Extracellular ATP and cancer: an overview with special reference to P2 purinergic receptors

G protein coupled P2Y2 receptor as a regulatory molecule in cancer progression

The occurrence and development of cancer involves the participation of many factors, its pathological mechanism is far more complicated than other diseases, and the treatment is also extremely difficult. Although the treatment of cancer adopts diversified methods to improve the survival rate and quality of life of patients, but the drug resistance, metastasis and recurrence of cancer cause most patients to fail in treatment. Therefore, exploring new molecular targets in cancer pathology is of great value for improving and preventing the treatment of cancer. Fortunately, the P2Y2 purinergic receptor (P2Y2 receptor) in the G protein-coupled receptor family has been recognized for regulating cancer progression. Agonist activated P2Y2 receptor has a certain contribution to the growth and metastasis of tumor cells. P2Y2 receptor activation participates in cancer progression by regulating calcium ion channels and classical signaling pathways (such as PLC-PKC and PI3K/AKT). It has the effect of anti-tumor therapy by inhibiting the activation of P2Y2 receptor (the use of antagonist) and reducing its expression. Therefore, in this article, we focus on the expression patterns of P2Y2 receptor in cancer and potential pharmacological targets as anti-cancer treatments.

Mitochondria: the gatekeepers between metabolism and immunity

Metabolism and immunity are crucial monitors of the whole-body homeodynamics. All cells require energy to perform their basic functions. One of the most important metabolic skills of the cell is the ability to optimally adapt metabolism according to demand or availability, known as metabolic flexibility. The immune cells, first line of host defense that circulate in the body and migrate between tissues, need to function also in environments in which nutrients are not always available. The resilience of immune cells consists precisely in their high adaptive capacity, a challenge that arises especially in the framework of sustained immune responses. Pubmed and Scopus databases were consulted to construct the extensive background explored in this review, from the Kennedy and Lehninger studies on mitochondrial biochemistry of the 1950s to the most recent findings on immunometabolism. In detail, we first focus on how metabolic reconfiguration influences the action steps of the immune system and modulates immune cell fate and function. Then, we highlighted the evidence for considering mitochondria, besides conventional cellular energy suppliers, as the powerhouses of immunometabolism. Finally, we explored the main immunometabolic hubs in the organism emphasizing in them the reciprocal impact between metabolic and immune components in both physiological and pathological conditions.

Mitochondrial Cation Signalling in the Control of Inflammatory Processes

Mitochondria are the bioenergetic organelles responsible for the maintenance of cellular homeostasis and have also been found to be associated with inflammation. They are necessary to induce and maintain innate and adaptive immune cell responses, acting as signalling platforms and mediators in effector responses. These organelles are also known to play a pivotal role in cation homeostasis as well, which regulates the inflammatory responses through the modulation of these cation channels. In particular, this review focuses on mitochondrial Ca2+ and K+ fluxes in the regulation of inflammatory response. Nevertheless, this review aims to understand the interplay of these inflammation inducers and pathophysiological conditions. In detail, we discuss some examples of chronic inflammation such as lung, bowel, and metabolic inflammatory diseases caused by a persistent activation of the innate immune response due to a dysregulation of mitochondrial cation homeostasis.

Metabolic Modeling Identifies a Novel Molecular Type of Glioblastoma Associated with Good Prognosis

Glioblastoma (GBM) is one of the most aggressive forms of cancer. Although IDH1 mutation indicates a good prognosis and a potential target for treatment, most GBMs are IDH1 wild-type. Identifying additional molecular markers would help to generate personalized therapies and improve patient outcomes. Here, we used our recently developed metabolic modeling method (genome-wide precision metabolic modeling, GPMM) to investigate the metabolic profiles of GBM, aiming to identify additional novel molecular markers for this disease. We systematically analyzed the metabolic reaction profiles of 149 GBM samples lacking IDH1 mutation. Forty-eight reactions showing significant association with prognosis were identified. Further analysis indicated that the purine recycling, nucleotide interconversion, and folate metabolism pathways were the most robust modules related to prognosis. Considering the three pathways, we then identified the most significant GBM type for a better prognosis, namely N⁺P^-. This type presented high nucleotide interconversion (N⁺) and low purine recycling (P^-). N⁺P^--type exhibited a significantly better outcome (log-rank p = 4.7 × 10^-7) than that of N^-P⁺. GBM patients with the N⁺P^--type had a median survival time of 19.6 months and lived 65% longer than other GBM patients. Our results highlighted a novel molecular type of GBM, which showed relatively high frequency (26%) in GBM patients lacking the IDH1 mutation, and therefore exhibits potential in GBM prognostic assessment and personalized therapy.

Insights of ethyl acetate fraction from Vassobia breviflora in multidrug-resistant bacteria and cancer cells: from biological to therapeutic

Cancer and infectious diseases are among the leading causes of death in the world. Despite the diverse array of treatments available, challenges posed by resistance, side effects, high costs, and inaccessibility persist. In the Solanaceae plant family, few studies with Vassobia breviflora species relating to biological activity are known, but promising results have emerged. The phytochemicals present in the ethyl acetate fraction were obtained using ESI-MS-QTOF, and the antioxidants assays 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radical capture (ABTS), plasma ferric reduction capacity (FRAP), and total antioxidant capacity (TAC). Cytotoxic activity was evaluated by MTT, Neutral Red, and lactate dehydrogenase (LDH) released. The production of reactive oxygen species, nitric oxide, and purinergic enzymes was also investigated. Antibacterial activity was measured through minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and antibiofilm activity, in addition to genotoxicity in plasmid DNA. Five major masses were identified D-glucopyranose II, allyl disulfide, γ-lactones, pharbilignoside, and one mass was not identified. V. breviflora exhibited relevant antioxidant and cytotoxic activity against the HeLa cell line and enhanced expression effect in modulation of purinergic signaling. Antibacterial activities in the assays in 7 ATCC strains and 8 multidrug-resistant clinical isolates were found. V. breviflora blocked biofilm formation in producing bacteria at the highest concentrations tested. However, there was no plasmid DNA cleavage at the concentrations tested. Data demonstrated that V. breviflora exhibited an antioxidant effect through several methods and proved to be a promising therapeutic alternative for use against tumor cells via purinergic signaling and multidrug-resistant microorganisms, presenting an anti-biofilm effect.

Approaches to monitor ATP levels in living cells: where do we stand?

ATP is the most universal and essential energy molecule in cells. This is due to its ability to store cellular energy in form of high-energy phosphate bonds, which are extremely stable and readily usable by the cell. This energy is key for a variety of biological functions such as cell growth and division, metabolism, and signaling, and for the turnover of biomolecules. Understanding how ATP is produced and hydrolyzed with a spatiotemporal resolution is necessary to understand its functions both in physiological and in pathological contexts. In this review, first we will describe the organization of the electron transport chain and ATP synthase, the main molecular motor for ATP production in mitochondria. Second, we will review the biochemical assays currently available to estimate ATP quantities in cells, and we will compare their readouts, strengths, and weaknesses. Finally, we will explore the palette of genetically encoded biosensors designed for microscopy-based approaches, and show how their spatiotemporal resolution opened up the possibility to follow ATP levels in living cells.

Extracellular ATP Mediates Cancer Cell Migration and Invasion Through Increased Expression of Cyclooxygenase 2

The tumor microenvironment plays a major role in the ability of the tumor cells to undergo metastasis. A major player of tumors gaining metastatic property is the inflammatory protein, cyclooxygenase 2 (COX-2). Several tumors show upregulation of this protein, which has been implicated in mediating metastasis in various cancer types such as of colon, breast and lung. In this report, we show that the concentration of extracellular ATP (eATP) is increased in response to cell death mediated by chemotherapeutic agents such as doxorubicin. By using three different cell-lines-HeLa (cervical), IMR-32 (neuronal) and MCF-7 (breast)-we show that this eATP goes on to act on purinergic (P2) receptors. Among the various P2 receptors expressed in these cells we identified P2X7, in IMR-32 and MCF-7 cells, and P2Y12, in HeLa cells, as important in modulating cell migration and invasion. Downstream of the P2 receptor activation, both p42/44 mitogen-activated protein kinase (MAPK) and the p38 MAPK are activated in these cells. These result in an increase in the expression of COX-2 mRNA and protein. We also observe an increase in the activity of matrix metalloproteinase 2 (MMP-2) enzyme in these cells. Blocking the P2 receptors not only blocks migration and invasion, but also COX-2 synthesis and MMP-2 activity. Our results show the link between purinergic receptors and COX-2 expression. Increased levels of ATP in the tumor microenvironment, therefore, leads to increased COX-2 expression, which, in turn, affords migratory and invasive properties to the tumor. This provides P2 receptor-based anti-inflammatory drugs (PBAIDs) a potential opportunity to be explored as cancer therapeutics.

