1
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Dale N, Butler J, Dospinescu VM, Nijjar S. Channel-mediated ATP release in the nervous system. Neuropharmacology 2023; 227:109435. [PMID: 36690324 DOI: 10.1016/j.neuropharm.2023.109435] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 01/10/2023] [Accepted: 01/19/2023] [Indexed: 01/21/2023]
Abstract
ATP is well established as a transmitter and modulator in the peripheral and central nervous system. While conventional exocytotic release of ATP at synapses occurs, this transmitter is unusual in also being released into the extracellular space via large-pored plasma membrane channels. This review considers the channels that are known to be permeable to ATP and some of the functions of channel-mediated ATP release. While the possibility of ATP release via channels mediating volume transmission has been known for some time, localised ATP release via channels at specialised synapses made by taste cells to the afferent nerve has recently been documented in taste buds. This raises the prospect that "channel synapses" may occur in other contexts. However, volume transmission and channel synapses are not necessarily mutually exclusive. We suggest that certain glial cells in the brain stem and hypothalamus, which possess long processes and are known to release ATP, may be candidates for both modes of ATP release -channel-mediated volume transmission in the region of their somata and more localised transmission possibly via either conventional or channel synapses from their processes at distal targets. Finally, we consider the different characteristics of vesicular and channel synapses and suggest that channel synapses may be advantageous in requiring less energy than their conventional vesicular counterparts. This article is part of the Special Issue on "Purinergic Signaling: 50 years".
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Affiliation(s)
- Nicholas Dale
- School of Life Sciences, University of Warwick, Coventry, CV4, AL, UK.
| | - Jack Butler
- School of Life Sciences, University of Warwick, Coventry, CV4, AL, UK
| | | | - Sarbjit Nijjar
- School of Life Sciences, University of Warwick, Coventry, CV4, AL, UK
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2
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Chang CWT, Poudyal N, Verdugo DA, Peña F, Stehberg J, Retamal MA. KI04 an Aminoglycosides-Derived Molecule Acts as an Inhibitor of Human Connexin46 Hemichannels Expressed in HeLa Cells. Biomolecules 2023; 13:411. [PMID: 36979346 PMCID: PMC10046693 DOI: 10.3390/biom13030411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2023] [Revised: 02/12/2023] [Accepted: 02/16/2023] [Indexed: 02/24/2023] Open
Abstract
BACKGROUND Connexins (Cxs) are proteins that help cells to communicate with the extracellular media and with the cytoplasm of neighboring cells. Despite their importance in several human physiological and pathological conditions, their pharmacology is very poor. In the last decade, some molecules derived from aminoglycosides have been developed as inhibitors of Cxs hemichannels. However, these studies have been performed in E. coli, which is a very simple model. Therefore, our main goal is to test whether these molecules have similar effects in mammalian cells. METHODS We transfected HeLa cells with the human Cx46tGFP and characterized the effect of a kanamycin-derived molecule (KI04) on Cx46 hemichannel activity by time-lapse recordings, changes in phosphorylation by Western blot, localization by epifluorescence, and possible binding sites by molecular dynamics (MD). RESULTS We observed that kanamycin and KI04 were the most potent inhibitors of Cx46 hemichannels among several aminoglycosides, presenting an IC50 close to 10 μM. The inhibitory effect was not associated with changes in Cx46 electrophoretic mobility or its intracellular localization. Interestingly, 5 mM DTT did not reverse KI04 inhibition, but the KI04 effect completely disappeared after washing out KI04 from the recording media. MD analysis revealed two putative binding sites of KI04 in the Cx46 hemichannel. RESULTS These results demonstrate that KI04 could be used as a Cx46 inhibitor and could help to develop future selective Cx46 inhibitors.
