction in BzATP potency by BSA was due to BzATP binding to BSA and that lipids prevented this binding. Consistent with this hypothesis, BzATP inhibited binding of the fluorescent lipid, DAUDA, to BSA. 7. In conclusion, BSA and lipids can markedly affect BzATP potency at P2X(7) receptors but this is probably a consequence of BzATP binding to BSA. This finding has important implications when using BzATP in vivo or in the presence of albumin.

Extracellular ATP-dependent suppression of proliferation and induction of differentiation of human HL-60 leukemia cells by distinct mechanisms

Extracellular ATP suppressed the growth of HL-60 leukemia cells and induced their differentiation as revealed by N-formyl-methionyl-leucyl-phenylalanine-induced beta-glucuronidase release. ATP degraded to ADP, AMP, and adenosine, and the effect of ATP on cell growth was mimicked by these metabolites added to the cultures. The stable analog alpha,beta-methylene ATP, however, had only a weak inhibitory effect on cell growth. Adenine nucleotide-induced growth suppression was reversed by uridine, suggesting the involvement of intracellular pyrimidine starvation secondary to adenosine accumulation. Consistent with this, ATP induced intracellular starvation of pyrimidine nucleotides, and this effect was also prevented by pretreatment of cells with uridine. The order of effectiveness of ATP-induced differentiation of HL-60 cells, unlike that for growth suppression, was ATP > ADP > AMP, and adenosine had no effect. Furthermore, uridine had no effect and the stable analog, alpha,beta-methylene ATP also induced HL-60 cell differentiation, suggesting that differentiation was due to ATP per se. We tested the hypothesis that ATP-induced differentiation arises from activation of adenylyl cyclase by the novel P2Y(11) receptor using the cell-permeable inhibitor of protein kinase A, Rp-CPT-cAMPS (8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate, Rp isomer). Rp-CPT-cAMPS (1-100 microM) prevented ATP-induced differentiation of HL-60 cells as assessed by fMLP-induced beta-glucuronidase release. However, Rp-CPT-cAMPS did not prevent ATP-induced growth suppression. Taken together, the data indicate that extracellular ATP suppresses HL-60 growth and induces their differentiation by distinct mechanisms. Growth suppression arises from adenosine generation and consequent pyrimidine starvation. Differentiation arises, at least in part, from a distinct mechanism involving the activation of cell surface P2 receptors coupled to cAMP generation and activation of protein kinase A.

Differential regulation of P2Y(11) receptor-mediated signalling to phospholipase C and adenylyl cyclase by protein kinase C in HL-60 promyelocytes

The regulatory mode of the P2Y(11) purinoceptor-mediated signalling cascades towards phospholipase C and adenylyl cyclase was studied in HL-60 promyelocytes. Treatment with the potent P2Y(11) receptor activator dATP evoked an elevated intracellular Ca(2+) concentration ([Ca(2+)](i)) and inositol 1,4,5-trisphosphate (IP(3)) production that was sustained for longer than 30 min. However, the dATP-induced responses were significantly inhibited by the activation of protein kinase C after a short exposure to phorbol 12-myristate 13-acetate (PMA). dATP also potently stimulated cyclic AMP production with half maximum effect seen at 23+/-7 microM dATP. In addition, a 5-min pretreatment with PMA enhanced the dATP-stimulated cyclic AMP accumulation. PMA potentiated the cyclic AMP production when adenylyl cyclase was activated directly by forskolin or indirectly by G protein activation after cholera toxin treatment. dATP also enhanced the forskolin-mediated cyclic AMP generation. Treatment of the cells with 10 microM U-73122, which almost completely blocked the dATP-stimulated IP(3) production and [Ca(2+)](i) rise, had no effect on cyclic AMP accumulation, while 10 microM 9-(tetrahydro-2-furyl)adenine (SQ 22536), which inhibited the adenylyl cyclase activation, did not effect the dATP-stimulated phosphoinositide turnover. Taken together, the results indicate that P2Y(11) receptor-mediated activation of phospholipase C and adenylyl cyclase occurs through independent pathways and is differentially regulated by protein kinase C in HL-60 cells.

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

Priming of NB4 promyelocytic cells with all-trans retinoic acid, followed by extracellular ATP in the presence of a phosphodiesterase inhibitor, elevated cAMP and activated protein kinase A. The order of potency for cAMP production was ATP (EC50 = 95 +/- 13 micromol/L) > ADP > AMP = adenosine. The order of potency of ATP analogues was 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (EC50 = 54 +/- 15 micromol/L) = adenosine 5'-O-(3-thio) triphosphate (EC50 = 66 +/- 4 micromol/L) > ATP > beta,gamma-methylene ATP (EC50 = 200 +/- 55 micromol/L). Adenosine 5'-O-thiomonophosphate and adenosine 5'-O-(2-thio) diphosphate inhibited ATP-induced cAMP production. Differentiation also occurred as measured by increased expression of CD11b and N-formyl peptide receptor and changes in cell morphology. UTP did not elevate cAMP or induce differentiation, indicating that P2Y2, P2Y4, and P2Y6 receptors were not involved. The P2Y11 receptor, a cAMP-linked receptor on promyelocytic HL-60 cells, was detected in NB4 cells by reverse transcription-polymerase chain reaction and northern blotting. This receptor has the same order of potency with respect to cAMP production as that observed in HL-60 cells.

