Adenosine receptor mediates motility in human melanoma cells

Targeting the adenosine signaling pathway in macrophages for cancer immunotherapy

One of the ways in which macrophages support tumorigenic growth is by producing adenosine, which acts to dampen antitumor immune responses and is generated by both tumor and immune cells in the tumor microenvironment (TME). Two cell surface expressed molecules, CD73 and CD39, boost catalytic adenosine triphosphate, leading to further increased adenosine synthesis, under hypoxic circumstances in the TME. There are four receptors (A1, A2A, A2B, and A3) expressed on macrophages that allow adenosine to perform its immunomodulatory effect. Researchers have shown that adenosine signaling is a key factor in tumor progression and an attractive therapeutic target for treating cancer. Several antagonistic adenosine-targeting biological therapies that decrease the suppressive action of tumor-associated macrophages have been produced and explored to transform this result from basic research into a therapeutic advantage. Here, we'll review the newest findings from studies of pharmacological compounds that target adenosine receptors, and their potential therapeutic value based on blocking the suppressive action of macrophages in tumors.

Istradefylline modulates purinergic enzymes and reduces malignancy-associated factors in B16F10 melanoma cells

ATP and adenosine exert pivotal roles in the development, maintenance, and metastatic spreading of melanoma. The action of such key melanoma tumor microenvironment (TME) constituents might be complementary or opposed, and their effects are not exclusive to immune cells but also to other host cells and tumor cells. The effects of ATP are controlled by the axis CD39/73, resulting in adenosine, the main actor in the TME, and A2A is the crucial mediator of its effects. We evaluated ATP and adenosine signaling through A2A on B16F10 melanoma cells using istradefylline (IST) (antiparkinsonian A2A antagonist) and caffeine (CAF) treatments after exposure to ATP and adenosine. Adenosine increased melanoma cell viability and proliferation in a concentration-dependent manner. ATP increases viability only as a substrate by CD39 to produce adenosine. Both IST and CAF are toxic to B16F10 cells, but only IST potentialized paclitaxel-induced cytotoxic effects, even decreasing its IC50 value. IST positively modulated CD39 and CD73 expression. CD39 activity was increased, and E-ADA was reduced, indicating that the melanoma cells promoted compensatory feedback in the production and maintenance of adenosine levels. A2A antagonism by IST reduced the factors associated with malignancy, like migration, adhesion, colony formation, and the capacity to produce melanin. Moreover, IST significantly increases nitric oxide (NO) production, which correlates to a decline in melanoma cell viability by apoptotic events. Altogether, our results suggest that adenosine signaling through A2A is essential for B16F10 cells, and its inhibition by IST causes compensatory purinergic enzymatic modulations. Furthermore, IST is a promising therapy that provides new ways to improve current melanoma treatments.

The therapeutic potential of targeting CD73 and CD73-derived adenosine in melanoma

The hypoxic environment of melanoma results in CD73 upregulation on the surface of various tumor microenvironment (TME) cells including tumor cells, stromal cells and infiltrated immune cells. Consequently, CD73 through both enzymatic and none enzymatic functions affect melanoma progression. Overaccumulation of CD73-derived adenosine through interaction with its four G coupled receptors (A₁AR, A_2AAR, A_2BAR, and A₃AR) mediate tumor growth, immune suppression, angiogenesis, and metastasis. This paper aims to comprehensively review the therapeutic potential of CD73 ectonucleotidase targeting in melanoma. To reach this goal, firstly, we summarize the structure, function, regulation, and clinical outcome of CD73 ectonucleotidase. Then, we depict the metabolism and signaling of CD73-derived adenosine along with its progressive role in development of melanoma. Furthermore, the therapeutic potentials of CD73 -adenosine axis targeting is assessed in both preclinical and clinical studies. Targeting CD73-derived adenosine via small molecule inhibitor or monoclonal antibodies studies especially in combination with immune checkpoint blockers including PD-1 and CTLA-4 have shown desirable results for management of melanoma in preclinical studies and several clinical trials have recently been started to evaluate the therapeutic potential of CD73-derived adenosine targeting in solid tumors. Indeed, targeting of CD73-derived adenosine signaling could be considered as a new therapeutic target in melanoma.

Medicinal Chemistry and Therapeutic Potential of Agonists, Antagonists and Allosteric Modulators of A1 Adenosine Receptor: Current Status and Perspectives

Adenosine is a purine nucleoside, responsible for the regulation of a wide range of physiological and pathophysiological conditions by binding with four G-protein-coupled receptors (GPCRs), namely A1, A2A, A2B and A3 adenosine receptors (ARs). In particular, A1 AR is ubiquitously present, mediating a variety of physiological processes throughout the body, thus represents a promising drug target for the management of various pathological conditions. Agonists of A1 AR are found to be useful for the treatment of atrial arrhythmia, angina, type-2 diabetes, glaucoma, neuropathic pain, epilepsy, depression and Huntington's disease, whereas antagonists are being investigated for the treatment of diuresis, congestive heart failure, asthma, COPD, anxiety and dementia. However, treatment with full A1 AR agonists has been associated with numerous challenges like cardiovascular side effects, off-target activation as well as desensitization of A1 AR leading to tachyphylaxis. In this regard, partial agonists of A1 AR have been found to be beneficial in enhancing insulin sensitivity and subsequently reducing blood glucose level, while avoiding severe CVS side effects and tachyphylaxis. Allosteric enhancer of A1 AR is found to be potent for the treatment of neuropathic pain, culminating the side effects related to off-target tissue activation of A1 AR. This review provides an overview of the medicinal chemistry and therapeutic potential of various agonists/partial agonists, antagonists and allosteric modulators of A1 AR, with a particular emphasis on their current status and future perspectives in clinical settings.

Differential effect of adenosine on rhabdomyosarcoma migration and proliferation

INTRODUCTION

Adenosine and its receptors are involved deeply in the regulation of tumour biology. Purine nucleotides are released from stressed cells in states of hypoxia or radiochemotherapy-induced cell damage. Adenosine exerts its effect through the P1 family of selective receptors. The purpose of the study was to evaluate the exact role of extracellular role on biology of Rhabdomyosarcoma (RMS) cells.

