Nucleotide P2Y1 receptor regulates EGF receptor mitogenic signaling and expression in epithelial cells

17-β-estradiol and phytoestrogens elicit NO production and vasodilatation through PI3K, PKA and EGF receptors pathways, evidencing functional selectivity

Endothelial cells express multiple receptors mediating estrogen responses; including the G protein-coupled estrogen receptor (GPER). Past studies on nitric oxide (NO) production elicited by estrogens raised the question whether 17-β-estradiol (E2) and natural phytoestrogens activate equivalent mechanisms. We hypothesized that E2 and phytoestrogens elicit NO production via coupling to distinct intracellular pathways signalling. To this aim, perfusion of E2 and phytoestrogens to the precontracted rat mesentery bed examined vasorelaxation, while fluorescence microscopy on primary endothelial cells cultures quantified single cell NO production determined following 4-amino-5-methylamino-2',7'-difluoroescein diacetate (DAF) incubation. Daidzein (DAI) and genistein (GEN) induced rapid vasodilatation associated to NO production. Multiple estrogen receptor activity was inferred based on the reduction of DAF-NO signals; G-36 (GPER antagonist) reduced 75 % of all estrogen responses, while fulvestrant (selective nuclear receptor antagonist) reduced significantly more the phytoestrogens responses than E2. The joint application of both antagonists abolished the E2 response but not the phytoestrogen-induced DAF-NO signals. Wortmannin or LY-294002 (PI3K inhibitors), reduced by 90% the E2-evoked signal while altering significantly less the DAI-induced response. In contrast, H-89 (PKA inhibitor), elicited a 23% reduction of the E2-induced signal while blocking 80% of the DAI-induced response. Desmethylxestospongin-B (IP3 receptor antagonist), decreased to equal extent the E2 or the DAI-induced signal. Epidermal growth factor (EGF) induced NO production, cell treatment with AG-1478, an EGF receptor kinase inhibitor reduced 90% DAI-induced response while only 53% the E2-induced signals; highlighting GPER induced EGF receptor trans-modulation. Receptor functional selectivity may explain distinct signalling pathways mediated by E2 and phytoestrogens.

Transactivation of receptor tyrosine kinases by purinergic P2Y and adenosine receptors

Transactivation of receptor tyrosine kinases (RTK) is a crosstalk mechanism exhibited by G-protein-coupled receptors (GPCR) to activate signaling pathways classically associated with growth factors. The discovery of RTK transactivation was a breakthrough in signal transduction that contributed to developing current concepts in intracellular signaling. RTK transactivation links GPCR signaling to important cellular processes, such as cell proliferation and differentiation, and explains the functional diversity of these receptors. Purinergic (P2Y and adenosine) receptors belong to class A of GPCR; in the present work, we systematically review the experimental evidence showing that purinergic receptors have the ability to transactivate RTK in multiple tissues and physiopathological conditions resulting in the modulation of cellular physiology. Of particular relevance, the crosstalk between purinergic receptors and epidermal growth factor receptor is a redundant pathway that participates in multiple pathophysiological processes. Specific and detailed knowledge of purinergic receptor-regulated pathways advances our understanding of the complexity of GPCR signal transduction and opens the way for pharmacologic intervention in the pathological context.

A Phosphoproteomics Data Resource for Systems-level Modeling of Kinase Signaling Networks

Building mechanistic models of kinase-driven signaling pathways requires quantitative measurements of protein phosphorylation across physiologically relevant conditions, but this is rarely done because of the insensitivity of traditional technologies. By using a multiplexed deep phosphoproteome profiling workflow, we were able to generate a deep phosphoproteomics dataset of the EGFR-MAPK pathway in non-transformed MCF10A cells across physiological ligand concentrations with a time resolution of <12 min and in the presence and absence of multiple kinase inhibitors. An improved phosphosite mapping technique allowed us to reliably identify >46,000 phosphorylation sites on >6600 proteins, of which >4500 sites from 2110 proteins displayed a >2-fold increase in phosphorylation in response to EGF. This data was then placed into a cellular context by linking it to 15 previously published protein databases. We found that our results were consistent with much, but not all previously reported data regarding the activation and negative feedback phosphorylation of core EGFR-ERK pathway proteins. We also found that EGFR signaling is biphasic with substrates downstream of RAS/MAPK activation showing a maximum response at <3ng/ml EGF while direct substrates, such as HGS and STAT5B, showing no saturation. We found that RAS activation is mediated by at least 3 parallel pathways, two of which depend on PTPN11. There appears to be an approximately 4-minute delay in pathway activation at the step between RAS and RAF, but subsequent pathway phosphorylation was extremely rapid. Approximately 80 proteins showed a >2-fold increase in phosphorylation across all experiments and these proteins had a significantly higher median number of phosphorylation sites (~18) relative to total cellular phosphoproteins (~4). Over 60% of EGF-stimulated phosphoproteins were downstream of MAPK and included mediators of cellular processes such as gene transcription, transport, signal transduction and cytoskeletal arrangement. Their phosphorylation was either linear with respect to MAPK activation or biphasic, corresponding to the biphasic signaling seen at the level of the EGFR. This deep, integrated phosphoproteomics data resource should be useful in building mechanistic models of EGFR and MAPK signaling and for understanding how downstream responses are regulated.

Nanomolar clodronate induces adenosine accumulation in the perfused rat mesenteric bed and mesentery-derived endothelial cells

The vesicular nucleotide transporter (VNUT) is critical for sympathetic co-transmission and purinergic transmission maintenance. To examine this proposal, we assessed whether the bisphosphonate clodronate, claimed as a potent in vitro VNUT blocker, modified spontaneous and/or the electrically evoked overflow of ATP/metabolites and NA from mesentery sympathetic perivascular nerve terminals. Additionally, in primary endothelial cell cultures derived from this tissue, we also evaluated whether clodronate interfered with ATP/metabolite cell outflow and metabolism of N⁶-etheno adenosine 5'-triphosphate (eATP), N⁶-etheno adenosine (eADO), and adenosine deaminase enzyme activity. Rat mesenteries were perfused in the absence or presence of .01-1,000 nM clodronate, 1-1,000 nM Evans blue (EB), and 1-10 µM DIDS; tissue perfusates were collected to determine ATP/metabolites and NA before, during, and after perivascular electrical nerve terminal depolarization. An amount of 1-1,000 nM clodronate did not modify the time course of ATP or NA overflow elicited by nerve terminal depolarization, and only 10 nM clodronate significantly augmented perfusate adenosine. Electrical nerve terminal stimulation increased tissue perfusion pressure that was significantly reduced only by 10 nM clodronate [90.0 ± 18.6 (n = 8) to 35.0 ± 10.4 (n = 7), p = .0277]. As controls, EB, DIDS, or reserpine treatment reduced the overflow of ATP/metabolites and NA in a concentration-dependent manner elicited by nerve terminal depolarization. Moreover, mechanical stimulation of primary endothelial cell cultures from the rat mesentery added with 10 or 100 nM clodronate increased adenosine in the cell media. eATP was metabolized by endothelial cells to the same extent with and without 1-1,000 nM clodronate, suggesting the bisphosphonate did not interfere with nucleotide ectoenzyme metabolism. In contrast, extracellular eADO remained intact, indicating that this nucleoside is neither metabolized nor transported intracellularly. Furthermore, only 10 nM clodronate inhibited (15.5%) adenosine metabolism to inosine in endothelial cells as well as in a commercial crude adenosine deaminase enzyme preparation (12.7%), and both effects proved the significance (p < .05). Altogether, present data allow inferring that clodronate inhibits adenosine deaminase activity in isolated endothelial cells as in a crude extract preparation, a finding that may account for adenosine accumulation following clodronate mesentery perfusion.

