Adenine nucleotides inhibit proliferation of the human lung adenocarcinoma cell line LXF-289 by activation of nuclear factor kappaB1 and mitogen-activated protein kinase pathways

Metabolomic, transcriptomic and genetic integrative analysis reveals important roles of adenosine diphosphate in haemostasis and platelet activation in non-small-cell lung cancer

Lung cancer is the leading cause of cancer‐related deaths in the world. The most prevalent subtype, accounting for 85% of cases, is non‐small‐cell lung cancer (NSCLC). Lung squamous cell carcinoma (LUSC) and lung adenocarcinoma (LUAD) are the most common subtypes. Despite recent advances in treatment, the low 5‐year survival rate of NSCLC patients (approximately 13%) reflects the lack of early diagnostic biomarkers and incomplete understanding of the underlying disease mechanisms. We hypothesized that integration of metabolomic, transcriptomic and genetic profiles of tumours and matched normal tissues could help to identify important factors and potential therapeutic targets that contribute to tumorigenesis. We integrated omics profiles in tumours and matched adjacent normal tissues of patients with LUSC (N = 20) and LUAD (N = 17) using multiple system biology approaches. We confirmed the presence of previously described metabolic pathways in NSCLC, particularly those mediating the Warburg effect. In addition, through our combined omics analyses we found that metabolites and genes that contribute to haemostasis, angiogenesis, platelet activation and cell proliferation were predominant in both subtypes of NSCLC. The important roles of adenosine diphosphate in promoting cancer metastasis through platelet activation and angiogenesis suggest this metabolite could be a potential therapeutic target.

Adenosine diphosphate-sensitive P2Y11 receptor inhibits endothelial cell proliferation by induction of cell cycle arrest in the S phase and induces the expression of inflammatory mediators

Extracellular adenosine diphosphate (ADP) mediates a wide range of physiological effects as an extracellular signaling molecule, including platelet aggregation, vascular tone, cell proliferation, and apoptosis by interacting with plasma membrane P2 receptors. However, the effect of ADP on cell proliferation was contradictory. In this study, we found that ADP significantly inhibited cell proliferation of human umbilical vein endothelial cells at high concentrations (50 to 100 µM). Treatment with ADP did not induce cell apoptosis but instead induced cell cycle arrest in the S phase, which may be partly due to the downregulation of cyclin B1. The inhibition of cell proliferation was blocked by suramin, a nonspecific antagonist of the P2 receptors, and high concentrations of ADP significantly upregulated the messenger RNA (mRNA) and protein expression of P2Y11 in endothelial cells. Moreover, the downregulation of P2Y11 by RNA interference reversed the inhibition of cell proliferation. In addition, ADP (100 µM) can induce the formation of cytosolic autophagy in endothelial cells and a rapid phosphorylation of extracellular signal regulated kinase (ERK) 1/2, which is a canonical signal molecule downstream of P2Y receptors, accompanied by a mRNA expression of proinflammatory cytokines such as intercellular adhesion molecule 1 and vascular cell adhesion molecule 1. Taken together, our study excludes a mechanism for extracellular ADP impairing endothelial cells proliferation via P2Y11 receptor by downregulating cyclin B1 and arresting cell cycle at the S phase, besides, ADP induces cell autophagy and mRNA expression of inflammatory cytokines, whether it is mediated by Erk signaling pathways needs further studies to confirm.

Nucleolin down-regulation is involved in ADP-induced cell cycle arrest in S phase and cell apoptosis in vascular endothelial cells

High concentration of extracellular ADP has been reported to induce cell apoptosis, but the molecular mechanisms remain not fully elucidated. In this study, we found by serendipity that ADP treatment of human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC) down-regulated the protein level of nucleolin in a dose- and time-dependent manner. ADP treatment did not decrease the transcript level of nucloelin, suggesting that ADP might induce nucleolin protein degradation. HUVEC and HAEC expressed ADP receptor P2Y13 receptor, but did not express P2Y1 or P2Y12 receptors. However, P2Y1, 12, 13 receptor antagonists MRS2179, PSB0739, MRS2211 did not inhibit ADP-induced down-regulation of nucleolin. Moreover, MRS2211 itself down-regulated nucleolin protein level. In addition, 2-MeSADP, an agonist for P2Y1, 12 and 13 receptors, did not down-regulate nucleolin protein. These results suggested that ADP-induced nucleolin down-regulation was not due to the activation of P2Y1, 12, or 13 receptors. We also found that ADP treatment induced cell cycle arrest in S phase, cell apoptosis and cell proliferation inhibition via nucleolin down-regulation. The over-expression of nucleolin by gene transfer partly reversed ADP-induced cell cycle arrest, cell apoptosis and cell proliferation inhibition. Furthermore, ADP sensitized HUVEC to cisplatin-induced cell death by the down-regulation of Bcl-2 expression. Taken together, we found, for the first time to our knowledge, a novel mechanism by which ADP regulates cell proliferation by induction of cell cycle arrest and cell apoptosis via targeting nucelolin.