MATERIAL AND METHODS

Series of in vitro studies accompanied by immunohistochemical, RQ-PCR and shRNA methods have characterised adenosine receptor expression on Rhabdomyosarcoma cell lines, normal skeletal muscle and effect of adenosine on Rhabdomyosarcoma growth and migration.

RESULTS

Extracellular adenosine (highest at 50 μM, p < 0.05) and AMP (highest at 300 μM, p < 0.05) markedly enhanced chemotaxis in the Boyden chamber assay The reaction is mostly governed by the A1 receptor, which is greatly overexpressed in Rhabdomyosarcoma as compared with normal skeletal muscle. Cell migration induced by adenosine and AMP is blocked by pertussis toxin, phospholipase C and MAP kinase inhibitor, which demonstrates the importance of these signalling pathways. High doses of adenosine have a detrimental effect on cellular proliferation, in a receptor-independent manner (≥ 500 μM; p < 0.05). The blockage of adenosine transporter by dipyridamole abolishes this effect, indicating involvement of an intrinsic pathway. Further increase of adenosine concentration, induced by deaminase inhibitors, augment the effect.

CONCLUSIONS

Our results suggest that adenosine and AMP trigger cell migration by binding to P1 receptors and directing cancer cells to the sites of hypoxia or cellular damage. Specifically by A1 receptor which is overexpressed in RMS.

CD73: an emerging checkpoint for cancer immunotherapy

CD73 is a novel immune checkpoint associated with adenosine metabolism that promotes tumor progression by suppressing antitumor immune response and promoting angiogenesis. The inhibition of CD73, in combination with immune checkpoint blockade, targeted therapy or conventional therapy, improves antitumor effects in numerous preclinical mouse models of cancer. Emerging evidence suggests that the combination of anti-CD73 and immune checkpoint blockade has promising clinical activity in patients with advanced solid tumors. In this review, we will discuss the specific role of CD73 on both tumor cells and nontumor cells in regulating tumor immunity and tumorigenesis and provide an update on the current view of the antitumor activity of targeting CD73 by mAb or small molecule selective inhibitors in preclinical and clinical settings.

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

The potential role of adenosine signaling in the pathogenesis of melanoma

Melanoma cancer cell proliferation, motility, invasion, and tumor growth is affected by the adenosine pathway that consists of adenosine-synthesizing enzymes, receptors, and their respective agonists/antagonists. Accumulating evidence suggests that ischemia and inflammation, two conditions associated with melanoma, display dysregulated adenosine metabolism, which implicates it as the mechanism responsible for the pathogenesis of melanoma, thereby resulting in advanced diagnosis and therapy. Suppression of adenosine signaling by inhibiting adenosine receptors or adenosine-generating enzymes (CD39 and CD73) on melanoma cells presents a novel therapeutic target for patients with melanoma. This review summarizes the role of adenosine signaling in the pathogenesis of melanoma to advance its understanding and hence improve therapeutics and management.

Multifaceted Effects of Extracellular Adenosine Triphosphate and Adenosine in the Tumor-Host Interaction and Therapeutic Perspectives

Cancer is still one of the world's most pressing health-care challenges, leading to a high number of deaths worldwide. Immunotherapy is a new developing therapy that boosts patient's immune system to fight cancer by modifying tumor-immune cells interaction in the tumor microenvironment (TME). Extracellular adenosine triphosphate (eATP) and adenosine (Ado) are signaling molecules released in the TME that act as modulators of both immune and tumor cell responses. Extracellular adenosine triphosphate and Ado activate purinergic type 2 (P2) and type 1 (P1) receptors, respectively, triggering the so-called purinergic signaling. The concentration of eATP and Ado within the TME is tightly controlled by several cell-surface ectonucleotidases, such as CD39 and CD73, the major ecto-enzymes expressed in cancer cells, immune cells, stromal cells, and vasculature, being CD73 also expressed on tumor-associated fibroblasts. Once accumulated in the TME, eATP boosts antitumor immune response, while Ado attenuates or suppresses immunity against the tumor. In addition, both molecules can mediate growth stimulation or inhibition of the tumor, depending on the specific receptor activated. Therefore, purinergic signaling is able to modulate both tumor and immune cells behavior and, consequently, the tumor-host interaction and disease progression. In this review, we discuss the role of purinergic signaling in the host-tumor interaction detailing the multifaceted effects of eATP and Ado in the inflammatory TME. Moreover, we present recent findings into the application of purinergic-targeting therapy as a potential novel option to boost antitumor immune responses in cancer.

Role of adenosine signaling in the pathogenesis of breast cancer

The plasma level of adenosine increases under ischemic and inflamed conditions in tumor microenvironment. Adenosine elicits a range of signaling pathways in tumors, resulting in either inhibition or enhancement of tumor growth depending upon different subtypes of adenosine receptors activation and type of cancer. Metabolism of adenosine-5'-triphosphate (ATP) and its derivatives including adenosine is dysregulated in the breast tumor microenvironment, supporting the role of this metabolite in the pathogenesis of breast cancer. Adenosine regulates inflammation, apoptosis, cell proliferation, and metastasis in breast cancer cells. This review summarizes the role of adenosine in the pathogenesis of breast cancer for a better understanding and hence a better management of this disease.

Differential impact of adenosine nucleotides released by osteocytes on breast cancer growth and bone metastasis

