Targeted disruption of cd39/ATP diphosphohydrolase results in disordered hemostasis and thromboregulation

CD39, or vascular adenosine triphosphate diphosphohydrolase, has been considered an important inhibitor of platelet activation. Unexpectedly, cd39-deficient mice had prolonged bleeding times with minimally perturbed coagulation parameters. Platelet interactions with injured mesenteric vasculature were considerably reduced in vivo and purified mutant platelets failed to aggregate to standard agonists in vitro. This platelet hypofunction was reversible and associated with purinergic type P2Y1 receptor desensitization. In keeping with deficient vascular protective mechanisms, fibrin deposition was found at multiple organ sites in cd39-deficient mice and in transplanted cardiac grafts. Our data indicate a dual role for adenosine triphosphate diphosphohydrolase in modulating hemostasis and thrombotic reactions.

CD39/ENTPD1 expression by CD4+Foxp3+ regulatory T cells promotes hepatic metastatic tumor growth in mice

BACKGROUND & AIMS

Adenosine mediates immune suppression and is generated by the ectonucleotidases CD39 (ENTPD1) and CD73 that are expressed on vascular endothelial cells and regulatory T cells (Tregs). Although tumor-infiltrating immune cells include Foxp3(+) Tregs, it is not clear whether local adenosine generation by Tregs promotes tumor growth in a CD39-dependent manner. In this study, we have examined the effect of CD39 expression by Tregs on effector immune cell responses to hepatic metastases in vivo.

METHODS

A model of hepatic metastatic cancer was developed with portal vein infusion of luciferase-expressing melanoma B16/F10 cells and MCA38 colon cancer cells in wild-type (wt) and mutant mice null for Cd39. Chimeric mice were generated by bone marrow transplantation (BMT) using Cd39 null or wt C57BL6 donors and irradiated recipient mice.

RESULTS

We demonstrate that hepatic growth of melanoma metastatic tumors was strongly inhibited in mice with Cd39 null vasculature or in wt mice with circulating Cd39 null bone marrow-derived cells. We show functional CD39 expression on CD4(+)Foxp3(+) Tregs suppressed antitumor immunity mediated by natural killer (NK) cells in vitro and in vivo. Finally, inhibition of CD39 activity by polyoxometalate-1, a pharmacologic inhibitor of nucleoside triphosphate diphosphohydrolase activity, significantly inhibited tumor growth (P < .001).

CONCLUSIONS

CD39 expression on Tregs inhibits NK activity and is permissive for metastatic growth. Pharmacologic or targeted inhibition of CD39 enzymatic activity may find utility as an adjunct therapy for secondary hepatic malignancies.

From the Cover: CD39 deletion exacerbates experimental murine colitis and human polymorphisms increase susceptibility to inflammatory bowel disease

CD39/ENTPD1 hydrolyzes proinflammatory nucleotides to generate adenosine. As purinergic mediators have been implicated in intestinal inflammation, we hypothesized that CD39 might protect against inflammatory bowel disease. We studied these possibilities in a mouse model of colitis using mice with global CD39 deletion. We then tested whether human genetic polymorphisms in the CD39 gene might influence susceptibility to Crohn's disease. We induced colitis in mice using Dextran Sodium Sulfate (DSS). Readouts included disease activity scores, histological evidence of injury, and markers of inflammatory activity. We used HapMap cell lines to find SNPs that tag for CD39 expression, and then compared the frequency of subjects with high vs. low CD39-expression genotypes in a case-control cohort for Crohn's disease. Mice null for CD39 were highly susceptible to DSS injury, with heterozygote mice showing an intermediate phenotype compared to wild type (WT). We identified a common SNP that tags CD39 mRNA expression levels in man. The SNP tagging low levels of CD39 expression was associated with increased susceptibility to Crohn's disease in a case-control cohort comprised of 1,748 Crohn's patients and 2,936 controls (P = 0.005-0.0006). Our data indicate that CD39 deficiency exacerbates murine colitis and suggest that CD39 polymorphisms are associated with inflammatory bowel disease in humans.

