Activation of P2Y2 purinoceptor inhibits the activity of the Na+/K+-ATPase in HeLa cells

Metabolic crosstalk: Extracellular ATP and the tumor microenvironment in cancer progression and therapy

Adenosine 5'-triphosphate (ATP) is a vital element in energy information. It plays a critical role in transmitting signals inside the body, which is necessary for controlling the life activities of all cells, including tumor cells [1]. Its significance extends from intracellular signaling pathways to tumor regression. Purinergic signaling, a form of extracellular paracrine signaling, relies on purine nucleotides. Extracellular ectonucleotidases convert these purine nucleotides to their respective di and mono-phosphate nucleoside forms, contributing significantly to immune biology, cancer biology, and inflammation studies. ATP functions as a mighty damage-linked molecular pattern when released outside the cell, accumulating in inflammatory areas. In the tumor microenvironment (TME), purinergic receptors such as ATP-gated ion channels P2X1-5 and G protein-coupled receptors (GPCR) (P2Y) interact with ATP and other nucleotides, influencing diverse immune cell activities. CD39 and CD73-mediated extracellular ATP degradation contributes to immunosuppression by diminishing ATP-dependent activation and generating adenosine (ADO), potentially hindering antitumor immunity and promoting tumor development. Unraveling the complexities of extracellular ATP (e-ATP) and ADO effects on the TME poses challenges in identifying optimal treatment targets, yet ongoing investigations aim to devise strategies combating e-ATP/ADO-induced immunosuppression, ultimately enhancing anti-tumor immunity. This review explores e-ATP metabolism, its purinergic signaling, and therapeutic strategies targeting associated receptors and enzymes.

Inflammatory profile in cervical cancer: influence of purinergic signaling and possible therapeutic targets

INTRODUCTION AND OBJECTIVE

Cervical cancer is the fourth most prevalent type of cancer in the world. The tumor microenvironment of this disease is associated with the production of several cytokines, pro and anti-inflammatory, and with the purinergic signaling system so that changes in these components are observed throughout the pathological process. The aim of this review is to understand the pathophysiology of cervical cancer based on immunological processes and purinergic signaling pathways, in addition to suggesting possibilities of therapeutic targets.

MATERIALS AND METHODS

To make up this review, studies covering topics of cervical cancer, inflammation and purinergic system were selected from the Pubmed.

RESULTS

The main pro-inflammatory cytokines involved are IL-17, IL-1β, IL-6, and IL-18, and among the anti-inflammatory ones, IL-10 and TGF-β stand out. As new therapeutic targets, P2X7 and A2A receptors have been suggested, since blocking P2X7 would lead to reduced release of pro-inflammatory cytokines, and blocking A2A would increase activation of cytotoxic T lymphocytes in the context of tumor combat. The association between the immune system and the purinergic system, already known in other types of disease, also presents possibilities for a better understanding of biomolecular processes and therapeutic possibilities in the context of cervical 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.

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.

Extracellular ATP activates hyaluronan synthase 2 (HAS2) in epidermal keratinocytes via P2Y2, Ca2+ signaling, and MAPK pathways

Extracellular nucleotides are used as signaling molecules by several cell types. In epidermis, their release is triggered by insults such as ultraviolet radiation, barrier disruption, and tissue wounding, and by specific nerve terminals firing. Increased synthesis of hyaluronan, a ubiquitous extracellular matrix glycosaminoglycan, also occurs in response to stress, leading to the attractive hypothesis that nucleotide signaling and hyaluronan synthesis could also be linked. In HaCaT keratinocytes, ATP caused a rapid and strong but transient activation of hyaluronan synthase 2 (HAS2) expression via protein kinase C-, Ca²⁺/calmodulin-dependent protein kinase II-, mitogen-activated protein kinase-, and calcium response element-binding protein-dependent pathways by activating the purinergic P2Y₂ receptor. Smaller but more persistent up-regulation of HAS3 and CD44, and delayed up-regulation of HAS1 were also observed. Accumulation of peri- and extracellular hyaluronan followed 4-6 h after stimulation, an effect further enhanced by the hyaluronan precursor glucosamine. AMP and adenosine, the degradation products of ATP, markedly inhibited HAS2 expression and, despite concomitant up-regulation of HAS1 and HAS3, inhibited hyaluronan synthesis. Functionally, ATP moderately increased cell migration, whereas AMP and adenosine had no effect. Our data highlight the strong influence of adenosinergic signaling on hyaluronan metabolism in human keratinocytes. Epidermal insults are associated with extracellular ATP release, as well as rapid up-regulation of HAS2/3, CD44, and hyaluronan synthesis, and we show here that the two phenomena are linked. Furthermore, as ATP is rapidly degraded, the opposite effects of its less phosphorylated derivatives facilitate a rapid shut-off of the hyaluronan response, providing a feedback mechanism to prevent excessive reactions when more persistent signals are absent.