Extracellular ATP has been shown to either inhibit or promote cancer growth and migration; however, the mechanism underlying this discrepancy remained elusive. Here we demonstrate the divergent roles of ATP and adenosine released by bone osteocytes on breast cancers. We showed that conditioned media (CM) collected from osteocytes treated with alendronate (AD), a bisphosphonate drug, inhibited the migration of human breast cancer MDA-MB-231 cells. Removal of the extracellular ATP by apyrase in CM abolished this effect, suggesting the involvement of ATP. ATP exerted its inhibitory effect through the activation of purinergic P2X receptor signaling in breast cancer cells evidenced by the attenuation of the inhibition by an antagonist, oxidized ATP, as well as knocking down P2X7 with small interfering RNA (siRNA), and the inhibition of migration by an agonist, BzATP. Intriguingly, ATP had a biphasic effect on breast cancer cells-lower dosage inhibited but higher dosage promoted its migration. The stimulatory effect on migration was blocked by an adenosine receptor antagonist, MRS1754, ARL67156, an ecto-ATPase inhibitor, and A2A receptor siRNA, suggesting that in contrast to ATP, adenosine, a metabolic product of ATP, promoted migration of breast cancer cells. Consistently, non-hydrolyzable ATP, ATPγS, only inhibited but did not promote cancer cell migration. ATP also had a similar inhibitory effect on the Py8119 mouse mammary carcinoma cells; however, adenosine had no effect owing to the absence of the A2A receptor. Consistently, ATPγS inhibited, whereas adenosine promoted anchorage-independent growth of MDA-MB-231 cells. Our in vivo xenograft study showed a significant delay of tumor growth with the treatment of ATPγS. Moreover, the extent of bone metastasis in a mouse intratibial model was significantly reduced with the treatment of ATPγS. Together, our results suggest the distinct roles of ATP and adenosine released by osteocytes and the activation of corresponding receptors P2X7 and A2A signaling on breast cancer cell growth, migration and bone metastasis.

Purinergic signalling and cancer

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

CD73-generated adenosine: orchestrating the tumor-stroma interplay to promote cancer growth

Despite the coming of age of cancer immunotherapy, clinical benefits are still modest. An important barrier to successful cancer immunotherapy is that tumors employ a number of mechanisms to facilitate immune escape, including the production of anti-inflammatory cytokines, the recruitment of regulatory immune subsets, and the production of immunosuppressive metabolites. Significant therapeutic opportunity exists in targeting these immunosuppressive pathways. One such immunosuppressive pathway is the production of extracellular adenosine by CD73, an ectonucleotidase overexpressed in various types of cancer. We hereafter review the biology of CD73 and its role in cancer progression and metastasis. We describe the role of extracellular adenosine in promoting tumor growth through paracrine and autocrine action on tumor cells, endothelial cells, and immune cells.

CF102 an A3 adenosine receptor agonist mediates anti-tumor and anti-inflammatory effects in the liver

The Gi protein-associated A(3) adenosine receptor (A(3) AR) is a member of the adenosine receptor family. Selective agonists at the A(3) AR, such as CF101 and CF102 were found to induce anti-inflammatory and anti-cancer effects. In this study, we examined the differential effect of CF102 in pathological conditions of the liver. The anti-inflammatory protective effect of CF101 was tested in a model of liver inflammation induced by Concanavalin A (Con. A) and the anti-cancer effect of CF102 was examined in vitro and in a xenograft animal model utilizing Hep-3B hepatocellular carcinoma (HCC) cells. The mechanism of action was explored by following the expression levels of key signaling proteins in the inflamed and tumor liver tissues, utilizing Western blot (WB) analysis. In the liver inflammation model, CF102 (100 µg/kg) markedly reduced the secretion of serum glutamic oxaloacetic transaminase and serum glutamic pyruvic transaminase in comparison to the vehicle-treated group. Mechanistically, CF102 treatment decreased the expression level of phosphorylated glycogen synthase kinase-3β, NF-κB, and TNF-α and prevented apoptosis in the liver. This was demonstrated by decreased expression levels of Fas receptor (FasR) and of the pro-apoptotic proteins Bax and Bad in liver tissues. In addition, CF102-induced apoptosis of Hep-3B cells both in vitro and in vivo via de-regulation of the PI3K-NF-κB signaling pathway, resulting in up-regulation of pro-apoptotic proteins. Taken together, CF102 acts as a protective agent in liver inflammation and inhibits HCC tumor growth. These results suggest that CF102 through its differential effect is a potential drug candidate to treat various pathological liver conditions.

The dietary flavonoid apigenin enhances the activities of the anti-metastatic protein CD26 on human colon carcinoma cells

There is accumulating evidence that secondary plant metabolites such as flavonoids may have anti-cancer properties, and yet the molecular pathways that lead to alterations in cancer cell behaviour remain unclear. We investigated the possible actions of apigenin, a flavone present in leafy vegetables like parsley, on the levels of CD26 in carcinoma cells. CD26 is a multifunctional cell-surface protein that through its associated dipeptidyl peptidase (DPPIV) and ecto-adenosine deaminase (eADA) enzyme activities is able to suppress pathways involved in tumour metastasis. CD26 is down-regulated in various cancers including colorectal carcinoma. Apigenin substantially up-regulated cell-surface CD26 on HT-29 and HRT-18 human colorectal cancer cells. Levels of CD26 protein, along with its associated DPPIV enzyme activity, capacity to bind eADA, and ability to link cells to fibronectin, were increased with a maximum after 24-48 h. Elevation of CD26 occurred at concentrations that were at least 10-fold less than those shown to affect cell growth, and 100-fold below those that could affect cell viability. Furthermore, the CD26 effect was enhanced when apigenin was paired with chemotherapeutic agents utilized in the treatment of advanced colorectal cancer including irinotecan, 5-fluorouracil and oxaliplatin. For irinotecan, apigenin caused a 4-fold increase in the potency of the drug. These results demonstrate that apigenin can increase the cellular levels of CD26 and its multiple functions, and may oppose the predicted effect of decreased DPPIV and eADA activities on carcinoma cells, which is to facilitate tumour growth and metastasis.

Novel point mutations attenuate autotaxin activity

BACKGROUND

The secreted enzyme autotaxin (ATX) stimulates tumor cell migration, tumorigenesis, angiogenesis, and metastasis. ATX hydrolyzes nucleotides, but its hydrolysis of lysophospholipids to produce lysophosphatidic acid (LPA) accounts for its biological activities. ATX has been identified only as a constitutively active enzyme, and regulation of its activity is largely unexplored. In spite of its presence in plasma along with abundant putative substrate LPC, the product LPA is found in plasma at unexpectedly low concentrations. It is plausible that the LPA-producing activity of ATX is regulated by its expression and by access to substrate(s). For this reason studying the interaction of enzyme with substrate is paramount to understanding the regulation of LPA production.