The P2X7 purinergic receptor: a potential therapeutic target for lung cancer

PURPOSE

Purinergic P2X7 receptor (P2X7R) is a gated ion channel for which adenosine triphosphate (ATP) is a ligand. Activated P2X7R is widely expressed in a variety of immune cells and tissues and is involved in a variety of physiological and pathological processes. Studies have confirmed that P2X7R is involved in the regulation of tumor cell growth, stimulating cell proliferation or inducing apoptosis. Recent studies have found that P2X7R is abnormally expressed in lung cancer and is closely related to the carcinogenesis and development of lung cancer. In this paper, we comprehensively describe the structure, function, and genetic polymorphisms of P2X7R. In particular, the role and therapeutic potential of P2X7R in lung cancer are discussed to provide new targets and new strategies for the treatment and prognosis of clinical lung cancer.

METHODS

The relevant literature on P2X7R and lung cancer from PubMed databases is reviewed in this article.

RESULTS

P2X7R regulates the function of lung cancer cells by activating multiple intracellular signaling pathways (such as the JNK, Rho, HMGB1 and EMT pathways), thereby affecting cell survival, growth, invasion, and metastasis and patient prognosis. Targeting P2X7R with inhibitors effectively suppresses the growth and metastasis of lung cancer cells.

CONCLUSION

In summary, P2X7R is expected to become a potential target for the treatment of lung cancer, and more clinical research is needed in the future to explore the effectiveness of P2X7R antagonists as treatments.

Purinergic Receptors: Elucidating the Role of these Immune Mediators in HIV-1 Fusion

Purinergic receptors are inflammatory mediators activated by extracellular nucleotides released by dying or injured cells. Several studies have described an important role for these receptors in HIV-1 entry, particularly regarding their activity on HIV-1 viral membrane fusion. Several reports identify purinergic receptor antagonists that inhibit HIV-1 membrane fusion; these drugs are suspected to act through antagonizing Env-chemokine receptor interactions. They also appear to abrogate activity of downstream mediators that potentiate activation of the NLRP3 inflammasome pathway. Here we review the literature on purinergic receptors, the drugs that inhibit their function, and the evidence implicating these receptors in HIV-1 entry.

P2X1 Selective Antagonists Block HIV-1 Infection through Inhibition of Envelope Conformation-Dependent Fusion

Purinergic receptors are well-established modulators of inflammatory processes, primarily through detection of extracellular nucleotides that are released by dying or infected cells. Emerging literature has demonstrated that inhibition of these inflammatory receptors can block HIV-1 productive infection and HIV-1-associated inflammation. The specificity of receptor type and mechanism of interaction has not yet been determined. Here, we characterize the inhibitory activity of P2X1 receptor antagonists, NF279 and NF449, in cell lines, primary cells, and a variety of HIV-1 envelope (Env) clades. NF279 and NF449 blocked productive infection at the level of viral membrane fusion, with a range of inhibitory activities against different HIV-1 Env isolates. A mutant virus carrying a truncation deletion of the C-terminal tail of HIV-1 Env glycoprotein 41 (gp41) showed reduced sensitivity to P2X1 antagonists, indicating that the sensitivity of inhibition by these molecules may be modulated by Env conformation. In contrast, a P2X7 antagonist, A438079, had a limited effect on productive infection and fusion. NF279 and NF449 interfered with the ability of the gp120 variable regions 1 and 2 (V1V2)-targeted broadly neutralizing antibody PG9 to block productive infection, suggesting that these drugs may antagonize HIV-1 Env at gp120 V1V2 to block viral membrane fusion. Our observations indicate that P2X1 antagonism can inhibit HIV-1 replication at the level of viral membrane fusion through interaction with Env. Future studies will probe the nature of these compounds in inhibiting HIV-1 fusion and the development of small molecules to block HIV-1 entry via this mechanism.IMPORTANCE While effective treatment can lower the severe morbidity and mortality associated with HIV-1 infection, patients infected with HIV-1 suffer from significantly higher rates of noncommunicable comorbidities associated with chronic inflammation. Emerging literature suggests a key role for P2X1 receptors in mediating this chronic inflammation, but the mechanism is still unknown. Here, we demonstrate that HIV-1 infection is reduced by P2X1 receptor antagonism. This inhibition is mediated by interference with HIV-1 Env and can impact a variety of viral clades. These observations highlight the importance of P2X1 antagonists as potential novel therapeutics that could serve to block a variety of different viral clades with additional benefits for their anti-inflammatory properties.

Inhibition by fluoxetine of LH-stimulated cyclic AMP synthesis in tumor Leydig cells partly involves AMPK activation

Fluoxetine (FLX), a widely used antidepressant primarily acting as a selective serotonin reuptake inhibitor (SSRI), has been shown to exhibit other mechanisms of action in various cell types. Consequently, it might have unexpected adverse effects not related to its intended use, possibly in the endocrine regulation of reproduction. We show in the present report that after a 1-hour preincubation of MLTC-1 Leydig cells with FLX, the intracellular cyclic adenosine monophosphate (cAMP) responses to Luteinizing Hormone (LH) and forskolin (FSK) are reduced through AMPK-dependent and -independent pathways respectively. FLX at low concentrations (12.5μM and 25μM) induced this inhibition without triggering AMPK phosphorylation, while higher FLX concentrations (50μM and 100μM) induced AMPK phosphorylation and lowered ATP concentration similarly to Metformin. Pretreatment with the specific AMPK inhibitor Compound C (CpdC), significantly diminished the inhibition of cAMP synthesis caused by high concentration of FLX. Moreover, as expected FLX also caused a decline of steroidogenesis which is under the control of cAMP. Taken together, these findings demonstrate that the inhibition of cAMP synthesis by FLX is dose-dependent and occurs in MLTC-1 cells through two mechanisms, AMPK-independent and AMPK-dependent, at low and high concentrations, respectively. FLX also inhibited hormone-induced steroidogenesis in MLTC-1 cells and mouse testicular Leydig cells, suggesting similar mechanisms in both cell types.

Purinergic Calcium Signals in Tumor-Derived Endothelium

Tumor microenvironment is particularly enriched with extracellular ATP (eATP), but conflicting evidence has been provided on its functional effects on tumor growth and vascular remodeling. We have previously shown that high eATP concentrations exert a strong anti-migratory, antiangiogenic and normalizing activity on human tumor-derived endothelial cells (TECs). Since both metabotropic and ionotropic purinergic receptors trigger cytosolic calcium increase ([Ca2+]c), the present work investigated the properties of [Ca2+]c events elicited by high eATP in TECs and their role in anti-migratory activity. In particular, the quantitative and kinetic properties of purinergic-induced Ca2+ release from intracellular stores and Ca2+ entry from extracellular medium were investigated. The main conclusions are: (1) stimulation of TECs with high eATP triggers [Ca2+]c signals which include Ca2+ mobilization from intracellular stores (mainly ER) and Ca2+ entry through the plasma membrane; (2) the long-lasting Ca2+ influx phase requires both store-operated Ca2+ entry (SOCE) and non-SOCE components; (3) SOCE is not significantly involved in the antimigratory effect of high ATP stimulation; (4) ER is the main source for intracellular Ca2+ release by eATP: it is required for the constitutive migratory potential of TECs but is not the only determinant for the inhibitory effect of high eATP; (5) a complex interplay occurs among ER, mitochondria and lysosomes upon purinergic stimulation; (6) high eUTP is unable to inhibit TEC migration and evokes [Ca2+]c signals very similar to those described for eATP. The potential role played by store-independent Ca2+ entry and Ca2+-independent events in the regulation of TEC migration by high purinergic stimula deserves future investigation.

