The P2X 7 receptor is a ligand-gated cation-selective channel that mediates ATP-induced apoptosis of cells of the immune system. We and others have shown that P2X 7 is nonfunctional both in lymphocytes and monocytes from some subjects. To study a possible genetic basis we sequenced DNA coding for the carboxyl-terminal tail of P2X 7 . In 9 of 45 normal subjects a heterozygous nucleotide substitution (1513A3 C) was found, whereas 1 subject carried the homozygous substitution that codes for glutamic acid to alanine at amino acid position 496. Surface expression of P2X 7 on lymphocytes was not affected by this E496A polymorphism, demonstrated both by confocal microscopy and immunofluorescent staining. Monocytes and lymphocytes from the E496A homozygote subject expressed nonfunctional receptor, whereas heterozygotes showed P2X 7 function that was half that of germline P2X 7 . Results of transfection experiments showed that the mutant P2X 7 receptor was nonfunctional when expressed at low receptor density but regained function at a high receptor density. This density dependence of mutant P2X 7 function was also seen on differentiation of fresh monocytes to macrophages with interferon-␥, which up-regulated mutant P2X 7 and partially restored its function. P2X 7 -mediated apoptosis of lymphocytes was impaired in homozygous mutant P2X 7 compared with germline (8.6 versus 35.2%). The data suggest that the glutamic acid at position 496 is required for optimal assembly of the P2X 7 receptor.Purinergic P2X 7 receptors are ligand-gated cation channels, present on cells of the immune and hemopoietic system, that have been shown to mediate the ATP-induced apoptotic death of monocytes (1), macrophages (2), and lymphocytes (3, 4). The P2X 7 receptor family has two transmembrane domains with intracellular amino and carboxyl termini and an oligomeric structure in the plasma membrane based on trimeric or larger complexes of identical subunits (5). Moreover, the P2X7 receptor does not appear to form heteropolymers with other P2X subtypes (6). The genes for both the rat and human P2X 7 receptors have now been cloned and show extensive homology (30 -40%) with the other members of the P2X receptor family, although P2X 7 differs in having a long carboxyl terminus of 240 amino acids from the inner membrane face (7). The genomic structure of P2X 7 consists of 13 exons, with exon 12 and exon 13 coding for the C-terminal tail of this molecule. There is strong evidence that this long carboxyl terminus is necessary for the permeability properties of the P2X 7 receptor, because truncation of this tail abolishes ATP-induced uptake of the fluorescent dye YoPro-1 (8). Studies of P2X 7 of macrophages or lymphocytes as well as of human embryonic kidney cells (HEK-293) expressing the cDNA for P2X 7 have shown features that are most unusual for a channel. These include the slow further dilatation following channel opening (9) and the activation of various proteases including membrane metalloproteases (10) and intracellular caspases (2, 11). The fully ...

The P2X 7 receptor is a ligand-gated channel that is highly expressed on mononuclear cells and that mediates ATP-induced apoptosis of these cells. Wide variations in the function of the P2X 7 receptor have been observed, in part because of a loss-of-function polymorphism that changes Glu-496 to Ala without affecting the surface expression of the receptor on lymphocytes. In this study a second polymorphism (Ile-568 to Asn) has been found in heterozygous dosage in three of 85 normal subjects and in three of 45 patients with chronic lymphocytic leukemia. P2X 7 function was measured by ATPinduced fluxes of Rb ؉ , Ba 2؉ , and ethidium ؉ into various lymphocyte subsets and was decreased to values of ϳ25% of normal. The expression of the P2X 7 receptor on lymphocytes was approximately half that of normal values as measured by the binding of fluorescein-conjugated monoclonal antibody. Transfection experiments showed that P2X 7 carrying the Ile-568 to Asn mutation was non-functional because of the failure of cell surface expression. The differentiation of monocytes to macrophages with interferon-␥ up-regulated P2X 7 function in cells heterozygous for the Ile-568 to Asn mutation to a value around 50% of normal. These data identify a second loss-of-function polymorphism within the P2X 7 receptor and show that Ile-568 is critical to the trafficking domain, which we have shown to lie between residues 551 and 581.The purinergic P2X 7 receptor is a ligand-gated channel, selective for cationic permeants, which has a wide distribution including cells of the immune and hemopoietic system (1, 2). Activation of this receptor by brief exposure to extracellular ATP opens a channel that allows Ca 2ϩ and Na ϩ influx and K ϩ efflux and that initiates a cascade of intracellular downstream events. These include the stimulation of phospholipase D (3, 4), the activation of membrane metalloproteases (5-7), and the stimulation of intracellular caspases, which eventually lead to the apoptotic death of the target cell (8, 9). P2X 7 activation also leads to extensive membrane blebbing (10), which is a typical morphological feature of the apoptotic process. P2X 7 receptors have two transmembrane domains with intracellular amino and carboxyl termini, and the P2X 7 receptor differs from other members of the P2X receptor family in having a long carboxyl terminus of 240 amino acids from the inner membrane face (11). This long carboxyl terminus is necessary for the permeability properties of the P2X 7 receptor because truncation of this tail abolishes ATP-induced uptake of the fluorescent dye Yo-Pro-1 (12). P2X 7 has an oligomeric structure in the membrane based on trimeric or larger complexes of identical subunits (13,14), and there is evidence that P2X 7 interacts with a number of structural and adhesion proteins in a complex at the cell surface (15). Phosphorylation of a tyrosine at amino acid 343 of the P2X 7 primary structure has been proposed as being important for maintaining the full activity of the P2X 7 channel (15). A number of regulatory d...

