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Segretain D, Di Marco M, Dufeu C, Carette D, Trubuil A, Pointis G. Cooperative cell-cell actin network remodeling to perform Gap junction endocytosis. Basic Clin Androl 2023; 33:20. [PMID: 37533006 PMCID: PMC10399049 DOI: 10.1186/s12610-023-00194-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 04/16/2023] [Indexed: 08/04/2023] Open
Abstract
BACKGROUND The endocytosis of Gap junction plaques (GJP) requires cytoskeletal forces to internalize such large membranous structures. Actin, which partners the connexin proteins constituting Gap junctions and is located close to Annular Gap Junctions (AGJ), could be actively involved in this physiological process. RESULTS Electron Microscopy and Light Microscopy images, associated with time-lapse analysis and 3D reconstruction, used at high resolution and enhanced using ImageJ based software analysis, revealed that: i) actin cables, originating from Donor cells, insert on the edge of GJP and contribute to their invagination, giving rise to AGJ, whereas actin cables on the Acceptor cell side of the plaque are not modified; ii) actin cables from the Donor cell are continuous with the actin network present over the entire GJP surface. These actin cables fuse at a single point distant from the plaque, which then detaches itself from the membrane, condensing to form an actin mass during the final internalization process; iii) the Acceptor cell participates in the last step of the endocytic invagination process by forming an annular actin structure known as an actin ring. CONCLUSIONS Together, these data suggest that the endocytosis of GJP is an example of a unique cooperative mechanism between the Donor (the traction of its actin cables) and the Acceptor cells (forming the actin ring).
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Affiliation(s)
- Dominique Segretain
- UMR S1147, Université Paris Descartes, 45 Rue Des Saints-Pères, 75006, Paris, France.
| | - Mathilde Di Marco
- UMR S1147, Université Paris Descartes, 45 Rue Des Saints-Pères, 75006, Paris, France
- Present Address: Institut Curie, PSL Research University, CNRS, UMR144, Structure and Membrane Compartments, 75005, Paris, France
| | - Chloé Dufeu
- Faculté de Pharmacie, Université Paris-Saclay, Saclay, France
| | | | - Alain Trubuil
- MaIAGE, INRAE, Université Paris-Saclay, 78352, Jouy-en-Josas, France
| | - Georges Pointis
- INSERM U 1065, Team 5 Physiopathological Control of Germ Cell Proliferation: Genomic and Non-Genomic Mechanisms, University of Nice Sophia-Antipolis, 151 Route Saint-Antoine de Ginestière BP 2 3194, 06204, Nice Cedex 3, France
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2
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Wang E, Geng A, Maniar AM, Mui BWH, Gong X. Connexin 50 Regulates Surface Ball-and-Socket Structures and Fiber Cell Organization. Invest Ophthalmol Vis Sci 2017; 57:3039-46. [PMID: 27281269 PMCID: PMC4913802 DOI: 10.1167/iovs.16-19521] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Purpose The roles of gap junction protein connexin 50 (Cx50) encoded by Gja8, during lens development are not fully understood. Connexin 50 knockout (KO) lenses have decreased proliferation of epithelial cells and altered fiber cell denucleation. We further investigated the mechanism for cellular defects in Cx50 KO (Gja8−/−) lenses. Methods Fiber cell morphology and subcellular distribution of various lens membrane/cytoskeleton proteins from wild-type and Cx50 KO mice were visualized by immunofluorescent staining and confocal microscopy. Results We observed multiple morphological defects in the cortical fibers of Cx50 KO lenses, including abnormal fiber cell packing geometry, decreased F-actin enrichment at tricellular vertices, and disrupted ball-and-socket (BS) structures on the long sides of hexagonal fibers. Moreover, only small gap junction plaques consisting of Cx46 (α3 connexin) were detected in cortical fibers and the distributions of the BS-associated beta-dystroglycan and ZO-1 proteins were altered. Conclusions Connexin 50 gap junctions are important for BS structure maturation and cortical fiber cell organization. Connexin 50–based gap junction plaques likely form structural domains with an array of membrane/cytoskeletal proteins to stabilize BS. Loss of Cx50-mediated coupling, BS disruption, and altered F-actin in Cx50 KO fibers, thereby contribute to the small lens and mild cataract phenotypes.