The sensing of mitochondrial DAMPs by non-immune cells

Mitochondria are the source of damage-associated molecular patterns (DAMPs), which are molecules that play a key modulatory role in immune cells. These molecules include proteins and peptides, such as N-formyl peptides and TFAM, as well as lipids, and metabolites such as cardiolipin, succinate and ATP, and also mitochondrial DNA (mtDNA). Recent data indicate that somatic cells sense mitochondrial DAMPs and trigger protective mechanisms in response to these signals. In this review we focus on the well-described effects of mitochondrial DAMPs on immune cells and also how these molecules induce immunogenic responses in non-immune cells. Special attention will be paid to the response to mtDNA.

Mitochondria-Derived Damage-Associated Molecular Patterns in Sepsis: From Bench to Bedside

Sepsis is one of the most serious health hazards. Current research suggests that the pathogenesis of sepsis is mediated by both pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Mitochondria are among the most important organelles in cells and determine their life and death. A variety of mitochondria-derived DAMPs (mtDAMPs) are similar to bacteria because mitochondria are derived from bacteria according to the mitochondrial endosymbiotic theory. Their activated signaling pathways extensively affect organ functions, the immune system, and metabolic functions in sepsis. In this review, we describe the essential roles of mtDAMPs in sepsis and discuss their research prospects and clinical importance.

ATP-loaded biomimetic nanoparticles as controlled release system for extracellular drugs in cancer applications

Purpose

The antitumoral effect of ATP requires its accumulation in the extracellular space to interact with membrane receptors in target cells. We propose the use of albumin nanoparticles (ANPs) coated with erythrocyte membranes (EMs) to load, deliver, release, and enhance the extracellular anticancer activity of ATP.

Materials and methods

ANPs were synthesized by desolvation method and optimal values of pH, albumin concentration, and ethanol volume were determined. EMs were derived from erythrocyte lysates and were coated on to ANPs using an extruder. Size was determined by transmission electron microscopy (TEM) and hydrodynamic size and zeta potential were determined by dynamic light scattering. Coating of the ANPs with the EMs was verified by TEM and confocal microscopy. Nanoparticle cell uptake was analyzed by confocal microscopy using HeLa and HEK-293 cell cultures treated with nanoparticles stained with 1,1′-diocta-decyl-3,3,3′,3′-tetramethylindodicarbocyanine, 4-chlorobenzenesulfonate salt (DiD) for EM-ANPs and Alexa 488 for ANPs. Cell viability was analyzed by [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) and Annexin V/propidium iodide assays.

Results

Optimal values of ANP preparation were as follows: pH=9, 10 mg/mL albumin concentration, and 2.33±0.04 mL ethanol volume. Size distributions as analyzed by TEM were as follows: ANPs =91.9±4.3 nm and EM-ANPs =98.3±5.1 nm; hydrodynamic sizes: ANPs =180.5±6.8 nm and EM-ANPs =197.8±3.2 nm; and zeta potentials: ANPs =17.8±3.5 mV, ANPs+ATP =−13.60±0.48 and EM-ANPs =−13.7±2.9 mV. The EMs coating the ANPs were observed by TEM and confocal microscopy. A fewer number of internalized EM-ANPs+ATP compared to non-coated ANPs+ATP was observed in HeLa and HEK-293 cells. Cell viability decreased up to 48.6%±2.0% with a concentration of 400 µM ATP after 72 hours of treatment and cell death is caused mainly via apoptosis.

Conclusion

Our current results show that it is possible to obtain nanoparticles from highly biocompatible, biodegradable materials and that their coating with EMs allows the regulation of the internalization process in order to promote extracellular activity of ATP.

Machine-Learning-Driven Surface-Enhanced Raman Scattering Optophysiology Reveals Multiplexed Metabolite Gradients Near Cells

The extracellular environment is a complex medium in which cells secrete and consume metabolites. Molecular gradients are thereby created near cells, triggering various biological and physiological responses. However, investigating these molecular gradients remains challenging because the current tools are ill-suited and provide poor temporal and special resolution while also being destructive. Herein, we report the development and application of a machine learning approach in combination with a surface-enhanced Raman spectroscopy (SERS) nanoprobe to measure simultaneously the gradients of at least eight metabolites in vitro near different cell lines. We found significant increase in the secretion or consumption of lactate, glucose, ATP, glutamine, and urea within 20 μm from the cells surface compared to the bulk. We also observed that cancerous cells (HeLa) compared to fibroblasts (REF52) have a greater glycolytic rate, as is expected for this phenotype. Endothelial (HUVEC) and HeLa cells exhibited significant increase in extracellular ATP compared to the control, shining light on the implication of extracellular ATP within the cancer local environment. Machine-learning-driven SERS optophysiology is generally applicable to metabolites involved in cellular processes, providing a general platform on which to study cell biology.

P2X Antagonists Inhibit HIV-1 Productive Infection and Inflammatory Cytokines Interleukin-10 (IL-10) and IL-1β in a Human Tonsil Explant Model

HIV-1 causes a persistent infection of the immune system that is associated with chronic comorbidities. The mechanisms that underlie this inflammation are poorly understood. Emerging literature has implicated proinflammatory purinergic receptors and downstream signaling mediators in HIV-1 infection. This study probed whether inhibitors of purinergic receptors would reduce HIV-1 infection and HIV-1-stimulated inflammation. An ex vivo human tonsil histoculture infection model was developed to support HIV-1 productive infection and stimulated the inflammatory cytokine interleukin-1 beta (IL-1β) and the immunosuppressive cytokine interleukin-10 (IL-10). This study tests whether inhibitors of purinergic receptors would reduce HIV-1 infection and HIV-1-stimulated inflammation. The purinergic P2X1 receptor antagonist NF449, the purinergic P2X7 receptor antagonist A438079, and azidothymidine (AZT) were tested in HIV-1-infected human tonsil explants to compare levels of inhibition of HIV-1 infection and HIV-stimulated inflammatory cytokine production. All drugs limited HIV-1 productive infection, but P2X-selective antagonists (NF449 and A438079) significantly lowered HIV-stimulated IL-10 and IL-1β. We further observed that P2X1- and P2X7-selective antagonists can act differentially as inhibitors of both HIV-1 infection and HIV-1-stimulated inflammation. Our findings highlight the differential effects of HIV-1 on inflammation in peripheral blood compared to those in lymphoid tissue. For the first time, we demonstrate that P2X-selective antagonists act differentially as inhibitors of both HIV-1 infection and HIV-1-stimulated inflammation. Drugs that block these pathways can have independent inhibitory activities against HIV-1 infection and HIV-induced inflammation.IMPORTANCE Patients who are chronically infected with HIV-1 experience sequelae related to chronic inflammation. The mechanisms of this inflammation have not been elucidated. Here, we describe a class of drugs that target the P2X proinflammatory signaling receptors in a human tonsil explant model. This model highlights differences in HIV-1 stimulation of lymphoid tissue inflammation and peripheral blood. These drugs serve to block both HIV-1 infection and production of IL-10 and IL-1β in lymphoid tissue, suggesting a novel approach to HIV-1 therapeutics in which both HIV-1 replication and inflammatory signaling are simultaneously targeted.

GATA Binding Protein 3 Boosts Extracellular ATP Hydrolysis and Inhibits Metastasis of Breast Cancer by Up-regulating Ectonucleoside Triphosphate Diphosphohydrolase 3

Despite remarkable advancements in our understanding of breast cancer, it remains the leading cause of cancer deaths in women. Distant recurrence and metastasis is the main reason for death due to breast cancer. It is well recognized that the GATA binding protein 3 (GATA3), a transcription factor, is a tumor suppressor in breast cancer. To date, the mechanistic molecular details of GATA3 remain elusive, because, as a transcription factor, it is not a direct executor in physiological and pathological processes. Here, we demonstrate that GATA3 reduces the ATP level in the breast cancer microenvironment and inhibits breast cancer metastasis by up-regulating ectonucleoside triphosphate diphosphohydrolase 3 (ENTPD3). The extracellular ATP concentration is significantly higher in tumor tissues than in normal tissues and promotes the migration of cancer cells from the primary site. ENTPD3 hydrolyzes ATP in tumor microenvironment and suppresses breast cancer metastasis. Furthermore, ENTPD3 inhibits epithelial-to-mesenchymal transition, a key program responsible for the development of metastatic disease. These findings provide novel insights into the tumor suppressor activity of GATA3.