Identification of ectonucleotidases CD39 and CD73 in innate protection during acute lung injury

Acute lung injury (ALI), such as that which occurs with mechanical ventilation, contributes to morbidity and mortality of critical illness. Nonetheless, in many instances, ALI resolves spontaneously through unknown mechanisms. Therefore, we hypothesized the presence of innate adaptive pathways to protect the lungs during mechanical ventilation. In this study, we used ventilator-induced lung injury as a model to identify endogenous mechanisms of lung protection. Initial in vitro studies revealed that supernatants from stretch-induced injury contained a stable factor which diminished endothelial leakage. This factor was subsequently identified as adenosine. Additional studies in vivo revealed prominent increases in pulmonary adenosine levels with mechanical ventilation. Because ectoapyrase (CD39) and ecto-5'-nucleotidase (CD73) are rate limiting for extracellular adenosine generation, we examined their contribution to ALI. In fact, both pulmonary CD39 and CD73 are induced by mechanical ventilation. Moreover, we observed pressure- and time-dependent increases in pulmonary edema and inflammation in ventilated cd39(-/-) mice. Similarly, pharmacological inhibition or targeted gene deletion of cd73 was associated with increased symptom severity of ventilator-induced ALI. Reconstitution of cd39(-/-) or cd73(-/-) mice with soluble apyrase or 5'-nucleotidase, respectively, reversed such increases. In addition, ALI was significantly attenuated and survival improved after i.p. treatment of wild-type mice with soluble apyrase or 5'-nucleotidase. Taken together, these data reveal a previously unrecognized role for CD39 and CD73 in lung protection and suggest treatment with their soluble compounds as a therapeutic strategy for noninfectious ALI.

Purification and cloning of a soluble ATP-diphosphohydrolase (apyrase) from potato tubers (Solanum tuberosum)

A soluble ATP-diphosphohydrolase (apyrase, EC 3.6.1.5) has been purified from potato tubers. Solanum tuberosum, to a specific activity of 10,000 mumol P(i)/mg/min. The cDNA corresponding to the potato apyrase has been isolated and termed RROP1. The deduced amino acid sequence contains a putative signal sequence, two hydrophobic regions at the carboxy terminus, two potential Asn-linked glycosylation sites, and four regions in the amino-terminal half that we term ACR (apyrase conserved regions) 1-4 that are highly conserved in known apyrases and related enzymes; garden pea nucleoside triphosphatase, Toxoplasma gondii nucleoside triphosphate hydrolases, and Saccharomyces cerevisiae golgi guanosine diphosphatase. A yeast 71.9-kDa hypothetical protein on chromosome V, a Caenorhabditis elegans hypothetical 61.3-kDa protein on chromosome III, and human CD39, a lymphoid cell activation antigen, also share the conserved ACR regions, but their ability to hydrolyze nucleotides has not been assessed.

CD39/ectonucleoside triphosphate diphosphohydrolase 1 provides myocardial protection during cardiac ischemia/reperfusion injury

BACKGROUND

Extracellular adenosine, generated from extracellular nucleotides via ectonucleotidases, binds to specific receptors and provides cardioprotection from ischemia and reperfusion. In the present study, we studied ecto-enzymatic ATP/ADP-phosphohydrolysis by select members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family during myocardial ischemia.

METHODS AND RESULTS

As a first step, we used a murine model of myocardial ischemia and in situ preconditioning and performed pharmacological studies with polyoxometalate 1, a potent E-NTPDase inhibitor (Na6[H2W12O40]). Polyoxometalate 1 treatment increased infarct sizes and abolished beneficial effects of preconditioning. To define relative contributions of distinct E-NTPDases, we investigated transcriptional responses of E-NTPDases 1 to 3 and 8 to preconditioning. We noted robust and selective induction of E-NTPDase 1 (CD39) transcript and protein. Histological analysis of preconditioned myocardium localized CD39 induction to endothelia and myocytes. Cd39-/- mice exhibited larger infarct sizes with ischemia (cd39+/+ 43.0+/-3.3% versus cd39-/- 52%+/-1.8; P<0.05), and cardioprotection was abrogated by preconditioning (cd39+/+ 13.3%+/-1.5 versus cd39-/- 50.5%+/-2.8; P<0.01). Heightened levels of injury after myocardial ischemia and negligible preconditioning benefits in cd39-/- mice were corrected by infusion of the metabolic product (AMP) or apyrase. Moreover, apyrase treatment of wild-type mice resulted in 43+/-4.2% infarct size reduction (P<0.01).

CONCLUSIONS

Taken together, these studies reveal E-NTPDase 1 in cardioprotection and suggest apyrase in the treatment of myocardial ischemia.