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Hejtmancik JF, Riazuddin SA, McGreal R, Liu W, Cvekl A, Shiels A. Lens Biology and Biochemistry. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 134:169-201. [PMID: 26310155 DOI: 10.1016/bs.pmbts.2015.04.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The primary function of the lens resides in its transparency and ability to focus light on the retina. These require both that the lens cells contain high concentrations of densely packed lens crystallins to maintain a refractive index constant over distances approximating the wavelength of the light to be transmitted, and a specific arrangement of anterior epithelial cells and arcuate fiber cells lacking organelles in the nucleus to avoid blocking transmission of light. Because cells in the lens nucleus have shed their organelles, lens crystallins have to last for the lifetime of the organism, and are specifically adapted to this function. The lens crystallins comprise two major families: the βγ-crystallins are among the most stable proteins known and the α-crystallins, which have a chaperone-like function. Other proteins and metabolic activities of the lens are primarily organized to protect the crystallins from damage over time and to maintain homeostasis of the lens cells. Membrane protein channels maintain osmotic and ionic balance across the lens, while the lens cytoskeleton provides for the specific shape of the lens cells, especially the fiber cells of the nucleus. Perhaps most importantly, a large part of the metabolic activity in the lens is directed toward maintaining a reduced state, which shelters the lens crystallins and other cellular components from damage from UV light and oxidative stress. Finally, the energy requirements of the lens are met largely by glycolysis and the pentose phosphate pathway, perhaps in response to the avascular nature of the lens. Together, all these systems cooperate to maintain lens transparency over time.
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Affiliation(s)
- J Fielding Hejtmancik
- Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - S Amer Riazuddin
- The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Rebecca McGreal
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Wei Liu
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Ales Cvekl
- Department of Genetics and Ophthalmology, Albert Einstein College of Medicine, Bronx, New York, USA; Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York, USA
| | - Alan Shiels
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri, USA.
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4
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Cheng C, Nowak RB, Gao J, Sun X, Biswas SK, Lo WK, Mathias RT, Fowler VM. Lens ion homeostasis relies on the assembly and/or stability of large connexin 46 gap junction plaques on the broad sides of differentiating fiber cells. Am J Physiol Cell Physiol 2015; 308:C835-47. [PMID: 25740157 PMCID: PMC4436989 DOI: 10.1152/ajpcell.00372.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2014] [Accepted: 03/03/2015] [Indexed: 12/31/2022]
Abstract
The eye lens consists of layers of tightly packed fiber cells, forming a transparent and avascular organ that is important for focusing light onto the retina. A microcirculation system, facilitated by a network of gap junction channels composed of connexins 46 and 50 (Cx46 and Cx50), is hypothesized to maintain and nourish lens fiber cells. We measured lens impedance in mice lacking tropomodulin 1 (Tmod1, an actin pointed-end capping protein), CP49 (a lens-specific intermediate filament protein), or both Tmod1 and CP49. We were surprised to find that simultaneous loss of Tmod1 and CP49, which disrupts cytoskeletal networks in lens fiber cells, results in increased gap junction coupling resistance, hydrostatic pressure, and sodium concentration. Protein levels of Cx46 and Cx50 in Tmod1(-/-);CP49(-/-) double-knockout (DKO) lenses were unchanged, and electron microscopy revealed normal gap junctions. However, immunostaining and quantitative analysis of three-dimensional confocal images showed that Cx46 gap junction plaques are smaller and more dispersed in DKO differentiating fiber cells. The localization and sizes of Cx50 gap junction plaques in DKO fibers were unaffected, suggesting that Cx46 and Cx50 form homomeric channels. We also demonstrate that gap junction plaques rest in lacunae of the membrane-associated actin-spectrin network, suggesting that disruption of the actin-spectrin network in DKO fibers may interfere with gap junction plaque accretion into micrometer-sized domains or alter the stability of large plaques. This is the first work to reveal that normal gap junction plaque localization and size are associated with normal lens coupling conductance.