Inhibition of ZL55 cell proliferation by ADP via PKC-dependent signalling pathway

Extracellular nucleotides can regulate cell proliferation in both normal and tumorigenic tissues. Here, we studied how extracellular nucleotides regulate the proliferation of ZL55 cells, a mesothelioma-derived cell line obtained from bioptic samples of asbestos-exposed patients. ADP and 2-MeS-ADP inhibited ZL55 cell proliferation, whereas ATP, UTP, and UDP were inactive. The nucleotide potency profile and the blockade of the ADP-mediated inhibitory effect by the phospholipase C inhibitor U-73122 suggest that P2Y1 receptor controls ZL55 cell proliferation. The activation of P2Y1 receptor by ADP leads to activation of intracellular transduction pathways involving [Ca²⁺ ]_i , PKC-δ/PKC-α, and MAPKs, ERK1/2 and JNK1/2. Cell treatment with ADP or 2-MeS-ADP also provokes the activation of p53, causing an accumulation of the G1 cyclin-dependent kinase inhibitors p21^WAF1 and p27^Kip . Inhibition of ZL55 cell proliferation by ADP was completely reversed by inhibiting MEK1/2, or JNK1/2, or PKC-δ, and PKC-α. Through the inhibition of ADP-activated transductional kinases it was found that PKC-δ was responsible for JNK1/2 activation. JNK1/2 has a role in transcriptional up-regulation of p53, p21^WAF1/CIP1 , and p27^kip1 . Conversely, the ADP-activated PKC-α provoked ERK1/2 phosphorylation. ERK1/2 increased p53 stabilization, required to G1 arrest of ZL55 cells. Concluding, the importance of the study is twofold: first, results shed light on the mechanism of cell cycle inhibition by ADP; second, results suggest that extracellular ADP may inhibit mesothelioma progression.

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

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

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.

AMP-activated protein kinase as regulator of P2Y(6) receptor-induced insulin secretion in mouse pancreatic β-cells

5'-AMP-activated protein kinase (AMPK) and its pharmacological modulators have been targeted for treating type 2 diabetes. Extracellular uridine 5'-diphosphate (UDP) activates P2Y6 receptors (P2Y6Rs) in pancreatic β-cells to release insulin and reduce apoptosis, which would benefit diabetes. Here, we studied the role of P2Y6R in activation of AMPK in MIN6 mouse pancreatic β-cells and insulin secretion. Treatment with a potent P2Y6R dinucleotide agonist MRS2957 (500nM) activated AMPK, which was blocked by P2Y6R-selective antagonist MRS2578. Also, MRS2957 induced phosphorylation of acetyl-coenzyme A carboxylase (ACC), a marker of AMPK activity. Calcium chelator BAPTA-AM, calmodulin-dependent protein kinase kinase (CaMKK) inhibitor STO-069 and IP3 receptor antagonist 2-APB attenuated P2Y6R-mediated AMPK phosphorylation revealing involvement of intracellular Ca(2+) pathways. P2Y6R agonist induced insulin secretion at high glucose, which was reduced by AMPK siRNA. Thus, P2Y6R has a crucial role in β-cell function, suggesting its potential as a therapeutic target in diabetes.

Spontaneous calcium oscillations regulate human cardiac progenitor cell growth

RATIONALE

The adult heart possesses a pool of progenitor cells stored in myocardial niches, but the mechanisms involved in the activation of this cell compartment are currently unknown.

OBJECTIVE

Ca2+ promotes cell growth raising the possibility that changes in intracellular Ca2+ initiate division of c-kit-positive human cardiac progenitor cells (hCPCs) and determine their fate.

METHODS AND RESULTS

Ca2+ oscillations were identified in hCPCs and these events occurred independently from coupling with cardiomyocytes or the presence of extracellular Ca2+. These findings were confirmed in the heart of transgenic mice in which enhanced green fluorescent protein was under the control of the c-kit promoter. Ca2+ oscillations in hCPCs were regulated by the release of Ca2+ from the endoplasmic reticulum through activation of inositol 1,4,5-triphosphate receptors (IP3Rs) and the reuptake of Ca2+ by the sarco-/endoplasmic reticulum Ca2+ pump (SERCA). IP3Rs and SERCA were highly expressed in hCPCs, whereas ryanodine receptors were not detected. Although Na+-Ca2+ exchanger, store-operated Ca2+ channels and plasma membrane Ca2+ pump were present and functional in hCPCs, they had no direct effects on Ca2+ oscillations. Conversely, Ca2+ oscillations and their frequency markedly increased with ATP and histamine which activated purinoceptors and histamine-1 receptors highly expressed in hCPCs. Importantly, Ca2+ oscillations in hCPCs were coupled with the entry of cells into the cell cycle and 5-bromodeoxyuridine incorporation. Induction of Ca2+ oscillations in hCPCs before their intramyocardial delivery to infarcted hearts was associated with enhanced engraftment and expansion of these cells promoting the generation of a large myocyte progeny.