P2Y1 receptor in the colonic submucosa of rats and its association with opioid‑induced constipation

The aim of the present study was to explore the expression changes of P2Y purinergic receptor 1 (P2Y1) in the distal colonic submucosa of opioid-induced constipation (OIC) rats and its association with the occurrence of OIC, an OIC rat model was generated by intraperitoneal injection of loperamide hydrochloride, a selective agonist of µ-opioid receptors (MORs). At 7 days post-treatment, the model was assessed by analyzing stool scores and calculating the gastrointestinal (GI) transit ratio of rats. The distribution of P2Y1-expressing neurons in the colonic submucosal plexus was demonstrated by immunofluorescence (IF). Western blotting was performed to evaluate the expression changes of MOR, P2Y1 and ATP synthase subunit β (ATPB) proteins in the colonic submucosa, while reverse transcription-quantitative PCR (RT-qPCR) analysis was performed to determine the relative mRNA expression of MOR and P2Y1. After 7 days, the feces of OIC rats exhibited an appearance of sausage-shaped pieces and both the stool weight and GI transit ratio of OIC rats were significantly decreased. IF revealed co-expression of P2Y1 and calbindin and MOR and ATPB in the nerve cells of the distal colonic submucosal plexus. Moreover, RT-qPCR analysis showed that the MOR mRNA levels were significantly increased in the distal colonic submucosa of OIC rats, while mRNA levels of P2Y1 were decreased. WB showed that in the distal colonic submucosa of OIC rats, MOR protein expression was increased, whereas that of P2Y1 was significantly decreased. GI transit ratio analysis suggested that the P2Y agonist ATP significantly relieved constipation symptoms in rats, while the P2Y inhibitor MRS2179 aggravated these symptoms. Finally, P2Y1 expression change was shown to be associated with the occurrence of OIC, while expression of MOR and P2Y1 was associated with OIC development in rats.

Functional characterization of HIC, a P2Y1 agonist, as a p53 stabilizer for prostate cancer cell death induction

Background: (1-(2-hydroxy-5-nitrophenyl)(4-hydroxyphenyl)methyl)indoline-4-carbonitrile (HIC), an agonist of the P2Y1 receptor (P2Y1R), induces cell death in prostate cancer cells. However, the molecular mechanism behind the inhibition of HIC in prostate cancer remains elusive. Methods & results: Here, to outline the inhibitory role of HIC on prostate cancer cells, PC-3 and DU145 cell lines were treated with the respective IC₅₀ concentrations, which reduced cell proliferation, adherence properties and spheroid formation. HIC was able to arrest the cell cycle at G1/S phase and also induced apoptosis and DNA damage, validated by gene expression profiling. HIC inhibited the prostate cancer cells' migration and invasion, revealing its antimetastatic ability. P2Y1R-targeted HIC affects p53, MAPK and NF-κB protein expression, thereby improving the p53 stabilization essential for G1/S arrest and cell death. Conclusion: These findings provide an insight on the potential use of HIC, which remains the mainstay treatment for prostate cancer.

Autocrine and paracrine purinergic signaling in the most lethal types of cancer

Cancer comprises a collection of diseases that occur in almost any tissue and it is characterized by an abnormal and uncontrolled cell growth that results in tumor formation and propagation to other tissues, causing tissue and organ malfunction and death. Despite the undeniable improvement in cancer diagnostics and therapy, there is an urgent need for new therapeutic and preventive strategies with improved efficacy and fewer side effects. In this context, purinergic signaling emerges as an interesting candidate as a cancer biomarker or therapeutic target. There is abundant evidence that tumor cells have significant changes in the expression of purinergic receptors, which comprise the G-protein coupled P2Y and AdoR families of receptors and the ligand-gated ion channel P2X receptors. Tumor cells also exhibit changes in the expression of nucleotidases and other enzymes involved in nucleotide metabolism, and the concentrations of extracellular nucleotides are significantly higher than those observed in normal cells. In this review, we will focus on the potential role of purinergic signaling in the ten most lethal cancers (lung, breast, colorectal, liver, stomach, prostate, cervical, esophagus, pancreas, and ovary), which together are responsible for more than 5 million annual deaths.

Does the prenatal factor or the postnatal factor contribute more to changes in the child sex ratio in India? An investigation in the context of fertility and mortality transition

There has been a drastic decline in the child sex ratio (number of females per 1000 males between ages 0 and 4) in India and many of its states. This study aimed to examine if prenatal factors, such as change in sex ratio at birth, or postnatal factors, such as change in relative mortality of females and males, contribute to this more by analysing the dynamics of the child sex ratio. Changes in the child sex ratio during 2001-2011 were decomposed into a 'fertility' component attributable to prenatal sex selection and a 'mortality' component attributable to sex differentials in postnatal survival at the country as well as the state level. Between the prenatal factor and the postnatal factor, the contribution of the latter to the declining child sex ratio has been greater than the former in India as a whole and in most of the states. By focusing on both prenatal and postnatal factors, the imbalance in the child sex ratio in the country can be reduced to a large extent.

Extracellular Vesicle-Mediated Purinergic Signaling Contributes to Host Microenvironment Plasticity and Metastasis in Triple Negative Breast Cancer

Metastasis accounts for over 90% of cancer-related deaths, yet the mechanisms guiding this process remain unclear. Secreted nucleoside diphosphate kinase A and B (NDPK) support breast cancer metastasis. Proteomic evidence confirms their presence in breast cancer-derived extracellular vesicles (EVs). We investigated the role of EV-associated NDPK in modulating the host microenvironment in favor of pre-metastatic niche formation. We measured NDPK expression and activity in EVs isolated from triple-negative breast cancer (MDA-MB-231) and non-tumorigenic mammary epithelial (HME1) cells using flow cytometry, western blot, and ATP assay. We evaluated the effects of EV-associated NDPK on endothelial cell migration, vascular remodeling, and metastasis. We further assessed MDA-MB-231 EV-induced proteomic changes in support of pre-metastatic lung niche formation. NDPK-B expression and phosphotransferase activity were enriched in MDA-MB-231 EVs that promote vascular endothelial cell migration and disrupt monolayer integrity. MDA-MB-231 EV-treated mice demonstrate pulmonary vascular leakage and enhanced experimental lung metastasis, whereas treatment with an NDPK inhibitor or a P2Y1 purinoreceptor antagonist blunts these effects. We identified perturbations to the purinergic signaling pathway in experimental lungs, lending evidence to support a role for EV-associated NDPK-B in lung pre-metastatic niche formation and metastatic outgrowth. These studies prompt further evaluation of NDPK-mediated EV signaling using targeted genetic silencing approaches.

P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction

Although often overlooked in our daily lives, saliva performs a host of necessary physiological functions, including lubricating and protecting the oral cavity, facilitating taste sensation and digestion and maintaining tooth enamel. Therefore, salivary gland dysfunction and hyposalivation, often resulting from pathogenesis of the autoimmune disease Sjögren's syndrome or from radiotherapy of the head and neck region during cancer treatment, severely reduce the quality of life of afflicted patients and can lead to dental caries, periodontitis, digestive disorders, loss of taste and difficulty speaking. Since their initial discovery in the 1970s, P2 purinergic receptors for extracellular nucleotides, including ATP-gated ion channel P2X and G protein-coupled P2Y receptors, have been shown to mediate physiological processes in numerous tissues, including the salivary glands where P2 receptors represent a link between canonical and non-canonical saliva secretion. Additionally, extracellular nucleotides released during periods of cellular stress and inflammation act as a tissue alarmin to coordinate immunological and tissue repair responses through P2 receptor activation. Accordingly, P2 receptors have gained widespread clinical interest with agonists and antagonists either currently undergoing clinical trials or already approved for human use. Here, we review the contributions of P2 receptors to salivary gland function and describe their role in salivary gland dysfunction. We further consider their potential as therapeutic targets to promote physiological saliva flow, prevent salivary gland inflammation and enhance tissue regeneration.