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Affiliation(s)
- Catherine Cheng
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California
| | - Roberta B Nowak
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California
| | - Junyuan Gao
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York; and
| | - Xiurong Sun
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York; and
| | - Sondip K Biswas
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia
| | - Woo-Kuen Lo
- Department of Neurobiology, Morehouse School of Medicine, Atlanta, Georgia
| | - Richard T Mathias
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York; and
| | - Velia M Fowler
- Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California;
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5
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Fast structural responses of gap junction membrane domains to AB5 toxins. Proc Natl Acad Sci U S A 2013; 110:E4125-33. [PMID: 24133139 DOI: 10.1073/pnas.1315850110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Gap junctions (GJs) represent connexin-rich membrane domains that connect interiors of adjoining cells in mammalian tissues. How fast GJs can respond to bacterial pathogens has not been known previously. Using Bessel beam plane illumination and confocal spinning disk microscopy, we found fast (~500 ms) formation of connexin-depleted regions (CDRs) inside GJ plaques between cells exposed to AB5 toxins. CDR formation appears as a fast redistribution of connexin channels within GJ plaques with minor changes in outline or geometry. CDR formation does not depend on membrane trafficking or submembrane cytoskeleton and has no effect on GJ conductance. However, CDR responses depend on membrane lipids, can be modified by cholesterol-clustering agents and extracellular K(+) ion concentration, and influence cAMP signaling. The CDR response of GJ plaques to bacterial toxins is a phenomenon observed for all tested connexin isoforms. Through signaling, the CDR response may enable cells to sense exposure to AB5 toxins. CDR formation may reflect lipid-phase separation events in the biological membrane of the GJ plaque, leading to increased connexin packing and lipid reorganization. Our data demonstrate very fast dynamics (in the millisecond-to-second range) within GJ plaques, which previously were considered to be relatively stable, long-lived structures.
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6
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Olk S, Zoidl G, Dermietzel R. Connexins, cell motility, and the cytoskeleton. ACTA ACUST UNITED AC 2010; 66:1000-16. [PMID: 19544403 DOI: 10.1002/cm.20404] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Connexins (Cx) comprise a family of transmembrane proteins, which form intercellular channels between plasma membranes of two adjoining cells, commonly known as gap junctions. Recent reports revealed that Cx proteins interact with diverse cellular components to form a multiprotein complex, which has been termed "Nexus". Potential interaction partners include proteins such as cytoskeletal proteins, scaffolding proteins, protein kinases and phosphatases. These interactions allow correct subcellular localization of Cxs and functional regulation of gap junction-mediated intercellular communication. Evidence is accruing that Cxs might have channel-independent functions, which potentially include regulation of cell migration, cell polarization and growth control. In the current review, we summarize recent knowledge on Cx interactions with cytoskeletal proteins and highlight some aspects of their role in cellular motility.
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Affiliation(s)
- Stephan Olk
- Department of Neuroanatomy and Molecular Brain Research, Ruhr-University Bochum, Bochum, Germany
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7
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Qu C, Gardner P, Schrijver I. The role of the cytoskeleton in the formation of gap junctions by Connexin 30. Exp Cell Res 2009; 315:1683-92. [PMID: 19285977 DOI: 10.1016/j.yexcr.2009.03.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2008] [Revised: 03/03/2009] [Accepted: 03/03/2009] [Indexed: 11/17/2022]
Abstract
Mutations in the genes that encode Connexin 26 (GJB2) and Connexin 30 (GJB6) are the most common known cause of hereditary nonsyndromic sensorineural deafness. Cx26 and Cx30 share a similar protein structure, as well as the same expression distribution pattern in the cochlea. Cx26 has different intracellular trafficking properties compared to those of Cx43 and Cx32, whose trafficking manner is consistent with the classical membrane protein secretory pathway. Until now, however, the trafficking patterns of Cx30 have not been studied. By means of an immunofluorescence staining approach, we found that the targeting of Cx30 to gap junctions in transfected HeLa cells is not affected by brefeldin A, suggesting a Golgi-independent feature, similar to Cx26. Nocodazole had a minimal effect on assembly and distribution of Cx30 gap junctions. Cytochalasin B-induced actin filament depolymerization, however, affected both the pattern and the distribution of Cx30 gap junctions. Co-localization with and/or interaction between Cx30 and microtubules and cortical actin filaments, but not with the tight/adherens junction protein ZO-1, was confirmed by immunofluorescence and/or immunoprecipitation methods. The results suggest that the cytoskeleton, and especially actin filaments, are important components in the processes of assembly, trafficking and stabilization of Cx30 gap junctions.
