Junctional ER Organization Affects Mechanotransduction at Cadherin-Mediated Adhesions

Cadherin-mediated adhesions (also known as adherens junctions) are adhesive complexes that connect neighboring cells in a tissue. While the role of the actin cytoskeleton in withstanding tension at these sites of contact is well documented, little is known about the involvement of microtubules and the associated endoplasmic reticulum (ER) network in cadherin mechanotransduction. Therefore, we investigated how the organization of ER extensions in close proximity of cadherin-mediated adhesions can affect such complexes, and vice versa. Here, we show that the extension of the ER to cadherin-mediated adhesions is tension dependent and appears to be cadherin-type specific. Furthermore, the different structural organization of the ER/microtubule network seems to affect the localization of ER-bound PTP1B at cadherin-mediated adhesions. This phosphatase is involved in the modulation of vinculin, a molecular clutch which enables differential engagement of the cadherin-catenin layer with the actomyosin cytoskeleton in response to tension. This suggests a link between structural organization of the ER/microtubule network around cadherin-specific adhesions, to control the mechanotransduction of adherens junctions by modulation of vinculin conformational state.

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Regulation of Adherens Junction Dynamics by Phosphorylation Switches

Journal of Signal Transduction ◽

10.1155/2012/125295 ◽

2012 ◽

Vol 2012 ◽

pp. 1-14 ◽

Cited By ~ 26

Author(s):

Cristina Bertocchi ◽

Megha Vaman Rao ◽

Ronen Zaidel-Bar

Keyword(s):

Actin Cytoskeleton ◽

Enzymatic Activity ◽

Adherens Junctions ◽

Adherens Junction ◽

Adaptor Proteins ◽

Cell Junction ◽

Internal Forces ◽

Adherens Junction Proteins ◽

Junction Proteins

Adherens junctions connect the actin cytoskeleton of neighboring cells through transmembrane cadherin receptors and a network of adaptor proteins. The interactions between these adaptors and cadherin as well as the activity of actin regulators localized to adherens junctions are tightly controlled to facilitate cell junction assembly or disassembly in response to changes in external or internal forces and/or signaling. Phosphorylation of tyrosine, serine, or threonine residues acts as a switch on the majority of adherens junction proteins, turning “on” or “off” their interactions with other proteins and/or their enzymatic activity. Here, we provide an overview of the kinases and phosphatases regulating phosphorylation of adherens junction proteins and bring examples of phosphorylation events leading to the assembly or disassembly of adherens junctions, highlighting the important role of phosphorylation switches in regulating their dynamics.

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The Drosophila afadin homologue Canoe regulates linkage of the actin cytoskeleton to adherens junctions during apical constriction

The Journal of Cell Biology ◽

10.1083/jcb.200904001 ◽

2009 ◽

Vol 186 (1) ◽

pp. 57-73 ◽

Cited By ~ 150

Author(s):

Jessica K. Sawyer ◽

Nathan J. Harris ◽

Kevin C. Slep ◽

Ulrike Gaul ◽

Mark Peifer

Keyword(s):

Actin Cytoskeleton ◽

Cell Shape ◽

Shape Change ◽

Adherens Junctions ◽

Apical Constriction ◽

Cell Shape Change ◽

Mediate Cell Adhesion ◽

Mediate Cell ◽

Actomyosin Cytoskeleton ◽

Core Part

Cadherin-based adherens junctions (AJs) mediate cell adhesion and regulate cell shape change. The nectin–afadin complex also localizes to AJs and links to the cytoskeleton. Mammalian afadin has been suggested to be essential for adhesion and polarity establishment, but its mechanism of action is unclear. In contrast, Drosophila melanogaster’s afadin homologue Canoe (Cno) has suggested roles in signal transduction during morphogenesis. We completely removed Cno from embryos, testing these hypotheses. Surprisingly, Cno is not essential for AJ assembly or for AJ maintenance in many tissues. However, morphogenesis is impaired from the start. Apical constriction of mesodermal cells initiates but is not completed. The actomyosin cytoskeleton disconnects from AJs, uncoupling actomyosin constriction and cell shape change. Cno has multiple direct interactions with AJ proteins, but is not a core part of the cadherin–catenin complex. Instead, Cno localizes to AJs by a Rap1- and actin-dependent mechanism. These data suggest that Cno regulates linkage between AJs and the actin cytoskeleton during morphogenesis.

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Role of IQGAP1 in endothelial barrier enhancement caused by OxPAPC

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00095.2016 ◽

2016 ◽

Vol 311 (4) ◽

pp. L800-L809 ◽

Cited By ~ 6

Author(s):

Yufeng Tian ◽

Xinyong Tian ◽

Grzegorz Gawlak ◽

Nicolene Sarich ◽

David B. Sacks ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Actin Polymerization ◽

