Nucleotide receptors: an emerging family of regulatory molecules in blood cells

Characterisation of a novel glycosylphosphatidylinositol-anchored mono-ADP-ribosyltransferase isoform in ovary cells

The mammalian mono-ADP-ribosyltransferases are a family of enzymes related to bacterial toxins that can catalyse both intracellular and extracellular mono-ADP-ribosylation of target proteins involved in different cellular processes, such as cell migration, signalling and inflammation. Here, we report the molecular cloning and functional characterisation of a novel glycosylphosphatidylinositol (GPI)-anchored mono-ADP-ribosyltransferase isoform from Chinese hamster ovary (CHO) cells (cARTC2.1) that has both NAD-glycohydrolase and arginine-specific ADP-ribosyltransferase activities. cARTC2.1 has the R-S-EXE active-site motif that is typical of arginine-specific ADP-ribosyltransferases, with Glu209 as the predicted catalytic amino acid. When over-expressed in CHO cells, the E209G single point mutant of cARTC2.1 cannot hydrolyse NAD(+), although it retains low arginine-specific ADP-ribosyltransferase activity. This ADP-ribosyltransferase activity was abolished only with an additional mutation in the R-S-EXE active-site motif, with both of the glutamate residues of the EKE sequence of cARTC2.1 mutated to glycine (E207/209G). These glutamate-mutated proteins localise to the plasma membrane, as does wild-type cARTC2.1. Thus, the partial or total loss of enzymatic activity of cARTC2.1 that arises from these mutations does not affect its cellular localisation. Importantly, an endogenous ADP-ribosyltransferase is indeed expressed and active in a subset of CHO cells, while a similar activity cannot be detected in ovarian cancer cells. With respect to this endogenous ecto-ART activity, we have identified two cell populations: ART-positive and ART-negative CHO cells. The subset of ART-positive cells, which represented 5% of the total cells, is tightly maintained in the CHO cell population.

Major contribution of the P2Y₁receptor in purinergic regulation of TNFα-induced vascular inflammation

BACKGROUND

Atherosclerosis is an inflammatory disease, and extracellular nucleotides are one of the factors possibly involved in vascular inflammation. The P2Y(1) receptor for adenosine 5'-diphosphate has been shown to be involved in the development of atherosclerosis in apolipoprotein E--deficient mice. Our aim is to determine whether the endothelial P2Y(1) receptor plays a role in leukocyte recruitment during vascular inflammation and characterize underlying mechanisms.

METHODS AND RESULTS

We show here that the P2Y(1) receptor plays a role in leukocyte recruitment in inflamed mouse femoral arteries. Moreover, in wild-type bone marrow--transplanted chimeric P2Y(1)-deficient mice with an apolipoprotein E--deficient background, a strong reduction of adhesion molecule--dependent leukocyte recruitment was observed after local injection of tumor necrosis factor and interleukin 1β, excluding a role for the platelet or other hematopoietic cell type P2Y(1) in these events. Similarly, the in vitro adhesion of isolated mouse monocytes to tumor necrosis factor α--stimulated murine endothelial cell monolayers and their migration across the cell layers were strongly reduced in P2Y(1)-deficient compared with wild-type endothelial cells, as was the expression of the adhesion molecules P-selectin, Vascular cell adhesion molecule 1, and intercellular adhesion molecule 1. Pharmacological inhibition using the selective antagonist MRS2500 also resulted in decreased expression of adhesion molecules. These events are related to the p38 mitogen-activated protein kinase and activating transcription factor 2 pathway. Finally, in vivo administration of MRS2500 resulted in strong reduction of leukocyte recruitment in inflamed femoral arteries of apolipoprotein E--deficient mice.

CONCLUSIONS

The data highlight a key role of the endothelial P2Y(1) receptor in acute vascular inflammation. Pharmacological targeting the P2Y(1) receptor could represent a promising approach for the treatment of vascular inflammation.

Extracellular ATP induces spikes in cytosolic free Ca(2+) but not in NADPH oxidase activity in neutrophils

In order to establish whether non-mitochondrial oxidase activity in human neutrophils is tightly related to cytosolic Ca(2+) concentration, we simultaneously measured Ca(2+) oscillations induced by ATP and oxidant production in single adherent neutrophils using confocal microscopy. ATP induced fast damped Ca(2+) spikes with a period of 15s and slower irregular spikes with a period greater than 50s. Spikes in Ca(2+) occurred in the absence of Ca(2+) influx, but the amplitude was damped by inhibition of Ca(2+) influx. Using the oxidation of hydroethidine as a cytosolic marker of oxidant production, we show that the generation of reactive oxygen species by neutrophils adherent to glass was accelerated by ATP. The step-up in NADPH oxidase activity followed the first elevation of cytosolic Ca(2+) but, despite subsequent spikes in Ca(2+) concentration, no oscillations in oxidase activity could be detected. ATP induced spikes in Ca(2+) in a very reproducible way and we propose that the Ca(2+) signal is an on-switch for oxidase activity, but the activity is apparently not directly correlated with spiking activity in cytosolic Ca(2+).

Targeting P2X₇ receptor inhibits the metastasis of murine P388D1 lymphoid neoplasm cells to lymph nodes

The P2X₇R (P2X₇ receptor) is an ATP-gated cation channel expressed in normal cells that participates in both cell proliferation and apoptosis. Here, we have confirmed P2X₇R expression on murine P388D1 lymphoid neoplasm cells. In addition, ATP-stimulated P2X₇R expression was found to trigger increased intracellular calcium flux. Furthermore, silencing with short hairpin RNA and blocking with P2X₇R antibody significantly reduced the metastasis of P388D1 cells to lymph nodes. These results indicate that inhibition of the expression and function of P2X₇R attenuates the metastatic ability of murine lymphoid neoplasm cell line P388D1, which represents a new potential target for anti-metastatic therapy.

Immune cell regulation by autocrine purinergic signalling

Stimulation of almost all mammalian cell types leads to the release of cellular ATP and autocrine feedback through a diverse array of purinergic receptors. Depending on the types of purinergic receptors that are involved, autocrine signalling can promote or inhibit cell activation and fine-tune functional responses. Recent work has shown that autocrine signalling is an important checkpoint in immune cell activation and allows immune cells to adjust their functional responses based on the extracellular cues provided by their environment. This Review focuses on the roles of autocrine purinergic signalling in the regulation of both innate and adaptive immune responses and discusses the potential of targeting purinergic receptors for treating immune-mediated disease.

P2X7 receptor drives osteoclast fusion by increasing the extracellular adenosine concentration

Defects in bone homeostasis are a major health problem. Osteoclast differentiation and activation have a crucial role in bone remodeling in health and disease. Osteoclasts are bone-resorbing cells derived from mononuclear phagocyte progenitors. The key event in osteoclast formation is fusion of mononucleate precursors to form mature multinucleated osteclasts. Here we provide evidence of an absolute requirement for the P2X7 receptor, ATP release, and adenosine signaling in human osteoclast formation, as shown by the following findings: macrophage-colony stimulating factor/receptor activator for nuclear factor-κB ligand (M-CSF/RANKL)-stimulated fusion of human monocytes is fully prevented by an anti-P2X7 mAb, by specific P2X7 pharmacological antagonists, or by inhibition of CD39/NTPDase; fusion-competent monocytes release ATP via the P2X7 receptor; accelerated degradation of released ATP by addition of either apyrase or hexokinase strongly increases fusion; removal of extracellular adenosine by adenosine deaminase blocks, while addition of exogenous adenosine strongly potentiates, fusion; and pharmacologic stimulation of the adenosine A2A receptor increases, while selective A2A blockade inhibits, fusion. These results show that the purinergic axis plays a crucial and as yet undescribed role in osteoclast formation and reconcile previous evidence advocating a key role for either ATP or adenosine receptors in multinucleated giant cell formation.