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Affiliation(s)
- Cheng-Wei T. Chang
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA
| | - Naveena Poudyal
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322-0300, USA
| | - Daniel A. Verdugo
- Laboratorio de Neurobiología, Facultad de Medicina y Facultad de Ciencias de la Vida, Instituto de Ciencias Biomédicas, Universidad Andres Bello, Santiago 7780272, Chile
| | - Francisca Peña
- Laboratorio de Neurobiología, Facultad de Medicina y Facultad de Ciencias de la Vida, Instituto de Ciencias Biomédicas, Universidad Andres Bello, Santiago 7780272, Chile
| | - Jimmy Stehberg
- Laboratorio de Neurobiología, Facultad de Medicina y Facultad de Ciencias de la Vida, Instituto de Ciencias Biomédicas, Universidad Andres Bello, Santiago 7780272, Chile
| | - Mauricio A. Retamal
- Center for Membrane Protein Research, Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA
- Programa de Comunicación Celular en Cáncer, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7610496, Chile
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3
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Oliveira MC, Verswyvel H, Smits E, Cordeiro RM, Bogaerts A, Lin A. The pro- and anti-tumoral properties of gap junctions in cancer and their role in therapeutic strategies. Redox Biol 2022; 57:102503. [PMID: 36228438 PMCID: PMC9557036 DOI: 10.1016/j.redox.2022.102503] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 09/06/2022] [Accepted: 10/06/2022] [Indexed: 11/24/2022] Open
Abstract
Gap junctions (GJs), essential structures for cell-cell communication, are made of two hemichannels (commonly called connexons), one on each adjacent cell. Found in almost all cells, GJs play a pivotal role in many physiological and cellular processes, and have even been linked to the progression of diseases, such as cancer. Modulation of GJs is under investigation as a therapeutic strategy to kill tumor cells. Furthermore, GJs have also been studied for their key role in activating anti-cancer immunity and propagating radiation- and oxidative stress-induced cell death to neighboring cells, a process known as the bystander effect. While, gap junction (GJ)-based therapeutic strategies are being developed, one major challenge has been the paradoxical role of GJs in both tumor progression and suppression, based on GJ composition, cancer factors, and tumoral context. Therefore, understanding the mechanisms of action, regulation, and the dual characteristics of GJs in cancer is critical for developing effective therapeutics. In this review, we provide an overview of the current understanding of GJs structure, function, and paradoxical pro- and anti-tumoral role in cancer. We also discuss the treatment strategies to target these GJs properties for anti-cancer responses, via modulation of GJ function.
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Affiliation(s)
- Maria C Oliveira
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, CEP 09210-580, Santo André, SP, Brazil.
| | - Hanne Verswyvel
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
| | - Evelien Smits
- Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
| | - Rodrigo M Cordeiro
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, CEP 09210-580, Santo André, SP, Brazil
| | - Annemie Bogaerts
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
| | - Abraham Lin
- Plasma Lab for Applications in Sustainability and Medicine-Antwerp (PLASMANT), Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium; Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Universiteitsplein 1, B-2610, Antwerp, Belgium
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4
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Fernández-Olivares A, Durán-Jara E, Verdugo DA, Fiori MC, Altenberg GA, Stehberg J, Alfaro I, Calderón JF, Retamal MA. Extracellular Cysteines Are Critical to Form Functional Cx46 Hemichannels. Int J Mol Sci 2022; 23:7252. [PMID: 35806258 PMCID: PMC9266770 DOI: 10.3390/ijms23137252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/16/2022] [Accepted: 06/18/2022] [Indexed: 12/10/2022] Open
Abstract
Connexin (Cxs) hemichannels participate in several physiological and pathological processes, but the molecular mechanisms that control their gating remain elusive. We aimed at determining the role of extracellular cysteines (Cys) in the gating and function of Cx46 hemichannels. We studied Cx46 and mutated all of its extracellular Cys to alanine (Ala) (one at a time) and studied the effects of the Cys mutations on Cx46 expression, localization, and hemichannel activity. Wild-type Cx46 and Cys mutants were expressed at comparable levels, with similar cellular localization. However, functional experiments showed that hemichannels formed by the Cys mutants did not open either in response to membrane depolarization or removal of extracellular divalent cations. Molecular-dynamics simulations showed that Cys mutants may show a possible alteration in the electrostatic potential of the hemichannel pore and an altered disposition of important residues that could contribute to the selectivity and voltage dependency in the hemichannels. Replacement of extracellular Cys resulted in "permanently closed hemichannels", which is congruent with the inhibition of the Cx46 hemichannel by lipid peroxides, through the oxidation of extracellular Cys. These results point to the modification of extracellular Cys as potential targets for the treatment of Cx46-hemichannel associated pathologies, such as cataracts and cancer, and may shed light into the gating mechanisms of other Cx hemichannels.