The P2X 7 receptor is a ligand-gated channel that is highly expressed on mononuclear cells of the immune system and that mediates ATP-induced apoptosis. Wide variations in the function of the P2X 7 receptor have been observed, explained in part by loss-of-function polymorphisms that change Glu 496 to Ala (E496A) and Ile 568 to Asn (I568N). In this study, a third polymorphism, which substitutes an uncharged glutamine for the highly positively charged Arg 307 (R307Q), has been found in heterozygous dosage in 12 of 420 subjects studied. P2X 7 function was measured by ATP-induced fluxes of Rb ؉ , Ba 2؉ , and ethidium ؉ into peripheral blood monocytes or various lymphocyte subsets and was either absent or markedly decreased. Transfection experiments showed that P2X 7 carrying the R307Q mutation lacked either channel or pore function despite robust protein synthesis and surface expression of the receptor. The monoclonal antibody (clone L4) that binds to the extracellular domain of wild type P2X 7 and blocks P2X 7 function failed to bind to the R307Q mutant receptor. Differentiation of monocytes to macrophages up-regulated P2X 7 function in cells heterozygous for the R307Q to a value 10 -40% of that for wild type macrophages. However, macrophages from a subject who was double heterozygous for R307Q/I568N remained totally non-functional for P2X 7 , and lymphocytes from the same subject also lacked ATP-stimulated phospholipase D activity. These data identify a third loss-of-function polymorphism affecting the human P2X 7 receptor, and since the affected Arg 307 is homologous to those amino acids essential for ATP binding to P2X 1 and P2X 2 , it is likely that this polymorphism abolishes the binding of ATP to the extracellular domain of P2X 7 .In cells of the hemopoietic and immune systems, extracellular ATP can induce cytolysis of lymphocytes (1), monocytes/ macrophages (2), and dendritic cells (3). It is generally accepted that these cytolytic effects of ATP are mediated by the P2X 7 receptor, which is a ligand-gated cation channel activated by extracellular ATP and highly expressed on these cell types (4, 5 P2X receptors have an oligomeric structure in the plasma membrane based on trimeric or larger complexes of identical subunits (20,21). Moreover the values of Hill coefficients derived from the sigmoid ATP dose-response curves of the P2X 7 (P2Z) receptor are consistent with multiple ATP-binding sites in each P2X 7 trimer (8,22,23). All seven members of the P2X receptor family have two transmembrane domains with intracellular amino and carboxyl termini. Little is known of the conformation of the extracellular domain containing the ATPbinding site(s). An analysis of the P2X subtype sequence homology has shown that the two transmembrane domains M1 and M2 are separated by an extracellular sequence containing a cysteine-rich region (residues 110 -170) followed by a segment from Phe 188 -Val 321 that may form six antiparallel ␤-pleated sheets homologous with members of the class II aminoacyl-tRNA synthetases (24). The ATP-...

P2X7 is a transmembrane receptor expressed in multiple cell types including neurons, dendritic cells, macrophages, monocytes, B and T cells where it can drive a wide range of physiological responses from pain transduction to immune response. Upon activation by its main ligand, extracellular ATP, P2X7 can form a nonselective channel for cations to enter the cell. Prolonged activation of P2X7, via high levels of extracellular ATP over an extended time period can lead to the formation of a macropore, leading to depolarization of the plasma membrane and ultimately to cell death. Thus, dependent on its activation state, P2X7 can either drive cell survival and proliferation, or induce cell death. In cancer, P2X7 has been shown to have a broad range of functions, including playing key roles in the development and spread of tumor cells. It is therefore unsurprising that P2X7 has been reported to be upregulated in several malignancies. Critically, ATP is present at high extracellular concentrations in the tumor microenvironment (TME) compared to levels observed in normal tissues. These high levels of ATP should present a survival challenge for cancer cells, potentially leading to constitutive receptor activation, prolonged macropore formation and ultimately to cell death. Therefore, to deliver the proven advantages for P2X7 in driving tumor survival and metastatic potential, the P2X7 macropore must be tightly controlled while retaining other functions. Studies have shown that commonly expressed P2X7 splice variants, distinct SNPs and posttranslational receptor modifications can impair the capacity of P2X7 to open the macropore. These receptor modifications and potentially others may ultimately protect cancer cells from the negative consequences associated with constitutive activation of P2X7. Significantly, the effects of both P2X7 agonists and antagonists in preclinical tumor models of cancer demonstrate the potential for agents modifying P2X7 function, to provide innovative cancer therapies. This review summarizes recent advances in understanding of the structure and functions of P2X7 and how these impact P2X7 roles in cancer progression. We also review potential therapeutic approaches directed against P2X7.