Purinergic signaling and tumor microenvironment in cervical Cancer

Cervical cancer is the fourth most common type of cancer incidence in the world female population, and it has become a public health problem worldwide. Several factors are involved in this type of cancer, including intrinsic factors related to the inflammatory process, such as extracellular nucleotides and adenosine-components of the purinergic system. The present review focuses on the role of the purinergic system in cervical cancer, especially regarding the interaction of extracellular nucleotides with their respective receptors expressed in the tumor microenvironment of cervical cancer and their role in the host immune response. The high concentrations of extracellular nucleotides in the tumor microenvironment of cervical cancer interfere in the regulation, proliferation, differentiation, and apoptosis of cancer cells of the uterine cervix through different P1 and P2 receptor subtypes. Such diverse cellular processes that are mediated by adenosine triphosphate and adenosine across the tumor microenvironment and that also have effects on host immune defense will be reviewed here in detail.

Dye D, Falasca M, Metharom P. Antiplatelet Drug Ticagrelor Enhances Chemotherapeutic Efficacy by Targeting the Novel P2Y12-AKT Pathway in Pancreatic Cancer Cells

Background: Extensive research has reported that extracellular ADP in the tumour microenvironment can stimulate platelets through interaction with the platelet receptor P2Y12. In turn, activated platelets release biological factors supporting cancer progression. Experimental data suggest that the tumour microenvironment components, of which platelets are integral, can promote chemotherapy resistance in pancreatic ductal adenocarcinoma (PDAC). Thus, overcoming chemoresistance requires combining multiple inhibitors that simultaneously target intrinsic pathways in cancer cells and extrinsic factors related to the tumour microenvironment. We aimed to determine whether ticagrelor, an inhibitor of the ADP–P2Y12 axis and a well-known antiplatelet drug, could be a therapeutic option for PDAC. Methods: We investigated a functional P2Y12 receptor and its downstream signalling in a panel of PDAC cell lines and non-cancer pancreatic cells termed hTERT-HPNE. We tested the synergistic effect of ticagrelor, a P2Y12 inhibitor, in combination with chemotherapeutic drugs (gemcitabine, paclitaxel and cisplatin), in vitro and in vivo. Results: Knockdown studies revealed that P2Y12 contributed to epidermal growth factor receptor (EGFR) activation and the expression of SLUG and ZEB1, which are transcriptional factors implicated in metastasis and chemoresistance. Studies using genetic and pharmacological inhibitors showed that the P2Y12–EGFR crosstalk enhanced cancer cell proliferation. Inhibition of P2Y12 signalling significantly reduced EGF-dependent AKT activation and promoted the anticancer activity of anti-EGFR treatment. Importantly, ticagrelor significantly decreased the proliferative capacity of cancer but not normal pancreatic cells. In vitro, synergism was observed when ticagrelor was combined with several chemodrugs. In vivo, a combination of ticagrelor with gemcitabine significantly reduced tumour growth, whereas gemcitabine or ticagrelor alone had a minimal effect. Conclusions: These findings uncover a novel effect and mechanism of action of the antiplatelet drug ticagrelor in PDAC cells and suggest a multi-functional role for ADP-P2Y12 signalling in the tumour microenvironment.

A high-density genetic linkage map and QTL mapping for growth and sex of yellow drum (Nibea albiflora)

A high-density genetic linkage map is essential for the studies of comparative genomics and gene mapping, and can facilitate assembly of reference genome. Herein, we constructed a high-density genetic linkage map with 8,094 SNPs selected from 113 sequenced fish of a F1 family. Ultimately, the consensus map spanned 3818.24 cM and covered nearly the whole genome (99.4%) with a resolution of 0.47 cM. 1,457 scaffolds spanning 435.15 Mb were anchored onto 24 linkage groups, accounting for 80.7% of the draft genome assembly of the yellow drum. Comparative genomic analyses with medaka and zebrafish genomes showed superb chromosome-scale synteny between yellow drum and medaka. QTL mapping and association analysis congruously revealed 22 QTLs for growth-related traits and 13 QTLs for sex dimorphism. Some important candidate genes such as PLA2G4A, BRINP3 and P2RY1 were identified from these growth-related QTL regions. A gene family including DMRT1, DMRT2 and DMRT3 was identified from these sex-related QTL regions on the linkage group LG9. We demonstrate that this linkage map can facilitate the ongoing marker-assisted selection and genomic and genetic studies for yellow drum.

Increased ATP and ADO Overflow From Sympathetic Nerve Endings and Mesentery Endothelial Cells Plus Reduced Nitric Oxide Are Involved in Diabetic Neurovascular Dysfunction

Since the mechanism of human diabetic peripheral neuropathy and vascular disease in type 1 diabetes mellitus remains unknown, we assessed whether sympathetic transmitter overflow is altered by this disease and associated to vascular dysfunction. Diabetes was induced by streptozotocin (STZ)-treatment and compared to vehicle-treated rats. Aliquots of the ex vivo perfused rat arterial mesenteric preparation, denuded of the endothelial layer, were collected to quantify analytically sympathetic nerve co-transmitters overflow secreted by the isolated mesenteries of both groups of rats. Noradrenaline (NA), neuropeptide tyrosine (NPY), and ATP/metabolites were detected before, during, and after electrical field stimulation (EFS, 20 Hz) of the nerve terminals surrounding the mesenteric artery. NA overflow was comparable in both groups; however, basal or EFS-secreted ir-NPY was 26% reduced (p < 0.05) in diabetics. Basal and EFS-evoked ATP and adenosine (ADO) overflow to the arterial mesentery perfusate increased twofold and was longer lasting in diabetics; purine tissue content was 37.8% increased (p < 0.05) in the mesenteries from STZ-treated group of rats. Perfusion of the arterial mesentery vascular territory with 100 μM ATP, 100 nM 2-MeSADP, or 1 μM UTP elicited vasodilator responses of the same magnitude in controls or diabetics, but the increase in luminally accessible NO was 60-70% lower in diabetics (p < 0.05). Moreover, the concentration-response curve elicited by two NO donors was displaced downwards (p < 0.01) in diabetic rats. Parallel studies using primary cultures of endothelial cells from the arterial mesentery vasculature revealed that mechanical stimulation induced a rise in extracellular nucleotides, which in the cells from diabetic rats was larger and longer-lasting when comparing the extracellular release of ATP and ADO values to those of vehicle-treated controls. A 5 min challenge with purinergic agonists elicited a cell media NO rise, which was reduced in the endothelial cells from diabetic rats. Present findings provide neurochemical support for the diabetes-induced neuropathy and show that mesenteric endothelial cells alterations in response to mechanical stimulation are compatible with the endothelial dysfunction related to vascular disease progress.

Pharmacological dissection of the cellular mechanisms associated to the spontaneous and the mechanically stimulated ATP release by mesentery endothelial cells: roles of thrombin and TRPV

Endothelial cells participate in extracellular ATP release elicited by mechanosensors. To characterize the dynamic interactions between mechanical and chemical factors that modulate ATP secretion by the endothelium, we assessed and compared the mechanisms participating in the spontaneous (basal) and mechanically stimulated secretion using primary cultures of rat mesentery endothelial cells. ATP/metabolites were determined in the cell media prior to (basal) and after cell media displacement or a picospritzer buffer puff used as mechanical stimuli. Mechanical stimulation increased extracellular ATP that peaked within 1 min, and decayed to basal values in 10 min. Interruption of the vesicular transport route consistently blocked the spontaneous ATP secretion. Cells maintained in media lacking external Ca²⁺ elicited a spontaneous rise of extracellular ATP and adenosine, but failed to elicit a further extracellular ATP secretion following mechanical stimulation. 2-APB, a TRPV agonist, increased the spontaneous ATP secretion, but reduced the mechanical stimulation-induced nucleotide release. Pannexin1 or connexin blockers and gadolinium, a Piezo1 blocker, reduced the mechanically induced ATP release without altering spontaneous nucleotide levels. Moreover, thrombin or related agonists increased extracellular ATP secretion elicited by mechanical stimulation, without modifying spontaneous release. In sum, present results allow inferring that the spontaneous, extracellular nucleotide secretion is essentially mediated by ATP containing vesicles, while the mechanically induced secretion occurs essentially by connexin or pannexin1 hemichannel ATP transport, a finding fully supported by results from Panx1^-/- rodents. Only the latter component is modulated by thrombin and related receptor agonists, highlighting a novel endothelium-smooth muscle signaling role of this anticoagulant.