An ecto-ATPase and an ecto-ATP diphosphohydrolase are expressed in rat brain

Extracellular nucleotides acting as signaling molecules are inactivated by hydrolysis catalyzed by ecto-nucleotidases. ATP is sequentially degraded via ADP and AMP to adenosine. Enzymes that can be involved in the extracellular hydrolysis chain are ecto-ATP diphosphohydrolase (ecto-apyrase), ecto-ATPase, ecto-ADPase and 5'-nucleotidase. Mammalian ecto-ATP diphosphohydrolase is a member of a family of apyrases sharing four "apyrase conserved regions" that presumably participate in the formation of the catalytic site. We report the presence of ecto-ATP diphosphohydrolase in rat brain and the primary structure of a new mammalian member of the apyrase family. Expression in CHO cells shows that it represents an ecto-ATPase. As revealed by Northern analysis of rat tissues, the ecto-ATPase is co-expressed with ecto-ATP diphosphohydrolase in heart, kidney, spleen, thymus, lung, skeletal muscle and brain. Signals for both ecto-nucleotidases are very weak in liver. mRNAs for both proteins are present in PC12 cells, suggesting that the two nucleotidases may be co-expressed in the same neural cell. Using computer-aided sequence analysis, primary structure and membrane topography are compared with those of other members of the apyrase family.

Differential catalytic properties and vascular topography of murine nucleoside triphosphate diphosphohydrolase 1 (NTPDase1) and NTPDase2 have implications for thromboregulation

Nucleoside triphosphate diphosphohydrolases (NTPDases) are a recently described family of ectonucleotidases that differentially hydrolyze the gamma and beta phosphate residues of extracellular nucleotides. Expression of this enzymatic activity has the potential to influence nucleotide P2 receptor signaling within the vasculature. We and others have documented that NTPDase1 (CD39, 78 kd) hydrolyzes both triphosphonucleosides and diphosphonucleosides and thereby terminates platelet aggregation responses to adenosine diphosphate (ADP). In contrast, we now show that NTPDase2 (CD39L1, 75 kd), a preferential nucleoside triphosphatase, activates platelet aggregation by converting adenosine triphosphate (ATP) to ADP, the specific agonist of P2Y(1) and P2Y(12) receptors. We developed specific antibodies to murine NTPDase1 and NTPDase2 and observed that both enzymes are present in the cardiac vasculature; NTPDase1 is expressed by endothelium, endocardium, and to a lesser extent by vascular smooth muscle, while NTPDase2 is associated with the adventitia of muscularized vessels, microvascular pericytes, and other cell populations in the subendocardial space. Moreover, NTPDase2 represents a novel marker for microvascular pericytes. Differential expression of NTPDases in the vasculature suggests spatial regulation of nucleotide-mediated signaling. In this context, NTPDase1 should abrogate platelet aggregation and recruitment in intact vessels by the conversion of ADP to adenosine monophosphate, while NTPDase2 expression would promote platelet microthrombus formation at sites of extravasation following vessel injury. Our data suggest that specific NTPDases, in tandem with ecto-5'-nucleotidase, not only terminate P2 receptor activation and trigger adenosine receptors but may also allow preferential activation of specific subsets of P2 receptors sensitive to ADP (e.g., P2Y(1), P2Y(3), P2Y(12)) and uridine diphosphate (P2Y(6)).

The salivary gland-specific apyrase of the mosquito Aedes aegypti is a member of the 5'-nucleotidase family

The saliva of hematophagous insects contains a variety of pharmacologically active substances that counteract the normal hemostatic response to injury in vertebrate hosts. The yellow-fever mosquito, Aedes aegypti, secretes an apyrase that inhibits ADP-dependent platelet aggregation. Apyrase was purified as an active enzyme from adult female salivary glands and subjected to tryptic digestion, and the resulting peptides were sequenced. The amino acid sequences obtained match the conceptual translation product of a cDNA clone isolated from an adult female salivary gland library. Sequence comparisons indicate similarities with a ubiquitous family of 5'-nucleotidases. The mosquito protein differs from other members of the family by lacking a carboxyl-terminal hydrophobic domain. The apparent conversion of a gene encoding an enzyme involved in a common metabolic event at the cellular level to a gene involved in the antihemostatic response of mosquitoes illustrates one way this particular insect has adapted to the challenges of bloodfeeding.