RESULTS

In this study we determine ATX hydrolytic activities toward several artificial and natural substrates. Two novel point mutations near the enzyme active site (H226Q and H434Q) confer attenuated activity toward all substrates tested. The Vmax for LPC compounds depends upon chain length and saturation; but this order does not differ among wild type and mutants. However the mutant forms show disproportionately low activity toward two artificial substrates, pNpTMP and FS-3. The mutant forms did not significantly stimulate migration responses at concentrations that produced a maximum response for WT-ATX, but this defect could be rescued by inclusion of exogenous LPC.

CONCLUSION

H226Q-ATX and H434Q-ATX are the first point mutations of ATX/NPP2 demonstrated to differentially impair substrate hydrolysis, with hydrolysis of artificial substrates being disproportionately lower than that of LPC. This implies that H226 and H434 are important for substrate interaction. Assays that rely on hydrolyses of artificial substrates (FS-3 and pNpTMP), or that rely on hydrolysis of cell-derived substrate, might fail to detect certain mutated forms of ATX that are nonetheless capable of producing LPA in the presence of sufficient exogenous substrate. H420Q-ATX could not be differentiated from WT-ATX, indicating that histidine at position 420 is not required for any of the activities of ATX tested in this study.

Diminution in adenine nucleotide hydrolysis by platelets and serum from rats submitted to Walker 256 tumour

Extracellular adenine nucleotide hydrolysis in the circulation is mediated by the action of an NTPDase (CD39, apyrase) and of a 5'-nucleotidase (CD73), presenting as a final product, adenosine. Among other properties described for adenine nucleotides, an anti-cancer activity is suggested, since ATP is considered a cytotoxic molecule in several tumour cell systems. Conversely, some studies demonstrate that adenosine presents a tumour-promoting activity. In this study, we evaluated the pattern of adenine nucleotide hydrolysis by serum and platelets from rats submitted to the Walker 256 tumour model. Extracellular adenine nucleotide hydrolysis by blood serum and platelets obtained from rats at, 6, 10 and 15 days after the subcutaneous Walker 256 tumour inoculation, was evaluated. Our results demonstrate a significant reduction in ATP, ADP and AMP hydrolysis in blood serum at 6, 10 and 15 days after tumour induction. In platelets, a significant reduction in ATP and AMP hydrolysis was observed at 10 and 15 days after tumour induction, while an inhibition of ADP hydrolysis was observed at all times studied. Based on these results, it is possible to suggest a physiologic protection mechanism against the tumoral process in circulation. The inhibition in nucleotide hydrolysis observed probably maintains ATP levels elevated (cytotoxic compound) and, at the same time, reduces the adenosine production (tumour-promoting molecule) in the circulation.

Three Nordic berries inhibit intestinal tumorigenesis in multiple intestinal neoplasia/+ mice by modulating beta-catenin signaling in the tumor and transcription in the mucosa

Berries contain a number of compounds that are proposed to have anticarcinogenic properties. We studied the effects and molecular mechanisms of wild berries with different phenolic profiles on intestinal tumorigenesis in multiple intestinal neoplasia/+ mice. The mice were fed a high-fat AIN93-G diet (Con) or AIN93-G diets containing 10% (w:w) freeze-dried bilberry, lingonberry (LB), or cloudberry (CB) for 10 wk. All 3 berries significantly inhibited the formation of intestinal adenomas as indicated by a 15-30% reduction in tumor number (P < 0.05). CB and LB also reduced tumor burden by over 60% (P < 0.05). Compared to Con, CB and LB resulted in a larger (P < 0.05) proportion of small adenomas (43, 69, and 64%, respectively) and a smaller proportion of large adenomas (56, 29, and 33%, respectively). Beta-catenin and cyclin D1 in the small and large adenomas and in the normal-appearing mucosa were measured by Western blotting and immunohistochemistry. CB resulted in decreased levels of nuclear beta-catenin and cyclin D1 and LB in the level of cyclin D1 in the large adenomas (P < 0.05). Early changes in gene expression in the normal-appearing mucosa were analyzed by Affymetrix microarrays, which revealed changes in genes implicated in colon carcinogenesis, including the decreased expression of the adenosine deaminase, ecto-5'-nucleotidase, and prostaglandin E2 receptor subtype EP4. Our results indicate that berries are potentially a rich source of chemopreventive components.

A multi-gene approach to differentiate papillary thyroid carcinoma from benign lesions: gene selection using support vector machines with bootstrapping

Selection of novel molecular markers is an important goal of cancer genomics studies. The aim of our analysis was to apply the multivariate bioinformatical tools to rank the genes - potential markers of papillary thyroid cancer (PTC) according to their diagnostic usefulness. We also assessed the accuracy of benign/malignant classification, based on gene expression profiling, for PTC. We analyzed a 180-array dataset (90 HG-U95A and 90 HG-U133A oligonucleotide arrays), which included a collection of 57 PTCs, 61 benign thyroid tumors, and 62 apparently normal tissues. Gene selection was carried out by the support vector machines method with bootstrapping, which allowed us 1) ranking the genes that were most important for classification quality and appeared most frequently in the classifiers (bootstrap-based feature ranking, BBFR); 2) ranking the samples, and thus detecting cases that were most difficult to classify (bootstrap-based outlier detection). The accuracy of PTC diagnosis was 98.5% for a 20-gene classifier, its 95% confidence interval (CI) was 95.9-100%, with the lower limit of CI exceeding 95% already for five genes. Only 5 of 180 samples (2.8%) were misclassified in more than 10% of bootstrap iterations. We specified 43 genes which are most suitable as molecular markers of PTC, among them some well-known PTC markers (MET, fibronectin 1, dipeptidylpeptidase 4, or adenosine A1 receptor) and potential new ones (UDP-galactose-4-epimerase, cadherin 16, gap junction protein 3, sushi, nidogen, and EGF-like domains 1, inhibitor of DNA binding 3, RUNX1, leiomodin 1, F-box protein 9, and tripartite motif-containing 58). The highest ranking gene, metallophosphoesterase domain-containing protein 2, achieved 96.7% of the maximum BBFR score.

Ecto-5'-nucleotidase promotes invasion, migration and adhesion of human breast cancer cells

PURPOSE

Associated with many molecules, metastasis includes cell adhesion to extracellular matrix, migration towards specific direction and invasion into local vessel of distant organs. The purpose of the present study was to evaluate the role of ecto-5'-nucleotidase (eN, ecto-5-NT, CD73) generated extracellular adenosine in biologically malignant behaviors of human breast cancer cell lines.