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.

Lung inflammation caused by adenosine-5'-triphosphate is mediated via Ca2+/PKCs-dependent COX-2/PGE2 induction

Up-regulation of cyclooxygenase (COX)-2 and prostaglandin E2 (PGE2) are implicated in lung inflammation. Adenosine 5'-triphosphate (ATP) has been shown to act via activation of P2 purinoceptors, leading to COX-2 expression in various inflammatory diseases. The mechanisms of ATP-induced COX-2 expression and PGE2 release remain unclear. We showed that pretreatment with the inhibitors of P2 receptors (PPADS and Suramin), Gq protein (GPA2A), phosphatidylcholine-phospholipase C (PC-PLC; D609), phosphoinositide-phospholipase C (PI-PLC; ET-18-OCH3), Ca(2+)/calmodulin-dependent protein kinase II (CaMKII; KN62), protein kinase C (PKC; Gö6976, Ro-318220, GF109203X, and rottlerin), MEK1/2 (PD98059), p38 MAPK (SB202190), and nuclear factor-kappaB (NF-κB; Bay11-7082) and the intracellular calcium chelator (BAPTA/AM) or transfection with siRNAs of these molecules and cPLA2 reduced ATPγS-induced COX-2 expression or PGE2 production in A549 cells. In addition, ATPγS-induced elevation of intracellular Ca(2+) concentration was attenuated by PPADS, Suramin, D609, or ET-18-OCH3. ATPγS-induced p38 MAPK, p42/p44 MAPK, and NF-κB p65 activation were inhibited by Gö6976, Ro-318220, GF109203X, or rottlerin. ATPγS also induced cPLA2 phosphorylation and activity, which were reduced via inhibition of P2 receptors, PKCs, p38 MAPK, and p42/p44 MAPK. ATPγS-induced cPLA2 expression was inhibited by SB202190, PD98059, or Bay11-7082. In the in vitro study, we established that ATPγS induced PGE2 generation via a cPLA2/COX-2-dependent pathway. In the in vivo study, we found that ATPγS induced COX-2 mRNA expression in the lungs and leukocyte (mainly eosinophils and neutrophils) count in bronchoalveolar lavage (BAL) fluid in mice via a P2 receptors-dependent signaling pathway. We concluded that ATPγS may induce lung inflammation via a cPLA2/COX-2/PGE2-dependent pathway.

Cell type-specific effects of Adenosine 5'-triphosphate and pyrophosphate on the antitumor activity of doxorubicin

Extracellular ATP is an important signaling molecule mediating quite divergent specific biological effects. Even though recent studies suggest a potential role of ATP in cancer progress, its real impact in chemotherapeutic efficacy remains unclear. In the present study, we investigated the effect of ATP on the cytotoxicity of doxorubicin in various cancer cell types and found that ATP had no effect on doxorubicin cytotoxicity in colon, prostate, breast, and cervical cancers or in osteosarcoma. In contrast, ATP has divergent effects on lung cancer cells: it can protect against doxorubicin-induced cell death in non-metastatic lung cancer CL1.0 cells, but not in highly metastatic CL1.5 cells. Both apoptotic (characterized by sub-G(1) peak, caspase 3 activation, poly(ADP-ribose) polymerase-1 cleavage) and necrotic (characterized by propidium iodide uptake and ROS production) features induced by doxorubicin in CL1.0 cells were reduced by ATP. In addition, ATP attenuated p53 accumulation, DNA damage (assessed by poly(ADP-ribose) formation and the comet assay) and topoisomerase II inhibition after doxorubicin treatment, and doxorubicin cytotoxicity was diminished by the p53 inhibitor pifithrin-α. Moreover, UTP, UDP, ADP, and pyrophosphate sodium pyrophosphate tetrabasic decahydrate diminished the antitumor effect of doxorubicin in CL1.0 cells, whereas purinergic P2 receptors antagonists did not abrogate the action of ATP. In summary, ATP fails to alter the antitumor efficacy of doxorubicin in most cancer cell types, except in CL1.0 cells, in which pyrophosphate mediates the cell protection afforded by ATP via attenuation of reactive oxygen species production, DNA damage, p53 accumulation, and caspase activation.