Ectonucleotidases of CD39 family modulate vascular inflammation and thrombosis in transplantation

Transplantation results in exposure of the graft vasculature to warm and cold ischemia, followed by perfusion by circulating blood constituents and obligatory oxidant stress. Further graft injury occurs as consequences of acute humoral cellular rejection or chronic transplant vasculopathy, or both. Extracellular nucleotide stimulation of purinergic type 2 (P2) receptors are key components of platelet, endothelial cell (EC), and leukocyte activation resulting in vascular thrombosis and inflammation in vivo. CD39, the prototype nucleoside triphosphate diphosphohydrolase (NTPDase-1) is highly expressed on endothelium; in contrast, CD39L1/NTPDase-2 (a preferential adenosine triphosphatase [ATPase]) is found on vascular adventitial cells. Both ectoenzymes influence thrombogenesis by the regulated hydrolysis of extracellular nucleotides that differentially regulate P2-receptor activity and function in platelets and vascular cells. The intracytoplasmic domains of NTPDase-1 may also independently influence cellular activation and proliferation. NTPDase activity is substantively lost in the vasculature of injured or rejected grafts. A role for NTPDase-1 in thromboregulation has been validated by generation of mutant mice either null for cd39 or overexpressing human CD39. Administration of soluble NTPDase or induction of CD39 by adenoviral vectors, or both, are also of benefit in several models of transplantation. Administration of soluble CD39 or targeted expression may have future therapeutic application in transplantation-associated and other vascular diseases.

An intestinal commensal symbiosis factor controls neuroinflammation via TLR2-mediated CD39 signalling

The mammalian immune system constitutively senses vast quantities of commensal bacteria and their products through pattern recognition receptors, yet excessive immune reactivity is prevented under homeostasis. The intestinal microbiome can influence host susceptibility to extra-intestinal autoimmune disorders. Here we report that polysaccharide A (PSA), a symbiosis factor for the human intestinal commensal Bacteroides fragilis, protects against central nervous system demyelination and inflammation during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, through Toll-like receptor 2 (TLR2). TLR2 mediates tissue-specific expansion of a critical regulatory CD39(+) CD4 T-cell subset by PSA. Ablation of CD39 signalling abrogates PSA control of EAE manifestations and inflammatory cytokine responses. Further, CD39 confers immune-regulatory phenotypes to total CD4 T cells and Foxp3(+) CD4 Tregs. Importantly, CD39-deficient CD4 T cells show an enhanced capability to drive EAE progression. Our results demonstrate the therapeutic potential and underlying mechanism by which an intestinal symbiont product modulates CNS-targeted demyelination.

Cloning, sequencing, and expression of a human brain ecto-apyrase related to both the ecto-ATPases and CD39 ecto-apyrases1

An extracellular ATPase (E-type ATPase) clone was isolated from a human brain cDNA library and sequenced. The transcript shows similarity to the previously published chicken smooth muscle and rat brain ecto-ATPase cDNAs, human CD39L1 cDNA (putative human ecto-ATPase), and mammalian CD39 (lymphoid cell activation antigen, ecto-apyrase, ATPDase, ATP-diphosphohydrolase) cDNAs. The full-length human brain cDNA encodes a 529 amino acid glycoprotein with a putative membrane spanning region near each terminus, with the majority of the protein found extracellularly. Expression of this clone in mammalian COS-1 cells yielded NaN3-sensitive ATPase and ADPase activity detectable both on intact cells and cell membrane preparations. The nucleotide hydrolysis ratio of the expressed protein is approx. 2.75:1 (ATPase:ADPase activity), classifying it as an ecto-apyrase. However, this hydrolysis ratio is intermediate between that observed for the ecto-ATPases and the CD39 ecto-apyrases (L. Plesner, Int. Rev. Cytol. 158 (1995) 141-214). Quantitative analyses of amino acid identities and similarities between this ecto-apyrase and other vertebrate E-type ATPases suggest that this human brain enzyme is nearly equally related to the ecto-ATPases and the CD39s, and phylogenetic analysis suggests that it could be an ancestral enzyme from which both ecto-ATPases and CD39 ecto-apyrases are derived.