Stim and Orai mediate constitutive Ca2+ entry and control endoplasmic reticulum Ca2+ refilling in primary cultures of colorectal carcinoma cells

Store-operated Ca²⁺ entry (SOCE) provides a major Ca²⁺ entry route in cancer cells. SOCE is mediated by the assembly of Stim and Orai proteins at endoplasmic reticulum (ER)-plasma membrane junctions upon depletion of the ER Ca²⁺ store. Additionally, Stim and Orai proteins underpin constitutive Ca²⁺ entry in a growing number of cancer cell types due to the partial depletion of their ER Ca²⁺ reservoir. Herein, we investigated for the first time the structure and function of SOCE in primary cultures of colorectal carcinoma (CRC) established from primary tumor (pCRC) and metastatic lesions (mCRC) of human subjects. Stim1-2 and Orai1-3 transcripts were equally expressed in pCRC and mCRC cells, although Stim1 and Orai3 proteins were up-regulated in mCRC cells. The Mn²⁺-quenching technique revealed that constitutive Ca2⁺ entry was significantly enhanced in pCRC cells and was inhibited by the pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3. The larger resting Ca²⁺ influx in pCRC was associated to their lower ER Ca²⁺ content as compared to mCRC cells. Pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3 prevented ER-dependent Ca²⁺ release, thereby suggesting that constitutive SOCE maintains ER Ca²⁺ levels. Nevertheless, pharmacological and genetic blockade of Stim1, Stim2, Orai1 and Orai3 did not affect CRC cell proliferation and migration. These data provide the first evidence that Stim and Orai proteins mediate constitutive Ca²⁺ entry and replenish ER with Ca²⁺ in primary cultures of CRC cells. However, SOCE is not a promising target to design alternative therapies for CRC.

The P2X7 Receptor in Inflammatory Diseases: Angel or Demon?

Under physiological conditions, adenosine triphosphate (ATP) is present at low levels in the extracellular milieu, being massively released by stressed or dying cells. Once outside the cells, ATP and related nucleotides/nucleoside generated by ectonucleotidases mediate a high evolutionary conserved signaling system: the purinergic signaling, which is involved in a variety of pathological conditions, including inflammatory diseases. Extracellular ATP has been considered an endogenous adjuvant that can initiate inflammation by acting as a danger signal through the activation of purinergic type 2 receptors-P2 receptors (P2Y G-protein coupled receptors and P2X ligand-gated ion channels). Among the P2 receptors, the P2X7 receptor is the most extensively studied from an immunological perspective, being involved in both innate and adaptive immune responses. P2X7 receptor activation induces large-scale ATP release via its intrinsic ability to form a membrane pore or in association with pannexin hemichannels, boosting purinergic signaling. ATP acting via P2X7 receptor is the second signal to the inflammasome activation, inducing both maturation and release of pro-inflammatory cytokines, such as IL-1β and IL-18, and the production of reactive nitrogen and oxygen species. Furthermore, the P2X7 receptor is involved in caspases activation, as well as in apoptosis induction. During adaptive immune response, P2X7 receptor modulates the balance between the generation of T helper type 17 (Th17) and T regulatory (Treg) lymphocytes. Therefore, this receptor is involved in several inflammatory pathological conditions. In infectious diseases and cancer, P2X7 receptor can have different and contrasting effects, being an angel or a demon depending on its level of activation, cell studied, type of pathogen, and severity of infection. In neuroinflammatory and neurodegenerative diseases, P2X7 upregulation and function appears to contribute to disease progression. In this review, we deeply discuss P2X7 receptor dual function and its pharmacological modulation in the context of different pathologies, and we also highlight the P2X7 receptor as a potential target to treat inflammatory related diseases.

Hyperthermia and associated changes in membrane fluidity potentiate P2X7 activation to promote tumor cell death

Extracellular ATP (eATP) accumulation within the tumor microenvironment (TME) has the potential to activate purinergic signaling. The eATP evoked signaling effects bolster antitumor immune responses while exerting direct cytotoxicity on tumor cells and vascular endothelial cells, mediated at least in part through P2X7 receptors. Approaches to augment purinergic signaling in TME e.g. by ectonucleotidase CD39 blockade, and/or boosting P2X7 functional responses, might be used as immunomodulatory therapies in cancer treatment. In this study, we delineated the translatable strategy of hyperthermia to demonstrate impacts on P2X7 responsiveness to eATP. Hyperthermia (40°C) was noted to enhance eATP-mediated cytotoxicity on MCA38 colon cancer cells. Increased membrane fluidity induced by hyperthermia boosted P2X7 functionality, potentiating pore opening and modulating downstream AKT/PRAS40/mTOR signaling events. When combined with cisplatin or mitomycin C, hyperthermia and eATP together markedly potentiate cancer cell death. Our data indicate that clinically tolerable hyperthermia with modulated P2X7-purinergic signaling will boost efficacy of conventional cancer treatments.

ATP-P2Y2-β-catenin axis promotes cell invasion in breast cancer cells

Extracellular adenosine 5'-triphosphate (ATP), secreted by living cancer cells or released by necrotic tumor cells, plays an important role in tumor invasion and metastasis. Our previous study demonstrated that ATP treatment in vitro could promote invasion in human prostate cancer cells via P2Y2, a preferred receptor for ATP, by enhancing EMT process. However, the pro-invasion mechanisms of ATP and P2Y2 are still poorly studied in breast cancer. In this study, we found that P2Y2 was highly expressed in breast cancer cells and associated with human breast cancer metastasis. ATP could promote the in vitro invasion of breast cancer cells and enhance the expression of β-catenin as well as its downstream target genes CD44, c-Myc and cyclin D1, while P2Y2 knockdown attenuated above ATP-driven events in vitro and in vivo. Furthermore, iCRT14, a β-catenin/TCF complex inhibitor, could also suppress ATP-driven migration and invasion in vitro. These results suggest that ATP promoted breast cancer cell invasion via P2Y2-β-catenin axis. Thus blockade of the ATP-P2Y2-β-catenin axis could suppress the invasive and metastatic potential of breast cancer cells and may serve as potential targets for therapeutic interventions of breast cancer.

Activation of P2X7 and P2Y11 purinergic receptors inhibits migration and normalizes tumor-derived endothelial cells via cAMP signaling

Purinergic signaling is involved in inflammation and cancer. Extracellular ATP accumulates in tumor interstitium, reaching hundreds micromolar concentrations, but its functional role on tumor vasculature and endothelium is unknown. Here we show that high ATP doses (>20 μM) strongly inhibit migration of endothelial cells from human breast carcinoma (BTEC), but not of normal human microvascular EC. Lower doses (1–10 mm result ineffective. The anti-migratory activity is associated with cytoskeleton remodeling and is significantly prevented by hypoxia. Pharmacological and molecular evidences suggest a major role for P2X7R and P2Y11R in ATP-mediated inhibition of TEC migration: selective activation of these purinergic receptors by BzATP mimics the anti-migratory effect of ATP, which is in turn impaired by their pharmacological or molecular silencing. Downstream pathway includes calcium-dependent Adenilyl Cyclase 10 (AC10) recruitment, cAMP release and EPAC-1 activation. Notably, high ATP enhances TEC-mediated attraction of human pericytes, leading to a decrease of endothelial permeability, a hallmark of vessel normalization. Finally, we provide the first evidence of in vivo P2X7R expression in blood vessels of murine and human breast carcinoma. In conclusion, we have identified a purinergic pathway selectively acting as an antiangiogenic and normalizing signal for human tumor-derived vascular endothelium.