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Affiliation(s)
- Chunyan Qu
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA
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8
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Maddala R, Skiba N, Vasantha Rao P. Lens fiber cell elongation and differentiation is associated with a robust increase in myosin light chain phosphorylation in the developing mouse. Differentiation 2007; 75:713-25. [PMID: 17459090 DOI: 10.1111/j.1432-0436.2007.00173.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Myosin II, a molecular motor, plays a critical role in cell migration, cell shape changes, cell adhesion, and cytokinesis. To understand the role of myosin II in lens fiber cell elongation and differentiation, we determined the distribution pattern of nonmuscle myosin IIA, IIB, and phosphorylated regulatory myosin light chain-2 (phospho-MLC) in frozen sections of the developing mouse lens by immunofluorescence analysis. While myosin IIA was distributed uniformly throughout the differentiating lens, including the epithelium and fibers, myosin IIB was localized predominantly to the epithelium and the posterior tips of the lens fibers. In contrast, immunostaining with a di-phospho-MLC antibody localized intensely and precisely to the elongating and differentiating primary and secondary lens fibers, co-localizing with actin filaments. An in situ analysis of Rho GTPase activation revealed that Rho-GTP was distributed uniformly throughout the embryonic lens, including epithelium and fibers. Inhibition of myosin light chain kinase (MLCK) activity by ML-7 in organ cultured mouse lenses led to development of nuclear lens opacity in association with abnormal fiber cell organization. Taken together, these data reveal a distinct spatial distribution pattern of myosin II isoforms in the developing lens and a robust activation of MLC phosphorylation in the differentiating lens fibers. Moreover, the regulation of MLC phosphorylation by MLCK appears to be critical for crystallin organization and for maintenance of lens transparency and lens membrane function.
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Affiliation(s)
- Rupalatha Maddala
- Department of Ophthalmology, Duke University School of Medicine, Box 3802, Erwin Road, Durham, North Carolina 27710, USA
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9
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Abstract
Varieties of cell-matrix or cell-cell adhesions are associated with the actin cytoskeleton. However, for gap junctions, which are both channels and adhesions, there has been little evidence for such an association. The purpose of this study was to determine if connexin 43 (Cx43) associates with actin and to determine if this association is altered under mechanical load in tenocytes, a mechanically sensitive cell. Avian tenocytes were subjected to multiple cyclic strain regimens and then fixed and examined immunohistochemically at various times poststrain to determine where Cx43 protein was localized within the cells in relation to actin filaments. Four percent of tenocytes had colocalization of actin filaments and Cx43, which was significantly increased with 5% cyclic strain. To confirm this phenomenon, human tenocytes and COS-7 cells were also subjected to cyclic strain and then fixed at the same times after strain. As with avian tenocytes, Cx43 was colocalized with actin in human tenocytes and COS-7 cells. The colocalization increased significantly after cyclic strain in human tenocytes but not in COS-7 cells. The lack of detectable changes in COS-7 cells may indicate that they are less mechanosensitive than tenocytes perhaps due to the less robust actin cytoskeleton seen in the COS-7 cells when compared to the tenocytes. Furthermore, inhibiting myosin II activity greatly reduced the immunohistochemically-detectable Cx43 on actin filaments. Connexins may associate with actin to stabilize gap junctions at the plasma membrane, ensuring that tenocytes remain coupled during periods of prolonged or intense mechanical loading.
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Affiliation(s)
- Michelle E Wall
- Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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10
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Rao PV, Maddala R. The role of the lens actin cytoskeleton in fiber cell elongation and differentiation. Semin Cell Dev Biol 2006; 17:698-711. [PMID: 17145190 PMCID: PMC1803076 DOI: 10.1016/j.semcdb.2006.10.011] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The vertebrate ocular lens is a fascinating and unique transparent tissue that grows continuously throughout life. During the process of differentiation into fiber cells, lens epithelial cells undergo dramatic morphological changes, membrane remodeling, polarization, transcriptional activation and elimination of cellular organelles including nuclei, concomitant with migration towards the lens interior. Most of these events are presumed to be influenced in large part, by dynamic reorganization of the cellular actin cytoskeleton and by intercellular and cell: extracellular matrix interactions. In light of recent and unprecedented advancement in our understanding of the mechanistic bases underlying regulation of actin cytoskeletal dynamics and the role of the actin cytoskeleton in cell function, this review attempts to summarize current knowledge regarding the role of the cellular actin cytoskeleton, in lens fiber cell elongation and differentiation, and regulation of actin cytoskeletal organization in the lens.