Evaluation of TP53 mutations with the AmpliChip p53 research test in chronic lymphocytic leukemia: correlation with clinical outcome and gene expression profiling

Given that TP53 alterations predict prognosis and response to therapy in chronic lymphocytic leukemia (CLL), screening for TP53 mutations has an increasing role in patient management. TP53 direct sequencing is a time-consuming method, while the AmpliChip p53 Research Test is a novel non time-consuming microarray-based resequencing assay and queries Exons 2-11. We evaluated the impact of TP53 mutations on clinical outcome by analyzing 98 untreated CLL using the AmpliChip p53 Research Test and direct sequencing and performed microarrays analysis on TP53 mutated and/or deleted cases. The AmpliChip p53 Research Test detected 17 mutations in 14 patients (17.3%); a significant association between TP53 mutations and del(17p) was recorded. From a clinical standpoint, a higher percentage of mutation was found in CLL with unfavorable outcome (17.2% vs. 7.1% in progressive vs. stable cases). Detection of TP53 mutations by the AmpliChip p53 Research Test was associated with a significantly worse survival (P = 0.0002). Comparison of the array and direct sequencing tests showed that the p53 Research Test detected more mutations, although it failed to identify two microdeletions. Finally, microarrays analysis showed a more distinctive signature associated with del(17p) than with TP53 mutations, likely due to a concomitant gene dosage effect. The AmpliChip p53 Research Test is a straightforward method that bears prognostic value. This study confirms a high percentage of TP53 mutations in CLL with unfavorable outcome and a significant association between TP53 aberrations and del(17p). Finally, specific gene expression profiles are recognized for TP53 alterations.

Activities of adenine nucleotide and nucleoside degradation enzymes in platelets of rats infected by Trypanosoma evansi

Nucleotide and nucleoside-degrading enzymes, such as nucleoside triphosphate diphosphohydrose (NTPDase), 5'-nucleotidase and adenosine deaminase (ADA) are present in the surface membranes of platelets, involved in clotting disturbances of Trypanosoma evansi-infected animals. Thus, this study was aimed at evaluating the activities of these enzymes in platelets of rats experimentally infected with T. evansi. Animals were divided into four groups, according to the level of parasitemia. Blood samples were collected on days 3 (group A: at the beginning of parasitemia), 5 (group B: high parasitemia) and 15 (group C: chronic infection), post-infection. Group D (control group) was composed of non-infected animals for platelet count, separation and enzymatic assays. Animals from groups A and B showed marked thrombocytopenia, but platelet count was not affected in chronically infected rats. NTPDase, 5'-nucleotidase and ADA activities decreased (p<0.05) in platelets from rats of groups A and B, when compared to the control group. In group C, only NTPDase and 5'-nucleoside activities decreased (p<0.001). The correlations between platelet count and nucleotide/nucleoside hydrolysis were positive and statistically significant (p<0.05) in groups A and B. Platelet aggregation was decreased in all infected groups, in comparison to the control group (p<0.05). It is concluded that the alterations observed in the activities of NTPDase, 5'-nucleotidase and ADA in platelets of T. evansi-infected animals might be related to thrombocytopenia, that by reducing the number of platelets, there was less release of ATP and ADP. Another possibility being suggested is that changes have occurred in the membrane of these cells, decreasing the expression of these enzymes in the cell membrane.

Purinergic regulation of airway inflammation

The immune and inflammatory responses initiated by the interaction of a pathogen with airway surfaces constitute vital mechanisms to eradicate an infection. Sentinel dendritic cells embedded in the mucosa migrate to the lymph nodes to induce immune responses, whereas epithelial cells release chemokines to recruit inflammatory cells engaged in the active destruction of the intruder. All immune and inflammatory cells are regulated by customized purinergic networks of receptors and ectonucleotidases. The general concept is that bacterial products induce ATP release, which activates P2 receptors to initiate an inflammatory response, and is terminated by the conversion of ATP into adenosine (ADO) to initiate P1 receptor-mediated negative feedback responses. However, this chapter exposes a far more complex purinergic regulation of critical functions, such as the differentiation of naive lymphocytes and the complex maturation and secretion of pro-cytokines (i.e. IL-1β) by the "inflammasome". This material also reconciles decades of research by exposing the specificity and plasticity of the signaling network expressed by each immune and inflammatory cell, which changes through cell differentiation and in response to infectious or inflammatory mediators. By the end of this chapter, the reader will have a new appreciation for this aspect of airway defenses, and several leads in terms of therapeutic applications for the treatment of chronic respiratory diseases.

Involvement of P2Y6 receptor in p38 MAPK-mediated COX-2 expression in response to UVB irradiation of human keratinocytes

Ultraviolet B (UVB) radiation induces inflammation in human skin. Extracellular nucleotides are released from cells in response to various stimuli and act as intercellular signaling molecules through activation of P2 receptors. In this study, we investigated the involvement of extracellular nucleotides and P2 receptors in UVB-radiation-induced inflammation using human keratinocyte-derived HaCaT cells. UVB radiation induced rapid ATP release from HaCaT cells; this was inhibited by pretreatment with anion transporter blockers or maxi-anion channel blockers. In addition, the radiation-induced activation of p38 MAPK was significantly blocked by pretreatment with ecto-nucleotidase (apyrase) or P2Y6 receptor antagonist (MRS2578). Expression of COX-2, mediated by activation of p38 MAPK, was also induced by UVB radiation. Both pretreatment with MRS2578 and knockdown of the P2Y6 receptor by siRNA transfection attenuated the induction of COX-2 in HaCaT cells exposed to UVB radiation. Our results indicate that UVB radiation evokes ATP release from human keratinocytes and also that activation of P2Y6 receptor mediates the UVB-radiation-induced activation of p38 MAPK and expression of COX-2. Thus P2Y6 receptor is a mediator of UVB-radiation-induced inflammatory responses in keratinocytes.

Opposite effects of 5-hydroxymethyluracil on mitogenic response of T cells stimulated through T-cell receptor or through T-cell receptor and CD28 co-receptor molecule

The effect of a synthetic analog of "minor" pyrimidine base 5-hydroxymethyluracil (0.01-10 μg/ml) on the mitogenic response of donor peripheral blood T cells was studied in vitro under conditions of lymphocyte stimulation through T-cell receptor (antiCD3 monoclonal antibodies) or through T-cell receptor and CD28 co-receptor molecule (antiCD3 and antiCD28 monoclonal antibodies). 5-hydroxymethyluracil suppressed the mitogenic response of T cells stimulated with antiCD3 antibodies, which was paralleled by an increase in the count of silent cells and decrease in the count of dividing lymphocytes, but not by stimulation of apoptosis of activated cells. Under conditions of integration of stimuli (lymphocyte stimulation with antiCD3 and antiCD28), 5-hydroxymethyluracil stimulated the mitogenic response, which was paralleled by suppression of activation apoptosis and increase in proliferative potential of cells.

Temporomandibular joint inflammation activates glial and immune cells in both the trigeminal ganglia and in the spinal trigeminal nucleus

BACKGROUND

Glial cells have been shown to directly participate to the genesis and maintenance of chronic pain in both the sensory ganglia and the central nervous system (CNS). Indeed, glial cell activation has been reported in both the dorsal root ganglia and the spinal cord following injury or inflammation of the sciatic nerve, but no data are currently available in animal models of trigeminal sensitization. Therefore, in the present study, we evaluated glial cell activation in the trigeminal-spinal system following injection of the Complete Freund's Adjuvant (CFA) into the temporomandibular joint, which generates inflammatory pain and trigeminal hypersensitivity.

RESULTS

CFA-injected animals showed ipsilateral mechanical allodynia and temporomandibular joint edema, accompanied in the trigeminal ganglion by a strong increase in the number of GFAP-positive satellite glial cells encircling neurons and by the activation of resident macrophages. Seventy-two hours after CFA injection, activated microglial cells were observed in the ipsilateral trigeminal subnucleus caudalis and in the cervical dorsal horn, with a significant up-regulation of Iba1 immunoreactivity, but no signs of reactive astrogliosis were detected in the same areas. Since the purinergic system has been implicated in the activation of microglial cells during neuropathic pain, we have also evaluated the expression of the microglial-specific P2Y12 receptor subtype. No upregulation of this receptor was detected following induction of TMJ inflammation, suggesting that any possible role of P2Y12 in this paradigm of inflammatory pain does not involve changes in receptor expression.

CONCLUSIONS

Our data indicate that specific glial cell populations become activated in both the trigeminal ganglia and the CNS following induction of temporomandibular joint inflammation, and suggest that they might represent innovative targets for controlling pain during trigeminal nerve sensitization.

The purinergic receptor P2Y2 receptor mediates chemotaxis of dendritic cells and eosinophils in allergic lung inflammation

BACKGROUND

Extracellular ATP contributes to the pathogenesis of asthma via signalling at purinergic receptors. However, the precise purinergic receptors subtypes mediating the pro-asthmatic effects of ATP have not been identified, yet.