Extracellular ATP a New Player in Cancer Metabolism: NSCLC Cells Internalize ATP In Vitro and In Vivo Using Multiple Endocytic Mechanisms

Intratumoral extracellular ATP concentrations are 1000 times higher than those in normal tissues of the same cell origin. However, whether or not cancer cells use the abundant extracellular ATP was unknown until we recently reported that cancer cells internalize ATP. The internalized ATP was found to substantially increase intracellular ATP concentration and promote cell proliferation and drug resistance in cancer cells. Here, using a nonhydrolyzable fluorescent ATP (NHF-ATP), radioactive and regular ATP, coupled with high and low molecular weight dextrans as endocytosis tracers and fluorescence microscopy and ATP assays, cultured human NSCLC A549 and H1299 cells as well as A549 tumor xenografts were found to internalize extracellular ATP at concentrations within the reported intratumoral extracellular ATP concentration range. In addition to macropinocytosis, both clathrin- and caveolae-mediated endocytosis significantly contribute to the ATP internalization, which led to an approximately 30% (within 45 minutes) or more than 50% (within 4 hours) increase in intracellular ATP levels after ATP incubation. This increase could not be accounted for by either purinergic receptor signaling or increased intracellular ATP synthesis rates in the ATP-treated cancer cells. These new findings significantly deepen our understanding of the Warburg effect by shedding light on how cancer cells in tumors, which are heterogeneous for oxygen and nutrition supplies, take up extracellular ATP and use the internalized ATP to perform multiple previously unrecognized functions of biological importance. They strongly suggest the existence of ATP sharing among cancer and stromal cells in tumors and simultaneously identify multiple new anticancer targets.

IMPLICATIONS

Extracellular ATP is taken up by human lung cancer cells and tumors via macropinocytosis and other endocytic processes to supplement their extra energy needs for cancer growth, survival, and drug resistance, thus providing novel targets for future cancer therapy. Mol Cancer Res; 14(11); 1087-96. ©2016 AACR.

Purinergic signaling and energy homeostasis in psychiatric disorders

Purinergic signaling regulates numerous vital biological processes in the central nervous system (CNS). The two principle purines, ATP and adenosine act as excitatory and inhibitory neurotransmitters, respectively. Compared to other classical neurotransmitters, the role of purinergic signaling in psychiatric disorders is not well understood or appreciated. Because ATP exerts its main effect on energy homeostasis, neuronal function of ATP has been underestimated. Similarly, adenosine is primarily appreciated as a precursor of nucleotide synthesis during active cell growth and division. However, recent findings suggest that purinergic signaling may explain how neuronal activity is associated neuronal energy charge and energy homeostasis, especially in mental disorders. In this review, we provide an overview of the synaptic function of mitochondria and purines in neuromodulation, synaptic plasticity, and neuron-glia interactions. We summarize how mitochondrial and purinergic dysfunction contribute to mental illnesses such as schizophrenia, bipolar disorder, autism spectrum disorder (ASD), depression, and addiction. Finally, we discuss future implications regarding the pharmacological targeting of mitochondrial and purinergic function for the treatment of psychiatric disorders.

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

SIGNIFICANCE

Mitochondria, vital cellular power plants to generate energy, are involved in immune responses. Mitochondrial damage-associated molecular patterns (DAMPs) are molecules that are released from mitochondria to extracellular space during cell death and include not only proteins but also DNA or lipids. Mitochondrial DAMPs induce inflammatory responses and are critically involved in the pathogenesis of various diseases.

RECENT ADVANCES

Recent studies elucidate the molecular mechanisms by which mitochondrial DAMPs are released and initiate immune responses by use of genetically modulated cells or animals. Importantly, the levels of mitochondrial DAMPs in patients are often associated with severity and prognosis of human diseases, such as infection, asthma, ischemic heart disease, and cancer.

CRITICAL ISSUES

Although mitochondrial DAMPs can represent proinflammatory molecules in various experimental models, their roles in human diseases may be multifunctional and complex. It remains unclear where and how mitochondrial DAMPs are liberated into extracellular spaces and exert their biological functions particularly in vivo. In addition, while mitochondria can secrete several types of DAMPs during cell death, the interaction of each mitochondrial DAMP (e.g., synergistic effects) remains unclear.

FUTURE DIRECTIONS

Regulation of mitochondrial DAMP-mediated immune responses may be important to alter the progression of human diseases. In addition, measuring mitochondrial DAMPs in patients may be clinically useful as biomarkers to predict prognosis or response to therapies. Further studies of the mechanisms by which mitochondrial DAMPs impact the initiation and progression of diseases may lead to the development of therapeutics specifically targeting this pathway. Antioxid.

Multidrug Resistance-Associated Protein 2 Expression Is Upregulated by Adenosine 5'-Triphosphate in Colorectal Cancer Cells and Enhances Their Survival to Chemotherapeutic Drugs

Extracellular adenosine 5’-triphosphate (ATP) is a signaling molecule that induces a plethora of effects ranging from the regulation of cell proliferation to modulation of cancerous cell behavior. In colorectal cancer, ATP was reported to stimulate epithelial cell proliferation and possibly promote resistance to anti-cancer treatments. However, the exact role of this danger-signaling molecule on cancerous intestinal epithelial cells (IECs) in response to chemotherapeutic agents remains unknown. To address how ATP may influence the response of cancerous IECs to chemotherapeutic agents, we used Caco-2 cells, which display enterocyte-like features, to determine the effect of ATP on the expression of multidrug resistance-associated protein 2 (MRP2). Gene and protein expression were determined by quantitative real-time PCR (qRT-PCR) and Western blotting. Resistance to etoposide, cisplatin and doxorubicin was determined by MTT assays in response to ATP stimulation of Caco-2 cells and in cells for which MRP2 expression was down-regulated by shRNA. ATP increased the expression of MRP2 at both the mRNA and protein levels. MRP2 expression involved an ATP-dependent stimulation of the MEK/ERK signaling pathway that was associated with an increase in relative resistance of Caco-2 cells to etoposide. Abolition of MRP2 expression using shRNA significantly reduced the protective effect of MRP2 toward etoposide as well as to cisplatin and doxorubicin. This study describes the mechanism by which ATP may contribute to the chemoresistance of cancerous IECs in colorectal cancer. Given the heterogeneity of colorectal adenocarcinoma responses to anti-cancer drugs, these findings call for further study to understand the role of P2 receptors in cancer drug therapy and to develop novel therapies aimed at regulating P2 receptor activity.

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

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

Raloxifene induces autophagy-dependent cell death in breast cancer cells via the activation of AMP-activated protein kinase

Raloxifene is a selective estrogen receptor modulator (SERM) that binds to the estrogen receptor (ER), and exhibits potent anti-tumor and autophagy-inducing effects in breast cancer cells. However, the mechanism of raloxifene-induced cell death and autophagy is not well-established. So, we analyzed mechanism underlying death and autophagy induced by raloxifene in MCF-7 breast cancer cells. Treatment with raloxifene significantly induced death in MCF-7 cells. Raloxifene accumulated GFP-LC3 puncta and increased the level of autophagic marker proteins, such as LC3-II, BECN1, and ATG12-ATG5 conjugates, indicating activated autophagy. Raloxifene also increased autophagic flux indicators, the cleavage of GFP from GFP-LC3 and only red fluorescence-positive puncta in mRFP-GFP-LC3-expressing cells. An autophagy inhibitor, 3-methyladenine (3-MA), suppressed the level of LC3-II and blocked the formation of GFP-LC3 puncta. Moreover, siRNA targeting BECN1 markedly reversed cell death and the level of LC3-II increased by raloxifene. Besides, raloxifene-induced cell death was not related to cleavage of caspases-7, -9, and PARP. These results indicate that raloxifene activates autophagy-dependent cell death but not apoptosis. Interestingly, raloxifene decreased the level of intracellular adenosine triphosphate (ATP) and activated the AMPK/ULK1 pathway. However it was not suppressed the AKT/mTOR pathway. Addition of ATP decreased the phosphorylation of AMPK as well as the accumulation of LC3-II, finally attenuating raloxifene-induced cell death. Our current study demonstrates that raloxifene induces autophagy via the activation of AMPK by sensing decreases in ATP, and that the overactivation of autophagy promotes cell death and thereby mediates the anti-cancer effects of raloxifene in breast cancer cells.