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Affiliation(s)
- P Vasantha Rao
- Departments of Ophthalmology, Pharmacology and Cancer Biology, Duke University School of Medicine, Durham, NC, USA.
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11
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Hervé JC, Bourmeyster N, Sarrouilhe D. Diversity in protein–protein interactions of connexins: emerging roles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1662:22-41. [PMID: 15033577 DOI: 10.1016/j.bbamem.2003.10.022] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2003] [Revised: 10/22/2003] [Accepted: 10/22/2003] [Indexed: 10/26/2022]
Abstract
Gap junctions, specialised membrane structures that mediate cell-to-cell communication in almost all tissues, are composed of channel-forming integral membrane proteins termed connexins. The activity of these intercellular channels is closely regulated, particularly by intramolecular modifications as phosphorylations of proteins by protein kinases, which appear to regulate the gap junction at several levels, including assembly of channels in the plasma membrane, connexin turnover as well as directly affecting the opening and closure ("gating") of channels. The regulation of membrane channels by protein phosphorylation/dephosphorylation processes commonly requires the formation of a multiprotein complex, where pore-forming subunits bind to auxiliary proteins (e.g. scaffolding proteins, catalytic and regulatory subunits), that play essential roles in channel localisation and activity, linking signalling enzymes, substrates and effectors into a structure frequently anchored to the cytoskeleton. The present review summarises the up-to-date progress regarding the proteins capable of interacting or at least of co-localising with connexins and their functional importance.
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Affiliation(s)
- Jean-Claude Hervé
- UMR CNRS no. 6558, Faculté de Sciences Fondamentales et Appliquées, Université de Poitiers, Pôle Biologie-Santé, 86022 Poitiers Cedex, France.
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12
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Nielsen PA, Baruch A, Shestopalov VI, Giepmans BNG, Dunia I, Benedetti EL, Kumar NM. Lens connexins alpha3Cx46 and alpha8Cx50 interact with zonula occludens protein-1 (ZO-1). Mol Biol Cell 2003; 14:2470-81. [PMID: 12808044 PMCID: PMC194895 DOI: 10.1091/mbc.e02-10-0637] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Connexin alpha1Cx43 has previously been shown to bind to the PDZ domain-containing protein ZO-1. The similarity of the carboxyl termini of this connexin and the lens fiber connexins alpha3Cx46 and alpha8Cx50 suggested that these connexins may also interact with ZO-1. ZO-1 was shown to be highly expressed in mouse lenses. Colocalization of ZO-1 with alpha3Cx46 and alpha8Cx50 connexins in fiber cells was demonstrated by immunofluorescence and by fracture-labeling electron microscopy but showed regional variations throughout the lens. ZO-1 was found to coimmunoprecipitate with alpha3Cx46 and alpha8Cx50, and pull-down experiments showed that the second PDZ domain of ZO-1 was involved in this interaction. Transiently expressed alpha3Cx46 and alpha8Cx50 connexins lacking the COOH-terminal residues did not bind to the second PDZ domain but still formed structures resembling gap junctions by immunofluorescence. These results indicate that ZO-1 interacts with lens fiber connexins alpha3Cx46 and alpha8Cx50 in a manner similar to that previously described for alpha1Cx43. The spatial variation in the interaction of ZO-1 with lens gap junctions is intriguing and is suggestive of multiple dynamic roles for this association.
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Affiliation(s)
- Peter A Nielsen
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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13
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Yamane Y, Shiga H, Asou H, Ito E. GAP junctional channel inhibition alters actin organization and calcium propagation in rat cultured astrocytes. Neuroscience 2002; 112:593-603. [PMID: 12074901 DOI: 10.1016/s0306-4522(02)00095-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Astrocytes are connected by gap junctions, which provide intercellular pathways that allow a direct exchange of ions and small metabolites including second messengers and the propagation of electric currents. The roles of gap junctional communication on whole-cell morphology, cytoskeletal organization, and intercellular communication in astrocytes are not yet clear even in vitro, though there are many studies that have examined the active relation between gap junctions and actin filaments in astrocytes. Here we examined the effects of gap junction inhibitors, which do not interrupt the formation but rather the function of gap junctions, on whole-cell morphology, cytoskeletal organization, and intercellular communication in rat cultured astrocytes. Functional blockade of gap junctions during the formation of an astrocytic monolayer resulted in discordance of actin stress fibers between neighboring cells, even though whole-cell morphology of these cells did not change by such treatment. Mechanical stimulation-induced calcium wave propagation was significantly reduced in these actin-discordance cells even after thorough wash out. Differentiation of astrocytes in the presence of gap junction inhibitors was associated with morphological disarrangement among neighboring cells due to disordered alignment of actin stress fibers between cells.Our results indicate that gap junctional communication enables cell-to-cell coordination of actin stress fibers in astrocytes, thus enhancing intercellular communication through calcium spread.