Isolation and proteomic characterization of the Arabidopsis Golgi defines functional and novel components involved in plant cell wall biosynthesis

The plant Golgi plays a pivotal role in the biosynthesis of cell wall matrix polysaccharides, protein glycosylation, and vesicle trafficking. Golgi-localized proteins have become prospective targets for reengineering cell wall biosynthetic pathways for the efficient production of biofuels from plant cell walls. However, proteomic characterization of the Golgi has so far been limited, owing to the technical challenges inherent in Golgi purification. In this study, a combination of density centrifugation and surface charge separation techniques have allowed the reproducible isolation of Golgi membranes from Arabidopsis (Arabidopsis thaliana) at sufficiently high purity levels for in-depth proteomic analysis. Quantitative proteomic analysis, immunoblotting, enzyme activity assays, and electron microscopy all confirm high purity levels. A composition analysis indicated that approximately 19% of proteins were likely derived from contaminating compartments and ribosomes. The localization of 13 newly assigned proteins to the Golgi using transient fluorescent markers further validated the proteome. A collection of 371 proteins consistently identified in all replicates has been proposed to represent the Golgi proteome, marking an appreciable advancement in numbers of Golgi-localized proteins. A significant proportion of proteins likely involved in matrix polysaccharide biosynthesis were identified. The potential within this proteome for advances in understanding Golgi processes has been demonstrated by the identification and functional characterization of the first plant Golgi-resident nucleoside diphosphatase, using a yeast complementation assay. Overall, these data show key proteins involved in primary cell wall synthesis and include a mixture of well-characterized and unknown proteins whose biological roles and importance as targets for future research can now be realized.

Inhibition of platelet function by recombinant soluble ecto-ADPase/CD39

Excessive platelet accumulation and recruitment, leading to vessel occlusion at sites of vascular injury, present major therapeutic challenges in cardiovascular medicine. Endothelial cell CD39, an ecto-enzyme with ADPase and ATPase activities, rapidly metabolizes ATP and ADP released from activated platelets, thereby abolishing recruitment. Therefore, a soluble form of CD39, retaining nucleotidase activities, would constitute a novel antithrombotic agent. We designed a recombinant, soluble form of human CD39, and isolated it from conditioned media from transiently transfected COS-1 cells and from stably transfected Chinese hamster ovary (CHO) cells. Conditioned medium from CHO cells grown under serum-free conditions was subjected to anti-CD39 immunoaffinity column chromatography, yielding a single approximately 66-kD protein with ATPase and ADPase activities. Purified soluble CD39 blocked ADP-induced platelet aggregation in vitro, and inhibited collagen-induced platelet reactivity. Kinetic analyses indicated that, while soluble CD39 had a Km for ADP of 5.9 microM and for ATP of 2.1 microM, the specificity constant kcat/Km was the same for both substrates. Intravenously administered soluble CD39 remained active in mice for an extended period of time, with an elimination phase half-life of almost 2 d. The data indicate that soluble CD39 is a potential therapeutic agent for inhibition of platelet-mediated thrombotic diatheses.

Extracellular ATP and adenosine: The Yin and Yang in immune responses?

Extracellular adenosine 5'-triphosphate (ATP) and adenosine molecules are intimately involved in immune responses. ATP is mostly a pro-inflammatory molecule and is released during hypoxic condition and by necrotic cells, as well as by activated immune cells and endothelial cells. However, under certain conditions, for instance at low concentrations or at prolonged exposure, ATP may also have anti-inflammatory properties. Extracellular ATP can activate both P2X and P2Y purinergic receptors. Extracellular ATP can be hydrolyzed into adenosine in a two-step enzymatic process involving the ectonucleotidases CD39 (ecto-apyrase) and CD73. These enzymes are expressed by many cell types, including endothelial cells and immune cells. The counterpart of ATP is adenosine, which is produced by breakdown of intra- or extracellular ATP. Adenosine has mainly anti-inflammatory effects by binding to the adenosine, or P1, receptors (A1, A2A, A2B, and A3). These receptors are also expressed in many cells, including immune cells. The final effect of ATP and adenosine in immune responses depends on the fine regulatory balance between the 2 molecules. In the present review, we will discuss the current knowledge on the role of these 2 molecules in the immune responses.