Recent evidence suggested that ATP acting via ionotropic (P2X) and metabotropic (P2Y) purinergic receptors might be involved in signaling between glial cells and within glial-neuronal networks. In contrast to their neuronal counterpart, the identity of P2X receptors in CNS glial cells is largely unknown. In the present study, antibodies recognizing the subunits P2X1-P2X7 were applied together with the astroglial marker S100beta and nuclear labeling with Hoechst 33342 to investigate semiquantitatively the distribution of the whole set of P2X receptors in astrocytes of the juvenile rat hippocampus. Expression of P2X1-P2X4, P2X6, and P2X7 subunits was observed in astrocytes of various hippocampal subregions, but the cells were completely devoid of P2X5 protein. S100beta-positive cells expressing subunits P2X3-P2X7 occurred evenly in the different subfields, while P2X1- and P2X2-positive astrocytes were distributed more heterogeneously. The staining pattern of P2X subunits also differed at the subcellular level. Antibodies against P2X2 and P2X4 labeled both astroglial cell bodies and processes. Immunoreactivity for P2X1 and P2X6 was mainly confined to somatic areas of S100beta-positive cells, whereas the subunit P2X3 was primarily localized along astroglial processes. Knowledge of the distribution of P2X receptors might provide a basis for a better understanding of their specific role in cell-cell signaling.

The appearance of P2X(7) receptors in normal prostate tissue adjacent to prostate tumours makes direct tumour biopsy less critical for positive cancer diagnosis and enables cancer progression to be monitored.

The present study investigated the topographical distribution of P2X(1)-P2X(6) receptor subtypes in the rat and common marmoset hindbrain by immunohistochemistry. In addition, double-labeling immunofluorescence was used to determine the extent of colocalization between catecholamine cell groups and the various P2X receptors. The data demonstrate a widespread distribution pattern for all six P2X receptors throughout both the rat hindbrain and the marmoset hindbrain, although distinctions between species, brain nuclei, and P2X receptor subtypes exist. In rat, dense staining for the P2X receptors was found in the nucleus of the solitary tract (NTS), medial vestibular nucleus, and medial and lateral parabrachial nuclei. Moderate staining was observed in the hypoglossal nucleus, cuneate nucleus, inferior olive, prepositus hypoglossi, rostral ventrolateral medulla (RVLM), and locus coeruleus. Staining was also observed in the gracile nucleus, the mesencephalic trigeminal nucleus, and the central pontine gray. In marmoset, prominent P2X receptor-like immunoreactivity occurred in the NTS, medial cuneate nucleus, prepositus hypoglossi, and medial vestibular nucleus. Moderate staining was observed in the area postrema, dorsal motor nucleus of the vagus, lateral cuneate, lateral reticular, spinal trigeminal nucleus, RVLM, and inferior olive. Immunofluorescent double labeling of tyrosine hydroxylase (TH)-containing cells revealed that all subtypes of P2X receptors show some degree of colocalization with TH. The highest proportion of TH and P2X receptor double labeling was in the A5 region (with the P2X(2) subunit), whereas the lowest proportion of double-labeled cells occurred in the C2 region of the NTS for the P2X(5) subunit. These findings support a role for extracellular adenosine 5'-triphosphate in fast synaptic neurotransmission within the brainstem.

In human erythrocytes, infection by the malaria parasite Plasmodium falciparum or oxidative stress induces a new organic osmolyte and anion permeability. To examine a role for autocrine purinoceptor signaling during this induction process, erythrocytic purinoceptor expression, and ATP release were determined. Furthermore, using pharmacological and genetic approaches the dependence on purinoceptor signaling of osmolyte permeability and Plasmodium development, both in vitro and in vivo, were assessed. Extracellular ATP did not induce an osmolyte permeability in non-infected or non-oxidized erythrocytes. ATP and other purinoceptor agonists increased the induction of osmolyte permeability during infection or oxidation as measured by isosmotic hemolysis and patch-clamp recording. Purinoceptor antagonists and apyrase decreased the induced permeability. The observed pharmacology suggested the involvement of P2Y purinoceptors. Accordingly, human erythrocytes expressed P2Y1 protein. Moreover, P2Y1-deficient mouse erythrocytes exhibited a delayed appearance of the osmolyte permeability during P. berghei infection- or oxidation compared with wild-type erythrocytes. Furthermore, the nonspecific purinoceptor antagonist suramin decreased in vitro growth and DNA/RNA amplification of P. falciparum in human erythrocytes and decreased in vivo growth of P. berghei. P. berghei developed slower in P2Y1-deficient mice in vivo compared with wild-type animals. In conclusion, induction of the osmolyte permeability in Plasmodium-infected erythrocytes involves autocrine purinoceptor signaling.