METHODS

In vivo studies were performed using the OVA-alum model. Functional expression of the P2Y(2) purinergic receptor subtype on human monocyte-derived dendritic cells and eosinophils was investigated using real-time PCR, migration assays, and production of reactive oxygen species.

RESULTS

Compared to wild-type animals P2Y(2) -/- mice showed reduced allergic airway inflammation which can be explained by defective migration of blood myeloid DCs towards ATP in vitro and in vivo, whereas the influence of ATP on maturation and cytokine production was not changed. Additionally, ATP failed to induce migration of bone marrow-derived eosinophils from P2Y(2) R-deficient animals. The relevance of our findings for humans was confirmed in functional studies with human monocyte-derived DCs and eosinophils. Interestingly, stimulation of human DCs derived from allergic individuals with house dust mite allergen induced functional up-regulation of the P2Y(2) R subtype. Furthermore, eosinophils isolated from asthmatic individuals expressed higher levels of P2Y(2) R compared to healthy controls. This was of functional relevance as these eosinophils were more sensitive to ATP-induced migration and production of reactive oxygen metabolites.

CONCLUSIONS

In summary, P2Y(2) R appears to be involved in asthmatic airway inflammation by mediating ATP-triggered migration of mDCs and eosinophils, as well as reactive oxygen species production. Together our data suggest that targeting P2Y(2) R might be a therapeutic option for the treatment of asthma.

Interactions between immunity and metabolism - contributions from the metabolic profiling of parasite-rodent models

A combined interdisciplinary research strategy is even more crucial in immunology than in many other biological sciences in order to comprehend the closely linked interactions between cell proliferation, molecular signalling and gene rearrangements. Because of the multi-dimensional nature of the immune system, an abundance of different experimental approaches has developed, with a main focus on cellular and molecular mechanisms. The role of metabolism in immunity has been underexplored so far, and yet researchers have made important contributions in describing associations of immune processes and metabolic pathways, such as the central role of the l-arginine pathway in macrophage activation or the immune regulatory functions of the nucleotides. Furthermore, metabolite supplement studies, including nutritional administration and labelled substrates, have opened up new means of manipulating immune mechanisms. Metabolic profiling has introduced a reproducible platform for systemic assessment of changes at the small-molecule level within a host organism, and specific metabolic fingerprints of several parasitic infections have been characterized by 1H NMR spectroscopy. The application of multivariate statistical methods to spectral data has facilitated recovery of biomarkers, such as increased acute phase protein signals, and enabled direct correlation to the relative cytokine levels, which encourages further application of metabolic profiling to explore immune regulatory systems.

Extracellular NAD+ shapes the Foxp3+ regulatory T cell compartment through the ART2-P2X7 pathway

CD4(+)CD25(+)FoxP3(+) regulatory T cells (T reg cells) play a major role in the control of immune responses but the factors controlling their homeostasis and function remain poorly characterized. Nicotinamide adenine dinucleotide (NAD(+)) released during cell damage or inflammation results in ART2.2-mediated ADP-ribosylation of the cytolytic P2X7 receptor on T cells. We show that T reg cells express the ART2.2 enzyme and high levels of P2X7 and that T reg cells can be depleted by intravenous injection of NAD(+). Moreover, lower T reg cell numbers are found in mice deficient for the NAD-hydrolase CD38 than in wild-type, P2X7-deficient, or ART2-deficient mice, indicating a role for extracellular NAD(+) in T reg cell homeostasis. Even routine cell preparation leads to release of NAD(+) in sufficient quantities to profoundly affect T reg cell viability, phenotype, and function. We demonstrate that T reg cells can be protected from the deleterious effects of NAD(+) by an inhibitory ART2.2-specific single domain antibody. Furthermore, selective depletion of T reg cells by systemic administration of NAD(+) can be used to promote an antitumor response in several mouse tumor models. Collectively, our data demonstrate that NAD(+) influences survival, phenotype, and function of T reg cells and provide proof of principle that acting on the ART2-P2X7 pathway represents a new strategy to manipulate T reg cells in vivo.

Immunomodulatory properties of pentoxifylline are mediated via adenosine-dependent pathways

The phosphodiesterase inhibitor pentoxifylline (PTX) exerts multiple beneficial immunomodulatory effects in states of hyperinflammation. However, the exact mechanism of action still remains elusive, and the clinical effects of PTX cannot be reliably predicted. In immune cells, the G protein-coupled adenosine A2A receptor (A2AR) exerts strong anti-inflammatory effects. As PTX amplifies signaling pathways downstream of Gs protein-coupled receptors, the A2AR-signaling pathway might be involved in the mediation of immune-suppressive effects of PTX. Here, we investigated this assumption in LPS-stimulated human polymorphonuclear (PMN) leukocytes and in anti-CD3/CD28-stimulated human T cells. In stimulated PMN leukocytes, PTX treatment led to a 4.5-fold decrease of the 50% inhibitory concentrations of adenosine on the H2O2 production; i.e., for adenosine plus PTX (in clinically relevant concentrations), an overadditive increase of inhibitory effects from less than 20% (estimated for each) to 56% (+/-5%) was found. In T cells, adenosine plus PTX revealed similar synergistic inhibitory effects on proinflammatory cytokine production. Inhibition of interferon gamma and TNF-alpha production increased from 7% (+/-1%) and 31% (+/-6%) (PTX alone) to 49% (+/-2%) and 69% (+/-6%), respectively. In T cells and PMN leukocytes, mRNA transcription of the A2AR was significantly increased upon stimulation, which was not influenced by PTX. In human PMN leukocytes and T cells, clinically relevant anti-inflammatory effects of PTX can be achieved only in the presence of sufficient adenosine concentrations. Sufficient adenosine levels might be a prerequisite for the accessibility of sepsis patients to treatment with PTX.

Dexamethasone enhances ATP-induced inflammatory responses in endothelial cells

The purinergic nucleotide ATP is released from stressed cells and is implicated in vascular inflammation. Glucocorticoids are essential to stress responses and are used therapeutically, yet little information is available that describes the effects of glucocorticoids on ATP-induced inflammation. In a human microvascular endothelial cell line, extracellular ATP-induced interleukin (IL)-6 secretion in a dose- and time-dependent manner. When cells were pretreated with dexamethasone, a prototypic glucocorticoid, ATP-induced IL-6 production was enhanced in a time- and dose-dependent manner. Mifepristone, a glucocorticoid receptor antagonist, blocked these effects. ATP-induced IL-6 release was significantly inhibited by a phospholipase C inhibitor [1-[6-[((17β)-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl]-1H-pyrrole-2,5-dione (U73122)] (63.2 ± 3%, p < 0.001) and abolished by a p38 mitogen-activated protein kinase inhibitor [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB 203580)] (88 ± 1%, p < 0.001). Cells treated with dexamethasone induced mRNA expression of the purinergic P2Y(2) receptor (P2Y(2)R) 1.8- ± 0.1-fold and, when stimulated with ATP, enhanced Ca(2+) release and augmented IL-6 mRNA expression. Silencing of the P2Y(2)R by its small interfering RNA decreased ATP-induced IL-6 production by 81 ± 1% (p < 0.001). Dexamethasone enhanced the transcription rate of P2Y(2)R mRNA and induced a dose-related increase in the activity of the P2Y(2)R promoter. Furthermore, dexamethasone-enhanced ATP induction of adhesion molecule transcription and augmented the release of IL-8. Dexamethasone leads to an unanticipated enhancement of endothelial inflammatory mediator production by extracellular ATP via a P2Y(2)R-dependent mechanism. These data define a novel positive feedback loop of glucocorticoids and ATP-induced endothelial inflammation.