P2X7 protein expression and polymorphism in non-small cell lung cancer (NSCLC)

Background

P2X7, a purinergic receptor, plays important roles in inflammatory diseases, but recently its expression has been found in several tumors, suggesting a potential role as a cancer cell biomarker. Moreover, the relative amount of P2X7 varies among human individuals due to numerous single nucleotide polymorphisms resulting in either a loss- or gain-of-function; the P2X7 gene is highly polymorphic, and polymorphisms in the promoter or coding region may modify its expression or function. A polymorphism in exon 13 of the P2X7 receptor gene at the +1513 position (Glu496Ala substitution, corresponding to SNP rs3751143) has been shown to eradicate the function of this receptor and has been correlated with histological variants and clinical parameters in thyroid cancer. Until now, no data regarding P2X7 expression and polymorphisms in lung cancer have been published; based on these premises, we decided to evaluate the impact of the P2X7 expression and polymorphisms in ninety-seven cases of non-small cell lung cancer (NSCLC).

Results

No significant difference in the genotype frequency of the A1513C polymorphism was found between the two histological variants of NSCLC, adenocarcinoma and squamous cell carcinoma, and no statistically significant associations were observed between P2X7 protein expression and the main clinico-pathological characteristics of the NSCLC patients.

Conclusions

Based on our results, P2X7 expression and polymorphisms seem to have no potential impact in patients with non-small cell lung cancer; however, further studies will surely provide deeper insights regarding the role of this receptor at the clinical level in NSCLC.

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.

Adenosine enhances progenitor cell recruitment and nerve growth via its A2B receptor during adult fin regeneration

A major issue in regenerative medicine is the control of progenitor cell mobilisation. Apoptosis has been reported as playing a role in cell plasticity, and it has been recently shown that apoptosis is necessary for organ and appendage regeneration. In this context, we explore its possible mode of action in progenitor cell recruitment during adult regeneration in zebrafish. Here, we show that apoptosis inhibition impairs blastema formation and nerve growth, both of which can be restored by exogenous adenosine acting through its A2B receptor. Moreover, adenosine increases the number of progenitor cells. Purinergic signalling is therefore an early and essential event in the pathway from lesion to blastema formation and provides new targets for manipulating cell plasticity in the adult.

P2X-selective purinergic antagonists are strong inhibitors of HIV-1 fusion during both cell-to-cell and cell-free infection

Human immunodeficiency virus type 1 (HIV-1) infection is chronic and presently still incurable. Antiretroviral drugs effectively suppress replication; however, persistent activation of inflammatory pathways remains a key cause of morbidity. Recent studies proposed that purinergic signaling is required for HIV-1 infection. Purinergic receptors are distributed throughout a wide variety of tissue types and detect extracellular ATP as a danger signal released from dying cells. We have explored how these pathways are involved in the transmission of HIV-1 from cell to cell through virological synapses. Infection of CD4+ T lymphocytes with HIV-1 in the presence of an inhibitor of P2X receptors effectively inhibited HIV-1 infection through both cell-free and cell-to-cell contact in a dose-dependent manner. Inhibition of direct cell-to-cell infection did not affect the formation of virological synapses or the subsequent cell-to-cell transfer of HIV-1. During both cell-free and cell-to-cell CD4+ T lymphocyte infection, purinergic antagonists blocked infection at the level of viral membrane fusion. During cell-to-cell transmission, we observed CXCR4 colocalization with the newly internalized virus particles within target lymphocytes and found that the purinergic antagonists did not impair the recruitment of the coreceptor CXCR4 to the site of Gag internalization in the target cell. In a screen of a library of purinergic antagonists, we found that the most potent inhibitors of HIV-1 fusion were those that target P2X receptors, while P2Y-selective receptor antagonists or adenosine receptor antagonists were ineffective. Our results suggest that P2X receptors may provide a therapeutic target and that purinergic antagonists may have potent activity against viral infection of CD4+ T lymphocytes by both cell-free and cell-to-cell transmission.

IMPORTANCE

This study identifies purinergic antagonists to be potent inhibitors of HIV-1 cell-free and cell-to-cell-mediated infection and provides a stepwise determination of when these compounds inhibit HIV-1 infection. These data provide a rationale for the development of novel antiretroviral therapies that have a dual role in both direct antiviral activity and the reduction of HIV-associated inflammation. Purinergic antagonists are shown here to have equivalent efficacy in inhibiting HIV infection via cell-free and cell-to-cell infection, and it is shown that purinergic receptors could provide an attractive therapeutic anti-HIV target that might avoid resistance by targeting a host signaling pathway that potently regulates HIV infection. The high-throughput screen of HIV-1 fusion inhibitors further defines P2X-selective compounds among the purinergic compounds as being the most potent HIV entry inhibitors. Clinical studies on these drugs for other inflammatory indications suggest that they are safe, and thus, if developed for use as anti-HIV agents, they could reduce both HIV replication and HIV-related inflammation.

Differentiating connexin hemichannels and pannexin channels in cellular ATP release

Adenosine triphosphate (ATP) plays a fundamental role in cellular communication, with its extracellular accumulation triggering purinergic signaling cascades in a diversity of cell types. While the roles for purinergic signaling in health and disease have been well established, identification and differentiation of the specific mechanisms controlling cellular ATP release is less well understood. Multiple mechanisms have been proposed to regulate ATP release with connexin (Cx) hemichannels and pannexin (Panx) channels receiving major focus. However, segregating the specific roles of Panxs and Cxs in ATP release in a plethora of physiological and pathological contexts has remained enigmatic. This multifaceted problem has arisen from the selectivity of pharmacological inhibitors for Panxs and Cxs, methodological differences in assessing Panx and Cx function and the potential compensation by other isoforms in gene silencing and genetic knockout models. Consequently, there remains a void in the current understanding of specific contributions of Panxs and Cxs in releasing ATP during homeostasis and disease. Differentiating the distinct signaling pathways that regulate these two channels will advance our current knowledge of cellular communication and aid in the development of novel rationally-designed drugs for modulation of Panx and Cx activity, respectively.

Natural compounds with P2X7 receptor-modulating properties

The adenosine 5'-triphosphate (ATP)-gated P2X7 receptor is a membrane-bound, non-selective cation channel, expressed in a variety of cell types. The P2X7 senses high extracellular ATP concentrations and seems to be implicated in a wide range of cellular functions as well as pathophysiological processes, including immune responses and inflammation, release of gliotransmitters and cytokines, cancer cell growth or development of neurodegenerative diseases. In the present study, we identified natural compounds and analogues that can block or sensitize the ATP (1 mM)-induced Ca(2+) response using a HEK293 cell line stably expressing human P2X7 and fluorometric imaging plate reader technology. For instance, teniposide potently blocked the human P2X7 at sub-miromolar concentrations, but not human P2X4 or rat P2X2. A marked block of ATP-induced Ca(2+) entry and Yo-Pro-1 uptake was also observed in human A375 melanoma cells and mouse microglial cells, both expressing P2X7. On the other hand, agelasine (AGL) and garcinolic acid (GA) facilitated the P2X7 response to ATP in all three cell populations. GA also enhanced the YO-PRO-1 uptake, whereas AGL did not affect the ATP-stimulated intracellular accumulation of this dye. According to the pathophysiological role of P2X7 in various diseases, selective modulators may have potential for further development, e.g. as neuroprotective or antineoplastic drugs.

Protease-activated receptor-2 induces migration of pancreatic cancer cells in an extracellular ATP-dependent manner

BACKGROUND

Protease-activated receptor 2 (PAR-2) is a G protein-coupled receptor suggested to play an important role in the proliferation and migration of tumor cells of epithelial origin. However, the role of PAR-2 in the setting of pancreatic cancer remains largely unexplored.

OBJECTIVES

To understand the importance of PAR-2 in pancreatic cancer cell migration.

METHODS AND RESULTS

The present study shows that PAR-2 does not affect pancreatic cancer cell proliferation but significantly induces the migration of pancreatic cancer cells in scratch assays. Interestingly, PAR-2 does not affect migration in a trans-well setting. This apparent discrepancy depends on extracellular ATP release in the scratch assays and the addition of exogenous (ATP)-induced PAR-2-dependent migration in trans-well assays, whereas a specific P2Y11 receptor antagonist prevents PAR-2-driven migration in scratch assays. In the scratch assays, inhibitors of Src, Rac, protein kinase C, mitogen-activated protein kinase kinase, p38, and epidermal growth factor (EGF) receptor blocked PAR-2-driven migration, whereas they did not affect fetal calf serum-driven wound closure.