MATERIALS AND METHODS

Two human breast cancer cell lines, T-47D with lower expression of CD73 and MB-MDA-231 with higher expression of CD73, were used to investigate the functions of CD73. The effects of CD73 over-expression on invasion, migration and adhesion were observed in T-47D transfected with pcDNA-NT5E plasmid. The effects of specific CD73 inhibitor, alpha, ss-methylene ADP (APCP), were observed in MB-MDA-231 cells.

RESULTS

The results showed CD-73 overexpression increased invasion, migration and adhesion to ECM of the pcDNA-NT5E transfected T-47D cells compared to the saline and mock vector controls. The increased cell mobility of CD-73-overexpressed T-47D cells was blocked by APCP. Adenosine increased the mobility of wild type T-47D cells. APCP inhibited the mobility of the MB-MDA-231 cells.

CONCLUSION

Taken together, our results indicated that CD73 may facilitate the adhesion, migration and invasion of human breast cancer cells through its enzyme activity of generating adenosine. This study provided a possibly molecular mechanism of metastasis of breast carcinoma.

RNA interference of ecto-5'-nucleotidase (CD73) inhibits human breast cancer cell growth and invasion

Metastasis is a leading cause of mortality and morbidity in breast cancer. Recently, dramatic overexpression of ecto-5'-nucleotidase (CD73), a glycosylphosphatidylinositol-anchored cell surface protein has been found in estrogen receptor-negative [ER (-)] breast cancer cell lines and in clinical samples. In this study, CD73 small interfering RNA (siRNA) plasmid was constructed and stably transfected into breast cancer cell MB-MDA-231 to determine the role of CD73 in breast cancer metastasis and the possible mechanism. Our study demonstrates that CD73 siRNA effectively inhibits CD73 gene expression at mRNA and protein level in MB-MDA-231 cells, leading to in vivo and in vitro growth suppression, prevention of adhesion to extracellular matrix (ECM), and inhibition of invasion and migration. These properties correlate with inhibition of matrix metalloproteinase (MMP)-2 and MMP-9 expression and activity as well as reduction of epidermal growth factor receptor (EGFR) expression. Demonstration of the role of CD73 in breast cancer may lead to new targeted therapies for breast cancer.

Quantifying the A1AR distribution in peritumoural zones around experimental F98 and C6 rat brain tumours

Quantification of growth in experimental F98 and C6 rat brain tumours was performed on 51 rat brains, 17 of which have been further assessed by 3D tumour reconstruction. Brains were cryosliced and radio-labelled with a ligand of the peripheral type benzodiazepine-receptor (pBR), (3)H-Pk11195 [(1-(2-chlorophenyl)-N-methyl-N-(1-methyl-propylene)-3-isoquinoline-carboxamide)] by receptor autoradiography. Manually segmented and automatically registered tumours have been 3D-reconstructed for volumetric comparison on the basis of (3)H-Pk11195-based tumour recognition. Furthermore automatically computed areas of -300 microm inner (marginal) zone as well as 300 microm and 600 microm outer tumour space were quantified. These three different regions were transferred onto other adjacent slices that had been labelled by receptor autoradiography with the A(1) Adenosine receptor (A(1)AR)-ligand (3)H-CPFPX ((3)H-8-cyclopentyl-3-(3-fluorpropyl)-1-propylxanthine) for quantitative assessment of A(1)AR in the three different tumour zones. Hence, a method is described for quantifying various receptor protein systems in the tumour as well as in the marginal invasive zones around experimentally implanted rat brain tumours and their representation in the tumour microenvironment as well as in 3D space. Furthermore, a tool for automatically reading out radio-labelled rat brain slices from auto radiographic films was developed, reconstructed into a consistent 3D-tumour model and the zones around the tumour were visualized. A(1)AR expression was found to depend upon the tumour volume in C6 animals, but is independent on the time of tumour development. In F98 animals, a significant increase in A(1)AR receptor protein was found in the Peritumoural zone as a function of time of tumour development and tumour volume.

Nucleotide metabolizing ecto-enzymes in Walker 256 tumor cells: molecular identification, kinetic characterization and biochemical properties

In this study we describe the molecular identification, kinetic characterization and biochemical properties of an E-NTPDase and an 5'-nucleotidase in Walker 256 cells. For the ATP, ADP and AMP hydrolysis there were optimum pH in the range 6.5-8.0, and absolute requirement for divalent cations (Mg(2+)>Ca(2+)). A significant inhibition of ATP and ADP hydrolysis was observed in the presence of high concentrations of sodium azide and 0.5 mM of Gadolinium chloride. These activities were insensitive to ATPase, adenylate kinase and alkaline phosphatase classical inhibitors. The K(m) values were 464.2+/-86.6 microM (mean+/-SEM, n=4), 137.0+/-31 microM (mean+/-SEM, n=5) and 44.8+/-10.2 microM (mean+/-SEM, n=4), and V(max) values were 655.0+/-94.6 (mean+/-SEM, n=4), 236.3+/-27.2 (mean+/-SEM, n=5) and 177.6+/-13.8 (mean+/-SEM, n=5) nmol of inorganic phosphate min(-1) mg of protein(-1) for ATP, ADP and AMP, respectively. Using RT-PCR analysis we identified the mRNA of two members of the ecto-nucleoside triphosphate diphosphohydrolase family (NTPDase 2 and 5) and a 5'-nucleotidase. The presence of NTPDases and 5'-nucleotidase enzymes in Walker 256 tumor cells may be important to regulate the ratio adenine nucleotides/adenine nucleoside extracellularly, therefore motivating tumor growth.