P2Y(13) receptor is responsible for ADP-mediated degranulation in RBL-2H3 rat mast cells

Extracellular ADP is known to play many important physiological roles. In this study, we identified the P2Y(13) receptor in a rat mast cell line (RBL-2H3) and explored the functional role of ADP, its endogenous agonist. ADP induced both intracellular calcium mobilization and release of hexosaminidase (Hex). In an assay of intracellular calcium, ADP was 100-fold less potent than and equally efficacious as the P2Y(1) receptor-selective agonist MRS2365. However, ADP was more potent and efficacious than MRS2365 in inducing Hex release and in enhancing antigen-induced Hex release. ADP-induced intracellular calcium mobilization was blocked by phospholipase C inhibitor U73122 and by P2Y(1) receptor-selective antagonist MRS2500, but not by pertussis toxin (PTX), suggesting a mechanism mediated by the G(q)-coupled P2Y(1) receptor, but not P2Y(13) (G(i)-coupled) or P2X receptors. ADP-induced Hex release was blocked by PTX and a selective P2Y(13) receptor antagonist MRS2211, but not by MRS2500 or P2Y(1) receptor-specific siRNA, suggesting a G(i)-coupled P2Y(13) receptor-related mechanism. Measurement of gene expression confirmed high expression of both P2Y(1) and P2Y(13) receptors (in comparison to a previously reported P2Y(14) receptor) in RBL-2H3 cells. Thus, we demonstrated that ADP-mediated intracellular calcium mobilization and Hex release in RBL-2H3 cells are via P2Y(1) and P2Y(13) receptors, respectively. Selective antagonists of the P2Y(13) receptor might be novel therapeutic agents for various allergic conditions.

Preservation of differentiation and clonogenic potential of human hematopoietic stem and progenitor cells during lyophilization and ambient storage

Progenitor cell therapies show great promise, but their potential for clinical applications requires improved storage and transportation. Desiccated cells stored at ambient temperature would provide economic and practical advantages over approaches employing cell freezing and subzero temperature storage. The objectives of this study were to assess a method for loading the stabilizing sugar, trehalose, into hematopoietic stem and progenitor cells (HPC) and to evaluate the effects of subsequent freeze-drying and storage at ambient temperature on differentiation and clonogenic potential. HPC were isolated from human umbilical cord blood and loaded with trehalose using an endogenous cell surface receptor, termed P2Z. Solution containing trehalose-loaded HPC was placed into vials, which were transferred to a tray freeze-dryer and removed during each step of the freeze-drying process to assess differentiation and clonogenic potential. Control groups for these experiments were freshly isolated HPC. Control cells formed 1450+/-230 CFU-GM, 430+/-140 BFU-E, and 50+/-40 CFU-GEMM per 50 microL. Compared to the values for the control cells, there was no statistical difference observed for cells removed at the end of the freezing step or at the end of primary drying. There was a gradual decrease in the number of CFU-GM and BFU-E for cells removed at different temperatures during secondary drying; however, there were no significant differences in the number of CFU-GEMM. To determine storage stability of lyophilized HPC, cells were stored for 4 weeks at 25 degrees C in the dark. Cells reconstituted immediately after lyophilization produced 580+/-90 CFU-GM ( approximately 40%, relative to unprocessed controls p<0.0001), 170+/-70 BFU-E (approximately 40%, p<0.0001), and 41+/-22 CFU-GEMM (approximately 82%, p = 0.4171), and cells reconstituted after 28 days at room temperature produced 513+/-170 CFU-GM (approximately 35%, relative to unprocessed controls, p<0.0001), 112+/-68 BFU-E (approximately 26%, p<0.0001), and 36+/-17 CFU-GEMM ( approximately 82%, p = 0.2164) These studies are the first to document high level retention of CFU-GEMM following lyophilization and storage for 4 weeks at 25 degrees C. This type of flexible storage stability would potentially permit the ability to ship and store HPC without the need for refrigeration.

ATP secreted by endothelial cells blocks CX₃CL 1-elicited natural killer cell chemotaxis and cytotoxicity via P2Y₁₁ receptor activation

Endothelial cells (ECs) represent a major source of actively secreted adenosine triphosphate (ATP). Natural killer (NK) cells can mediate vascular injury in several pathologic conditions, including cytomegalovirus infection and vascular leak syndrome. We studied NK-cell expression of P2 receptors and the role of these nucleotide receptors in the regulation of endothelial-NK cell cross-talk. NK cells from healthy subjects expressed P2Y(₁,₂,₄,₆,₁₁,₁₂,₁₃,₁₄) and P2X(₁,₄,₅,₆,₇) receptors. NK cells stimulated with ATP, but not uridine triphosphate, increased intracellular Ca²(+) and chemokinesis. Moreover, ATP, but not uridine triphosphate, inhibited NK chemotaxis in response to CX₃CL1, whereas chemotaxis to CXCL12 was increased. CX₃CL1 elicited killing of human umbilical vein ECs and human coronary artery ECs by NK cells. However, in the presence of ATP, CX₃CL1 failed to stimulate killing of ECs. Such inhibitory effect was lost on exogenous addition of the ATP-hydrolyzing enzyme apyrase or by pharmacologic inhibition of the P2Y₁₁R, and correlated with increased intracellular cyclic adenosine monophosphate concentrations induced by ATP or other P2Y₁₁R agonists, including NAD(+). Extracellular ATP regulates NK-cell cytotoxicity via P2Y₁₁R activation, protecting ECs from CX₃CL1-elicited NK cell-mediated killing. These findings point out the P2Y₁₁R as a potential target for pharmacologic intervention aimed at reducing NK-mediated vascular injury.

Pannexin-1 hemichannel-mediated ATP release together with P2X1 and P2X4 receptors regulate T-cell activation at the immune synapse

Engagement of T cells with antigen-presenting cells requires T-cell receptor (TCR) stimulation at the immune synapse. We previously reported that TCR stimulation induces the release of cellular adenosine-5'-triphosphate (ATP) that regulates T-cell activation. Here we tested the roles of pannexin-1 hemichannels, which have been implicated in ATP release, and of various P2X receptors, which serve as ATP-gated Ca(2+) channels, in events that control T-cell activation. TCR stimulation results in the translocation of P2X1 and P2X4 receptors and pannexin-1 hemichannels to the immune synapse, while P2X7 receptors remain uniformly distributed on the cell surface. Removal of extracellular ATP or inhibition, mutation, or silencing of P2X1 and P2X4 receptors inhibits Ca(2+) entry, nuclear factors of activated T cells (NFAT) activation, and induction of interleukin-2 synthesis. Inhibition of pannexin-1 hemichannels suppresses TCR-induced ATP release, Ca(2+) entry, and T-cell activation. We conclude that pannexin-1 hemichannels and P2X1 and P2X4 receptors facilitate ATP release and autocrine feedback mechanisms that control Ca(2+) entry and T-cell activation at the immune synapse.

P2X(7) receptor-mediated release of cathepsins from macrophages is a cytokine-independent mechanism potentially involved in joint diseases

The ATP-gated P2X(7) receptor (P2X(7)R) is a promising therapeutic target in chronic inflammatory diseases with highly specific antagonists currently under clinical trials for rheumatoid arthritis. Anti-inflammatory actions of P2X(7)R antagonists are considered to result from inhibition of P2X(7)R-induced release of proinflammatory cytokines from activated macrophages. However, P2X(7)Rs are also expressed in resting macrophages, suggesting that P2X(7)R may also signal via cytokine-independent mechanisms involved in joint disease. In this study, we examined P2X(7)R function in resting human lung macrophages and mouse bone marrow-derived macrophages and found that ATP induced rapid release of the lysosomal cysteine proteases cathepsin B, K, L, and S and that was independent of the presence of the proinflammatory cytokines IL-1beta and IL-18. Cathepsins released into the medium were effective to degrade collagen extracellular matrix. ATP-induced cathepsin release was abolished by P2X(7)R antagonists, absent from P2X(7)R(-/-) mouse macrophages, and not associated with cell death. Our results suggest P2X(7)R activation may play a novel and direct role in tissue damage through release of cathepsins independently of its proinflammatory actions via IL-1 cytokines.

