An introduction to the special issue “The contribution of pannexin-1, connexins and CALHM ATP-release channels to purinergic signalling”

Pannexin channels are newly discovered ATP release channels expressed throughout the body. Pannexin 1 (Panx1) channels have become of great interest as they appear to participate in a multitude of signalling cascades, including regulation of vascular function. Although numerous Panx1 pharmacological inhibitors have been discovered, these inhibitors are not specific for Panx1 and have additional effects on other proteins. Therefore, molecular tools, such as RNA interference and knockout animals, are needed to demonstrate the role of pannexins in various cellular functions. This review focuses on the known roles of Panx1 related to purinergic signalling in the vasculature focusing on post-translational modifications and channel gating mechanisms that may participate in the regulated release of ATP.

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Pannexin-1 Deficient Mice Have an Increased Susceptibility for Atrial Fibrillation and Show a QT-Prolongation Phenotype

Cellular Physiology and Biochemistry ◽

10.1159/000438645 ◽

2016 ◽

Vol 38 (2) ◽

pp. 487-501 ◽

Cited By ~ 9

Author(s):

Stella Petric ◽

Sofia Klein ◽

Lisa Dannenberg ◽

Tillman Lahres ◽

Lukas Clasen ◽

...

Keyword(s):

Atrial Fibrillation ◽

Cardiac Electrophysiology ◽

Electrophysiological Study ◽

Atp Release ◽

Release Channel ◽

Knock Out ◽

Pannexin 1 ◽

Significant Prolongation ◽

Knock Out Mice

Background/Aims: Pannexin-1 (Panx1) is an ATP release channel that is ubiquitously expressed and coupled to several ligand-gated receptors. In isolated cardiac myocytes, Panx1 forms large conductance channels that can be activated by Ca2+ release from the sarcoplasmic reticulum. Here we characterized the electrophysiological function of these channels in the heart in vivo, taking recourse to mice with Panx1 ablation. Methods: Cardiac phenotyping of Panx1 knock-out mice (Panx1-/-) was performed by employing a molecular, cellular and functional approach, including echocardiography, surface and telemetric ECG recordings with QT analysis, physical stress testing and quantification of heart rate variability. In addition, an in vivo electrophysiological study entailed programmed electrical stimulation using an intracardiac octapolar catheter. Results: Panx1 deficiency results in a higher incidence of AV-block, delayed ventricular depolarisation, significant prolongation of QT- and rate corrected QT-interval and a higher incidence of atrial fibrillation after intraatrial burst stimulation. Conclusion: Panx1 seems to play an important role in murine cardiac electrophysiology and warrants further consideration in the context of hereditary forms of atrial fibrillation.

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Pannexin-1 Channels as Mediators of Neuroinflammation

International Journal of Molecular Sciences ◽

10.3390/ijms22105189 ◽

2021 ◽

Vol 22 (10) ◽

pp. 5189

Author(s):

Joon Ho Seo ◽

Miloni S. Dalal ◽

Jorge E. Contreras

Keyword(s):

Immune Cells ◽

Neurological Diseases ◽

Atp Release ◽

Innate Immune ◽

Innate Immune Cells ◽

Damage Site ◽

Pannexin 1 ◽

Cytokines And Chemokines ◽

Secondary Damage ◽

Dying Cells

Neuroinflammation is a major component of central nervous system (CNS) injuries and neurological diseases, including Alzheimer’s disease, multiple sclerosis, neuropathic pain, and brain trauma. The activation of innate immune cells at the damage site causes the release of pro-inflammatory cytokines and chemokines, which alter the functionality of nearby tissues and might mediate the recruitment of leukocytes to the injury site. If this process persists or is exacerbated, it prevents the adequate resolution of the inflammation, and ultimately enhances secondary damage. Adenosine 5′ triphosphate (ATP) is among the molecules released that trigger an inflammatory response, and it serves as a chemotactic and endogenous danger signal. Extracellular ATP activates multiple purinergic receptors (P2X and P2Y) that have been shown to promote neuroinflammation in a variety of CNS diseases. Recent studies have shown that Pannexin-1 (Panx1) channels are the principal conduits of ATP release from dying cells and innate immune cells in the brain. Herein, we review the emerging evidence that directly implicates Panx-1 channels in the neuroinflammatory response in the CNS.

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A2A Receptor-induced Overexpression of Pannexin-1 Hemichannels Indirectly Mediates Adenosine Fibrogenic Actions in Subcutaneous Human Fibroblasts by Favoring ATP Release

10.21203/rs.3.rs-787071/v1 ◽

2021 ◽

Author(s):

Carina Herman-de-Sousa ◽

Maria Adelina Costa ◽

Rafaela Pedro Silva ◽

Fátima Ferreirinha ◽

Severino Ribeiro ◽

...