Expression of ecto-5'-nucleotidase (eN, CD73) in cell lines from various stages of human melanoma

Ecto-5'-nucleotidase is a GPI-anchored enzyme localized in cell membrane lipid rafts. Although it is highly expressed in many tumour cells, its specific function during tumorigenesis is unclear. We have found that, among different melanoma cells, upregulated expression of ecto-5'-nucleotidase is associated with a highly invasive phenotype. Analysis of other cell membrane proteins involved in melanoma adhesion and metastasis demonstrated that expression of alpha5, beta1, beta3-integrin subunits and CD44 was elevated gradually in accordance with increasing metastatic potential. Expression of alphav-integrin and caveolin-1 was seen mostly in cells derived from metastatic melanomas. Furthermore, in contrast to N-cadherin, which was unaltered in all lines, we could not detect E-cadherin in any cell type. Functional assays demonstrated that highly expressed ecto-5'-nucleotidase is a catalytically competent protein that is very sensitive to inhibition by concanavalin A. The interaction with concanavalin A also caused increased association of ecto-5'-nucleotidase-rich lipid rafts with much heavier cytoskeletal complexes as determined by density gradient centrifugation. A similar shift towards heavier cytoskeletal fractions also took place with other proteins coexpressed with ecto-5'-nucleotidase, such as alphav, alpha5, beta1 and beta3-integrins, caveolin-1 and CD44. As ConA-induced clustering may reflect the interactions of membrane proteins with extracellular matrix, we also analysed the effect of several extracellular matrix proteins on the in-situ activity of ecto-5'-nucleotidase in WM9 cells and found that tenascin C strongly inhibited ecto-5'-nucleotidase activity and adenosine generation from AMP. We also developed WM9 cells with reduced ecto-5'-nucleotidase expression and tested differences in cell adhesion on various extracellular matrix proteins. WM9 cells attached significantly weaker to tenascin C layer. These observations indicate that expression of ecto-5'-nucleotidase correlates with a number of metastasis-related markers and thus may have a function in this process. Furthermore, our data suggest that, in addition to generating adenosine, ecto-5'-nucleotidase may have independent roles in adhesion and interaction with extracellular matrix components in melanoma.

Adenosine downregulates DPPIV on HT-29 colon cancer cells by stimulating protein tyrosine phosphatase(s) and reducing ERK1/2 activity via a novel pathway

The multifunctional cell-surface protein dipeptidyl peptidase IV (DPPIV/CD26) is aberrantly expressed in many cancers and plays a key role in tumorigenesis and metastasis. Its diverse cellular roles include modulation of chemokine activity by cleaving dipeptides from the chemokine NH(2)-terminus, perturbation of extracellular nucleoside metabolism by binding the ecto-enzyme adenosine deaminase, and interaction with the extracellular matrix by binding proteins such as collagen and fibronectin. We have recently shown that DPPIV can be downregulated from the cell surface of HT-29 colorectal carcinoma cells by adenosine, which is a metabolite that becomes concentrated in the extracellular fluid of hypoxic solid tumors. Most of the known responses to adenosine are mediated through four different subtypes of G protein-coupled adenosine receptors: A(1), A(2A), A(2B), and A(3). We report here that adenosine downregulation of DPPIV from the surface of HT-29 cells occurs independently of these classic receptor subtypes, and is mediated by a novel cell-surface mechanism that induces an increase in protein tyrosine phosphatase activity. The increase in protein tyrosine phosphatase activity leads to a decrease in the tyrosine phosphorylation of ERK1/2 MAP kinase that in turn links to the decline in DPPIV mRNA and protein. The downregulation of DPPIV occurs independently of changes in the activities of protein kinases A or C, phosphatidylinositol 3-kinase, other serine/threonine phosphatases, or the p38 or JNK MAP kinases. This novel action of adenosine has implications for our ability to manipulate adenosine-dependent events within the solid tumor microenvironment.

Novel signaling pathways mediating reciprocal control of keratinocyte migration and wound epithelialization through M3 and M4 muscarinic receptors

To test the hypothesis that keratinocyte (KC) migration is modulated by distinct muscarinic acetylcholine (ACh) receptor subtypes, we inactivated signaling through specific receptors in in vitro and in vivo models of reepithelialization by subtype-selective antagonists, small interfering RNA, and gene knockout in mice. KC migration and wound reepithelialization were facilitated by M4 and inhibited by M3. Additional studies showed that M4 increases expression of "migratory" integrins alpha5beta1, alphaVbeta5, and alphaVbeta6, whereas M3 up-regulates "sedentary" integrins alpha2beta1 and alpha3beta1. Inhibition of migration by M3 was mediated through Ca2+-dependent guanylyl cyclase-cyclic GMP-protein kinase G signaling pathway. The M4 effects resulted from inhibition of the inhibitory pathway involving the adenylyl cyclase-cyclic AMP-protein kinase A pathway. Both signaling pathways intersected at Rho, indicating that Rho kinase provides a common effector for M3 and M4 regulation of cell migration. These findings offer novel insights into the mechanisms of ACh-mediated modulation of KC migration and wound reepithelialization, and may aid the development of novel methods to promote wound healing.

Adenosine down-regulates the surface expression of dipeptidyl peptidase IV on HT-29 human colorectal carcinoma cells: implications for cancer cell behavior

Dipeptidyl peptidase IV (DPPIV) is a multifunctional cell-surface protein that, as well as having dipeptidase activity, is the major binding protein for adenosine deaminase (ADA) and also binds extracellular matrix proteins such as fibronectin and collagen. It typically reduces the activity of chemokines and other peptide mediators as a result of its enzymatic activity. DPPIV is aberrantly expressed in many cancers, and decreased expression has been linked to increases in invasion and metastasis. We asked whether adenosine, a purine nucleoside that is present at increased levels in the hypoxic tumor microenvironment, might affect the expression of DPPIV at the cell surface. Treatment with a single dose of adenosine produced an initial transient (1 to 4 hours) modest (approximately 10%) increase in DPPIV, followed by a more profound (approximately 40%) depression of DPPIV protein expression at the surface of HT-29 human colon carcinoma cells, with a maximal decline being reached after 48 hours, and persisting for at least a week with daily exposure to adenosine. This down-regulation ofDPPIV occurred at adenosine concentrations comparable to those present within the extracellular fluid of colorectal tumors growing in vivo, and was not elicited by inosine or guanosine. Neither cellular uptake of adenosine nor its phosphorylation was necessary for the down-regulation of DPPIV. The decrease in DPPIV protein at the cell surface was paralleled by decreases in DPPIV enzyme activity, binding of ADA, and the ability of the cells to bind to and migrate on cellular fibronectin. Adenosine, at concentrations that exist within solid tumors, therefore acts at the surface of colorectal carcinoma cells to decrease levels and activities of DPPIV. This down-regulation of DPPIV may increase the sensitivity of cancer cells to the tumor-promoting effects of adenosine and their response to chemokines and the extracellular matrix, facilitating their expansion and metastasis.