CONCLUSION

IP3R-mediated Ca2+ mobilization control hCPC growth and their regenerative potential.

Expression of purinergic receptors and modulation of P2X7 function by the inflammatory cytokine IFNgamma in human epithelial cells

The cervical epithelial cell line, HeLa, is one of the oldest and most commonly used cell lines in cell biology laboratories. Although a truncated P2X(7) receptor has recently been identified in HeLa cells, the expression of other purinergic receptors or the function of the P2X(7) protein has not been characterized. We here show that HeLa cells express transcripts for most P2X and P2Y purinergic receptors. Treatment of cells with ATP or other P2X(7) agonists does not stimulate cell death, but can induce atypical calcium fluxes and ion currents. Cervical epithelial cells represent an important target for sexually-transmitted pathogens and are commonly exposed to pro-inflammatory cytokines such as IFNgamma. Stimulation of HeLa cells with IFNgamma upregulates expression of P2X(7) mRNA and full-length protein, modifies ATP-dependent calcium fluxes, and renders the cells sensitive to ATP-induced apoptosis, which can be blocked by a P2X(7) antagonist. IFNgamma treatment also increased dramatically the sensitivity of the intestinal epithelial cell line, HCT8, to ATP-induced apoptosis. Significantly, IFNgamma also stimulated P2X(7) expression on human intestinal tissues. Responses to other purinergic receptor ligands suggest that HeLa cells may also express functional P2Y(1), P2Y(2) and P2Y(6) receptors, which could be relevant for modulating ion homeostasis in the cells.

Molecular modeling of purinergic receptor P2Y12 and interaction with its antagonists

Purinergic receptors are a class of cell surface receptors for purines that prefer ATP or ADP over adenosine. The surface receptors for extracellular nucleotides are called P2 receptors. They are activated by both pyrimidine and purine nucleotides. ADP initiates platelet aggregation by 'simultaneous activation of two G protein-coupled receptors, P2Y1 and P2Y12. P2Y12 has been shown to be the target of the thienopyridine drugs, ticlopidine and clopidogrel. Here, the active sites of P2Y12 for ATP as well as ADP are predicted by bioinformatics and molecular modeling. First, the three-dimensional (3D) structure of P2Y12 was constructed by InsightII/Homology module using the corresponding bovine rhodopsin (PDB code: 1HZX) as the template. Then the primary structures were optimized by energy minimization that has been successfully accepted by the Protein Data Bank (PDB code: 1VZ1). Second, a simple scoring matrix was built up based on the analysis of 13 known ATP-binding proteins. And the most probable active sites of P2Y12 were predicted using the scoring matrix, which include three distant areas: "head area" (LGTGPLRTFV, 87-96), "middle area" (VGLITNGLAM, 38-47, and LGAKILSVVI, 139-148), and "bottom area" (RTRGVGKVPR, 222-231). Subsequently the structural model of P2Y12 was docked with ATP/ADP in comparison with P2Y1 (PDB code 1ddd). As a comparison, we docked its antagonists, such as ticlopidine and clopidogrel, to the most probable sites and calculated their intermolecular energy. Our results imply that P2Y12 has the potential to be inhibited by ADP/ATP analogs, and it suggests that P2Y12 acts as a target of new drugs that inhibit platelet aggregation.

Evidence for the existence of P2Y1,2,4 receptor subtypes in HEK-293 cells: reactivation of P2Y1 receptors after repetitive agonist application