Amplification loop of the inflammatory process is induced by P2X7R activation in intestinal epithelial cells in response to neutrophil transepithelial migration

Inflammatory bowel diseases (IBD) are characterized during their active phase by polymorphonuclear leukocyte (PMNL) transepithelial migration. The efflux of PMNL into the mucosa is associated with the production of proinflammatory cytokines and the release of ATP from damaged and necrotic cells. The expression and function of purinergic P2X(7) receptor (P2X(7)R) in intestinal epithelial cells (IEC) and its potential role in the "cross talk" between IEC and PMNL have not been explored. The aims of the present study were 1) to examine P2X(7)R expression in IEC (T84 cells) and in human intestinal biopsies; 2) to detect any changes in P2X(7)R expression in T84 cells during PMNL transepithelial migration, and during the active and quiescent phases of IBD; and 3) to test whether P2X(7)R stimulation in T84 monolayers can induce caspase-1 activation and IL-1beta release by IEC. We found that a functional ATP-sensitive P2X(7)R is constitutively expressed at the apical surface of IEC T84 cells. PMNL transmigration regulates dynamically P2X(7)R expression and alters its distribution from the apical to basolateral surface of IEC during the early phase of PMNL transepithelial migration in vitro. P2X(7)R expression was weak in intestinal biopsies obtained during the active phase of IBD. We show that activation of epithelial P2X(7)R is mandatory for PMNL-induced caspase-1 activation and IL-1beta release by IEC. Overall, these changes in P2X(7)R function may serve to tailor the intensity of the inflammatory response and to prevent IL-1beta overproduction and inflammatory disease.

Lymphangiogenesis, myeloid cells and inflammation

The lymphatic system is essential for the maintenance of tissue fluid balance, immune surveillance and the absorption of fatty acids in the gastrointestinal tract. The lymphatic circulation is also a key player in disease processes such as cancer metastasis, lymphedema and various inflammatory disorders. With the identification of specific growth factors for lymphatic endothelial cells and markers that distinguish blood and lymphatic vessels, as well as the development of in vivo imaging technologies that provide new tools to examine the lymphatic drainage function in real time, many advancements have been made in lymphatic vascular research during the past few years. Despite these significant achievements, our understanding of the role of lymphatics in disease processes other than cancer metastasis is still rather limited. The current review will focus on the recent progress made in studies of lymphatics in inflammatory disorders.

Purinergic receptor inhibition prevents the development of smoke-induced lung injury and emphysema

Extracellular ATP acts as a "danger signal" and can induce inflammation by binding to purinergic receptors. Chronic obstructive pulmonary disease is one of the most common inflammatory diseases associated with cigarette smoke inhalation, but the underlying mechanisms are incompletely understood. In this study, we show that endogenous pulmonary ATP levels are increased in a mouse model of smoke-induced acute lung inflammation and emphysema. ATP neutralization or nonspecific P2R-blockade markedly reduced smoke-induced lung inflammation and emphysema. We detected an upregulation the purinergic receptors subtypes on neutrophils (e.g., P2Y2R), macrophages, and lung tissue from animals with smoke-induced lung inflammation. By using P2Y(2)R deficient ((-/-)) animals, we show that ATP induces the recruitment of blood neutrophils to the lungs via P2Y(2)R. Moreover, P2Y(2)R deficient animals had a reduced pulmonary inflammation following acute smoke-exposure. A series of experiments with P2Y(2)R(-/-) and wild type chimera animals revealed that P2Y(2)R expression on hematopoietic cell plays the pivotal role in the observed effect. We demonstrate, for the first time, that endogenous ATP contributes to smoke-induced lung inflammation and then development of emphysema via activation of the purinergic receptor subtypes, such as P2Y(2)R.

Large-conductance channel formation mediated by P2X7 receptor activation is regulated through distinct intracellular signaling pathways in peritoneal macrophages and 2BH4 cells

The P2X(7) receptor (P2X7R) is a ligand-gated ATP receptor that acts as a low- and large-conductance channel (pore) and is known to be coupled to several downstream effectors. Recently, we demonstrated that the formation of a large-conductance channel associated with the P2X(7) receptor is induced by increasing the intracellular Ca(2+) concentration (Faria et al., Am J Physiol Cell Physiol 297:C28-C42, 2005). Here, we investigated the intracellular signaling pathways associated with P2X(7) large-conductance channel formation using the patch clamp technique in conjunction with fluorescent imaging and flow cytometry assays in 2BH4 cells and peritoneal macrophages. Different antagonists were applied to investigate the following pathways: Ca(2+)-calmodulin, phospholipase A, phospholipase D, phospholipase C, protein kinase C (PKC), mitogen-activated protein kinase (MAPK), MAPK/extracellular signal-regulated kinase, phosphoinositide 3-kinase (PI3K), and cytoskeletal proteins. Macroscopic ionic currents induced by 1 mM ATP were reduced by 85% in the presence of PKC antagonists. The addition of antagonists for MAPK, PI3K, and the cytoskeleton (actin, intermediary filament, and microtubule) blocked 92%, 83%, and 95% of the ionic currents induced by 1 mM ATP, respectively. Our results show that PKC, MAPK, PI3K, and cytoskeletal components are involved in P2X(7) receptor large-channel formation in 2BH4 cells and peritoneal macrophages.

A potential role for P2X7R in allergic airway inflammation in mice and humans

P2X₇R deficiency is associated with a less severe outcome in acute and chronic inflammatory disorders. Recently, we demonstrated that extracellular adenosine triphosphate is involved in the pathogenesis of asthma by modulating the function of dendritic cells (DCs). However, the role of the purinergic receptor subtype P2X₇ is unknown. To elucidate the role of P2X₇R in allergic airway inflammation (AAI) in vitro and in vivo, P2X₇R expression was measured in lung tissue and immune cells of mice or in humans with allergic asthma. By using a specific P2X₇R-antagonist and P2X₇R-deficient animals, the role of this receptor in acute and chronic experimental asthma was explored. P2X₇R was found to be up-regulated during acute and chronic asthmatic airway inflammation in mice and humans. In vivo experiments revealed the functional relevance of this finding because selective P2X₇R inhibition or P2X₇R deficiency was associated with reduced features of acute and chronic asthma in the ovalbumin-alum or HDM model of AAI. Experiments with bone marrow chimeras emphasized that P2X₇R expression on hematopoietic cells is responsible for the proasthmatic effects of P2X₇R signaling. In the DC-driven model of AAI, P2X₇R-deficient DCs showed a reduced capacity to induce Th2 immunity in vivo. Up-regulation of P2X₇R on BAL macrophages and blood eosinophils could be observed in patients with chronic asthma. Our data suggest that targeting P2X₇R on hematopoietic cells (e.g., DCs or eosinophils) might be a new therapeutic option for the treatment of asthma.

Trophic activity of a naturally occurring truncated isoform of the P2X7 receptor

P2X7 is the largest member of the P2X subfamily of purinergic receptors. A typical feature is the carboxyl tail, which allows formation of a large pore. Recently a naturally occurring truncated P2X7 splice variant, isoform B (P2X7B), has been identified. Here we show that P2X7B expression in HEK293 cells, a cell type lacking endogenous P2X receptors, mediated ATP-stimulated channel activity but not plasma membrane permeabilization, raised endoplasmic reticulum Ca(2+) content, activated the transcription factor NFATc1, increased the cellular ATP content, and stimulated growth. In addition, P2X7B-transfected HEK293 cells (HEK293-P2X7B), like most tumor cells, showed strong soft agar-infiltrating ability. When coexpressed with full-length P2X7 (P2X7A), P2X7B coassembled with P2X7A into a heterotrimer and potentiated all known responses mediated by this latter receptor. P2X7B mRNA was found to be widely distributed in human tissues, especially in the immune and nervous systems, and to a much higher level than P2X7A. Finally, P2X7B expression was increased on mitogenic stimulation of peripheral blood lymphocyte. Altogether, these data show that P2X7B is widely expressed in several human tissues, modulates P2X7A functions, participates in the control of cell growth, and may help understand the role of the P2X7 receptor in the control of normal and cancer cell proliferation.

Human eosinophils recognize endogenous danger signal crystalline uric acid and produce proinflammatory cytokines mediated by autocrine ATP

Eosinophils are multifunctional leukocytes involved in various inflammatory processes, as well as tissue remodeling and immunoregulation. During inflammation and infection, injured cells and damaged tissues release uric acid and monosodium urate (MSU) crystals as important endogenous danger signals. Uric acid is also implicated in the immunogenic effects of an authentic Th2 adjuvant, aluminum hydroxide. Eosinophils often localize at sites of Th2-type chronic inflammation; therefore, we hypothesized that eosinophils may react to endogenous danger signals. We found that human eosinophils migrate toward soluble uric acid and MSU crystals in a gradient-dependent manner. Eosinophils incubated with MSU crystals, but not those incubated with uric acid solution, produced elevated levels of IL-6 and IL-8/CXCL8. Other cytokines and chemokines, including IL-1beta, IL-10, IL-17, IFN-gamma, CCL2, CCL3, CCL4, TNF-alpha, G-CSF, GM-CSF, fibroblast growth factor, vascular endothelial growth factor, and TGF-beta, were also produced by eosinophils incubated with MSU crystals. Eosinophils exposed to MSU crystals rapidly (i.e., within 1 min of exposure) released ATP into the extracellular milieu. Importantly, this autocrine ATP was necessary for eosinophils to produce cytokines in response to MSU crystals, and P2 nucleotide receptors, in particular P2Y(2), are likely involved in this positive feedback loop. Finally, at higher concentrations, MSU crystals promoted P2R-dependent release of a granule protein (eosinophil-derived neurotoxin) and cell death. Thus, human eosinophils may respond to particulate damage-associated endogenous danger signals. These responses by eosinophils to tissue damage may explain the self-perpetuating nature of chronic inflammation in certain human diseases, such as asthma.