CONCLUSION

Taken together, PAR-2 activation drives pancreatic cancer cell migration via an EGF-Src-Rac-p38/mitogen-activated protein kinase kinase/EGF1/2 signaling pathway, which is facilitated by extracellular ATP. Targeting the PAR-2/ATP-driven signaling pathway may therefore limit cell migration, which could inhibit pancreatic cancer metastasis.

Triptolide-mediated inhibition of interferon signaling enhances vesicular stomatitis virus-based oncolysis

Preclinical and clinical trials demonstrated that use of oncolytic viruses (OVs) is a promising new therapeutic approach to treat multiple types of cancer. To further improve their viral oncolysis, experimental strategies are now combining OVs with different cytotoxic compounds. In this study, we investigated the capacity of triptolide - a natural anticancer molecule - to enhance vesicular stomatitis virus (VSV) oncolysis in OV-resistant cancer cells. Triptolide treatment increased VSV replication in the human prostate cancer cell line PC3 and in other VSV-resistant cells in a dose- and time-dependent manner in vitro and in vivo. Mechanistically, triptolide (TPL) inhibited the innate antiviral response by blocking type I interferon (IFN) signaling, downstream of IRF3 activation. Furthermore, triptolide-enhanced VSV-induced apoptosis in a dose-dependent fashion in VSV-resistant cells, as measured by annexin-V, cleaved caspase-3, and B-cell lymphoma 2 staining. In vivo, using the TSA mammary adenocarcinoma and PC3 mouse xenograft models, combination treatment with VSV and triptolide delayed tumor growth and prolonged survival of tumor-bearing animals by enhancing viral replication. Together, these results demonstrate that triptolide inhibition of IFN production sensitizes prostate cancer cells to VSV replication and virus-mediated apoptosis.

High dose of extracellular ATP switched autophagy to apoptosis in anchorage-dependent and anchorage-independent hepatoma cells

Extracellular adenosine triphosphate (eATP) transduces purinergic signal and plays an important regulatory role in many biological processes, including tumor cell growth and cell death. A large amount of eATP exists in the fast-growing tumor center and inflammatory tumor microenvironment. Tumor cells could acquire anoikis resistance and anchorage independence in tumor microenvironment and further cause metastatic lesion. Whether such a high amount of eATP has any effect on the anchored and non-anchored tumor cells in tumor microenvironment has not been elucidated and is investigated in this study. Our data showed that autophagy helped hepatoma cells to maintain survival under the treatment of no more than 1 mM of eATP. Only when eATP concentration reached a relatively high level (2.5 mM), cell organelle could not be further maintained by autophagy, and apoptosis and cell death occurred. In hepatoma cells under treatment of 2.5 mM of eATP, an AMP-activated protein kinase (AMPK) pathway was dramatically activated while mTOR signaling pathway was suppressed in coordination with apoptosis. Further investigation showed that the AMPK/mTOR axis played a key role in tipping the balance between autophagy-mediated cell survival and apoptosis-induced cell death under the treatment of eATP. This work provides evidence to explain how hepatoma cells escape from eATP-induced cytotoxicity as well as offers an important clue to consider effective manipulation of cancer.

Extracellular ATP regulates FoxO family of transcription factors and cell cycle progression through PI3K/Akt in MCF-7 cells

BACKGROUND

Forkhead Box-O (FoxO) transcription factors regulate the expression of many genes involved in suppression. Released nucleotides can regulate intracellular signaling pathways through membrane-bound purinergic receptors, to promote or prevent malignant cell transformation. We studied the role of extracellular ATP in the modulation of Forkhead Box O (FoxO) transcription factors and of cell cycle progression in MCF-7 breast cancer cells.

METHODS

Western blot analysis, cell transfections with siRNA against Akt, immunocytochemistry, subcellular fractionation studies and flow cytometry analysis were performed.

RESULTS

ATP induced the phosphorylation of FoxO1/3a at threonine 24/32, whereas reduced the expression of FoxO1. In addition, ATP increased the expression of the cyclins D1 and D3 and down-regulated the cell cycle inhibitory proteins p21Cip1 and p27Kip1. The use of the phosphatidylinositol 3 kinase (PI3K) inhibitor, Ly294002, and/or of siRNA to reduce the expression of the serine/threonine kinase Akt showed that these effects are mediated by the PI3K/Akt signaling pathway. ATP induced the translocation of FoxO3a from the nucleus to the cytoplasm. Also, ATP increased the number of cells in the S phase of cell cycle; this effect was reverted by the use of Ly294002 and the proteasome inhibitor bortezomib.

CONCLUSION

Extracellular ATP induces the inactivation of FoxO transcription factors and cell cycle progression through the PI3K/Akt pathway in MCF-7 cells.

GENERAL SIGNIFICANCE

These findings provide new molecular basis for further understanding the mechanisms involved in ATP signal transduction in breast cancer cells, and should be considered for the development of effective breast cancer therapeutic strategies.

Purinergic signalling in bone

Purinergic signaling in bone was first proposed in the early 1990s with the observation that extracellular ATP could modulate events crucial to the normal functioning of bone cells. Since then the expression of nearly all the P2Y and P2X receptors by osteoblasts and osteoclasts has been reported, mediating multiple processes including cell proliferation, differentiation, function, and death. This review will highlight the most recent developments in the field of purinergic signaling in bone, with a special emphasis on recent work resulting from the European Framework 7 funded collaboration ATPBone, as well as Arthritis Research UK and Bone Research Society supported projects.

P2X7 receptor activation mediates organic cation uptake into human myeloid leukaemic KG-1 cells

The P2X7 purinergic receptor is an ATP-gated cation channel with an emerging role in neoplasia. In this study we demonstrate that the human KG-1 cell line, a model of acute myelogenous leukaemia, expresses functional P2X7. RT-PCR and immunochemical techniques demonstrated the presence of P2X7 mRNA and protein respectively in KG-l cells, as well as in positive control multiple myeloma RPMI 8226 cells. Flow cytometric measurements demonstrated that ATP induced ethidium(+) uptake into KG-l cells suspended in sucrose medium (EC(50) of ≈ 3 μM), but not into cells in NaCl medium. In contrast, ATP induced ethidium(+) uptake into RPMI 8226 cells suspended in either sucrose or NaCl medium (EC(50) of ≈ 3 or ≈ 99 μM, respectively), as well as into RPMI 8226 cells in KCl medium (EC(50) of ≈ 18 μM). BzATP and to a lesser extent ATPγS and αβ-methylene ATP, but not ADP or UTP, also induced ethidium(+) uptake into KG-1 cells. ATP-induced ethidium(+) uptake was completely impaired by the P2X7 antagonists, AZ10606120 and A-438079. ATP-induced ethidium(+) uptake was also impaired by probenecid but not by carbenoxolone, both pannexin-1 antagonists. ATP induced YO-PRO-1(2+) and propidium(2+) uptake into KG-1 cells. Finally, sequencing of full-length P2X7 cDNA identified several single nucleotide polymorphisms (SNPs) in KG-1 cells including H155Y, A348T, T357S and Q460R. RPMI 8226 cells contained A348T, A433V and H521Q SNPs. In conclusion, the KG-1 cell line expresses functional P2X7. This cell line may help elucidate the signalling pathways involved in P2X7-induced survival and invasiveness of myeloid leukaemic cells.

Involvement of P2Y13 receptor in suppression of neuronal differentiation

We examined the receptor-mediated effects of extracellular ATP on neuronal differentiation of PC12 cells, Neuro2a cells and MEB5 cells by using a series of receptor antagonists. The P2Y13 receptor antagonist MRS2211 significantly accelerated neurite outgrowth in all cases. Treatment with nerve growth factor (NGF) alone activated ERK1/2 in PC12 cells, and the activation was further increased by MRS2211. These results suggest involvement of P2Y13 receptor in suppression of neuronal differentiation. Thus, P2Y13 receptor antagonists might be candidates for treatment of neurodegenerative diseases.