Functional characterization of rat ecto-ATPase and ecto-ATP diphosphohydrolase after heterologous expression in CHO cells

The recently cloned ecto-ATPase and ecto-apyrase (ecto-ATP diphosphohydrolase) are plasma-membrane-bound enzymes responsible for the extracellular degradation of nucleoside 5'-triphosphates and nucleoside 5'-diphosphates. We expressed the rat-derived enzymes in CHO cells to compare their molecular and functional properties. Sequence-specific polyclonal antibodies differentiate between the two proteins and reveal identical molecular masses of 70-80 kDa. Both enzymes are stimulated by either Ca2+ or Mg2+ and reveal a broad substrate specificity towards purine and pyrimidine nucleotides. Whereas ecto-apyrase hydrolyzes nucleoside 5'-diphosphates at a rate approximately 20-30% lower than nucleoside-5'-triphosphates, ecto-ATPase hydrolyzes nucleoside-5'-diphosphates only to a marginal extent. The sensitivity of the two enzymes to the inhibitors of P2 receptors suramin, PPADS and reactive blue differs. Hydrolysis of ATP by ecto-ATPase leads to the accumulation in the medium of extracellular ADP as an intermediate product, whereas ecto-apyrase dephosphorylates ATP directly to AMP. Our results suggest that previous data describing extracellular hydrolysis of ATP by a variety of intact cellular systems with unidentified ecto-nucleotidases may be explained by the coexpression of ecto-ATPase and ecto-apyrase.

A role for ectophosphatase in xenobiotic resistance

Xenobiotic resistance in animals, plants, yeast, and bacteria is known to involve ATP binding cassette transporters that efflux invading toxins. We present data from yeast and a higher plant indicating that xenobiotic resistance also involves extracellular ATP degradation. Transgenic upregulation of ecto-ATPase alone confers resistance to organisms that have had no previous exposure to toxins. Similarly, cells that are deficient in extracellular ATPase activity are more sensitive to xenobiotics. On the basis of these and other supporting data, we hypothesize that the hydrolysis of extracellular ATP by phosphatases and ATPases may be necessary for the resistance conferred by P-glycoprotein.

Trapping cDNAs encoding secreted proteins from the salivary glands of the malaria vector Anopheles gambiae

The signal sequence trap method was used to isolate cDNAs corresponding to proteins containing secretory leader peptides and whose genes are expressed specifically in the salivary glands of the malaria vector Anopheles gambiae. Fifteen unique cDNA fragments, ranging in size from 150 to 550 bp, were isolated and sequenced in a first round of immunoscreening in COS-7 cells. All but one of the cDNAs contained putative signal sequences at their 5' ends, suggesting that they were likely to encode secreted or transmembrane proteins. Expression analysis by reverse transcription-PCR showed that at least six cDNA fragments were expressed specifically in the salivary glands. Fragments showing a high degree of similarity to D7 and apyrase, two salivary gland-specific genes previously found in Aedes aegypti, were identified. Of interest, three different D7-related cDNAs that are likely to represent a new gene family were found in An. gambiae. Moreover, three salivary gland-specific cDNA fragments that do not show similarity to known proteins in the databases were identified, and the corresponding full length cDNAs were cloned and sequenced. RNA in situ hybridization to whole female salivary glands showed patterns of expression that overlap only in part those observed in the culicine mosquito A. aegypti.

Upregulation of CD39/NTPDases and P2 receptors in human pancreatic disease

Chronic inflammation, fibrosis, atrophy, malignant transformation, and thromboembolic events are hallmarks of chronic pancreatic disease. Extracellular nucleotides have been implicated as inflammatory mediators in many pathological situations. However, there are minimal data detailing expression of ectonucleotidases and type-2 purinergic receptors (P2R) in chronic pancreatitis and pancreatic cancer. We have therefore defined tissue distribution and localization of the CD39 family of ectonucleotidases and associated P2R in human disease. Transcripts of ectonucleotidases (CD39 and CD39L1) together with P2R (P2X7, P2Y2, and P2Y6) are significantly increased in both chronic pancreatitis and pancreatic cancer. CD39 and CD39L1 are preferentially associated with the vasculature and stromal elements in pathological tissues. P2X7 mRNA upregulation was associated with chronic pancreatitis, and heightened protein expression was found to be localized to infiltrating cells. P2Y2 was markedly upregulated in biopsies of pancreatic cancer tissues and expressed by fibroblasts adjacent to tumors. High-tissue mRNA levels of CD39 significantly correlated with better long-term survival after tumor resection in patients with pancreatic cancer. Heightened expression patterns and localization patterns of CD39, P2X7, and P2Y2 infer associations with chronic inflammation and neoplasia of the pancreas. Our data suggest distinct roles for CD39 and P2-purinergic signaling in both tissue remodeling and fibrogenesis with respect to human pancreatic diseases.