ATP, ADPbetaS and UTP induced a comparable rise in the intracellular Ca2+ concentration ([Ca2+]i) in HEK-293 cells using fura-2 microfluorimetry. The responses persisted in Ca2+-free medium, but were abolished following depletion of intracellular Ca2+ stores by cyclopiazonic acid. Cross-desensitisation experiments demonstrated that exposure to ADPbetaS has no marked effect on UTP-induced [Ca2+]i transients and vice versa. Whereas the P2Y1 receptor-selective antagonist 2'-deoxy-N6-methyladenosine 3',5'-diphosphate (MRS 2179) abolished the responses to ADPbetaS, it decreased and did not alter the responses to ATP and UTP respectively. Although the P2Y1/P2Y4 receptor-preferential antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) abolished the responses to ADPbetaS, and decreased those to ATP, it also depressed the UTP-induced [Ca2+]i transients. Suramin, an antagonist with preference for P2Y2 receptors decreased both the ATP- and UTP-induced [Ca2+]i reactions. After numerous splittings, HEK-293 cells failed to react to ADPbetaS; however, repeated superfusion with this P2Y1 receptor agonist restored the [Ca2+]i signals. In agreement with the functional data, real-time polymerase chain reaction and immunocytochemical studies indicated the presence of P2Y1, P2Y2 and P2Y4 receptors. Our findings raise doubt with respect to the reliability of HEK-293 cells as expression systems for recombinant P2X receptors, because of a possible functional interaction with endogenous P2Y receptors.

Differential signalling of purinoceptors in HeLa cells through the extracellular signal-regulated kinase and protein kinase C pathways

We have previously shown that HeLa cells express P2Y2 and P2Y6 receptors endogenously and determined the pathways by which the P2Y2 controls proliferation and Na+/K+ATPase activity. Our objective in this study was to investigate the hypothesis that P2Y6 also controls proliferation and Na+/K+ATPase activity; the pathways used in these actions were partially characterised. We found that P2Y6 activation controlled cell proliferation but not the activity of the Na+/K+ATPase. UDP activation of P2Y6 provoked: (a) an increase in free cytosolic calcium; (b) the activation of protein kinase C-alpha, -beta, -delta, -epsilon, and -zeta but not of PKC-iota and -eta; (c) the phosphorylation of the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2); (d) the expression of c-Fos protein. The P2Y6 induced cell proliferation was blocked by the mitogen-activated protein kinase kinase (MAPKK) inhibitor PD098059, thereby indicating that the ERK pathway mediates the mitogenic signalling of P2Y6. PKC and phosphoinositide 3-kinase (PI3K) inhibitors were tested at two different time points of ERK1/2 phosphorylation (10 and 60 min). The results suggest that novel PKCs and PI3K initiate the response but both conventional and atypical PKCs are required for the maintenance of the UDP-induced phosphorylation of ERK1/2. The induction of c-Fos was greatly diminished by conventional or atypical PKC-zeta inhibition, suggesting that it may be due to PKC-alpha/beta and -zeta activity. These observations demonstrate that UDP acts as a proliferative agent in HeLa cells activating multiple signalling pathways involving conventional, novel, and atypical PKCs, PI3K, and ERK. Of these pathways, conventional and atypical PKCs appear responsible for the induction of c-Fos, while ERK is responsible for cell proliferation and depends upon both novel and atypical PKCs and PI3K activities.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Activation of P2Y2 receptor induces c-FOS protein through a pathway involving mitogen-activated protein kinases and phosphoinositide 3-kinases in HeLa cells

The effects of P2Y2 purinoceptor activation on c-Fos expression and the signaling pathways evoked by extracellular ATP/UTP in HeLa cells were investigated. We found that P2Y2 activation induced c-Fos protein and phosphorylated the extracellular signal-regulated kinases 1 and 2 (ERK1/2). The P2Y2-stimulated c-Fos induction was partly blocked (a) by U73122, a phospholipase C inhibitor, (b) by Gö6976, a conventional PKC inhibitor, (c) by PD098059, a mitogen-activated protein kinase kinase inhibitor, and, moreover, (d) by the inhibitors of phosphoinositide 3-kinases (PI3K), LY294002 and wortmannin. When Gö6976 and PD098059, or Gö6976 and wortmannin, were combined there was a totally inhibition of P2Y2-induced c-Fos increase. Either U73122 or Gö6976 did not inhibit ERK1/2 phosphorylation induced by ATP/UTP, while it was inhibited by LY294002 (or wortmannin) and by staurosporine. Additionally, wortmannin inhibited the cytosol-to-membrane translocation of PKC- epsilon induced by ATP/UTP. These data indicated that agonist-induced PI3K and downstream PKC- epsilon activation mediated the effect of ATP/UTP on ERK1/2 activation. To test the biological consequences of ERK1/2 activation, the effect of P2Y2 on cell functions were examined. P2Y2 stimulation increased cell proliferation and this effect was attenuated by PD098059 in a dose-dependent manner, thereby indicating that the ERK pathway mediates mitogenic signaling by P2Y2. In conclusion, the activation of conventional PKCs through P2Y2 receptor acts in concert with ERK and PI3K/PKC- epsilon pathways to induce c-Fos protein and HeLa cell proliferation.