Galectin-8 induces partial epithelial-mesenchymal transition with invasive tumorigenic capabilities involving a FAK/EGFR/proteasome pathway in Madin-Darby canine kidney cells

Epithelial cells can acquire invasive and tumorigenic capabilities through epithelial–mesenchymal-transition (EMT). The glycan-binding protein galectin-8 (Gal-8) activates selective β1-integrins involved in EMT and is overexpressed by certain carcinomas. Here we show that Gal-8 overexpression or exogenous addition promotes proliferation, migration, and invasion in nontumoral Madin–Darby canine kidney (MDCK) cells, involving focal-adhesion kinase (FAK)-mediated transactivation of the epidermal growth factor receptor (EGFR), likely triggered by α5β1integrin binding. Under subconfluent conditions, Gal-8–overexpressing MDCK cells (MDCK-Gal-8^H) display hallmarks of EMT, including decreased E-cadherin and up-regulated expression of vimentin, fibronectin, and Snail, as well as increased β-catenin activity. Changes related to migration/invasion included higher expression of α5β1 integrin, extracellular matrix-degrading MMP13 and urokinase plasminogen activator/urokinase plasminogen activator receptor (uPA/uPAR) protease systems. Gal-8–stimulated FAK/EGFR pathway leads to proteasome overactivity characteristic of cancer cells. Yet MDCK-Gal-8^H cells still develop apical/basolateral polarity reverting EMT markers and proteasome activity under confluence. This is due to the opposite segregation of Gal-8 secretion (apical) and β1-integrins distribution (basolateral). Strikingly, MDCK-Gal-8^H cells acquired tumorigenic potential, as reflected in anchorage-independent growth in soft agar and tumor generation in immunodeficient NSG mice. Therefore, Gal-8 can promote oncogenic-like transformation of epithelial cells through partial and reversible EMT, accompanied by higher proliferation, migration/invasion, and tumorigenic properties.

Extracellular ATP protects pancreatic duct epithelial cells from alcohol-induced damage through P2Y1 receptor-cAMP signal pathway

Extracellular adenosine-5'-triphosphate (ATP) regulates cell death and survival of neighboring cells. The detailed effects are diverse depending on cell types and extracellular ATP concentration. We addressed the effect of ATP on ethanol-induced cytotoxicity in epithelial cells, the cell type that experiences the highest concentrations of alcohol. Using pancreatic duct epithelial cells (PDEC), we found that a micromolar range of ATP reverses all intracellular toxicity mechanisms triggered by exceptionally high doses of ethanol and, thus, improves cell viability dramatically. Out of the many purinergic receptors expressed in PDEC, the P2Y1 receptor was identified to mediate the protective effect, based on pharmacological and siRNA assays. Activation of P2Y1 receptors increased intracellular cyclic adenosine monophosphate (cAMP). The protective effect of ATP was mimicked by forskolin and 8-Br-cAMP but inhibited by a protein kinase A (PKA) inhibitor, H-89. Finally, ATP reverted leakiness of PDEC monolayers induced by ethanol and helped to maintain epithelial integrity. We suggest that purinergic receptors reduce extreme alcohol-induced cell damage via the cAMP signal pathway in PDEC and some other types of cells.

H89 enhances the sensitivity of cancer cells to glyceryl trinitrate through a purinergic receptor-dependent pathway

High doses of the organic nitrate glyceryl trinitrate (GTN), a nitric oxide (NO) donor, are known to trigger apoptosis in human cancer cells. Here, we show that such a cytotoxic effect can be obtained with subtoxic concentrations of GTN when combined with H89, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulphonamide.2HCl. This synergistic effect requires the generation of reactive oxygen species (ROS) from H89 and NO from GTN treatment that causes cGMP production and PKG activation. Furthermore, the GTN/H89 synergy was attenuated by inhibition of P2-purinergic receptors with suramin and competition with ATP/UDP. By down-regulating genes with antisense oligonucleotides, P2-purinergic receptors P2X3, P2Y1, and P2Y6 were found to have a role in creating this cytotoxic effect. Thus, H89 likely acts as an ATP mimetic synergizing with GTN to trigger apoptosis in aggressive cancer cells.

Contribution of extracellular ATP on the cell-surface F1F0-ATP synthase-mediated intracellular triacylglycerol accumulation

Cell-surface F1F0-ATP synthase was involved in the cell signaling mediating various biological functions. Recently, we found that cell-surface F1F0-ATP synthase plays a role on intracellular triacylglycerol accumulation in adipocytes, and yet, the underlying mechanisms remained largely unknown. In this study, we investigated the role of extracellular ATP on the intracellular triacylglycerol accumulation. We demonstrated that significant amounts of ATP were produced extracellularly by cultured 3T3-L1 adipocytes and that the antibodies against α and β subunits of F1F0-ATP synthase inhibited the extracellular ATP production. Piceatannol, a F1F0-ATP synthase inhibitor, and apyrase, an enzyme which degrades extracellular ATP, suppressed triacylglycerol accumulation. The selective P2Y1 receptor antagonist MRS2500 significantly inhibited triacylglycerol accumulation, whereas the selective P2X receptor antagonist NF279 has less effect. The present results indicate that cell-surface F1F0-ATP synthase on adipocytes is functional in extracellular ATP production and that the extracellular ATP produced contributes, at least in part, to the cell-surface F1F0-ATP synthase-mediated intracellular triacylglycerol accumulation in adipocytes through P2Y1 receptor.

Extracellular ATP and other nucleotides-ubiquitous triggers of intercellular messenger release

Extracellular nucleotides, and ATP in particular, are cellular signal substances involved in the control of numerous (patho)physiological mechanisms. They provoke nucleotide receptor-mediated mechanisms in select target cells. But nucleotides can considerably expand their range of action. They function as primary messengers in intercellular communication by stimulating the release of other extracellular messenger substances. These in turn activate additional cellular mechanisms through their own receptors. While this applies also to other extracellular messengers, its omnipresence in the vertebrate organism is an outstanding feature of nucleotide signaling. Intercellular messenger substances released by nucleotides include neurotransmitters, hormones, growth factors, a considerable variety of other proteins including enzymes, numerous cytokines, lipid mediators, nitric oxide, and reactive oxygen species. Moreover, nucleotides activate or co-activate growth factor receptors. In the case of hormone release, the initially paracrine or autocrine nucleotide-mediated signal spreads through to the entire organism. The examples highlighted in this commentary suggest that acting as ubiquitous triggers of intercellular messenger release is one of the major functional roles of extracellular nucleotides. While initiation of messenger release by nucleotides has been unraveled in many contexts, it may have been overlooked in others. It can be anticipated that additional nucleotide-driven messenger functions will be uncovered with relevance for both understanding physiology and development of therapy.