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Affiliation(s)
- Ainoa Fernández-Olivares
- Programa de Comunicación Celular en Cáncer, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7780272, Chile; (A.F.-O.); (I.A.)
| | - Eduardo Durán-Jara
- Centro de Medicina Regenerativa, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7780272, Chile;
| | - Daniel A. Verdugo
- Laboratorio de Neurobiología, Instituto de Ciencias Biomédicas, Facultad de Medicina y Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 7780272, Chile; (D.A.V.); (J.S.)
| | - Mariana C. Fiori
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA; (M.C.F.); (G.A.A.)
| | - Guillermo A. Altenberg
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, USA; (M.C.F.); (G.A.A.)
| | - Jimmy Stehberg
- Laboratorio de Neurobiología, Instituto de Ciencias Biomédicas, Facultad de Medicina y Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 7780272, Chile; (D.A.V.); (J.S.)
| | - Iván Alfaro
- Programa de Comunicación Celular en Cáncer, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7780272, Chile; (A.F.-O.); (I.A.)
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Santiago 7690000, Chile
| | - Juan Francisco Calderón
- Centro de Genética y Genómica, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7780272, Chile
| | - Mauricio A. Retamal
- Programa de Comunicación Celular en Cáncer, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7780272, Chile; (A.F.-O.); (I.A.)
- Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Santiago 7690000, Chile
- Centro de Fisiología Celular e Integrativa, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago 7690000, Chile
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5
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Retamal MA, Fernandez-Olivares A, Stehberg J. Over-activated hemichannels: A possible therapeutic target for human diseases. Biochim Biophys Acta Mol Basis Dis 2021; 1867:166232. [PMID: 34363932 DOI: 10.1016/j.bbadis.2021.166232] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 07/21/2021] [Accepted: 07/26/2021] [Indexed: 12/14/2022]
Abstract
In our body, all the cells are constantly sharing chemical and electrical information with other cells. This intercellular communication allows them to respond in a concerted way to changes in the extracellular milieu. Connexins are transmembrane proteins that have the particularity of forming two types of channels; hemichannels and gap junction channels. Under normal conditions, hemichannels allow the controlled release of signaling molecules to the extracellular milieu. However, under certain pathological conditions, over-activated hemichannels can induce and/or exacerbate symptoms. In the last decade, great efforts have been put into developing new tools that can modulate these over-activated hemichannels. Small molecules, antibodies and mimetic peptides have shown a potential for the treatment of human diseases. In this review, we summarize recent findings in the field of hemichannel modulation via specific tools, and how these tools could improve patient outcome in certain pathological conditions.
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Affiliation(s)
- Mauricio A Retamal
- Universidad del Desarrollo, Programa de Comunicación Celular en Cáncer, Santiago, Chile; Universidad del Desarrollo, Centro de Fisiología Celular e Integrativa, Santiago, Chile.
| | | | - Jimmy Stehberg
- Laboratorio de Neurobiología, Instituto de Ciencias Biomédicas, Facultad de medicina y Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago, Chile
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Huckstep H, Fearnley LG, Davis MJ. Measuring pathway database coverage of the phosphoproteome. PeerJ 2021; 9:e11298. [PMID: 34113485 PMCID: PMC8162239 DOI: 10.7717/peerj.11298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/29/2021] [Indexed: 12/02/2022] Open
Abstract
Protein phosphorylation is one of the best known post-translational mechanisms playing a key role in the regulation of cellular processes. Over 100,000 distinct phosphorylation sites have been discovered through constant improvement of mass spectrometry based phosphoproteomics in the last decade. However, data saturation is occurring and the bottleneck of assigning biologically relevant functionality to phosphosites needs to be addressed. There has been finite success in using data-driven approaches to reveal phosphosite functionality due to a range of limitations. The alternate, more suitable approach is making use of prior knowledge from literature-derived databases. Here, we analysed seven widely used databases to shed light on their suitability to provide functional insights into phosphoproteomics data. We first determined the global coverage of each database at both the protein and phosphosite level. We also determined how consistent each database was in its phosphorylation annotations compared to a global standard. Finally, we looked in detail at the coverage of each database over six experimental datasets. Our analysis highlights the relative strengths and weaknesses of each database, providing a guide in how each can be best used to identify biological mechanisms in phosphoproteomic data.