Diadenosine homodinucleotide products of ADP-ribosyl cyclases behave as modulators of the purinergic receptor P2X7

ADP-ribosyl cyclases from both vertebrates and invertebrates were previously shown to produce two isomers of P1,P2 diadenosine 5',5'"-P1, P2-diphosphate, P18 and P24, from cyclic ADP-ribose (cADPR) and adenine. P18 and P24 are characterized by an unusual N-glycosidic linkage in one of the adenylic mononucleotides (Basile, G., Taglialatela-Scafati, O., Damonte, G., Armirotti, A., Bruzzone, S., Guida, L., Franco, L., Usai, C., Fattorusso, E., De Flora, A., and Zocchi, E. (2005) Proc. Natl. Acad. Sci. U.S.A. 102, 14509-14514). P24, but not P18, proved to increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) in HeLa cells and to negatively affect mitochondrial function. Here we show that micromolar P24, but not P18, triggers a slow and sustained influx of extracellular Ca(2+) through the opening of the purinergic receptor/channel P2X7. On the other hand, P18 inhibits the Ca(2+) influx induced by 0.6 mm ATP in HEK293 cells stably transfected with P2X7, with an IC(50) of approximately 1 mum. Thus, P18 is devoid of intrinsic P2X7 stimulatory activity and behaves as an ATP antagonist. A P2X7-mediated increase of the basal [Ca(2+)](i) has been demonstrated to negatively affect Schwann cell (SC) function in rats with the inherited, peripheral neuropathy Charcot-Marie-Tooth 1A (CMT1A) (Nobbio, L., Sturla, L., Fiorese, F., Usai, C., Basile, G., Moreschi, I., Benvenuto, F., Zocchi, E., De Flora, A., Schenone, A., and Bruzzone S. (2009) J. Biol. Chem. 284, 23146-23158). Preincubation of CMT1A SC with 200 nm P18 restored the basal [Ca(2+)](i) to values similar to those recorded in wild-type SC. These results identify P18 as a new P2X7 antagonist, potentially useful in the treatment of CMT1A.

Two haplotypes of the P2X(7) receptor containing the Ala-348 to Thr polymorphism exhibit a gain-of-function effect and enhanced interleukin-1beta secretion

The P2X(7) receptor is an ATP-gated cation channel expressed in immune cells and plays a role in proinflammatory cytokine release from monocytes and macrophages. This study investigated the coinheritance of 12 functionally relevant single nucleotide polymorphisms (SNPs) in the human P2X(7) gene (P2RX7), and the functional effect of each singly and in combination was assessed by measurements of ATP-induced currents and ethidium(+) uptake. Genotyping of 3430 Caucasian subjects identified 4 common haplotypes in addition to the common (wild-type) P2X(7)-1. Two haplotypes (denoted P2X(7)-2 and P2X(7)-4) contained various combinations of gain-of-function SNPs. P2X(7)-4 was identified uniquely by the Gln-460 to Arg polymorphism (rs2230912). When expressed in HEK-293 cells, recombinant P2X(7)-2, and P2X(7)-4 haplotypes displayed a 3-fold and 5-fold increase, respectively, in receptor function compared to the wild-type P2X(7)-1. Both P2X(7) haplotypes contained the Ala-348>Thr polymorphism (rs1718119), and this mutation was critical for the gain-of-function effect. Peripheral blood monocytes and erythrocytes from subjects homozygous for gain-of-function P2X(7) haplotypes exhibited increased ATP-induced ethidium(+) uptake and (86)Rb(+) efflux, respectively, and this correlated with increased IL-1beta secretion from LPS-primed monocytes. Inheritance of these P2X(7) haplotypes predisposing to increased proinflammatory cytokine secretion may be important in genetic association studies of inflammatory, infectious, and psychiatric disorders.

Involvement of purinergic signaling in cellular response to gamma radiation

Recent studies have suggested a bystander effect in nonirradiated cells adjacent to irradiated cells; however, the mechanism is poorly understood. In this study, we investigated the involvement of both extracellular nucleotides and activation of P2 receptors in cellular responses to gamma radiation using human HaCaT keratinocytes. The concentration of ATP in culture medium was increased after gamma irradiation (0.1-1.0 Gy), suggesting that radiation induces ATP release from cells. Intracellular Ca(2+) concentration was elevated when conditioned medium from irradiated cells was transferred to nonirradiated cells, and this elevation was suppressed by apyrase (ecto-nucleotidase), indicating the involvement of extracellular nucleotides in this event. Further, we examined the activation of ERK1/2 by gamma radiation and nucleotides (ATP and UTP). Both gamma radiation and nucleotides induced activation of ERK1/2. Next, the effect of inhibitors of P2 receptors on radiation-induced activation of ERK1/2 was examined. The activation of ERK1/2 was blocked by suramin (P2Y inhibitor), MRS2578 (P2Y(6) antagonist) and apyrase. These results suggest that both released nucleotides and activation of P2Y receptors are involved in gamma-radiation-induced activation of ERK1/2. We conclude that ionizing radiation induces release of nucleotides from cells, leading to activation of P2Y receptors, which in turn would result in a variety of biological effects.

Enzymes that hydrolyze adenine nucleotides in platelets and polymorphisms in the alpha2 gene of integrin alpha2beta1 in patients with von Willebrand disease

Von Willebrand disease (VWD) is one of the most common inherited bleeding diseases caused by a qualitative or quantitative deficiency of the von Willebrand factor (FvW). FvW is a multimeric glycoprotein synthesized by megakaryocytes and endothelial cells and it is present in the subendothelial matrix, blood plasma, platelets, and endothelium. This glycoprotein plays an important role in thrombus formation by initiating platelet adhesion to sites of injury as well as platelet aggregation. The aim of this study was to evaluate the activities of enzymes that hydrolyze adenine nucleotides in platelets, ristocetin-induced platelet aggregation (RIPA), and polymorphisms of the alpha2 gene of alpha2beta1 integrin from VWD patients. Platelet nucleoside triphosphate diphosphohydrolase (NTPDase), 5'-nucleotidase, and ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activities were verified in 14 VWD patients. For RIPA determination, a final concentration of 1.25 mg/ml of ristocetin was used. Polymorphisms of the alpha2 gene were analyzed through PCR. Platelet NTPDase and E-NPP were decreased in VWD patients. 5'-Nucleotidase activity was not statistically significant between controls and VWD patients. RIPA was significantly reduced, with an allelic frequency of 78.57% for 807C in VWD patients. Our results indicated reduced platelet NTPDase and E-NPP activities which might be related to the low platelet adhesiveness. The prevalence of the 807C allele might account for the variability in bleeding in VWD.

Gene expression profiling defines the role of ATP-exposed keratinocytes in skin inflammation

BACKGROUND

Various environmental stimuli, e.g., mechanical stress, osmolarity change, oxidative stress, and microbial products trigger ATP release from cells. It is well known that ATP regulates cell growth, differentiation, terminal differentiation, and cell-to-cell communication in keratinocytes. Moreover, extracellular ATP stimulates the expression and release of IL-6 and modulates the production several chemokines by keratinocytes.

OBJECTIVE

To investigate the role of ATP-stimulated keratinocytes in skin inflammation and immune response.

METHODS

We identified genes whose expression is augmented in ATP-stimulated human keratinocytes by DNA microarray. These microarray data were validated by quantitative real-time RT-PCR. Furthermore, we confirmed the observed mRNA change at protein level by ELISA and Western blotting.