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Affiliation(s)
- Y Yamane
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan
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14
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Johnson RG, Meyer RA, Li XR, Preus DM, Tan L, Grunenwald H, Paulson AF, Laird DW, Sheridan JD. Gap junctions assemble in the presence of cytoskeletal inhibitors, but enhanced assembly requires microtubules. Exp Cell Res 2002; 275:67-80. [PMID: 11925106 DOI: 10.1006/excr.2002.5480] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The role of cytoskeletal elements in gap junction (GJ) assembly has been studied using Novikoff hepatoma cells treated with cytochalasin B (CB) to disrupt actin filaments or with colchicine or nocodazole to disrupt microtubules. After 60 min of cell reaggregation, freeze-fracture was used to evaluate quantitatively the "initiation," "maturation," and "growth" phases of GJ assembly. The development of junctional permeability to fluorescent dyes was also analyzed. The only effects of CB on the structure or permeability of the developing junctions involved an elongation of GJ aggregates and a small decrease in formation plaque areas. Colchicine (but not the inactive form, lumicolchicine) prevented the enhancement of GJ growth by cholesterol, but its effect on basal growth was equivocal. Nocodazole inhibited the growth of GJ, even under basal conditions, without an effect on initiation. Nocodazole also blocked the forskolin-enhanced increase in the growth of GJs and, in living MDCK cells, reduced the movement of transport intermediates containing green fluorescent protein-tagged connexin43. Thus, neither actin filaments nor microtubules appear to restrict GJ assembly by anchoring intramembrane GJ proteins, nor are they absolutely required for functional GJs to form. However, microtubules are necessary for enhanced GJ growth and likely for facilitating connexin trafficking under basal conditions.
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Affiliation(s)
- Ross G Johnson
- Department of Genetics, Cell Biology, and Development, University of Minnesota, St. Paul, Minnesota 55108, USA.
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15
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Lo WK, Wen XJ, Zhou C. Regional differences in actin stability in the rat lens as visualized by immunofluorescence labeling under the influence of pH. Exp Eye Res 2000; 71:323-7. [PMID: 10973741 DOI: 10.1006/exer.2000.0881] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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16
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Woo MK, Lee A, Fischer RS, Moyer J, Fowler VM. The lens membrane skeleton contains structures preferentially enriched in spectrin-actin or tropomodulin-actin complexes. CELL MOTILITY AND THE CYTOSKELETON 2000; 46:257-68. [PMID: 10962480 DOI: 10.1002/1097-0169(200008)46:4<257::aid-cm3>3.0.co;2-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The spectrin-based membrane skeleton plays an important role in determining the distributions and densities of receptors, ion channels, and pumps, thus influencing cell shape and deformability, cell polarity, and adhesion. In the paradigmatic human erythrocyte, short tropomodulin-capped actin filaments are cross-linked by spectrin into a hexagonal network, yet the extent to which this type of actin filament organization is utilized in the membrane skeletons of nonerythroid cells is not known. Here, we show that associations of tropomodulin and spectrin with actin in bovine lens fiber cells are distinct from that of the erythrocyte and imply a very different molecular organization. Mechanical disruption of the lens fiber cell membrane skeleton releases tropomodulin and actin-containing oligomeric complexes that can be isolated by gel filtration column chromatography, sucrose gradient centrifugation and immunoadsorption. These tropomodulin-actin complexes do not contain spectrin. Instead, spectrin is associated with actin in different complexes that do not contain tropomodulin. Immunofluorescence staining of isolated fiber cells further demonstrates that tropomodulin does not precisely colocalize with spectrin along the lateral membranes of lens fiber cells. Taken together, our data suggest that tropomodulin-capped actin filaments and spectrin-cross-linked actin filaments are assembled in distinct structures in the lens fiber cell membrane skeleton, indicating that it is organized quite differently from that of the erythrocyte membrane skeleton.