Adenosine stimulation of proliferation of breast carcinoma cell lines: Evaluation of the [3H]thymidine assay system and modulatory effects of the cellular microenvironment in vitro

The purine nucleoside adenosine is produced at increased levels in the tissues of solid cancers as a result of local hypoxia. Adenosine inhibits the cell-mediated anti-tumor immune response, promotes tumor cell migration and angiogenesis, and stimulates the proliferation of tumor cells. We examined the stimulatory effect of adenosine on DNA synthesis, cell cycle progression, and cell proliferation in MCF7 and T-47D breast carcinoma cell lines in culture, and identified factors that modulate the growth response. The ability of adenosine to stimulate DNA synthesis, as measured by the incorporation of [(3)H]thymidine, was independent of the total radioactivity of the [(3)H]thymidine up to 10 microCi/ml, total thymidine concentrations up to 100 microM, and the labeling interval. It was also not affected by the presence of low-molecular-weight compounds (such as thymidine and adenosine) in the serum used to supplement the medium. Adenosine stimulated DNA synthesis and cell proliferation with an EC(50) of 4-6 microM and a maximum response at 30-100 microM, when given as a single addition. The stimulatory effect of adenosine involved progression through the cell cycle and a genuine increase in cell number, in the absence of significant apoptotic or necrotic cell death. The mitogenic effect of adenosine was dependent upon the culture cell density, with an optimum adenosine response at around 50% of confluent density. The response was also highly dependent upon the form of the serum addition to the growth medium, with the best response elicited in the presence of low concentrations of nonfetal bovine serum, although adenosine was mitogenic under standard culture conditions. The effects of serum supplementation and cell density were not due to differences in the rate of adenosine metabolism by either serum or cellular enzymes, but appeared to result from changes in the sensitivity to adenosine of the cell population in response to environmental cues. We, therefore, find that adenosine is consistently mitogenic for human breast carcinoma cells, and that the [(3)H]thymidine incorporation assay is a valid measure of this response. The data are consistent with the stimulatory effect of adenosine on cell proliferation being modulated by the local cellular environment.

Adenosine stimulation of the proliferation of colorectal carcinoma cell lines. Roles of cell density and adenosine metabolism

Adenosine is a purine nucleoside which is present at micromolar concentrations in the extracellular fluid of solid cancers as a result of tissue hypoxia. Adenosine acts to promote tumor survival by inhibiting the cell-mediated anti-tumor immune response. However, its role in modulating proliferation of the tumor cell population is unclear. Differing results have been obtained using adenosine analogues or by interfering with adenosine metabolism. We examined the effect of adenosine itself on DNA synthesis and cell growth in six different human and mouse colorectal carcinoma cell lines, from different sites and at different stages of differentiation. Adenosine given as a single dose consistently stimulated DNA synthesis and cell proliferation in all cell lines tested, with an EC(50) of 3.8-30 microM and a maximum stimulation being reached at 10-100 microM. AMP and ATP also stimulated cell proliferation at similar doses. The stimulation by adenosine varied depending upon the culture cell density, with the greatest mitogenic effect at subconfluent densities. Adenosine was metabolized by cellular adenosine deaminase and adenosine kinase. The half-life (t(1/2)) for the decline in adenosine concentration in the medium following a single addition was between 40 min and 3 hr depending on the cell line and culture conditions. The rate of production of endogenous adenosine was low under normoxic culture conditions. Continuous dosing of cultures with adenosine to provide a steady-state concentration showed that proliferation could be stimulated by low micromolar concentrations of adenosine. We conclude that adenosine is stimulatory to the growth of human colorectal carcinoma cells at concentrations present within the tumor extracellular environment.

A glance at adenosine receptors: novel target for antitumor therapy

Adenosine can be released from a variety of cells throughout the body, as the result of increased metabolic rates, in concentrations that can have a profound impact on the vasculature, immunoescaping, and growth of tumor masses. It is recognized that the concentrations of this nucleoside are increased in cancer tissues. Therefore, it is not surprising that adenosine has been shown to be a crucial factor in determining the cell progression pathway, either during apoptosis or during cytostatic state. From the perspective of cancer, the most important question then may be "Can activation and/or blockade of the pathways downstream of the adenosine receptor contribute to tumor development?" Rigorous examinations of the role of adenosine in in vivo and in vitro systems need to be investigated. The present review therefore proposes multiple adenosine-sustained ways that could prime tumor development together with the critical combinatorial role played by adenosine receptors in taking a choice between proliferation and death. This review proposes that adenosine acts as a potent regulator of normal and tumor cell growth. It is hypothesized that this effect is dependent on extracellular adenosine concentrations, cell surface expression of different adenosine receptor subtypes, and signal transduction mechanisms activated following the binding of specific agonists. We venture to suggest that the clarification of the role of adenosine and its receptors in cancer development may hold great promise for the treatment of chemotherapy in patients affected by malignancies.

Regulation of cell morphology and adhesion by the tuberous sclerosis complex (TSC1/2) gene products in human kidney epithelial cells through increased E-cadherin/beta-catenin activity

We investigated the effects of overexpression of the tuberous sclerosis-1 and -2 (TSC1/2) gene products (hamartin and tuberin, respectively) in the human kidney epithelial cell line 293 with an inducible expression system. As we had observed previously in fibroblasts, 293 cells overexpressing hamartin and/or tuberin grew more slowly in vitro. However, here we also observed that the 293 overexpressing cells underwent a dramatic morphological change in which groups of cells formed compact clusters. The overexpressing cells also displayed decreased dissociation and increased reaggregation in vitro. These changes were found to be associated with an increased level of E-cadherin, which is known to regulate cell-cell interactions in epithelial cells, and of its binding partner beta-catenin. Consistent with the role of E-cadherin in these effects, we found that the observed changes in 293 cell morphology, dissociation, and adhesion were calcium-dependent, and were reproduced by overexpression of E-cadherin. In contrast, overexpression of TSC1 in rat embryo fibroblasts, which lack E-cadherin, failed to elicit the same changes as in 293 cells. We conclude that the hamartin/tuberin complex exerted a direct effect on the morphology and adhesive properties of 293 cells through regulation of the level and/or activity of cellular E-cadherin/beta-catenin.