Keyword(s):

Inflammatory Mediators ◽

Connexin 43 ◽

Myofascial Pain ◽

Subcutaneous Tissue ◽

Human Fibroblasts ◽

Atp Release ◽

Collagen Production ◽

Pannexin 1 ◽

A2a Receptors ◽

Inflammatory Conditions

Abstract Disorganization of the subcutaneous tissue due to inflammation and fibrosis is a common feature in patients with myofascial pain. Dermal accumulation of adenosine favours collagen production by human subcutaneous fibroblasts (HSCF) via A2A receptors (A2AR) activation. Adenosine mimics the fibrogenic effect of inflammatory mediators (e.g. histamine, bradykinin), which act by promoting ATP release from HSCF via pannexin-1 (Panx1) and/or connexin-43 (Cx43) hemichannels. However, this mechanism was never implicated in the A2AR-mediated actions. NECA and CGS21680C, two enzymatically-stable A2AR agonists, increased Panx-1, but reduced Cx43, immunoreactivity in cultured HSCF. This effect was accompanied by increases in ATP release and collagen production by HSCF. Involvement of A2AR was verified upon blockage of NECA and CGS21680 effects with the selective A2AR antagonist, SCH442416. Inhibition of Panx1 hemichannels with probenecid also decreased ATP release and collagen production by HSCF under similar conditions. Superfluous ATP release by HSCF exposed to A2AR agonists overexpressing Panx1 hemichannels contributes to keep high [Ca2+]i levels in the presence of inflammatory mediators, like histamine. Adenosine A2AR-induced Panx1 overexpression was shown here for the first time; this feature indirectly implicates ATP release in the fibrogenic vicious cycle putatively operated by the nucleoside in subcutaneous tissue fibrosis and myofascial inflammatory conditions.

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ATP triggers macropinocytosis that internalizes and is regulated by PANX1

10.1101/2020.11.19.389072 ◽

2020 ◽

Author(s):

Andrew K.J. Boyce ◽

Emma van der Slagt ◽

Juan C. Sanchez-Arias ◽

Leigh Anne Swayne

Keyword(s):

Neuroblastoma Cells ◽

Atp Release ◽

Surface Proteins ◽

Cell Area ◽

Release Channel ◽

Cross Sectional ◽

Pannexin 1 ◽

Disease States ◽

Cellular Area ◽

Area Expansion

ABSTRACTMacropinocytosis is an endocytic process that allows cells to respond to changes in their environment by internalizing nutrients and cell surface proteins, as well as modulating cell size. Here, we identify that adenosine triphosphate (ATP) triggers macropinocytosis in murine neuroblastoma cells, thereby internalizing the ATP release channel pannexin 1 (PANX1) while concurrently increasing cross-sectional cellular area. Amiloride, a potent inhibitor of macropinocytosis-associated GTPases, abolished ATP-induced PANX1 internalization and cell area expansion. Transient expression of the GTP-hydrolysis resistant GTPase ARF6 Q67L led to increased PANX1 internalization and increased cell area equivalent to levels seen with ATP stimulation. Mutation of an extracellular tryptophan (W74) in PANX1 abolished ATP-evoked cell area enlargement suggesting that PANX1 regulates this form of macropinocytosis. This novel role of PANX1 in macropinocytosis could be particularly important for disease states implicating PANX1, such as cancer, where ATP can act as a purinergic regulator of cell growth/metastasis and as a supplementary energy source following internalization.

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Structure versus function: Are new conformations of pannexin 1 yet to be resolved?

The Journal of General Physiology ◽

10.1085/jgp.202012754 ◽

2021 ◽

Vol 153 (5) ◽

Author(s):

Carsten Mim ◽

Guy Perkins ◽

Gerhard Dahl

Keyword(s):

Structural Information ◽

Purinergic Signaling ◽

Atp Release ◽

Strong Support ◽

Decisive Role ◽

Chloride Ions ◽

Pannexin 1 ◽

Selective Membrane ◽

Selective Channel ◽

Structure Versus

Pannexin 1 (Panx1) plays a decisive role in multiple physiological and pathological settings, including oxygen delivery to tissues, mucociliary clearance in airways, sepsis, neuropathic pain, and epilepsy. It is widely accepted that Panx1 exerts its role in the context of purinergic signaling by providing a transmembrane pathway for ATP. However, under certain conditions, Panx1 can also act as a highly selective membrane channel for chloride ions without ATP permeability. A recent flurry of publications has provided structural information about the Panx1 channel. However, while these structures are consistent with a chloride selective channel, none show a conformation with strong support for the ATP release function of Panx1. In this Viewpoint, we critically assess the existing evidence for the function and structure of the Panx1 channel and conclude that the structure corresponding to the ATP permeation pathway is yet to be determined. We also list a set of additional topics needing attention and propose ways to attain the large-pore, ATP-permeable conformation of the Panx1 channel.