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Affiliation(s)
- Hannah Huckstep
- Division of Bioinformatics, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia
| | - Liam G. Fearnley
- Department of Medical Biology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia
- Division of Population Health, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
| | - Melissa J. Davis
- Division of Bioinformatics, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
- Department of Medical Biology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia
- Department of Clinical Pathology, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Melbourne, Victoria, Australia
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7
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Van Campenhout R, Gomes AR, De Groof TW, Muyldermans S, Devoogdt N, Vinken M. Mechanisms Underlying Connexin Hemichannel Activation in Disease. Int J Mol Sci 2021; 22:ijms22073503. [PMID: 33800706 PMCID: PMC8036530 DOI: 10.3390/ijms22073503] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 03/22/2021] [Accepted: 03/26/2021] [Indexed: 02/07/2023] Open
Abstract
Gap junctions and connexin hemichannels mediate intercellular and extracellular communication, respectively. While gap junctions are seen as the “good guys” by controlling homeostasis, connexin hemichannels are considered as the “bad guys”, as their activation is associated with the onset and dissemination of disease. Open connexin hemichannels indeed mediate the transport of messengers between the cytosol and extracellular environment and, by doing so, fuel inflammation and cell death in a plethora of diseases. The present mini-review discusses the mechanisms involved in the activation of connexin hemichannels during pathology.
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Affiliation(s)
- Raf Van Campenhout
- Department of Pharmaceutical and Pharmacological Sciences, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; (R.V.C.); (A.R.G.)
| | - Ana Rita Gomes
- Department of Pharmaceutical and Pharmacological Sciences, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; (R.V.C.); (A.R.G.)
| | - Timo W.M. De Groof
- Department of Medical Imaging, In Vivo Cellular and Molecular Imaging Laboratory, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; (T.W.M.D.G.); (N.D.)
| | - Serge Muyldermans
- Laboratory of Cellular and Molecular Immunology, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium;
| | - Nick Devoogdt
- Department of Medical Imaging, In Vivo Cellular and Molecular Imaging Laboratory, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; (T.W.M.D.G.); (N.D.)
| | - Mathieu Vinken
- Department of Pharmaceutical and Pharmacological Sciences, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium; (R.V.C.); (A.R.G.)
- Correspondence: ; Tel.: +32-2-4774587
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8
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Wu X, Zhang W, Li Y, Lin X. Structure and Function of Cochlear Gap Junctions and Implications for the Translation of Cochlear Gene Therapies. Front Cell Neurosci 2019; 13:529. [PMID: 31827424 PMCID: PMC6892400 DOI: 10.3389/fncel.2019.00529] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Accepted: 11/13/2019] [Indexed: 12/23/2022] Open
Abstract
Connexins (Cxs) are ubiquitous membrane proteins that are found throughout vertebrate organs, acting as building blocks of the gap junctions (GJs) known to play vital roles in the normal function of many organs. Mutations in Cx genes (particularly GJB2, which encodes Cx26) cause approximately half of all cases of congenital hearing loss in newborns. Great progress has been made in understanding GJ function and the molecular mechanisms for the role of Cxs in the cochlea. Data reveal that multiple types of Cxs work together to ensure normal development and function of the cochlea. These findings include many aspects not proposed in the classic K+ recycling theory, such as the formation of normal cochlear morphology (e.g., the opening of the tunnel of Corti), the fine-tuning of the innervation of nerve fibers to the hair cells (HCs), the maturation of the ribbon synapses, and the initiation of the endocochlear potential (EP). New data, especially those collected from targeted modification of major Cx genes in the mouse cochlea, have demonstrated that Cx26 plays an essential role in the postnatal maturation of the cochlea. Studies also show that Cx26 and Cx30 assume very different roles in the EP generation, given that only Cx26 is required for normal hearing. This article will review our current understanding of the molecular structure, cellular distribution, and major functions of cochlear GJs. Potential implications of the knowledge of cochlear GJs on the design and implementation of translational studies of cochlear gene therapies for Cx mutations are also discussed.