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Affiliation(s)
- M K Woo
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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Yamane Y, Shiga H, Asou H, Haga H, Kawabata K, Abe K, Ito E. Dynamics of astrocyte adhesion as analyzed by a combination of atomic force microscopy and immuno-cytochemistry: the involvement of actin filaments and connexin 43 in the early stage of adhesion. ARCHIVES OF HISTOLOGY AND CYTOLOGY 1999; 62:355-61. [PMID: 10596946 DOI: 10.1679/aohc.62.355] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We observed the time-dependent morphological alteration of astrocytes during their adhesion by atomic force microscopy (AFM) and investigated the relationships between this morphological alteration and the localization of actin filaments and connexin 43 by immunocytochemistry. The fine processes observed as fine ridge-like structures by AFM were closely concerned with actin filaments by immunocytochemistry. During the adhesion of astrocytes, actin filaments appeared to be aligned regularly beyond the borders among different cells. Detectable connexin immunoreactivity was changed in the following regions: 1) the tips of fine cell processes and the cell margin when astrocytes started to adhere; 2) the border of cells when astrocytes tightly adhered; and 3) non-specific sites when astrocytes became a cluster. In the former two cases, the immunopositive spots for connexin were observed to colocalize with the tips of cell processes with actin filaments. These results strongly suggest that connexin associated with actin filaments at the tip of cell processes plays an important role in the early stage of the adhesion of astrocytes. These observations afford valuable clues for understanding the glial communication.
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Affiliation(s)
- Y Yamane
- Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan
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18
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Abstract
We have studied the role of actin fiber assembly on calcium signaling in astrocytes. We found that (1) after astrocytes have been placed in culture, it takes several hours for organization of the definitive actin cytoskeleton. Actin organization and the number of cells engaged in calcium signaling increased in parallel. (2) Disruption of the actin cytoskeleton attenuated the calcium wave propagation; cytochalasin D treatment reduced the number of astrocytes engaged in calcium signaling. (3) Propagation of calcium waves depends on cytoskeletal function; inhibition of myosin light chain kinase suppressed wave activity. (4) Astrocytic calcium signaling is mediated by release of ATP and purinergic receptor stimulation, because agents that interfere with this cascade attenuated or reduced calcium signaling. Because purinergic receptors are fully functional shortly after plating and not affected by cytochalasin D, these observations indicate that cytoskeleton organization is a prerequisite for interastrocytic calcium signaling mediated by release of ATP.
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19
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Abstract
The distribution and organization of actin filament bundles were studied in cortical fiber cells of rat lenses at various ages (3 days to 2.5 months old), using thin-section electron microscopy, immunocytochemistry and immunoblotting. Electron microscopy showed that actin bundles were regularly found along cortical fiber cell membranes of the lens at all ages studied. The actin bundles were commonly arranged in three distinct units, one bundle in each fiber cell, located at the intersections where three hexagonal fiber cells meet as seen in cross sections. These actin bundles were approximately 150 nm in diameter and were composed of 7-nm small filaments. They were aligned parallel to the long axis of fiber cells as judged by both cross and longitudinal sections. The outside border of each bundle was always surrounded by a zone of 10-nm intermediate filaments which have the same orientation as that of the actin bundles. In longitudinal sections, elongated actin bundles were always parallel to the cell membranes. A number of individual actin bundles sometimes were found to form a chain with periodic short intervals. In addition, actin bundles were frequently associated with adherens junctions near the intersections and other regions of fiber cell membranes. By immunoelectron microscopy, we demonstrated that these filament bundles indeed contained actins. By rhodamine-phalloidin labelling, we found that labeled actin bundles appeared as large, distinct dots at the corners of hexagonal fiber cells in all ages studied. In addition, non-bundle F-actins were labeled preferentially along the cell membranes of the short sides of hexagonal fiber cells. This resulted in a unique zigzag pattern of actin labeling commonly seen in the cortical fiber cells of a mature rat lens. Finally, we showed that alpha-actinin was associated with the actin bundles in the fiber cells by immunofluorescent double labeling and immunoblotting. It is suggested that this unique arrangement of actin bundles in fiber cells may provide a stabilizing structure for forming a sharp angle at each corner of fiber cells, thereby the hexagonal shape of the cells can be maintained.