ATP and related purines stimulate motility, spatial congregation, and coalescence in red algal spores

Adenosine 5'-triphosphate (ATP) is a versatile extracellular signal along the tree of life, whereas cAMP plays a major role in vertebrates as an intracellular messenger for hormones, transmitters, tastants, and odorants. Since red algal spore coalescence may be considered analogous to the congregation process of social amoeba, which is stimulated by cAMP, we ascertained whether exogenous applications of ATP, cAMP, adenine, or adenosine modified spore survival and motility, spore settlement and coalescence. Concentration-response studies were performed with carpospores of Mazzaella laminarioides (Gigartinales), incubated with and without added purines. Stirring of algal blades released ADP/ATP to the cell media in a time-dependent manner. 10-300 μM ATP significantly increased spore survival; however, 1,500 μM ATP, cAMP or adenine induced 100% mortality within less than 24 h; the exception was adenosine, which up to 3,000 μM, did not alter spore survival. ATP exposure elicited spore movement with speeds of 2.2-2.5 μm · s(-1) . 14 d after 1,000 μM ATP addition, spore abundance in the central zone of the plaques was increased 2.7-fold as compared with parallel controls. Likewise, 1-10 μM cAMP or 30-100 μM adenine also increased central zone spore abundance, albeit these purines were less efficacious than ATP; adenosine up to 3,000 μM did not influence settlement. Moreover, 1,000 μM ATP markedly accelerated coalescence, the other purines caused a variable effect. We conclude that exogenous cAMP, adenine, but particularly ATP, markedly influence red algal spore physiology; effects are compatible with the expression of one or more membrane purinoceptor(s), discarding adenosine receptor participation.

A functional landscape of resistance to ALK inhibition in lung cancer

We conducted a large-scale functional genetic study to characterize mechanisms of resistance to ALK inhibition in ALK-dependent lung cancer cells. We identify members of known resistance pathways and additional putative resistance drivers. Among the latter were members of the P2Y purinergic receptor family of G-protein-coupled receptors (P2Y1, P2Y2, and P2Y6). P2Y receptors mediated resistance in part through a protein-kinase-C (PKC)-dependent mechanism. Moreover, PKC activation alone was sufficient to confer resistance to ALK inhibitors, whereas combined ALK and PKC inhibition restored sensitivity. We observed enrichment of gene signatures associated with several resistance drivers (including P2Y receptors) in crizotinib-resistant ALK-rearranged lung tumors compared to treatment-naive controls, supporting a role for these identified mechanisms in clinical ALK inhibitor resistance.

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.

Epidermal growth factor receptor endocytic traffic perturbation by phosphatidate phosphohydrolase inhibition: new strategy against cancer

Epidermal growth factor receptor (EGFR) exaggerated (oncogenic) function is currently targeted in cancer treatment with drugs that block receptor ligand binding or tyrosine kinase activity. Because endocytic trafficking is a crucial regulator of EGFR function, its pharmacological perturbation might provide a new anti-tumoral strategy. Inhibition of phosphatidic acid (PA) phosphohydrolase (PAP) activity has been shown to trigger PA signaling towards type 4 phosphodiesterase (PDE4) activation and protein kinase A inhibition, leading to internalization of empty/inactive EGFR. Here, we used propranolol, its l- and d- isomers and desipramine as PAP inhibitors to further explore the effects of PAP inhibition on EGFR endocytic trafficking and its consequences on EGFR-dependent cancer cell line models. PAP inhibition not only made EGFR inaccessible to stimuli but also prolonged the signaling lifetime of ligand-activated EGFR in recycling endosomes. Strikingly, such endocytic perturbations applied in acute/intermittent PAP inhibitor treatments selectively impaired cell proliferation/viability sustained by an exaggerated EGFR function. Phospholipase D inhibition with FIPI (5-fluoro-2-indolyl des-chlorohalopemide) and PDE4 inhibition with rolipram abrogated both the anti-tumoral and endocytic effects of PAP inhibition. Prolonged treatments with a low concentration of PAP inhibitors, although without detectable endocytic effects, still counteracted cell proliferation, induced apoptosis and decreased anchorage-independent growth of cells bearing EGFR oncogenic influences. Overall, our results show that PAP inhibitors can counteract EGFR oncogenic traits, including receptor overexpression or activating mutations resistant to current tyrosine kinase inhibitors, perturbing EGFR endocytic trafficking and perhaps other as yet unknown processes, depending on treatment conditions. This puts PAP activity forward as a new suitable target against EGFR-driven malignancy.

Central role for hydrogen peroxide in P2Y1 ADP receptor-mediated cellular responses in vascular endothelium

ADP activates a family of cell surface receptors that modulate signaling pathways in a broad range of cells. ADP receptor antagonists are widely used to treat cardiovascular disease states. These studies identify a critical role for the stable reactive oxygen species hydrogen peroxide (H2O2) in mediating cellular responses activated by the G protein-coupled P2Y1 receptor for ADP. We found that ADP-dependent phosphorylation of key endothelial signaling proteins--including endothelial nitric oxide synthase, AMP-activated protein kinase, and the actin-binding MARCKS protein--was blocked by preincubation with PEG-catalase, which degrades H2O2. ADP treatment promoted the H2O2-dependent phosphorylation of c-Abl, a nonreceptor tyrosine kinase that modulates the actin cytoskeleton. Cellular imaging experiments using fluorescence resonance energy transfer-based biosensors revealed that ADP-stimulated activation of the cytoskeleton-associated small GTPase Rac1 was independent of H2O2. However, Rac1-dependent activation of AMP-activated protein kinase, the signaling phospholipid phosphatidylinositol-(4, 5)-bisphosphate, and the c-Abl-interacting protein CrkII are mediated by H2O2. We transfected endothelial cells with differentially targeted HyPer2 H2O2 biosensors and found that ADP promoted a marked increase in H2O2 levels in the cytosol and caveolae, and a smaller increase in mitochondria. We performed a screen for P2Y1 receptor-mediated receptor tyrosine kinase transactivation and discovered that ADP transactivates Fms-like tyrosine kinase 3 (Flt3), a receptor tyrosine kinase expressed in these cells. Our observation that P2Y1 receptor-mediated responses involve Flt3 transactivation may identify a unique mechanism whereby cancer chemotherapy with receptor tyrosine kinase inhibitors promotes vascular dysfunction. Taken together, these findings establish a critical role for endogenous H2O2 in control of ADP-mediated signaling responses in the vascular wall.

Sonic Hedgehog modulates EGFR dependent proliferation of neural stem cells during late mouse embryogenesis through EGFR transactivation

Sonic Hedgehog (Shh/GLI) and EGFR signaling pathways modulate Neural Stem Cell (NSC) proliferation. How these signals cooperate is therefore critical for understanding normal brain development and function. Here we report a novel acute effect of Shh signaling on EGFR function. We show that during late neocortex development, Shh mediates the activation of the ERK1/2 signaling pathway in Radial Glial cells (RGC) through EGFR transactivation. This process is dependent on metalloprotease activity and accounts for almost 50% of the EGFR-dependent mitogenic response of late NSCs. Furthermore, in HeLa cancer cells, a well-known model for studying the EGFR receptor function, Shh also induces cell proliferation involving EGFR activation, as reflected by EGFR internalization and ERK1/2 phosphorylation. These findings may have important implications for understanding the mechanisms that regulate NSC proliferation during neurogenesis and may lead to novel approaches to the treatment of tumors.

Transactivation of EGFR/PI3K/Akt involved in ATP-induced inflammatory protein expression and cell motility

Phenotype transition of vascular smooth muscle cells (VSMCs) is important in vascular diseases, such as atherosclerosis and restenosis. Once released, ATP may promote activation of VSMCs by stimulating cyclooxygenase-2 (COX-2), cytosolic phospholipase A(2) (cPLA(2)) expression and prostaglandin (PG)E(2) synthesis via activation of MAPKs and NF-κB. However, whether alternative signaling pathways participated in regulating COX-2 and cPLA(2) expression associated with cell migration were investigated in rat VSMCs. Western blot analysis, RT-PCR, promoter assay and PGE(2) ELISA were used to determine expression of COX-2, cPLA(2) and PGE(2). Specific inhibitors and siRNAs against various protein kinases or transcription factors were used to investigate the related signaling components in inflammatory protein induction by ATPγS. We found that ATPγS-induced COX-2 and cPLA(2) expression and PGE(2) release was attenuated by the pharmacological inhibitors or transfection with siRNA against PKCδ, c-Src, EGFR, PI3-K, Akt, p44/p42 MAPK or Elk-1. Moreover, ATPγS-stimulated phosphorylation of PKCδ, c-Src, EGFR, Akt, p42/p44 MAPK and Elk-1, suggesting the participation of PKCδ/c-Src/EGFR/PI3-K/Akt/p42/p44 MAPK cascade in mediating Elk-1 activities in VSMCs. In addition, migration assay revealed that ATPγS promoted cell mobility through up-regulation of COX-2 and cPLA(2) expression and PGE(2) release, which was attenuated by pretreatment with PGE(2) receptor antagonists. Taken together, these data showed that ATPγS up-regulated the expression of COX-2 and cPLA(2) through transactivation of PKCδ/c-Src/EGFR/PI3K/Akt/Elk-1 pathway. Newly synthesized PGE(2) acted on its receptors to promote cell motility of ATPγS-stimulated VSMCs.