Cloning and characterization of mouse nucleoside triphosphate diphosphohydrolase-8

A novel mammalian plasma membrane bound nucleoside triphosphate diphosphohydrolase (NTPDase), named NTPDase8, has been cloned and characterized. Analysis of cDNA reveals an open reading frame of 1491 base pairs encoding a protein of 497 amino acid residues with an estimated molecular mass of 54650 Da and a predicted isoelectric point of 5.94. In a mouse, the genomic sequence is located on chromosome 2A3 and is comprised of 10 exons. The deduced amino acid sequence reveals eight putative N-glycosylation sites, two transmembrane domains, five apyrase-conserved regions, and 20-50% amino acid identity with other mammalian NTPDases. mRNA expression was detected in liver, jejunum, and kidney. Both intact cells and crude cell lysates from COS-7 cells expressing NTPDase8 hydrolyzed P2 receptor agonists, namely, ATP, ADP, UTP, and UDP, but did not hydrolyze AMP. There was an absolute requirement for divalent cations for the catalytic activity (Ca(2+) > Mg(2+)) with an optimal pH between 5.5 and 8.0 for ATP and 6.4 for ADP hydrolysis. Kinetic parameters derived from analysis of crude cell lysates showed that the enzyme had lower apparent K(m) values for adenine nucleotides and for triphosphonucleosides (K(m,app) of 13 microM for ATP, 41 microM for ADP, 47 microM for UTP, and 171 microM for UDP). Hydrolysis of triphosphonucleosides resulted in a transient accumulation of the corresponding diphosphonucleoside, as expected from the apparent K(m) values. Enzymatic properties of NTPDase8 differ from those of other NTPDases suggesting an alternative way to modulate nucleotide levels and consequently P2 receptor activation.

CD73 is expressed by human regulatory T helper cells and suppresses proinflammatory cytokine production and Helicobacter felis-induced gastritis in mice

BACKGROUND

Regulatory T cells (known as "Treg") express apyrases (CD39) and ecto-5'-nucleotidase (CD73) and contribute to their inhibitory function by generating adenosine. We investigated the expression of CD39 and CD73 on human T helper (Th) cells and the role of CD73 in regulating Helicobacter felis-induced gastritis and colonization.

METHODS

Human CD4+ Th cells, gastric T cells, or Treg subsets were stimulated and assayed for the expression of CD39 and CD73 by means of reverse-transcriptase polymerase chain reaction and flow cytometry. The effect of CD73 on proliferation and cytokine production was assessed, and the presence of gastritis, proinflammatory cytokine expression, or colonization of H. felis was evaluated in CD73-deficient (CD73-/-) mice or recipient mice given control or CD73-/- Treg.

RESULTS

CD4+ T cells expressed CD39 and CD73, particularly in CD25+Foxp3+ Treg from peripheral blood or gastric mucosa. Activation significantly increased CD73 expression on all Th cells. Inhibition of CD73 enhanced production of interferon-gamma. Gastritis in H. felis-infected CD73-/- mice was significantly worse than that in wild-type mice and was accompanied by increased levels of proinflammatory cytokines and reduced bacterial colonization, whereas Treg from CD73-/- mice did not inhibit gastritis.

CONCLUSION

CD39 and CD73 expressed by Th cells contribute to local accumulation of adenosine and attenuation of gastritis, which may favor persistent infection.

Purification, cloning, and expression of an apyrase from the bed bug Cimex lectularius. A new type of nucleotide-binding enzyme