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Affiliation(s)
- W K Lo
- Department of Anatomy, Morehouse School of Medicine, 720 Westview Drive, SW, Atlanta, GA 30310, USA
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Tenbroek EM, Louis CF, Johnson R. The differential effects of 12-O-tetradecanoylphorbol-13-acetate on the gap junctions and connexins of the developing mammalian lens. Dev Biol 1997; 191:88-102. [PMID: 9356174 DOI: 10.1006/dbio.1997.8703] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Epithelial cells in primary ovine lens cultures express the gap junction proteins connexin43 (Cx43) and connexin49 (Cx49; a.k.a. MP70), a homologue of mouse connexin50. In contrast, lens cultures of differentiated, fiber-like cells (termed lentoid cells) express Cx49 and connexin46 (Cx46), but not Cx43. To investigate the regulation of lens cell gap junctions by protein kinase C (PKC), differentiating lens cultures were treated with the PKC activator 12-O-tetradecanoylphorbol-13-acetate (beta-TPA). Within 10 min, beta-TPA significantly inhibited the transfer of Lucifer Yellow dye between epithelial, but not lentoid, cells. This inhibition was correlated with the phosphorylation of Cx43 and was followed by the gradual disappearance of Cx43 from cell interfaces. The protein kinase inhibitor staurosporine prevented Cx43 phosphorylation and the loss of Cx43 from intercellular junctions. Following treatment of cultures with beta-TPA for 2-6 hr, Cx49 disappeared from epithelial cell interfaces, and by 24 hr of beta-TPA treatment, levels of Cx49 detected on immunoblots of purified epithelial membrane fractions had also diminished significantly. The beta-TPA-induced loss of Cx49 both from regions of epithelial cell contact and from isolated membranes was correlated with the disappearance of Cx49 mRNA. In contrast to the epithelial connexins, the lentoid connexins Cx49 and Cx46 were unaffected by even extended beta-TPA treatment. In spite of lentoid dye transfer being refractory to beta-TPA, significant levels of PKC-alpha (a beta-TPA-sensitive isoform) were detected in the lentoid cell. The response of lens gap junctions to beta-TPA depends upon the stage of differentiation and the complement of connexins expressed. The contrasting effects of beta-TPA on Cx43 and Cx49 in lens epithelial cells indicate a fundamental difference in the regulation of these connexin proteins in the developing mammalian lens.
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Affiliation(s)
- E M Tenbroek
- Department of Genetics and Cell Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
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21
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Abstract
Gap junction channels are formed by paired oligomeric membrane hemichannels called connexons, which are composed of proteins of the connexin family. Experiments with transfected cell lines and paired Xenopus oocytes have demonstrated that heterotypic intercellular channels which are formed by two connexons, each composed of a different connexin, can selectively occur. Studies by Stauffer [Stauffer, K. A. (1995) J. Biol. Chem. 270, 6768-6772] have shown that recombinant Cx26 and Cx32 coinfected into insect cells may form heteromeric connexons. By solubilizing and subfractionating individual connexons from ovine lenses, we show by immunoprecipitation that connexons can contain two different connexins forming heteromeric assemblies in vivo.
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Affiliation(s)
- J X Jiang
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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Wolburg H, Rohlmann A. Structure--function relationships in gap junctions. INTERNATIONAL REVIEW OF CYTOLOGY 1995; 157:315-73. [PMID: 7706021 DOI: 10.1016/s0074-7696(08)62161-0] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Gap junctions are metabolic and electrotonic pathways between cells and provide direct cooperation within and between cellular nets. They are among the cellular structures most frequently investigated. This chapter primarily addresses aspects of the assembly of the gap junction channel, considering the insertion of the protein into the membrane, the importance of phosphorylation of the gap junction proteins for coupling modulation, and the formation of whole channels from two hemichannels. Interactions of gap junctions with the subplasmalemmal cytoplasm on the one side and with tight junctions on the other side are closely considered. Furthermore, reviewing the significance and alterations of gap junctions during development and oncogenesis, respectively, including the role of adhesion molecules, takes up a major part of the chapter. Finally, the literature on gap junctions in the central nervous system, especially between astrocytes in the brain cortex and horizontal cells in the retina, is summarized and new aspects on their structure-function relationship included.
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Affiliation(s)
- H Wolburg
- Institute of Pathology, University of Tübingen, Germany
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