Purines were long thought to be restricted to the intracellular compartment, where they are used for energy transactions, nucleic acid synthesis, and a multiplicity of biochemical reactions. However, ...it is now clear that both adenosine and adenosine triphosphate are (i) abundant biochemical components of the tumor microenvironment, (ii) potent modulators of immune cell responses and cytokine release, and (iii) key players in host-tumor interaction. Moreover, both ATP and adenosine directly affect tumor cell growth. Adenosine is a powerful immunosuppressant (mainly acting at A2A receptors) and a modulator of cell growth (mainly acting at A3 receptors). ATP is a proinflammatory (acting at P2Y1, P2Y2, P2Y4, P2Y6, and P2Y12, and at P2X4 and P2X7 receptors), an immunosuppressant (acting at P2Y11), and a growth-promoting agent (acting at P2Y1, P2Y2, and P2X7 receptors). This complex signaling network generates an array of inhibitory and stimulatory responses that affect immune cell function, tumor growth, and metastatic dissemination. Investigation of purinergic signaling has increased our understanding of the tumor microenvironment and opened new and exciting avenues for the development of novel therapeutics.
The known seven mammalian receptor subunits (P2X1–7) form cationic channels gated by ATP. Three subunits compose a receptor channel. Each subunit is a polypeptide consisting of two transmembrane ...regions (TM1 and TM2), intracellular N‐ and C‐termini, and a bulky extracellular loop. Crystallization allowed the identification of the 3D structure and gating cycle of P2X receptors. The agonist‐binding pocket is located at the intersection of two neighbouring subunits. In addition to the mammalian P2X receptors, their primitive ligand‐gated counterparts with little structural similarity have also been cloned. Selective agonists for P2X receptor subtypes are not available, but medicinal chemistry supplied a range of subtype‐selective antagonists, as well as positive and negative allosteric modulators. Knockout mice and selective antagonists helped to identify pathological functions due to defective P2X receptors, such as male infertility (P2X1), hearing loss (P2X2), pain/cough (P2X3), neuropathic pain (P2X4), inflammatory bone loss (P2X5), and faulty immune reactions (P2X7).
Inflammasomes are the central processing units (CPUs) responsible for decoding and integrating signals of foreignness, damage, danger, and distress released by pathogens, cells, and tissues. It was ...initially thought that the inflammasomes participated only in pathogen recognition and in the pathogenesis of a few, rare, hereditary inflammatory disorders. On the contrary, it is now clear that they have a central role in the pathogenesis of basically all types of chronic inflammation, in metabolic diseases and cancer. So far, six or possibly eight inflammasome subtypes have been identified. Their main, but by no means exclusive, function is to catalyze conversion of pro-IL-1β and pro-IL-18 into their respective mature forms. However, the different inflammasome subtypes may also participate in additional responses, e.g., proliferation, regulation of glycolytic metabolism, or cell activation, albeit it is not clear whether these effects are still mediated through IL-1β release or via modulation of other caspase-1-dependent or -independent pathways. Central to inflammasome organization and activity are proteins belonging to the nucleotide binding domain, leucine-rich repeat, or NOD-like receptor family. One relevant exception is the AIM2 inflammasome. NOD-like receptors belong to the superfamily of pattern recognition receptors, a group of highly conserved molecules specialized in the recognition of invariant molecular patterns diffused across species. Given their potent proinflammatory activity, it is anticipated that inflammasome activation is tightly controlled. In this review, I will summarize essential features of the known NOD-like receptors, the basic molecular structure of inflammasomes, their participation in pathophysiological responses, and their possible exploitation for therapy.
Modulation of the biochemical composition of the tumour microenvironment is a new frontier of cancer therapy. Several immunosuppressive mechanisms operate in the milieu of most tumours, a condition ...that makes antitumour immunity ineffective. One of the most potent immunosuppressive factors is adenosine, which is generated in the tumour microenvironment owing to degradation of extracellular ATP. Accruing evidence over the past few years shows that ATP is one of the major biochemical constituents of the tumour microenvironment, where it acts at P2 purinergic receptors expressed on both tumour and host cells. Stimulation of P2 receptors has different effects depending on the extracellular ATP concentration, the P2 receptor subtype engaged and the target cell type. Among P2 receptors, the P2X purinergic receptor 7 (P2X7R) subtype appears to be a main player in host-tumour cell interactions. Preclinical studies in several tumour models have shown that P2X7R targeting is potentially a very effective anticancer treatment, and many pharmaceutical companies have now developed potent and selective small molecule inhibitors of P2X7R. In this Review, we report on the multiple mechanisms by which extracellular ATP shapes the tumour microenvironment and how its stimulation of host and tumour cell P2 receptors contributes to determining tumour fate.
The Elusive P2X7 Macropore Di Virgilio, Francesco; Schmalzing, Günther; Markwardt, Fritz
Trends in cell biology,
20/May , Letnik:
28, Številka:
5
Journal Article
Recenzirano
ATP, which is released under pathological conditions and is considered a damage-associated molecular pattern (DAMP), activates P2X7 receptors (P2X7Rs), trimeric plasma membrane ion channels selective ...for small cations. P2X7Rs are partners in NOD-like receptor containing a pyrin (NLRP3) inflammasome activation and promoters of tumor cell growth. P2X7R overstimulation triggers the ATP-dependent opening of a nonselective plasma membrane pore, known as a ‘macropore’, which allows fluxes of large hydrophilic molecules. The pathophysiological functions of P2X7R are thought to be dependent on activation of this conductance pathway, yet its molecular identity is unknown. Recent reports show that P2X7R permeability to organic solutes is an early and intrinsic property of the channel itself. A better understanding of P2X7R-dependent changes in plasma membrane permeability will allow a rationale development of novel anti-inflammatory and anticancer drugs.