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.

Signal transduction and white cell maturation via extracellular ATP and the P2Y11 receptor

Extracellular ATP promotes a wide range of physiological effects in many tissues. Of particular interest is the effect of ATP on leukaemia-derived HL-60 and NB4 cell lines, which are induced to mature to neutrophil-like cells. The differentiation process appears to be mediated by ATP binding to a cell-surface purinergic P2Y receptor, resulting in the stimulation of adenylyl cyclase, elevation of cAMP levels and activation of protein kinase A. In 1997, a novel ATP-selective P2Y receptor, P2Y11, was cloned and shown to be linked to both cAMP and Ca2+ signalling pathways. The pharmacological profile of ATP analogues used by P2Y11 for cAMP production in transfected cells is reviewed in the present paper and shown to be closely similar to the profiles for cAMP production and differentiation of myeloblastic HL-60 cells and promyelocytic NB4 cells, both of which express P2Y11. Additional data are provided showing that HL-60 mature to neutrophil-like cells in response to extracellular ATP, as measured by upregulation of the N-formyl peptide receptor, N-formyl peptide-mediated actin polymerization and superoxide production. It is proposed that P2Y11 is responsible for the ATP-mediated differentiation of these cells lines and that this receptor may play a role in the maturation of granulocytic progenitors in the bone marrow.

Rapid up-regulation of P2Y messengers during granulocytic differentiation of HL-60 cells

HL-60 cells are human promyelocytic cells expressing two ATP receptors: the P2Y(2) and P2Y(11) subtypes. Our Northern blotting experiments have shown that P2Y(2) and P2Y(11) messengers were up-regulated in these cells, rapidly and independently of protein synthesis, following treatment with granulocytic differentiating agents such as retinoic acid, dimethylsulfoxide, granulocyte-colony stimulating factor, dibutyryl cyclic AMP and ATP. AR-C67085 and adenosine 5'-O-(3-thiotriphosphate), two potent agonists of the recombinant P2Y(11) receptor, increased intracellular cAMP concentration in HL-60 cells more potently than ATP itself. These observations support the conclusion that the effect of ATP on HL-60 cell differentiation is mediated by the P2Y(11) receptor.

Advances in signalling by extracellular nucleotides. the role and transduction mechanisms of P2Y receptors

Nucleotides are ubiquitous intercellular messengers whose actions are mediated by specific receptors. Since the first clonings in 1993, it is known that nucleotide receptors belong to two families: the ionotropic P2X receptors and the metabotropic P2Y receptors. Five human P2Y receptor subtypes have been cloned so far and a sixth one must still be isolated. In this review we will show that they differ by their preference for adenine versus uracil nucleotides and triphospho versus diphospho nucleotides, as well as by their transduction mechanisms and cell expression.

Effects of AMP derivatives on cyclic AMP levels in NG108-15 cells

1. In NG108-15 neuroblastomaxglioma hybrid cells, ATP stimulates intracellular cyclic AMP formation, which is inhibited by both adenosine (P(1)) and P2 receptor antagonists. In the present study, we examined the effects of several AMP derivatives in NG108-15 cells and mouse neuroblastoma N18TG-2 cells. 2. Adenosine 2'-monophosphate (A2P), adenosine 3'-monophosphate (A3P) and adenosine 5'-phosphosulphate (A5PS) increased cyclic AMP levels with similar concentration-dependencies in NG108-15 cells. 3. Increases in cyclic AMP by AMP derivatives were inhibited by the P2 receptor antagonist PPADS, but not by suramin. Effects of AMP derivatives were also inhibited by P(1) receptor antagonists ZM241385, XAC, DPCPX and partially by alloxazine. The ecto-nucleotidase inhibitor alpha, beta-methyleneADP was without effect. 4. In contrast, AMP derivatives did not change cyclic AMP levels in N18TG-2 cells. Accumulation of cyclic AMP in N18TG-2 cells was stimulated by adenosine A(2) receptor agonists CGS21680 and NECA, but not by ATP or beta, gamma-methyleneATP, agonists for cyclic AMP production in NG108-15 cells. 5. Reverse transcription-coupled polymerase chain reaction (RT - PCR) analyses revealed that N18TG-2 cells express both A(2A) and A(2B) receptors, while NG108-15 cells express mainly A(2A) receptors. 6. AMP derivatives did not affect the P2X and P2Y receptors expressed in NG108-15 cells. 7. These results suggest that A2P, A3P and A5PS act as agonists for cyclic AMP production and that these compounds are valuable tools for determinating the mechanism of ATP-stimulated cyclic AMP response in NG108-15 cells.