CAI inhibits the growth of small cell lung cancer cells

The effects of carboxyamido-triazole (CAI) on small cell lung cancer (SCLC) cells were investigated. Using SCLC cell lines NCI-H209 or H345, 20 micro M CAI had little effect on basal cytosolic Ca(2+) but inhibited the ability of 10 nM bombesin (BB) or 1 nM neurotensin (NT) to elevate cytosolic Ca(2+). Also, CAI, impaired the ability of BB or NT to cause tyrosine phosphorylation of focal adhesion kinase. In contrast, CAI did not affect the ability of (125I-Tyr(4))BB or 125I-NT to bind with high affinity to NCI-H345 cells. These results indicate that CAI impairs SCLC second messenger activation, but not neuropeptide receptor binding. Using a MTT growth assay, CAI inhibited the proliferation of NCI-H209 or H345 cells in a concentration-dependent manner with little proliferation occurring using 100 micro M CAI. Also, CAI inhibited colony formation of NCI-H209 or H345 cells in a dose-dependent manner in vitro. In vivo, CAI (2 mg/day by gavage) inhibited significantly NCI-H209 xenograft proliferation in nude mice. Animals treated daily with CAI had significantly reduced CD31 immunostaining of microvessels in the tumor. Also, CAI inhibited the increase in vascular endothelial cell growth factor (VEGF) mRNA after addition of BB to SCLC cells. These results suggest that CAI inhibits the growth of SCLC cells as well as the angiogenesis of SCLC tumors in a VEGF-dependent manner.

Involvement of the muscarinic acetylcholine receptor in inhibition of cell migration

Activation of G protein-coupled receptors is known to stimulate cell migration, but receptor-mediated signals inhibiting cell migration have not been identified. We investigated the ability of transfected human M(3) muscarinic acetylcholine receptors (mAChR) to regulate the migration of Chinese hamster ovary (CHO) cells. Single cells migrated on colloidal gold applied to fibronectin-coated plates, and videomicroscopy was used to measure cell spreading and migration. Activation of M(3) mAChR with the agonist carbachol was found to inhibit cell migration, whereas direct activation of protein kinase C (PKC) with PMA was found to stimulate migration. The amount of cell adhesion and spreading was found to be equivalent for carbachol- and PMA-treated cells. Selective inactivation of conventional PKC isoforms with Go6976 (C(24)H(18)N(4)O) abolished the PMA-mediated increase in cell migration. In contrast, the mAChR-mediated decrease in migration was not altered by Go6976, but was abolished when both novel and conventional PKC isoforms were inactivated by calphostin C or chelerythrine. These findings suggest involvement of conventional PKC isoforms in the stimulation of migration and of novel PKC isoforms in the inhibition of migration. Carbachol- but not PMA-treated cells exhibited an elongated morphology reminiscent of migrating cells that cannot detach their trailing edges from the substratum. Similarly, carbachol-treated cells detached less readily from fibronectin than control or PMA-treated cells when integrin activity was diminished by the chelation of Ca(2+) and Mg(2+). Finally, the carbachol-induced diminution of cell detachment was preserved after inhibition of the conventional PKC isoforms with Go6976, but was abrogated by treatment with either calphostin C or chelerythrine. These findings suggest that mAChR activation diminishes the ability of cells to detach from the substratum, resulting in diminished migration. This is in contrast to the direct activation of PKC with PMA, which stimulates migration.

Immunolocalization of A1 adenosine receptors in mammalian spermatozoa

The presence of A1 adenosine receptors (A1AR) in mammalian spermatozoa was previously demonstrated by radiochemical and immunochemical detection. This study was performed to investigate the cellular location of the A1AR to determine whether these receptors were somehow connected with ecto-adenosine deaminase and to evaluate their function in calcium uptake. By immunofluorescence staining we showed that in mammalian spermatozoa A1AR were constantly localized in the acrosomal region. This finding was confirmed by immunogold detection. Confocal analyses with anti-A1 and anti-ADA antibodies showed a high degree of co-localization. Calcium loading assay showed that this association was functional and affected calcium accumulation in mammalian spermatozoa. Therefore, we concluded that the acrosomal localization of A1AR was a constant feature in mammalian sperm. Moreover, these A1 receptors were functionally coupled to ecto-ADA and were able to modulate calcium uptake into an IP3-gated store.(J Histochem Cytochem 48:1163-1171, 2000)

Genomic structure and promoter analysis of the ecto-phosphodiesterase I gene (PDNP3) expressed in glial cells

PDNP (phosphodiesterase I/nucleotide pyrophosphatase) is one of a series of ectoenzymes that are involved in hydrolysis of extracellular nucleotides. PDNP possesses ATPase (EC 3.6.1.3) and ATP pyrophosphatase (EC 3.6.1.8) activities. Mammalian PDNP consists of three closely related family proteins (PDNP1, -2, and -3), and they are expressed in different cell types and at different developmental stages. Rat PDNP3 is expressed in a subset of immature glial cells and in the alimentary tract. Human PDNP3 is expressed in glioma cells, prostate, and uterus, but not in the alimentary tract. We have cloned genomic DNA containing the whole coding region of the human PDNP3 gene and determined its exon-intron structure. The human PDNP3 gene spans over 60 kb and is organized into 25 exons and 24 introns. We determined the nucleotide sequence of the 5'-flanking region of human and rat PDNP3 genes. The upstream region of both species lacks a canonical TATA box and contains a putative binding site for CCAAT enhancer-binding proteins near the transcription start site. Promoter activity analysis of the 5'-flanking region revealed that the sequence around the CCAAT box is required for its transcriptional activity in 9L rat glioma cells. A gel shift assay demonstrated that 9L nuclear extract contains proteins that bind to this region.

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.