RESULTS

The statistical analysis of the microarray data revealed that, besides IL-6, the expression of several novel genes such as IL-20, CXCL1-3, and ATF3 was significantly augmented in ATP-stimulated keratinocytes. These data was validated by quantitative real-time RT-PCR. We also confirmed the augmented production of IL-6, IL-20, CXCL1 by ELISA and that of ATF3 by Western blotting. Since both IL-6 and IL-20 that can stimulate STAT3 were produced by the ATP-stimulated keratinocytes, we examined their phosphorylation of STAT3. The study demonstrated biphasic activation of STAT3 after ATP stimulation, which was composed of a first peak at 1-2 h and a second peak at 12-24 h. The latter peak was significantly suppressed by anti-IL-6 antibody.

CONCLUSION

These studies characterized (1) STAT3 activation, (2) chemotaxis for neutrophils via CXCL1-3, and (3) ATF3 activation as possible roles of ATP-stimulated keratinocytes in skin inflammation and immune response.

Structural determination of functional units of the nucleotide binding domain (NBD94) of the reticulocyte binding protein Py235 of Plasmodium yoelii

BACKGROUND

Invasion of the red blood cells (RBC) by the merozoite of malaria parasites involves a large number of receptor ligand interactions. The reticulocyte binding protein homologue family (RH) plays an important role in erythrocyte recognition as well as virulence. Recently, it has been shown that members of RH in addition to receptor binding may also have a role as ATP/ADP sensor. A 94 kDa region named Nucleotide-Binding Domain 94 (NBD94) of Plasmodium yoelii YM, representative of the putative nucleotide binding region of RH, has been demonstrated to bind ATP and ADP selectively. Binding of ATP or ADP induced nucleotide-dependent structural changes in the C-terminal hinge-region of NBD94, and directly impacted on the RBC binding ability of RH.

METHODOLOGY/PRINCIPAL FINDINGS

In order to find the smallest structural unit, able to bind nucleotides, and its coupling module, the hinge region, three truncated domains of NBD94 have been generated, termed NBD94(444-547), NBD94(566-663) and NBD94(674-793), respectively. Using fluorescence correlation spectroscopy NBD94(444-547) has been identified to form the smallest nucleotide binding segment, sensitive for ATP and ADP, which became inhibited by 4-Chloro-7-nitrobenzofurazan. The shape of NBD94(444-547) in solution was calculated from small-angle X-ray scattering data, revealing an elongated molecule, comprised of two globular domains, connected by a spiral segment of about 73.1 A in length. The high quality of the constructs, forming the hinge-region, NBD94(566-663) and NBD94(674-793) enabled to determine the first crystallographic and solution structure, respectively. The crystal structure of NBD94(566-663) consists of two helices with 97.8 A and 48.6 A in length, linked by a loop. By comparison, the low resolution structure of NBD94(674-793) in solution represents a chair-like shape with three architectural segments.

CONCLUSIONS

These structures give the first insight into how nucleotide binding impacts on the overall structure of RH and demonstrates the potential use of this region as a novel drug target.

Exocytosis and protein secretion in Trypanosoma

Background

Human African trypanosomiasis is a lethal disease caused by the extracellular parasite Trypanosoma brucei. The proteins secreted by T. brucei inhibit the maturation of dendritic cells and their ability to induce lymphocytic allogenic responses. To better understand the pathogenic process, we combined different approaches to characterize these secreted proteins.

Results

Overall, 444 proteins were identified using mass spectrometry, the largest parasite secretome described to date. Functional analysis of these proteins revealed a strong bias toward folding and degradation processes and to a lesser extent toward nucleotide metabolism. These features were shared by different strains of T. brucei, but distinguished the secretome from published T. brucei whole proteome or glycosome. In addition, several proteins had not been previously described in Trypanosoma and some constitute novel potential therapeutic targets or diagnostic markers. Interestingly, a high proportion of these secreted proteins are known to have alternative roles once secreted. Furthermore, bioinformatic analysis showed that a significant proportion of proteins in the secretome lack transit peptide and are probably not secreted through the classical sorting pathway. Membrane vesicles from secretion buffer and infested rat serum were purified on sucrose gradient and electron microscopy pictures have shown 50- to 100-nm vesicles budding from the coated plasma membrane. Mass spectrometry confirmed the presence of Trypanosoma proteins in these microvesicles, showing that an active exocytosis might occur beyond the flagellar pocket.

Conclusions

This study brings out several unexpected features of the secreted proteins and opens novel perspectives concerning the survival strategy of Trypanosoma as well as possible ways to control the disease. In addition, concordant lines of evidence support the original hypothesis of the involvement of microvesicle-like bodies in the survival strategy allowing Trypanosoma to exchange proteins at least between parasites and/or to manipulate the host immune system.

Biochemical characterization of soluble nucleotide pyrophosphatase/phosphodiesterase activity in rat serum

Biochemical properties of nucleotide pyrophosphatase/phosphodiesterase (NPP) in rat serum have been described by assessing its nucleotide phosphodiesterase activity, using p-nitrophenyl-5'-thymidine monophosphate (p-Nph-5'-TMP) as a substrate. It was demonstrated that NPP activity shares some typical characteristics described for other soluble NPP, such as divalent cation dependence, strong alkaline pH optimum (pH 10.5), inhibition by glycosaminoglycans, and K (m) for p-Nph-5'-TMP hydrolysis of 61.8 +/- 5.2 microM. In order to characterize the relation between phosphodiesterase and pyrophosphatase activities of NPP, we have analyzed the effects of different natural nucleotides and nucleotide analogs. ATP, ADP, and AMP competitively inhibited p-Nph-5'-TMP hydrolysis with K (i) values ranging 13-43 microM. Nucleotide analogs, alpha,beta-metATP, BzATP, 2-MeSATP, and dialATP behaved as competitive inhibitors, whereas alpha,beta-metADP induced mixed inhibition, with K (i) ranging from 2 to 20 microM. Chromatographic analysis revealed that alpha,beta-metATP, BzATP, and 2-MeSATP were catalytically degraded in the serum, whereas dialATP and alpha,beta-metADP resisted hydrolysis, implying that the former act as substrates and the latter as true competitive inhibitors of serum NPP activity. Since NPP activity is involved in generation, breakdown, and recycling of extracellular adenine nucleotides in the vascular compartment, the results suggest that both hydrolyzable and non-hydrolyzable nucleotide analogs could alter the amplitude and direction of ATP actions and could have potential therapeutic application.

P2 receptor-mediated signaling in mast cell biology

Mast cells are widely recognized as effector cells of allergic inflammatory reactions. They contribute to the pathogenesis of different chronic inflammatory diseases, wound healing, fibrosis, thrombosis/fibrinolysis, and anti-tumor immune responses. In this paper, we summarized the role of P2X and P2Y receptors in mast cell activation and effector functions. Mast cells are an abundant source of ATP which is stored in their granules and secreted upon activation. We discuss the contribution of mast cells to the extracellular ATP release and to the maintenance of extracellular nucleotides pool. Recent publications highlight the importance of purinergic signaling for the pathogenesis of chronic airway inflammation. Therefore, the role of ATP and P2 receptors in allergic inflammation with focus on mast cells was analyzed. Finally, ATP functions as mast cell autocrine/paracrine factor and as messenger in intercellular communication between mast cells, nerves, and glia in the central nervous system.

Abnormal expression of P2X family receptors in Chinese pediatric acute leukemias

Nucleotides are new players in intercellular communication network. P2X family receptors are ATP-gated plasma membrane ion channels with diverse biological functions. Their distribution patterns and significance in pediatric leukemias have not been established. Here we investigated the expression of P2X receptors in BMMC samples from Chinese pediatric acute leukemias. Real-time PCR and Western blot results showed that P2X1, P2X4, P2X5 and P2X7 receptors were simultaneously over expressed in leukemias compared with controls, whereas P2X2, P2X3 and P2X6 were absent or marginally expressed in both groups. It was worth noting that the co-expression feature of them, especially between P2X4 and P2X7, could be observed and the highest expression of P2X7 was detected in relapsed patients. Moreover, concomitant decrease of P2X4, P2X5 and P2X7 expressions was observed at CR stage in a follow-up study. Functional P2X7 was also verified. These results suggested that P2X1, P2X4, P2X5 and P2X7 were hematopoiesis-related P2X receptors, and their signaling, especially for P2X7, might play important roles in pediatric leukemias. P2X receptors might co-operatively contribute to the malignant phenotype in human pediatric leukemias.