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Pannexin-1 mediated ATP release in adipocytes is sensitive to glucose and insulin and modulates lipolysis and macrophage migration

10.1101/380469 ◽

2018 ◽

Author(s):

Marco Tozzi ◽

Jacob B. Hansen ◽

Ivana Novak

Keyword(s):

Adipose Tissue ◽

Purinergic Receptors ◽

Purinergic Signaling ◽

Cell Metabolism ◽

Atp Release ◽

Extracellular Atp ◽

Adrenergic Stimulation ◽

Pannexin 1 ◽

White Adipocytes ◽

Obesity And Diabetes

One-sentence summaryInsulin inhibits ATP release in adipocytesAbstractExtracellular ATP signaling is involved in many physiological and pathophysiological processes, and purinergic receptors are targets for drug therapy in several diseases, including obesity and diabetes. Adipose tissue has crucial functions in lipid and glucose metabolism and adipocytes express purinergic receptors. However, the sources of extracellular ATP in adipose tissue are not yet characterized.Here, we show that upon adrenergic stimulation white adipocytes release ATP through the pannexin-1 pore that is regulated by a cAMP-PKA dependent pathway. The ATP release correlates with increased cell metabolism, and extracellular ATP induces Ca2+ signaling and lipolysis in adipocytes and promotes macrophages migration. Most importantly, ATP release is markedly inhibited by insulin, and thereby auto/paracrine purinergic signaling in adipose tissue would be attenuated. Furthermore, we define the signaling pathway for insulin regulated ATP release.Our findings reveal the insulin-pannexin-1-purinergic signaling cross-talk in adipose tissue and we propose that deregulation of this signaling may underlie adipose tissue inflammation and type-2 diabetes.

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A Disease-associated Variant in the ATP Release Channel Pannexin 1♦

Journal of Biological Chemistry ◽

10.1074/jbc.p116.717934 ◽

2016 ◽

Vol 291 (24) ◽

pp. 12444-12444

Keyword(s):

Atp Release ◽

Release Channel ◽

Pannexin 1

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P2X7 receptor cross-talk regulates ATP-induced pannexin 1 internalization

Biochemical Journal ◽

10.1042/bcj20170257 ◽

2017 ◽

Vol 474 (13) ◽

pp. 2133-2144 ◽

Cited By ~ 24

Author(s):

Andrew K.J. Boyce ◽

Leigh Anne Swayne

Keyword(s):

Nervous System ◽

Cross Talk ◽

Purinergic Receptors ◽

Atp Release ◽

Extracellular Atp ◽

Signalling Pathways ◽

Physical Interaction ◽

Cell Periphery ◽

Dependent Manner ◽

Pannexin 1

In the nervous system, extracellular ATP levels transiently increase in physiological and pathophysiological circumstances, effecting key signalling pathways in plasticity and inflammation through purinergic receptors. Pannexin 1 (Panx1) forms ion- and metabolite-permeable channels that mediate ATP release and are particularly enriched in the nervous system. Our recent study demonstrated that elevation of extracellular ATP triggers Panx1 internalization in a concentration- and time-dependent manner. Notably, this effect was sensitive to inhibition of ionotropic P2X7 purinergic receptors (P2X7Rs). Here, we report our novel findings from the detailed investigation of the mechanism underlying P2X7R–Panx1 cross-talk in ATP-stimulated internalization. We demonstrate that extracellular ATP triggers and is required for the clustering of P2X7Rs and Panx1 on Neuro2a cells through an extracellular physical interaction with the Panx1 first extracellular loop (EL1). Importantly, disruption of P2X7R–Panx1 clustering by mutation of tryptophan 74 within the Panx1 EL1 inhibits Panx1 internalization. Notably, P2X7R–Panx1 clustering and internalization are independent of P2X7R-associated intracellular signalling pathways (Ca2+ influx and Src activation). Further analysis revealed that cholesterol is required for ATP-stimulated P2X7R–Panx1 clustering at the cell periphery. Taken together, our data suggest that extracellular ATP induces and is required for Panx1 EL1-mediated, cholesterol-dependent P2X7R–Panx1 clustering and endocytosis. These findings have important implications for understanding the role of Panx1 in the nervous system and provide important new insights into Panx1–P2X7R cross-talk.

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