Pharmacological characterization of the human P2Y11 receptor

1 The human P2Y11 receptor is coupled to both the phosphoinositide and the cyclic AMP pathways. A pharmacological characterization of the recombinant human P2Y11 receptor has been conducted following stable expression in two different cell lines: the 1321N1 astrocytoma cells for inositol trisphosphate measurements and the CHO-K1 cells for cyclic AMP assays. The rank order of potency of a series of nucleotides was almost identical for the two pathways: ATPgammaS approximately BzATP > dATP > ATP > ADPbetaS > 2MeSATP. 2 ADPbetaS, AMPalphaS and A3P5PS behaved as partial agonists of the human P2Y11 receptor. At high concentrations, these three nucleotides were able to partially inhibit the ATP response. 3 Suramin was a more potent antagonist than reactive blue 2, whereas pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid was completely inactive. The P2Y11 receptor proved to be sensitive to suramin in a competitive way with an apparent Ki value of 0.82+/-0. 07 microM. 4 The ATP derivative AR-C67085 (2-propylthio-beta, gamma-dichloromethylene-D-ATP), a potent inhibitor of ADP-induced platelet aggregation, was the most potent agonist of the P2Y11 receptor, among the various nucleotides tested. 5 The pharmacological profile of the recombinant human P2Y11 receptor is closely similar to that of the cyclic AMP-coupled P2 receptor recently described in HL-60 cells, suggesting that it is the same receptor.

Regulation of cyclic AMP by extracellular ATP in cultured brain capillary endothelial cells

1 In primary unpassaged rat brain capillary endothelial cell cultures (RBECs), using reverse-transcriptase PCR with primers specific for P2Y receptor subtypes, we detected mRNA for P2Y2, P2Y4 and P2Y6, but not P2Y1 receptors. 2 None of the various nucleotides tested reduced forskolin elevated cyclic AMP levels in RBECs. ATP and ATPgammaS, as well as adenosine, enhanced cyclic AMP accumulation in the presence of forskolin. 3 Comparison of the concentration response curves to ATPgammaS with those for ATP and adenosine, at different incubation times, indicated that the response to purine nucleotides was not wholly dependent on conversion to adenosine. Adenosine deaminase abolished the response to adenosine but only reduced the response to ATP by about 50%. These results suggest the participation of a receptor responsive to nucleotides. 4 Isobutylmethylxanthine and 8-sulphophenyltheophylline prevented the cyclic AMP response, while neither 8-cyclopentyl-1, 3-dipropylxanthine nor SCH58261 were effective antagonists. 2-chloradenosine gave a robust response, but neither 2-chloro-N6-cyclopentyladenosine nor CGS 21680 were agonists. 5 These results show that adenosine and ATP can elevate the cyclic AMP levels of brain endothelial cells by acting on receptors which have a pharmacology apparently distinct from known P2Y and adenosine receptors.

P2 receptor subtypes in the cardiovascular system

Extracellular nucleotides have been implicated in a number of physiological functions. Nucleotides act on cell-surface receptors known as P2 receptors, of which several subtypes have been cloned. Both ATP and ADP are stored in platelets and are released upon platelet activation. Furthermore, nucleotides are also released from damaged or broken cells. Thus during vascular injury nucleotides play an important role in haemostasis through activation of platelets, modulation of vascular tone, recruitment of neutrophils and monocytes to the site of injury, and facilitation of adhesion of leucocytes to the endothelium. Nucleotides also moderate these functions by generating nitric oxide and prostaglandin I2 through activation of endothelial cells, and by activating different receptor subtypes on vascular smooth muscle cells. In the heart, P2 receptors regulate contractility through modulation of L-type Ca2+ channels, although the molecular mechanisms involved are still under investigation. Classical pharmacological studies have identified several P2 receptor subtypes in the cardiovascular system. Molecular pharmacological studies have clarified the nature of some of these receptors, but have complicated the picture with others. In platelets, the classical P2T receptor has now been resolved into three P2 receptor subtypes: the P2Y1, P2X1 and P2TAC receptors (the last of these, which is coupled to the inhibition of adenylate cyclase, is yet to be cloned). In peripheral blood leucocytes, endothelial cells, vascular smooth muscle cells and cardiomyocytes, the effects of classical P2X, P2Y and P2U receptors have been found to be mediated by more than one P2 receptor subtype. However, the exact functions of these multiple receptor subtypes remain to be understood, as P2-receptor-selective agonists and antagonists are still under development.