An enzyme that hydrolyzes the phosphodiester bonds of nucleoside tri- and diphosphates, but not monophosphates, thus displaying apyrase (EC 3.6.1.5) activity, was purified from salivary glands of the bed bug, Cimex lectularius. The purified C. lectularius apyrase was an acidic protein with a pI of 5.1 and molecular mass of approximately 40 kDa that inhibited ADP-induced platelet aggregation and hydrolyzed platelet agonist ADP with specific activity of 379 units/mg protein. Amplification of C. lectularius cDNA corresponding to the N-terminal sequence of purified apyrase produced a probe that allowed identification of a 1.3 kilobase pair cDNA clone coding for a protein of 364 amino acid residues, the first 35 of which constituted the signal peptide. The processed form of the protein was predicted to have a molecular mass of 37.5 kDa and pI of 4.95. The identity of the product of the cDNA clone with native C. lectularius apyrase was proved by immunological testing and by expressing the gene in a heterologous host. Immune serum made against a synthetic peptide with sequence corresponding to the C-terminal region of the predicted cDNA clone recognized both C. lectularius apyrase fractions eluted from a molecular sieving high pressure liquid chromatography and the apyrase active band from chromatofocusing gels. Furthermore, transfected COS-7 cells secreted a Ca2+-dependent apyrase with a pI of 5.1 and immunoreactive material detected by the anti-apyrase serum. C. lectularius apyrase has no significant sequence similarity to any other known apyrases, but homologous sequences have been found in the genome of the nematode C. elegans and in mouse and human expressed sequence tags from fetal and tumor EST libraries.

Metabolic control of excessive extracellular nucleotide accumulation by CD39/ecto-nucleotidase-1: implications for ischemic vascular diseases

Platelets are responsible for maintaining vascular integrity. In thrombocytopenic states, vascular permeability and fragility increase, presumably due to the absence of this platelet function. Chemical or physical injury to a blood vessel induces platelet activation and platelet recruitment. This is beneficial for the arrest of bleeding (hemostasis), but when an atherosclerotic plaque is ulcerated or fissured, it becomes an agonist for vascular occlusion (thrombosis). Experiments in the late 1980s cumulatively indicated that endothelial cell CD39-an ecto-ADPase-reduced platelet reactivity to most agonists, even in the absence of prostacyclin or nitric oxide. As discussed herein, CD39 rapidly and preferentially metabolizes ATP and ADP released from activated platelets to AMP, thereby drastically reducing or even abolishing platelet aggregation and recruitment. Since ADP is the final common agonist for platelet recruitment and thrombus formation, this finding highlights the significance of CD39. A recombinant, soluble form of human CD39, solCD39, has enzymatic and biological properties identical to the full-length form of the molecule and strongly inhibits human platelet aggregation induced by ADP, collagen, arachidonate, or TRAP (thrombin receptor agonist peptide). In sympathetic nerve endings isolated from guinea pig hearts, where neuronal ATP enhances norepinephrine exocytosis, solCD39 markedly attenuated norepinephrine release. This suggests that NTPDase (nucleoside triphosphate diphosphohydrolase) could exert a cardioprotective action by reducing ATP-mediated norepinephrine release, thereby offering a novel therapeutic approach to myocardial ischemia and its consequences. In a murine model of stroke, driven by excessive platelet recruitment, solCD39 reduced the sequelae of stroke, without an increase in intracerebral hemorrhage. CD39 null mice, generated by deletion of apyrase-conserved regions 2 to 4, exhibited a decrease in postischemic perfusion and an increase in cerebral infarct volume when compared with controls. "Reconstitution" of CD39 null mice with solCD39 reversed these changes. We hypothesize that solCD39 has potential as a novel therapeutic agent for thrombotic diatheses.

The salivary apyrase of the blood-sucking sand fly Phlebotomus papatasi belongs to the novel Cimex family of apyrases

Apyrases are enzymes that hydrolyze nucleotide di- and triphosphates to orthophosphate and mononucleotides. At least two families of enzymes, belonging to the 5′-nucleotidase and to the actin/heat shock 70/sugar kinase superfamily, have evolved independently to serve the apyrase reaction. Both families require either Ca(2+) or Mg(2+) for their action. A novel apyrase enzyme sequence, with no homology to any other known protein sequence, was found recently in the salivary glands of the hematophagous bed bug Cimex lectularius. This enzyme functions exclusively with Ca(2+). Here, we report the finding of a cDNA similar to that of the C. lectularius salivary apyrase isolated from a salivary gland cDNA library of Phlebotomus papatasi. Transfection of insect cells with the P. papatasi salivary gland apyrase cDNA resulted in the secretion of a Ca(2+)-dependent apyrase whose activity was indistinguishable from that in salivary homogenates of P. papatasi. Homologous sequences were found in humans, in another sand fly (Lutzomyia longipalpis), in the fruit fly Drosophila melanogaster, in the nematode Caenorhabditis elegans and in the protozoan Cryptosporidium parvum, indicating that this family of enzymes is widespread among animal species.