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Affiliation(s)
- Xuewen Wu
- Department of Otolaryngology, Head-Neck and Surgery, Xiangya Hospital of Central South University, Changsha, China
- Department of Otolaryngology, Emory University School of Medicine, Atlanta, GA, United States
| | - Wenjuan Zhang
- Department of Otolaryngology, Wuhan Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yihui Li
- Department of Pharmacy, Changsha Hospital of Traditional Medicine, Changsha, China
| | - Xi Lin
- Department of Otolaryngology, Emory University School of Medicine, Atlanta, GA, United States
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9
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Nielsen BS, Zonta F, Farkas T, Litman T, Nielsen MS, MacAulay N. Structural determinants underlying permeant discrimination of the Cx43 hemichannel. J Biol Chem 2019; 294:16789-16803. [PMID: 31554662 DOI: 10.1074/jbc.ra119.007732] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 09/24/2019] [Indexed: 02/03/2023] Open
Abstract
Connexin (Cx) gap junction channels comprise two hemichannels in neighboring cells, and their permeability is well-described, but permeabilities of the single Cx hemichannel remain largely unresolved. Moreover, determination of isoform-specific Cx hemichannel permeability is challenging because of concurrent expression of other channels with similar permeability profiles and inhibitor sensitivities. The mammalian Cx hemichannels Cx30 and Cx43 are gated by extracellular divalent cations, removal of which promotes fluorescent dye uptake in both channels but atomic ion conductance only through Cx30. To determine the molecular determinants of this difference, here we employed chimeras and mutagenesis of predicted pore-lining residues in Cx43. We expressed the mutated channels in Xenopus laevis oocytes to avoid background activity of alternative channels. Oocytes expressing a Cx43 hemichannel chimera containing the N terminus or the first extracellular loop from Cx30 displayed ethidium uptake and, unlike WT Cx43, ion conduction, an observation further supported by molecular dynamics simulations. Additional C-terminal truncation of the chimeric Cx43 hemichannel elicited an even greater ion conductance with a magnitude closer to that of Cx30. The inhibitory profile for the connexin hemichannels depended on the permeant, with conventional connexin hemichannel inhibitors having a higher potency toward the ion conductance pathway than toward fluorescent dye uptake. Our results demonstrate a permeant-dependent, isoform-specific inhibition of connexin hemichannels. They further reveal that the outer segments of the pore-lining region, including the N terminus and the first extracellular loop, together with the C terminus preclude ion conductance of the open Cx43 hemichannel.
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Affiliation(s)
- Brian Skriver Nielsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Francesco Zonta
- Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University, Shanghai 201210, China
| | - Thomas Farkas
- Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Thomas Litman
- Department of Immunology and Microbiology, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Morten Schak Nielsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen, Denmark
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10
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Cohen-Barak E, Godsel LM, Koetsier JL, Hegazy M, Kushnir-Grinbaum D, Hammad H, Danial-Farran N, Harmon R, Khayat M, Bochner R, Peled A, Rozenblat M, Krausz J, Sarig O, Johnson JL, Ziv M, Shalev SA, Sprecher E, Green KJ. The Role of Desmoglein 1 in Gap Junction Turnover Revealed through the Study of SAM Syndrome. J Invest Dermatol 2019; 140:556-567.e9. [PMID: 31465738 DOI: 10.1016/j.jid.2019.08.433] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Revised: 07/15/2019] [Accepted: 08/02/2019] [Indexed: 11/18/2022]
Abstract
An effective epidermal barrier requires structural and functional integration of adherens junctions, tight junctions, gap junctions (GJ), and desmosomes. Desmosomes govern epidermal integrity while GJs facilitate small molecule transfer across cell membranes. Some patients with severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome, caused by biallelic desmoglein 1 (DSG1) mutations, exhibit skin lesions reminiscent of erythrokeratodermia variabilis, caused by mutations in connexin (Cx) genes. We, therefore, examined whether SAM syndrome-causing DSG1 mutations interfere with Cx expression and GJ function. Lesional skin biopsies from SAM syndrome patients (n = 7) revealed decreased Dsg1 and Cx43 plasma membrane localization compared with control and nonlesional skin. Cultured keratinocytes and organotypic skin equivalents depleted of Dsg1 exhibited reduced Cx43 expression, rescued upon re-introduction of wild-type Dsg1, but not Dsg1 constructs modeling SAM syndrome-causing mutations. Ectopic Dsg1 expression increased cell-cell dye transfer, which Cx43 silencing inhibited, suggesting that Dsg1 promotes GJ function through Cx43. As GJA1 gene expression was not decreased upon Dsg1 loss, we hypothesized that Cx43 reduction was due to enhanced protein degradation. Supporting this, PKC-dependent Cx43 S368 phosphorylation, which signals Cx43 turnover, increased after Dsg1 depletion, while lysosomal inhibition restored Cx43 levels. These data reveal a role for Dsg1 in regulating epidermal Cx43 turnover.