Shockwaves increase T-cell proliferation and IL-2 expression through ATP release, P2X7 receptors, and FAK activation

Shockwaves elicited by transient pressure disturbances are used to treat musculoskeletal disorders. Previous research has shown that shockwave treatment affects T-cell function, enhancing T-cell proliferation and IL-2 expression by activating p38 mitogen-activated protein kinase (MAPK) signaling. Here we investigated the signaling pathway by which shockwaves mediate p38 MAPK phosphorylation. We found that shockwaves at an intensity of 0.18 mJ/mm(2) induce the release of extracellular ATP from human Jurkat T-cells at least in part by affecting cell viability. ATP released into the extracellular space stimulates P2X7-type purinergic receptors that induce the activation of p38 MAPK and of focal adhesion kinase (FAK) by phosphorylation on residues Tyr397 and Tyr576/577. Elimination of released ATP with apyrase or inhibition of P2X7 receptors with the antagonists KN-62 or suramin significantly weakens FAK phosphorylation, p38 MAPK activation, IL-2 expression, and T-cell proliferation. Conversely, addition of exogenous ATP causes phosphorylation of FAK and p38 MAPK. Silencing of FAK expression also reduces these cell responses to shockwave treatment. We conclude that shockwaves enhance p38 MAPK activation, IL-2 expression, and T-cell proliferation via the release of cellular ATP and feedback mechanisms that involve P2X7 receptor activation and FAK phosphorylation.

Alpha-defensins secreted by dysplastic granulocytes inhibit the differentiation of monocytes in chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic disorder that occurs in elderly patients. One of the main diagnostic criteria is the accumulation of heterogeneous monocytes in the peripheral blood. We further explored this cellular heterogeneity and observed that part of the leukemic clone in the peripheral blood was made of immature dysplastic granulocytes with a CD14(-)/CD24(+) phenotype. The proteome profile of these cells is dramatically distinct from that of CD14(+)/CD24(-) monocytes from CMML patients or healthy donors. More specifically, CD14(-)/CD24(+) CMML cells synthesize and secrete large amounts of alpha-defensin 1-3 (HNP1-3). Recombinant HNPs inhibit macrophage colony-stimulating factor (M-CSF)-driven differentiation of human peripheral blood monocytes into macrophages. Using transwell, antibody-mediated depletion, suramin inhibition of purinergic receptors, and competitive experiments with uridine diphosphate (UDP)/uridine triphosphate (UTP), we demonstrate that HNP1-3 secreted by CD14(-)/CD24(+) cells inhibit M-CSF-induced differentiation of CD14(+)/CD24(-) cells at least in part through P2Y6, a receptor involved in macrophage differentiation. Altogether, these observations suggest that a population of immature dysplastic granulocytes contributes to the CMML phenotype through production of alpha-defensins HNP1-3 that suppress the differentiation capabilities of monocytes.

Homocysteine decreases extracellular nucleotide hydrolysis in rat platelets

Hyperhomocysteinemia is an independent risk factor for atherothrombotic disease. Platelets play an important role in cardiovascular disease and release pro-aggregates mediators when activated, such as ADP, a physiological agonist involved in normal hemostasis and thrombosis. NTPDases and 5'-nucleotidase are ecto-enzymes that hydrolyze ATP, ADP and AMP to adenosine playing an important role on blood flow and thrombogenesis by regulating ADP catabolism. The aim of the present study was evaluate extracellular adenine nucleotide hydrolysis of rat platelets exposed to homocysteine in vitro and in vivo. In vitro homocysteine (Hcy) in the concentration range of 20 to 500 microM caused a significant decrease on ATP (around 30%) and ADP (around 45%) hydrolysis, respectively, while AMP hydrolysis was not altered. Hcy was not able to inhibit the hydrolysis of ATP and ADP catalyzed by purified apyrase at the same concentrations tested in vitro on platelets, suggesting an indirect effect. The inhibitory effect of Hcy on platelets was prevented by antioxidants agents in vitro and in vivo. Furthermore homocysteine treatment increased platelet aggregation induced by ADP. Based on the results presented herein, we propose that inhibition of extracellular ATP and ADP hydrolysis caused by homocysteine was probably due oxidative stress, since antioxidants prevented such effects. These findings may contribute to an increase platelet response to ADP and consequence development of thrombotic risk attributed to hyperhomocysteinemia.

NF546 [4,4'-(carbonylbis(imino-3,1-phenylene-carbonylimino-3,1-(4-methyl-phenylene)-carbonylimino))-bis(1,3-xylene-alpha,alpha'-diphosphonic acid) tetrasodium salt] is a non-nucleotide P2Y11 agonist and stimulates release of interleukin-8 from human monocyte-derived dendritic cells

The G protein-coupled P2Y(11) receptor is involved in immune system modulation. In-depth physiological evaluation is hampered, however, by a lack of selective and potent ligands. By screening a library of sulfonic and phosphonic acid derivatives at P2Y(11) receptors recombinantly expressed in human 1321N1 astrocytoma cells (calcium and cAMP assays), the selective non-nucleotide P2Y(11) agonist NF546 [4,4'-(carbonylbis(imino-3,1-phenylene-carbonylimino-3,1-(4-methyl-phenylene)carbonylimino))-bis(1,3-xylene-alpha,alpha'-diphosphonic acid) tetrasodium salt] was identified. NF546 had a pEC(50) of 6.27 and is relatively selective for P2Y(11) over P2Y(1), P2Y(2), P2Y(4), P2Y(6), P2Y(12), P2X(1), P2X(2), and P2X(2)-X(3). Adenosine-5'-O-(3-thio)triphosphate (ATPgammaS), a nonhydrolyzable analog of the physiological P2Y(11) agonist ATP, and NF546 use a common binding site as suggested by molecular modeling studies and their competitive behavior toward the nanomolar potency antagonist NF340 [4,4'-(carbonylbis(imino-3,1-(4-methyl-phenylene)carbonylimino))bis(naphthalene-2,6-disulfonic acid) tetrasodium salt] in Schild analysis. The pA(2) of NF340 was 8.02 against ATPgammaS and 8.04 against NF546 (calcium assays). NF546 was further tested for P2Y(11)-mediated effects in monocyte-derived dendritic cells. Similarly to ATPgammaS, NF546 led to thrombospondin-1 secretion and inhibition of lipopolysaccharide-stimulated interleukin-12 release, whereas NF340 inhibited these effects. Further, for the first time, it was shown that ATPgammaS or NF546 stimulation promotes interleukin 8 (IL-8) release from dendritic cells, which could be inhibited by NF340. In conclusion, we have described the first selective, non-nucleotide agonist NF546 for P2Y(11) receptors in both recombinant and physiological expression systems and could show a P2Y(11)-stimulated IL-8 release, further supporting the immunomodulatory role of P2Y(11) receptors.

Extracellular NAD(+) induces a rise in [Ca(2+)](i) in activated human monocytes via engagement of P2Y(1) and P2Y(11) receptors

Extracellular nicotinamide adenine dinucleotide (NAD(+)) is known to increase the intracellular calcium concentration [Ca(2+)](i) in different cell types and by various mechanisms. Here we show that NAD(+) triggers a transient rise in [Ca(2+)](i) in human monocytes activated with lipopolysaccharide (LPS), which is caused by a release of Ca(2+) from IP(3)-responsive intracellular stores and an influx of extracellular Ca(2+). By the use of P2 receptor-selective agonists and antagonists we demonstrate that P2 receptors play a role in the NAD(+)-induced calcium response in activated monocytes. Of the two subclasses of P2 receptors (P2X and P2Y) the P2Y receptors were considered the most likely candidates, since they share calcium signaling properties with NAD(+). The identification of P2Y(1) and P2Y(11) as receptor subtypes responsible for the NAD(+)-triggered increase in [Ca(2+)](i) was supported by several lines of evidence. First, specific P2Y(1) and P2Y(11) receptor antagonists inhibited the NAD(+)-induced increase in [Ca(2+)](i). Second, NAD(+) was shown to potently induce calcium signals in cells transfected with either subtype, whereas untransfected cells were unresponsive. Third, NAD(+) caused an increase in [cAMP](i), prevented by the P2Y(11) receptor-specific antagonist NF157.