Reciprocal sympatho-sensory control: functional role of nucleotides and calcitonin gene-related peptide in a peripheral neuroeffector junction

The rat vas deferens has scattered sensory afferens plus a dense network of sympathetic motor efferens; these fibers are not known to interact functionally. We ascertained whether sensory fibers modulate the release of sympathetic transmitters through the release of calcitonin gene-related peptide (CGRP) and reciprocally assessed whether sympathetic transmitters modulate the overflow of ir-CGRP from sensory fibers. The tissue overflow of electrically evoked sympathetic co-transmitters (ATP/metabolites, noradrenaline (NA), and immunoreactive neuropeptide tyrosine (ir-NPY)) and the motor responses elicited were quantified following either exogenous CGRP or capsaicin application to elicit peptide release. Conversely, the outflow of ir-CGRP was examined in the presence of sympathetic transmitters. Exogenous CGRP reduced in a concentration-dependent manner the electrically evoked outflow of ATP/metabolites, NA, and ir-NPY with EC(50) values of 1.3, 0.18, and 1.9 nM, respectively. CGRP also reduced the basal NA overflow. The CGRP-evoked modulation was blocked by CGRP8-37 or H-89. Release of endogenous CGRP by capsaicin significantly reduced the basal overflow of NA, ir-NPY, and the electrically evoked sympathetic transmitter release. ADP, 2-methylthioadenosine-5'-O-diphosphate (2-MeSADP), or UTP decreased the electrically evoked ir-CGRP overflow, whereas clonidine, α,β-methyleneadenosine 5'-triphosphate (α,β-mATP), or adenosine (ADO) were inactive. CGRP acting postjunctionally also reduced the motor responses elicited by exogenous NA, ATP, or electrically evoked contractions. We conclude that CGRP exerts a presynaptic modulator role on sympathetic nerve endings and reciprocally ATP or related nucleotides influence the release of ir-CGRP from sensory fibers, highlighting a dynamic sympatho-sensory control between sensory fibers and sympathetic nerve ending. Postjunctional CGRP receptors further contribute to reduce the tissue sympathetic motor tone implying a pre and postjunctional role of CGRP as a sympathetic tone modulator.

Functional relevance of biased signaling at the angiotensin II type 1 receptor

Angiotensin II type 1 receptor antagonists (AT1R blockers, or ARBs) are used commonly in the treatment of cardiovascular disorders such as heart failure and hypertension. Their clinical success arises from their ability to prevent deleterious Gα(q) protein activation downstream of AT1R, which leads to a decrease in morbidity and mortality. Recent studies have identified AT1R ligands that concurrently inhibit Gα(q) protein-dependent signaling and activate Gα(q) protein-independent/β-arrestin-dependent signaling downstream of AT1R, events that may actually improve cardiovascular performance more than conventional ARBs. The ability of such ligands to induce intracellular signaling events in an AT1R-β-arrestin-dependent manner while preventing AT1R-Gα(q) protein activity defines them as biased AT1R ligands. This mini-review will highlight recent studies that have defined biased signaling at the AT1R and discuss the possible clinical relevance of β-arrestin-biased AT1R ligands in the cardiovascular system.

Interaction of purinergic receptors with GPCRs, ion channels, tyrosine kinase and steroid hormone receptors orchestrates cell function

Extracellular purines and pyrimidines have emerged as key regulators of a wide range of physiological and pathophysiological cellular processes acting through P1 and P2 cell surface receptors. Increasing evidence suggests that purinergic receptors can interact with and/or modulate the activity of other classes of receptors and ion channels. This review will focus on the interactions of purinergic receptors with other GPCRs, ion channels, receptor tyrosine kinases, and steroid hormone receptors. Also, the signal transduction pathways regulated by these complexes and their new functional properties are discussed.

Involvement of P2X receptors in the regulation of insulin secretion, proliferation and survival in mouse pancreatic β-cells

In order to clarify the functional role of ionotropic purinergic (P2X) receptors in pancreatic β-cells, we examined the effect of several P2 receptor agonists and antagonists on insulin secretion by mouse pancreatic islets, mouse Beta-TC6 cell proliferation and survival of dispersed islet cells in culture. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed the expression of mRNAs of P2X(4) receptor in mouse islets and P2X(1), P2X(2), P2X(3), P2X(4), P2X(5) and P2X(7) receptors in Beta-TC6 cells. The presence of P2X(4) receptor proteins in islets and Beta-TC6 cells was confirmed by immunofluorescent staining and Western blot analysis. We have previously found that the functional P2Y(1) receptor but not P2Y(2) and P2Y(4) receptors was present in islets. In this study we found that a nonspecific P2 receptor agonist, ATP (1 μM) stimulated insulin secretion by islets in the presence of high glucose (20 mM) in culture. The effect of ATP was partially inhibited by a P2 receptor antagonist PPADS as well as a P2Y(1) receptor antagonist MRS2179. In addition, a P2X(4) receptor potentiator ivermectin per se augmented glucose-induced insulin secretion and slightly potentiated the effect of ATP. These results suggested the involvement of P2Y(1)and P2X receptors. We also found that ATP inhibited proliferation of Beta-TC6 cells in a concentration-dependent manner during 72 h culture. The inhibitory effect of ATP was completely reversed by PPADS and partially by treating cells with small interfering RNA targeted for P2X(4) receptor mRNA. Furthermore, we found that the phosphorylation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) was suppressed by treatment with ATP in Beta-TC6 cells. In addition, we found that ATP reduced the cell viability and DNA synthesis of islet cells in culture. The effect of ATP on the cell viability was blocked by PPADS or MRS2179. These results suggested that P2X receptors as well as the P2Y(1) receptor played a role in the modulation of insulin secretion, proliferation and cell viability in mouse pancreatic β-cells.

Phosphatidic acid induces ligand-independent epidermal growth factor receptor endocytic traffic through PDE4 activation

Endocytic traffic can control cell surface versus intracellular distribution of empty/inactive EGFR, an thus its accessibility to external stimuli, through a pathway involving down regulation of PKA activity mediated by PA signaling towards PDE4. This novel control mechanism can trans-modulate EGFR function by heterologous stimuli of PLD.

Endocytosis modulates EGFR function by compartmentalizing and attenuating or enhancing its ligand-induced signaling. Here we show that it can also control the cell surface versus intracellular distribution of empty/inactive EGFR. Our previous observation that PKA inhibitors induce EGFR internalization prompted us to test phosphatidic acid (PA) generated by phospholipase D (PLD) as an endogenous down-regulator of PKA activity, which activates rolipram-sensitive type 4 phosphodiesterases (PDE4) that degrade cAMP. We found that inhibition of PA hydrolysis by propranolol, in the absence of ligand, provokes internalization of inactive (neither tyrosine-phosphorylated nor ubiquitinated) EGFR, accompanied by a transient increase in PA levels and PDE4s activity. This EGFR internalization is mimicked by PA micelles and is strongly counteracted by PLD2 silencing, rolipram or forskolin treatment, and PKA overexpression. Accelerated EGFR endocytosis seems to be mediated by clathrin-dependent and -independent pathways, leading to receptor accumulation in juxtanuclear recycling endosomes, also due to a decreased recycling. Internalized EGFR can remain intracellular without degradation for several hours or return rapidly to the cell surface upon discontinuation of the stimulus. This novel regulatory mechanism of EGFR, also novel function of signaling PA, can transmodulate receptor accessibility in response to heterologous stimuli.