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Affiliation(s)
- Eran Cohen-Barak
- Departments of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Dermatology, "Emek" Medical Center, Afula, Israel; Bruce and Ruth Rappaport Faculty of Medicine, Technion, Haifa, Israel
| | - Lisa M Godsel
- Departments of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Jennifer L Koetsier
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Marihan Hegazy
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | | | - Helwe Hammad
- Department of Dermatology, "Emek" Medical Center, Afula, Israel
| | | | - Robert Harmon
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Morad Khayat
- The Genetic Institute, "Emek" Medical Center, Afula, Israel
| | - Ron Bochner
- Department of Dermatology, Tel Aviv Medical Center, Tel Aviv, Israel
| | - Alon Peled
- Department of Dermatology, Tel Aviv Medical Center, Tel Aviv, Israel; Department of Human Molecular Genetics & Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Mati Rozenblat
- Department of Dermatology, "Emek" Medical Center, Afula, Israel
| | - Judit Krausz
- Department of Pathology, "Emek" Medical Center, Afula, Israel
| | - Ofer Sarig
- Department of Dermatology, Tel Aviv Medical Center, Tel Aviv, Israel
| | - Jodi L Johnson
- Departments of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Michael Ziv
- Department of Dermatology, "Emek" Medical Center, Afula, Israel
| | - Stavit A Shalev
- Bruce and Ruth Rappaport Faculty of Medicine, Technion, Haifa, Israel; The Genetic Institute, "Emek" Medical Center, Afula, Israel
| | - Eli Sprecher
- Department of Dermatology, Tel Aviv Medical Center, Tel Aviv, Israel; Department of Human Molecular Genetics & Biochemistry, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Kathleen J Green
- Departments of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA; Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, IL, USA.
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Nielsen BS, Alstrom JS, Nicholson BJ, Nielsen MS, MacAulay N. Permeant-specific gating of connexin 30 hemichannels. J Biol Chem 2017; 292:19999-20009. [PMID: 28982982 DOI: 10.1074/jbc.m117.805986] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 09/28/2017] [Indexed: 11/06/2022] Open
Abstract
Gap junctions confer interconnectivity of the cytoplasm in neighboring cells via docking of two connexons expressed in each of the adjacent membranes. Undocked connexons, referred to as hemichannels, may open and connect the cytoplasm with the extracellular fluid. The hemichannel configuration of connexins (Cxs) displays isoform-specific permeability profiles that are not directly determined by the size and charge of the permeant. To further explore Ca2+-mediated gating and permeability features of connexin hemichannels, we heterologously expressed Cx30 hemichannels in Xenopus laevis oocytes. The sensitivity toward divalent cation-mediated gating differed between small atomic ions (current) and fluorescent dye permeants, indicating that these permeants are distinctly gated. Three aspartate residues in Cx30 (Asp-50, Asp-172, and Asp-179) have been implicated previously in the Ca2+ sensitivity of other hemichannel isoforms. Although the aspartate at position Asp-50 was indispensable for divalent cation-dependent gating of Cx30 hemichannels, substitutions of the two other residues had no significant effect on gating, illustrating differences in the gating mechanisms between connexin isoforms. Using the substituted cysteine accessibility method (SCAM), we evaluated the role of possible pore-lining residues in the permeation of ions and ethidium through Cx30 hemichannels. Of the cysteine-substituted residues, interaction of a proposed pore-lining cysteine at position 37 with the positively charged compound [2-(trimethylammonium)ethyl] methane thiosulfonate bromide (MTS-ET) increased Cx30-mediated currents with unperturbed ethidium permeability. In summary, our results demonstrate that the permeability of hemichannels is regulated in a permeant-specific manner and underscores that hemichannels are selective rather than non-discriminating and freely diffusable pores.
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Affiliation(s)
| | | | - Bruce J Nicholson
- Department of Biochemistry, School of Medicine, University of Texas Health Science Center, San Antonio, Texas 78229
| | - Morten Schak Nielsen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark
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Nielsen BS, Hansen DB, Ransom BR, Nielsen MS, MacAulay N. Connexin Hemichannels in Astrocytes: An Assessment of Controversies Regarding Their Functional Characteristics. Neurochem Res 2017; 42:2537-2550. [DOI: 10.1007/s11064-017-2243-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 03/17/2017] [Accepted: 03/17/2017] [Indexed: 12/19/2022]
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Hertz L, Chen Y. Importance of astrocytes for potassium ion (K+) homeostasis in brain and glial effects of K+ and its transporters on learning. Neurosci Biobehav Rev 2016; 71:484-505. [DOI: 10.1016/j.neubiorev.2016.09.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Revised: 08/12/2016] [Accepted: 09/23/2016] [Indexed: 10/20/2022]
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