Purines as potential morphogens during embryonic development

Components of purinergic signalling are expressed in the early embryo raising the possibility that ATP, ADP and adenosine may contribute to the mechanisms of embryonic development. We summarize the available data from four developmental models—mouse, chick, Xenopus and zebrafish. While there are some notable examples where purinergic signalling is indeed important during development, e.g. development of the eye in the frog, it is puzzling that deletion of single components of purinergic signalling often results in rather minor developmental phenotypes. We suggest that a key step in further analysis is to perform combinatorial alterations of expression of purinergic signalling components to uncover their roles in development. We introduce the concept that purinergic signalling could create novel morphogenetic fields to encode spatial location via the concentration of ATP, ADP and adenosine. We show that using minimal assumptions and the known properties of the ectonucleotidases, complex spatial patterns of ATP and adenosine can be set up. These patterns may provide a new way to assess the potential of purinergic signalling in developmental processes.

P2Y11 impairs cell proliferation by induction of cell cycle arrest and sensitizes endothelial cells to cisplatin-induced cell death

Extracellular ATP mediates a wide range of physiological effects, including cell proliferation, differentiation, maturation, and migration. However, the effect of ATP on cell proliferation has been contradictory, and the mechanism is not fully understood. In the current study, we found that extracellular ATP significantly inhibited the proliferation of human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs). Treatment with ATP did not induce cell apoptosis but instead induced cell cycle arrest in S phase. ATP induced the phosphorylation of ERK1/2, but the ERK inhibitors, U0126 and PD9809, did not regulate the inhibition of cell proliferation induced by ATP. However, ATP-induced inhibition of cell proliferation was blocked by suramin, a nonspecific antagonist of the P2Y receptors, and endothelial cells expressed P2Y11, a P2Y receptor that specifically binds ATP. Moreover, the down-regulation of P2Y11 by RNA interference not only reversed the inhibition of cell proliferation but also ameliorated cell cycle arrest in S phase. In addition, P2Y11 sensitized endothelial cells to cisplatin-induced cell death by down-regulation of the expression of Bcl-2. Taken together, these results suggest that extracellular ATP impairs cell proliferation by triggering signaling to induce cell cycle arrest and sensitizes cell to death via P2Y11 in endothelial cells.

Purinergic signaling in wound healing and airway remodeling

Airway epithelia are continuously damaged by airborne pollutants, pathogens and allergens, and they rely on intrinsic mechanisms to restore barrier integrity. Epithelial repair is a multi-step process including cell migration into the wounded area, proliferation, differentiation and matrix deposition. Each step requires the secretion of various molecules, including growth factors, integrins and matrix metalloproteinases. Evidence is emerging that purinergic signaling promotes repair in human airway epithelia. An injury induces ATP release, which binds P2Y(2) receptors (P2Y(2)Rs) to initiate protein kinase C (PKC)-dependent oxidative activation of TNFα-converting enzyme (TACE), which then releases the membrane-bound ligands of the epidermal growth factor receptor (EGFR). The P2Y(2)R- and EGFR-dependent signaling cascades converge to induce mediator release, whereas the latter also induces cytoskeletal rearrangement for cell migration and proliferation. Similar roles for purinergic signaling are reported in pulmonary endothelial cells, smooth muscle cells and fibroblasts. In chronic airway diseases, the aberrant regulation of extracellular purines is implicated in the development of airway remodeling by mucus cell metaplasia and hypersecretion, excess collagen deposition, fibrosis and neovascularization. This chapter describes the crosstalk between these signaling cascades and discusses the impact of deregulated purinergic signaling in chronic lung diseases.