Extracellular ATP causes reversible permeabilization of mammalian cell plasma membranes due to P2X7R-dependent formation of a large conductance pore (the ‘macropore’).
ATP is a major constituent of the inflammatory microenvironment and P2X7R has a key role in inflammation and immunity.
Most P2X7R-stimulated immune responses depend on the activation of this permeability pathway, but the underlying mechanism is unknown.
Recent electrophysiological and cell biological investigations now converge on a unified mechanistic explanation and provide hints as to the biochemical basis for the endogenous modulation of this pathway.
It is anticipated that this new knowledge will have great impact on the design of novel anti-inflammatory drugs.
Adenosine triphosphate (ATP) accumulates at sites of tissue injury and inflammation. Effects of extracellular ATP are mediated by plasma membrane receptors named P2 receptors (P2Rs). The P2R most ...involved in inflammation and immunity is the P2X7 receptor (P2X7R), expressed by virtually all cells of innate and adaptive immunity. P2X7R mediates NLRP3 inflammasome activation, cytokine and chemokine release, T lymphocyte survival and differentiation, transcription factor activation, and cell death. Ten human P2RX7 gene splice variants and several SNPs that produce complex haplotypes are known. The P2X7R is a potent stimulant of inflammation and immunity and a promoter of cancer cell growth. This makes P2X7R an appealing target for anti-inflammatory and anti-cancer therapy. However, an in-depth knowledge of its structure and of the associated signal transduction mechanisms is needed for an effective therapeutic development.
Extracellular ATP is a common constitutent of the inflammatory milieu, where it modulates immune cell responses by activating a family of plasma membrane receptors named P2. In this review, Di Virgilio et al. discuss the central role played by the P2X7 receptor in promoting inflammation and driving innate and adaptive immunity.
ATP, the energy exchange factor that connects anabolism and catabolism, is required for major reactions and processes that occur in living cells, such as muscle contraction, phosphorylation and ...active transport. ATP is also the key molecule in extracellular purinergic signaling mechanisms, with an established crucial role in inflammation and several additional disease conditions. Here, we describe detailed protocols to measure the ATP concentration in isolated living cells and animals using luminescence techniques based on targeted luciferase probes. In the presence of magnesium, oxygen and ATP, the protein luciferase catalyzes oxidation of the substrate luciferin, which is associated with light emission. Recombinantly expressed wild-type luciferase is exclusively cytosolic; however, adding specific targeting sequences can modify its cellular localization. Using this strategy, we have constructed luciferase chimeras targeted to the mitochondrial matrix and the outer surface of the plasma membrane. Here, we describe optimized protocols for monitoring ATP concentrations in the cytosol, mitochondrial matrix and pericellular space in living cells via an overall procedure that requires an average of 3 d. In addition, we present a detailed protocol for the in vivo detection of extracellular ATP in mice using luciferase-transfected reporter cells. This latter procedure may require up to 25 d to complete.
Purines and their derivatives, most notably adenosine and ATP, are the key molecules controlling intracellular energy homoeostasis and nucleotide synthesis. Besides, these purines support, as ...chemical messengers, purinergic transmission throughout tissues and species. Purines act as endogenous ligands that bind to and activate plasmalemmal purinoceptors, which mediate extracellular communication referred to as "purinergic signalling". Purinergic signalling is cross-linked with other transmitter networks to coordinate numerous aspects of cell behaviour such as proliferation, differentiation, migration, apoptosis and other physiological processes critical for the proper function of organisms. Pathological deregulation of purinergic signalling contributes to various diseases including neurodegeneration, rheumatic immune diseases, inflammation, and cancer. Particularly, gout is one of the most prevalent purine-related disease caused by purine metabolism disorder and consequent hyperuricemia. Compelling evidence indicates that purinoceptors are potential therapeutic targets, with specific purinergic agonists and antagonists demonstrating prominent therapeutic potential. Furthermore, dietary and herbal interventions help to restore and balance purine metabolism, thus addressing the importance of a healthy lifestyle in the prevention and relief of human disorders. Profound understanding of molecular mechanisms of purinergic signalling provides new and exciting insights into the treatment of human diseases.
Severe pneumonia which shares several of the features of acute respiratory distress syndrome (ARDS) is the main cause of morbidity and mortality in Coronavirus disease 19 (Covid‐19) for which there ...is no effective treatment, so far. ARDS is caused and sustained by an uncontrolled inflammatory activation characterized by a massive release of cytokines (cytokine storm), diffuse lung oedema, inflammatory cell infiltration, and disseminated coagulation. Macrophage and T lymphocyte dysfunction plays a central role in this syndrome. In several experimental in vitro and in vivo models, many of these pathophysiological changes are triggered by stimulation of the P2X7 receptor. We hypothesize that this receptor might be an ideal candidate to target in Covid‐19‐associated severe pneumonia.
Linked Articles
This article is part of a themed issue on The Pharmacology of COVID‐19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc
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