Nucleotides and epidermal growth factor induce parallel cytoskeletal rearrangements and migration in cultured adult murine neural stem cells

AIM

The adult subventricular zone (SVZ) contains neural stem cells that generate neuroblasts migrating to the olfactory bulb (OB) and differentiating into interneurones. The molecular cues controlling essential functions within the neurogenesis pathway such as proliferation, short and long distance migration, functional integration and cell survival are poorly understood. We have previously shown that cultured adult neural stem cells express a considerable variety of nucleotide receptors and that nucleotides and epidermal growth factor (EGF) induce converging intracellular signalling pathways that carry potential for synergism in the control of neural stem cell proliferation and cell survival. Here we investigate the role of EGF and the nucleotides ATP, ADPbetaS and UTP in neural stem cell migration.

METHODS

Neural stem cells were prepared from adult mice and subjected to adherent culture. Labelling of F-actin was performed with tetramethylrhodamine isothiocyanate-phalloidin. Images were processed for quantitative evaluation of fluorescence labelling. Agonist-induced phosphorylation of AKT and focal adhesion kinase was analysed by quantitative Western blotting. Agonist-dependent cell migration was assayed using 48-well microchemotaxis chambers.

RESULTS

Nucleotides and EGF induce the formation of stress fibres, an increase in the cortical actin cytoskeleton and in cell spreading. This is associated with increased phosphorylation of AKT and focal adhesion kinase. Using microchemotaxis chambers we demonstrate a parallel increase in cell migration.

CONCLUSION

Our results suggest that nucleotides and EGF acting as paracrine or autocrine signalling substances can be of relevance for structuring and maintaining the cytoarchitecture of the SVZ and the stream of neuroblasts migrating to the OB.

Purinergic mechanisms in breast cancer support intravasation, extravasation and angiogenesis

Several advances have recently expanded models of tumor growth and promoted the concept of tumor homeostasis, the hypothesis that primary tumors exert an anti-proliferative effect on both themselves and subclinical secondary metastases. Recent trials indicate that the characterization of tumor growth as uncontrolled is inconsistent with animal models, clinical models, and epidemiological models. There is a growing body of evidence which lends support to an updated concept of tumor growth: tumor homeostasis. In the case of breast cancer, if not all metastasizing tumors, these advances suggest an inconvenient truth. That is, if breast tumor cells metastasize to distant sites early in the tumorigenesis process, then removal of a breast tumor may hasten the development of its metastases. We explore the heretofore unappreciated notion that nucleotides generated by tumor cells following the secretion of an ADP-kinase can promote metastasis and support angiogenesis. Evidence is presented that blockade of the actions of nucleotides in the setting of newly diagnosed breast cancer may provide a useful adjunct to current anti-angiogenesis treatment.

Low-intensity pulsed ultrasound-dependent osteoblast proliferation occurs by via activation of the P2Y receptor: role of the P2Y1 receptor

Low-intensity pulsed ultrasound (LIPUS) is commonly used in the treatment of fractures and nonunion-promoting acceleration of healing fractures. In this report, we investigated the implication of the P2 receptors in osteoblast proliferation induced with LIPUS treatment. We observed that ADP, ATP, UTP, and UDP promote osteoblast increase and an increase of intracellular Ca(2+), through activation of P2Y receptors. Osteoblasts' expression of the P2Y(1), P2Y(2), P2Y(4), P2Y(6), P2Y(11), P2Y(12), and P2Y(13) receptors was confirmed. In addition, the participation of the P2Y(1) receptor in osteoblast increase and the ADP-dependent increase of Ca(2+) concentration were shown. Furthermore, release of ATP/purines was induced by LIPUS treatment. Finally, LIPUS-dependent osteoblast increase was abolished in the presence of the Ca(2+) chelator (BAPTA), the inositol 1,4,5-trisphosphate receptor antagonist (2-APB), and the selective P2Y(1) receptor antagonist (MRS2179). In conclusion, LIPUS treatment induces osteoblastogenesis via the release of purines, such as ATP, activating P2Y receptors, mainly the P2Y(1) receptor.

UTP controls cell surface distribution and vasomotor activity of the human P2Y2 receptor through an epidermal growth factor receptor-transregulated mechanism

Extracellular nucleotides transmit signals into the cells through the P2 family of cell surface receptors. These receptors are amply expressed in human blood vessels and participate in vascular tone control; however, their signaling mechanisms remain unknown. Here we show that in smooth muscle cells of isolated human chorionic arteries, the activation of the P2Y(2) receptor (P2Y(2)R) induces not only its partition into membrane rafts but also its rapid internalization. Cholesterol depletion with methyl-beta-cyclodextrin reduced the association of the agonist-activated receptor into membrane rafts but did not affect either the UTP-mediated vasoconstrictions or the vasomotor responses elicited by both serotonin and KCl. Ex vivo perfusion of human chorionic artery segments with 1-10 mum UTP, a selective P2Y(2)R agonist, displaced the P2Y(2)R localization into membrane rafts within 1 min, a process preceded by the activation of both RhoA and Rac1 GTPases. AG1478, a selective and potent inhibitor of the epidermal growth factor receptor tyrosine kinase activity, not only blocked the UTP-induced vasomotor activity but also abrogated both RhoA and Rac1 activation, the P2Y(2)R association with membrane rafts, and its internalization. Altogether, these results show for the first time that the plasma membrane distribution of the P2Y(2)R is transregulated by the epidermal growth factor receptor, revealing an unsuspected functional interplay that controls both the membrane distribution and the vasomotor activity of the P2Y(2)R in intact human blood vessels.

Desensitization of endothelial P2Y1 receptors by PKC-dependent mechanisms in pressurized rat small mesenteric arteries

BACKGROUND AND PURPOSE

Extracellular nucleotides play a crucial role in the regulation of vascular tone and blood flow. Stimulation of endothelial cell P2Y1 receptors evokes concentration-dependent full dilatation of resistance arteries. However, this GPCR can desensitize upon prolonged exposure to the agonist. Our aim was to determine the extent and nature of P2Y1 desensitization in isolated and pressurized rat small mesenteric arteries.

EXPERIMENTAL APPROACH

The non-hydrolyzable selective P2Y1 agonist ADPbetaS (3 microM) was perfused through the lumen of arteries pressurized to 70 mmHg. Changes in arterial diameter and endothelial cell [Ca(2+)](i) were obtained in the presence and absence of inhibitors of protein kinase C (PKC).

KEY RESULTS

ADPbetaS evoked rapid dilatation to the maximum arterial diameter but faded over time to a much-reduced plateau closer to 35% dilatation. This appeared to be due to desensitization of the P2Y1 receptor, as subsequent endothelium-dependent dilatation to acetylcholine (1 microM) remained unaffected. Luminal treatment with the PKC inhibitors BIS-I (1 microM) or BIS-VIII (1 microM) tended to augment concentration-dependent dilatation to ADPbetaS (0.1-3 microM) and prevented desensitization. Another PKC inhibitor, Gö 6976 (1 microM), was less effective in preventing desensitization. Measurements of endothelial cell [Ca(2+)](i) in pressurized arteries confirmed the P2Y1 receptor but not M(3) muscarinic receptor desensitization.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate for the first time the involvement of PKC in the desensitization of endothelial P2Y1 receptors in pressurized rat mesenteric arteries, which may have important implications in the control of blood flow by circulating nucleotides.