Effect of adenosine 5'-triphosphate infusions on the nutritional status and survival of preterminal cancer patients

The aim of the study was to investigate the effect of intravenous infusions of adenosine 5'-triphosphate (ATP) on nutritional status and survival in preterminal cancer patients. Ninety-nine preterminal cancer patients (estimated life expectancy 1-6 months) with mixed tumor types were randomly allocated to receive either intravenous ATP weekly (8-10 h/week, maximum 50 microg/kg/min) for 8 weeks, or no ATP (control group). Nutritional status parameters were assessed until 8 weeks, and analyzed by repeated-measures analysis of covariance. Cox proportional hazards models were fitted to assess the effect of ATP on short-term (0-8 weeks) and long-term (0-6 months) survival. Fifty-one patients were randomized to ATP and 48 to the control group. Results showed a significant favorable effect of ATP on triceps skin fold thickness [between-group difference per 8 weeks 1.76 mm, 95% confidence interval (CI): 0.48-3.12 mm; P = 0.009] and on short-term survival [0-8 weeks hazard ratio (HR): 0.40, 95% CI: 0.17-0.95; P = 0.037]. In weight-stable patients and in lung cancer patients, long-term survival (0-6 months) was also significantly better in ATP-treated patients (weight-stable patients HR: 0.40, 95% CI: 0.19-0.83; P = 0.014; patients with lung cancer: HR: 0.35, 95% CI: 0.14-0.88; P = 0.025). In conclusion, in this population of preterminal cancer patients, ATP infusions, at the dose and schedule studied, had a favorable effect on triceps skin fold thickness and survival, especially in weight-stable patients and patients with lung cancer. Larger studies are warranted to confirm these findings and to further define the effect of ATP on tumor growth and survival.

The biological functions of NF-kappaB1 (p50) and its potential as an anti-cancer target

Nuclear factor-kappaB (NF-kappaB) is a key transcriptional factor family that consists of five members in mammalian cells, including NF-kappaB1 (p50), NF-kappaB2 (p52), RelA (p65), RelB and c-Rel. NF-kappaB is implicated in multiple physiological and pathological processes, including cell proliferation and differentiation, inflammatory and immune response, cell survival and apoptosis, cellular stress reactions and tumorigenesis. Recent studies by our group and others have highlighted the novel functions of the p50 protein. In this review, we will focus on the regulation and functions of NF-kappaB p50.

Hetero-oligomerization of the P2Y11 receptor with the P2Y1 receptor controls the internalization and ligand selectivity of the P2Y11 receptor

Nucleotides signal through purinergic receptors such as the P2 receptors, which are subdivided into the ionotropic P2X receptors and the metabotropic P2Y receptors. The diversity of functions within the purinergic receptor family is required for the tissue-specificity of nucleotide signalling. In the present study, hetero-oligomerization between two metabotropic P2Y receptor subtypes is established. These receptors, P2Y1 and P2Y11, were found to associate together when co-expressed in HEK293 cells. This association was detected by co-pull-down, immunoprecipitation and FRET (fluorescence resonance energy transfer) experiments. We found a striking functional consequence of the interaction between the P2Y11 receptor and the P2Y1 receptor where this interaction promotes agonist-induced internalization of the P2Y11 receptor. This is remarkable because the P2Y11 receptor by itself is not able to undergo endocytosis. Co-internalization of these receptors was also seen in 1321N1 astrocytoma cells co-expressing both P2Y11 and P2Y1 receptors, upon stimulation with ATP or the P2Y1 receptor-specific agonist 2-MeS-ADP. 1321N1 astrocytoma cells do not express endogenous P2Y receptors. Moreover, in HEK293 cells, the P2Y11 receptor was found to functionally associate with endogenous P2Y1 receptors. Treatment of HEK293 cells with siRNA (small interfering RNA) directed against the P2Y1 receptor diminished the agonist-induced endocytosis of the heterologously expressed GFP-P2Y11 receptor. Pharmacological characteristics of the P2Y11 receptor expressed in HEK293 cells were determined by recording Ca2+ responses after nucleotide stimulation. This analysis revealed a ligand specificity which was different from the agonist profile established in cells expressing the P2Y11 receptor as the only metabotropic nucleotide receptor. Thus the hetero-oligomerization of the P2Y1 and P2Y11 receptors allows novel functions of the P2Y11 receptor in response to extracellular nucleotides.