Inhibition of ecto-ATPase activity by curcumin in hepatocellular carcinoma HepG2 cells

Effects of curcumin, a major constituent of turmeric, on ecto-nucleotidases have not been clarified. Here, we investigated whether curcumin affects ecto-nucleotidase activities in human hepatocellular carcinoma HepG2 cells. In the cells, high levels of Mg(2+)-dependent activity of ecto-nucleotidases were observed in the presence of 1 mM adenosine triphosphate (ATP). The activity was inhibited by ecto-ATPase inhibitors such as suramin, ZnCl(2) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. On the other hand, the activity was significantly decreased at alkaline pH (pH 9) and was not inhibited by levamisole, an inhibitor of alkaline phosphatase. In the presence of ATP, curcumin inhibited the activity in a concentration-dependent manner (IC(50) = 6.2 μM). In contrast, curcumin had no effects on ecto-nucleotidase activity in the presence of ADP (1 mM) or AMP (1 mM). The K (m) value for ATP hydrolysis of curcumin-sensitive ecto-ATPase was similar to the value of NTPDase2, an isoform of ecto-nucleoside triphosphate diphosphohydrolase. These results suggest that curcumin is a potent inhibitor of ecto-ATPase and may affect extracellular ATP-dependent responses.

Role of the purinergic system in patients with cervical intraepithelial neoplasia and uterine cancer

INTRODUCTION

Cervical cancer remains the second leading cause of death among women. Intraepithelial neoplasias and uterine invasive cancer are frequently associated with disturbances in coagulation and changes in the concentrations of adenine nucleotides. This work intended to analyze changes in extracellular adenine nucleotide hydrolysis and blood platelet aggregation in patients diagnosed for cervical intraepithelial neoplasia in different stages as well as uterine invasive cancer.

PATIENTS AND METHODS

NTPDase, E-NPP, 5'-nucleotidase, total ADA and its isoforms (ADA1 and ADA2), as well as the platelet aggregation from patients with different stages of cervical intraepithelial neoplasia (NICs I, NIC II, NIC III) and uterine invasive cancer were verified.

RESULTS

Neither ATP hydrolysis nor E-NPP activity was changed by the neoplasia stage. On the other hand, ADP and AMP hydrolysis as well as ADA activity were enhanced in NIC I group. AMP hydrolysis was also increased in the cancer group. ADA 1 was the ADA isoform found in platelets from both control and patient groups.

CONCLUSION

Our results showed for the first time that NTPDase, 5'-nucleotidase, E-NPP and ADA are not sensible regarding the grade of neoplasia development, since no significant difference was found between the groups studied. Only ADP hydrolysis and ADA activity showed a significant enhancement in NIC I group related to the other stages possibly as a result of the beginning of the neoplasic transformation. This increase could be reflecting a body's reaction against the probable high adenosine levels. We propose for the first time that the ADA isoform present in platelets is ADA 1.

Vascular CD39/ENTPD1 directly promotes tumor cell growth by scavenging extracellular adenosine triphosphate

Extracellular adenosine triphosphate (ATP) is known to boost immune responses in the tumor microenvironment but might also contribute directly to cancer cell death. CD39/ENTPD1 is the dominant ectonucleotidase expressed by endothelial cells and regulatory T cells and catalyzes the sequential hydrolysis of ATP to AMP that is further degraded to adenosine by CD73/ecto-5'-nucleotidase. We have previously shown that deletion of Cd39 results in decreased growth of transplanted tumors in mice, as a result of both defective angiogenesis and heightened innate immune responses (secondary to loss of adenosinergic immune suppression). Whether alterations in local extracellular ATP and adenosine levels as a result of CD39 bioactivity directly affect tumor growth and cytotoxicity has not been investigated to date. We show here that extracellular ATP exerts antitumor activity by directly inhibiting cell proliferation and promoting cancer cell death. ATP-induced antiproliferative effects and cell death are, in large part, mediated through P2X(7) receptor signaling. Tumors in Cd39 null mice exhibit increased necrosis in association with P2X(7) expression. We further demonstrate that exogenous soluble NTPDase, or CD39 expression by cocultured liver sinusoidal endothelial cells, stimulates tumor cell proliferation and limits cell death triggered by extracellular ATP. Collectively, our findings indicate that local expression of CD39 directly promotes tumor cell growth by scavenging extracellular ATP. Pharmacological or targeted inhibition of CD39 enzymatic activity may find utility as an adjunct therapy in cancer management.

The therapeutic potential of adenosine triphosphate as an immune modulator in the treatment of HIV/AIDS: a combination approach with HAART

Extracellular adenosine triphosphate (eATP) is a potent molecule that has the capacity to modulate various aspects of cell functions including gene expression. This element of modulation is essential to the role of ATP as a therapeutic agent. The hypothesis presented is that ATP can have an important impact on the treatment of HIV infection. This is supported in part by published research, although a much greater role for ATP is suggested than prior authors ever thought possible. ATP has the ability to enhance the immune system and could thus improve the host's own defense mechanisms to eradicate the virus-infected cells and restore normal immune function. This could provide effective therapy when used in conjunction with highly active antiretroviral therapies (HAART) to eliminate the latently infected cells. The key lies in applying ATP through the methodology described. This article presents a strategy for using ATP therapeutically along with background evidence to substantiate the importance of using ATP in the treatment of HIV infection.

Extracellular heat shock protein (Hsp)70 and Hsp90α assist in matrix metalloproteinase-2 activation and breast cancer cell migration and invasion

Breast cancer is second only to lung cancer in cancer-related deaths in women, and the majority of these deaths are caused by metastases. Obtaining a better understanding of migration and invasion, two early steps in metastasis, is critical for the development of treatments that inhibit breast cancer metastasis. In a functional proteomic screen for proteins required for invasion, extracellular heat shock protein 90 alpha (Hsp90α) was identified and shown to activate matrix metalloproteinase 2 (MMP-2). The mechanism of MMP-2 activation by Hsp90α is unknown. Intracellular Hsp90α commonly functions with a complex of co-chaperones, leading to our hypothesis that Hsp90α functions similarly outside of the cell. In this study, we show that a complex of co-chaperones outside of breast cancer cells assists Hsp90α mediated activation of MMP-2. We demonstrate that the co-chaperones Hsp70, Hop, Hsp40, and p23 are present outside of breast cancer cells and co-immunoprecipitate with Hsp90α in vitro and in breast cancer conditioned media. These co-chaperones also increase the association of Hsp90α and MMP-2 in vitro. This co-chaperone complex enhances Hsp90α-mediated activation of MMP-2 in vitro, while inhibition of Hsp70 in conditioned media reduces this activation and decreases cancer cell migration and invasion. Together, these findings support a model in which MMP-2 activation by an extracellular co-chaperone complex mediated by Hsp90α increases breast cancer cell migration and invasion. Our studies provide insight into a novel pathway for MMP-2 activation and suggest Hsp70 as an additional extracellular target for anti-metastatic drug development.

Emerging role of damage-associated molecular patterns derived from mitochondria in inflammation

Cell death and injury often lead to release or exposure of intracellular molecules called damage-associated molecular patterns (DAMPs) or cell death-associated molecules. These molecules are recognized by the innate immune system by pattern recognition receptors - the same receptors that detect pathogen-associated molecular patterns, thus revealing similarities between pathogen-induced and non-infectious inflammatory responses. Many DAMPs are derived from the plasma membrane, nucleus, endoplasmic reticulum and cytosol. Recently, mitochondria have emerged as other organelles that function as a source of DAMPs. Here, we highlight the significance of mitochondrial DAMPs and discuss their contribution to inflammation and development of human pathologies.

Extracellular ATP signaling during differentiation of C2C12 skeletal muscle cells: role in proliferation

Evidence shows that extracellular ATP signals influence myogenesis, regeneration and physiology of skeletal muscle. Present work was aimed at characterizing the extracellular ATP signaling system of skeletal muscle C2C12 cells during differentiation. We show that mechanical and electrical stimulation produces substantial release of ATP from differentiated myotubes, but not from proliferating myoblasts. Extracellular ATP-hydrolyzing activity is low in myoblasts and high in myotubes, consistent with the increased expression of extracellular enzymes during differentiation. Stimulation of cells with extracellular nucleotides produces substantial Ca(2+) transients, whose amplitude and shape changed during differentiation. Consistently, C2C12 cells express several P2X and P2Y receptors, whose level changes along with maturation stages. Supplementation with either ATP or UTP stimulates proliferation of C2C12 myoblasts, whereas excessive doses were cytotoxic. The data indicate that skeletal muscle development is accompanied by major functional changes in extracellular ATP signaling.