Coordinate pathways for nucleotide and EGF signaling in cultured adult neural progenitor cells

The adult subventricular zone (SVZ) contains astrocyte-like stem cells capable of generating new neurons for the olfactory bulb. Adult neurogenesis is driven by a variety of signal systems that can induce synergistic or opposing cellular responses. It is therefore important to gain insight into the underlying downstream signaling pathways. We have previously shown that the nucleotides ADPbetaS and UTP induce rapid Ca2+ transients in cultured SVZ-derived adult neural progenitors and augment growth-factor-mediated progenitor cell proliferation. Here, we investigated signaling pathways elicited by ADPbetaS, UTP and epidermal growth factor (EGF). All three agonists elicit ERK1/2 and CREB phosphorylation but the temporal characteristics differ between the nucleotides and EGF. Differentiation of the progenitors alters the receptor profile. Oligodendrocytes and young neurons, but not astrocytes, lose responsiveness to the agonists. Inhibition experiments are indicative of an ADPbetaS-elicited EGF receptor transactivation. Whereas UTP acts via the P2Y2 receptor, ADPbetaS exerts its function via the P2Y1 receptor and the P2Y13 receptor. Our data demonstrate that nucleotides and EGF induce converging, but also differential, intracellular signaling pathways and suggest that they carry the potential to act synergistically in the control of cell proliferation and cell survival in adult neurogenesis.

beta-Arrestin mediates beta1-adrenergic receptor-epidermal growth factor receptor interaction and downstream signaling

beta1-Adrenergic receptor (beta1AR) stimulation confers cardioprotection via beta-arrestin-de pend ent transactivation of epidermal growth factor receptors (EGFRs), however, the precise mechanism for this salutary process is unknown. We tested the hypothesis that the beta1AR and EGFR form a complex that differentially directs intracellular signaling pathways. beta1AR stimulation and EGF ligand can each induce equivalent EGFR phosphorylation, internalization, and downstream activation of ERK1/2, but only EGF ligand causes translocation of activated ERK to the nucleus, whereas beta1AR-stimulated/EGFR-transactivated ERK is restricted to the cytoplasm. beta1AR and EGFR are shown to interact as a receptor complex both in cell culture and endogenously in human heart, an interaction that is selective and undergoes dynamic regulation by ligand stimulation. Although catecholamine stimulation mediates the retention of beta1AR-EGFR interaction throughout receptor internalization, direct EGF ligand stimulation initiates the internalization of EGFR alone. Continued interaction of beta1AR with EGFR following activation is dependent upon C-terminal tail GRK phosphorylation sites of the beta1AR and recruitment of beta-arrestin. These data reveal a new signaling paradigm in which beta-arrestin is required for the maintenance of a beta1AR-EGFR interaction that can direct cytosolic targeting of ERK in response to catecholamine stimulation.

ATP-mediated activation of the NADPH oxidase DUOX1 mediates airway epithelial responses to bacterial stimuli

Activation of the NADPH oxidase homolog dual oxidase 1 (DUOX1) within the airway epithelium represents a key mechanism of innate airway host defense, through enhanced production of H2O2, which mediates cellular signaling pathways that regulate the production of various inflammatory mediators. Production of the CXC chemokine interleukin (IL)-8/CXCL8 forms a common epithelial response to many diverse stimuli, including bacterial and viral triggers, environmental oxidants, and other biological mediators, suggesting the potential involvement of a common signaling pathway that may involve DUOX1-dependent H2O2 production. Following previous reports showing that DUOX1 is activated by extracellular ATP and purinergic receptor stimulation, this study demonstrates that airway epithelial IL-8 production in response to several bacterial stimuli involves ATP release and DUOX1 activation. ATP-mediated DUOX1 activation resulted in the activation of ERK1/2 and NF-kappaB pathways, which was associated with epidermal growth factor receptor (EGFR) ligand shedding by ADAM17 (a disintegrin and metalloproteinase-17). Although ATP-mediated ADAM17 activation and IL-8 release were not prevented by extracellular H2O2 scavenging by catalase, these responses were attenuated by intracellular scavengers of H2O2 or related oxidants, suggesting an intracellular redox signaling mechanism. Both ADAM17 activation and IL-8 release were suppressed by inhibitors of EGFR/ERK1/2 signaling, which can regulate ADAM17 activity by serine/threonine phosphorylation. Collectively, our results indicate that ATP-mediated DUOX1 activation represents a common response mechanism to several environmental stimuli, involving H2O2-dependent EGFR/ERK activation, ADAM17 activation, and EGFR ligand shedding, leading to amplified epithelial EGFR activation and IL-8 production.

BM88/Cend1 regulates stimuli-induced intracellular calcium mobilization

In neurogenesis, little is known about signal transduction pathways upstream of gene expression however, mounting evidence suggests that calcium release from internal stores plays a critical role. We have previously demonstrated that BM88 is a neuronal lineage-specific regulator of cell cycle exit and differentiation; we now report a link between BM88 and calcium signaling. Calcium imaging experiments revealed that P2Y-induced calcium mobilization is diminished in mouse neuroblastoma Neuro 2a cells stably transfected with BM88 (N2A-BM88 cells) as compared with N2A cells or N2A cells differentiated with retinoic acid. This effect is not restricted to N2A cells but is also observed in HeLa cells that are transiently transfected with BM88, indicating that cells of both neural and non-neural origin respond similarly. Further, activation of P2Y1 but not purinergic P2X receptors induces proliferation of N2A and to a lesser extent of N2A-BM88 cells. Conversely, knockdown of BM88 facilitates N2A cell proliferation both under stimulating and non-stimulating conditions. Importantly, N2A-BM88 cells are less susceptible to apoptosis triggered by C2-ceramide and exhibit reduced C2-ceramide-induced intracellular calcium release. Higher calcium uptake from mitochondria and/or lower calcium levels inside the endoplasmic reticulum may explain the reduced calcium mobilization in response to BM88. Overall, our data reveal a novel signaling mechanism by which BM88 interferes with calcium release from inositol 1,4,5-trisphosphate-sensitive stores and exerts anti-proliferative and anti-apoptotic functions.

P2Y1 receptor activation elicits its partition out of membrane rafts and its rapid internalization from human blood vessels: implications for receptor signaling

The nucleotide P2Y(1) receptor (P2Y(1)R) is expressed in both the endothelial and vascular smooth muscle cells; however, its plasma membrane microregionalization and internalization in human tissues remain unknown. We report on the role of membrane rafts in P2Y(1)R signaling by using sodium carbonate or OptiPrep sucrose density gradients, Western blot analysis, reduction of tissue cholesterol content, and vasomotor assays of endothelium-denuded human chorionic arteries. In tissue extracts prepared either in sodium carbonate or OptiPrep, approximately 20 to 30% of the total P2Y(1)R mass consistently partitioned into raft fractions and correlated with vasomotor activity. Vessel treatment with methyl beta-cyclodextrin reduced the raft partitioning of the P2Y(1)R and obliterated the P2Y(1)R-mediated contractions but not the vasomotor responses elicited by either serotonin or KCl. Perfusion of chorionic artery segments with 100 nM 2-methylthio ADP or 10 nM [[(1R,2R,3S,4R,5S)-4-[6-amino-2-(methylthio)-9H-purin-9-yl] 2,3dihydroxybicyclo[3.1.0]hex-1-yl]methyl] diphosphoric acid mono ester trisodium salt (MRS 2365), a selective P2Y(1)R agonist, not only displaced within 4 min the P2Y(1)R localization out of membrane rafts but also induced its subsequent internalization. 2'-Deoxy-N(6)-methyladenosine 3',5'-bisphosphate tetrasodium salt (MRS 2179), a specific P2Y(1)R antagonist, did not cause a similar displacement but blocked the agonist-induced exit from rafts. Neither adenosine nor uridine triphosphate displaced the P2Y(1)R from the membrane raft, further evidencing the pharmacodynamics of the receptor-ligand interaction. Vascular reactivity assays showed fading of the ligand-induced vasoconstrictions, a finding that correlated with the P2Y(1)R exit from raft domains and internalization. These results demonstrate in intact human vascular smooth muscle the association of the P2Y(1)R to membrane rafts, highlighting the role of this microdomain in P2Y(1)R signaling.