Adherens Junctions ◽

Adherens Junction ◽

Cell Junctions ◽

Endothelial Barrier ◽

Cell Junction ◽

Protective Effects ◽

P120 Catenin

Oxidized 1-palmitoyl-2-arachidonoyl- sn-glycero-3-phosphatidylcholine (OxPAPC) attenuates agonist-induced endothelial cell (EC) permeability and increases pulmonary endothelial barrier function via enhancement of both the peripheral actin cytoskeleton and cell junctions mediated by Rac1 and Cdc42 GTPases. This study evaluated the role for the multifunctional Rac1/Cdc42 effector and regulator, IQ domain containing GTPase-activating protein (IQGAP1), as a molecular transducer of the OxPAPC-mediated EC barrier-enhancing signal. IQGAP1 knockdown in endothelial cells by gene-specific small-interfering RNA abolished OxPAPC-induced enlargement of VE-cadherin-positive adherens junctions, suppressed peripheral accumulation of actin polymerization regulators, namely cortactin, neural Wiskott-Aldrich syndrome protein (N-WASP), and actin-related protein 3, and attenuated remodeling of the peripheral actin cytoskeleton. Inhibition of OxPAPC-induced barrier enhancement by IQGAP1 knockdown was due to suppressed Rac1 and Cdc42 activation. Expression of an IQGAP1 truncated mutant showed that the GTPase regulatory domain of IQGAP1 was essential for the OxPAPC-induced membrane localization of cortactin, adherens junction proteins VE-cadherin and p120-catenin, as well as for EC permeability response. IQGAP1 knockdown attenuated the protective effect of OxPAPC against thrombin-induced cell contraction, cell junction disruption, and EC permeability. These results demonstrate for the first time the role of IQGAP1 as a critical transducer of OxPAPC-induced Rac1/Cdc42 signaling to the actin cytoskeleton and adherens junctions, which promotes cortical cytoskeletal remodeling and EC barrier-protective effects of oxidized phospholipids.

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Ca2+-ATPases in non-failing and failing heart: evidence for a novel cardiac sarco/endoplasmic reticulum Ca2+-ATPase 2 isoform (SERCA2c)

Biochemical Journal ◽

10.1042/bj20051427 ◽

2006 ◽

Vol 395 (2) ◽

pp. 249-258 ◽

Cited By ~ 58

Author(s):

Saoussen Dally ◽

Raymonde Bredoux ◽

Elisabeth Corvazier ◽

Jens P. Andersen ◽

Johannes D. Clausen ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Turnover Rate ◽

Normal Subjects ◽

The Novel ◽

Hek 293 ◽

Transfected Cells ◽

293 Cells ◽

Mrna Variant ◽

Close Proximity

We recently documented the expression of a novel human mRNA variant encoding a yet uncharacterized SERCA [SR (sarcoplasmic reticulum)/ER (endoplasmic reticulum) Ca2+-ATPase] protein, SERCA2c [Gélébart, Martin, Enouf and Papp (2003) Biochem. Biophys. Res. Commun. 303, 676–684]. In the present study, we have analysed the expression and functional characteristics of SERCA2c relative to SERCA2a and SERCA2b isoforms upon their stable heterologous expression in HEK-293 cells (human embryonic kidney 293 cells). All SERCA2 proteins induced an increased Ca2+ content in the ER of intact transfected cells. In microsomes prepared from transfected cells, SERCA2c showed a lower apparent affinity for cytosolic Ca2+ than SERCA2a and a catalytic turnover rate similar to SERCA2b. We further demonstrated the expression of the endogenous SERCA2c protein in protein lysates isolated from heart left ventricles using a newly generated SERCA2c-specific antibody. Relative to the known uniform distribution of SERCA2a and SERCA2b in cardiomyocytes of the left ventricle tissue, SERCA2c was only detected in a confined area of cardiomyocytes, in close proximity to the sarcolemma. This finding led us to explore the expression of the presently known cardiac Ca2+-ATPase isoforms in heart failure. Comparative expression of SERCAs and PMCAs (plasma-membrane Ca2+-ATPases) was performed in four nonfailing hearts and five failing hearts displaying mixed cardiomyopathy and idiopathic dilated cardiomyopathies. Relative to normal subjects, cardiomyopathic patients express more PMCAs than SERCA2 proteins. Interestingly, SERCA2c expression was significantly increased (166±26%) in one patient. Taken together, these results demonstrate the expression of the novel SERCA2c isoform in the heart and may point to a still unrecognized role of PMCAs in cardiomyopathies.

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MICROGLIA AND ASTROCYTES OF THE HUMAN BRAIN SUBSTANTIA NIGRA

Medical academic journal ◽

10.17816/maj191s1135 ◽

2019 ◽

Vol 19 (1S) ◽

pp. 135-135

Author(s):

D E Korzhevskii ◽

D A Sufieva ◽

M A Brovko

Keyword(s):

Substantia Nigra ◽

Human Brain ◽

Structural Organization ◽

Active Role ◽

Microglial Cells ◽

Experimental Medicine ◽

Special Role ◽

Saint Petersburg ◽

Close Proximity

In recent years, attention of researches has focused on glial cells of different brain formations - astrocytes and microglial cells. This is due to active role of these cells in ensuring synaptic plasticity and regulation of neurogenesis. The study aimed at analyzing the structural organization of microglia and astrocytes of the human brain substantia nigra, which is the main dopaminergic nerve center. For the study, material from the archive of the Morphology Department (Institute of Experimental Medicine, Saint Petersburg, Russia) was used. Cells were detected using immunocytochemical markers (GFAP for astrocytes and Iba-1 for microglia). It has been established that microglial cells bodies in substantia nigra are located in neuropile singly. In pars compacta of substantia nigra these cells distributed relatively evenly, rarely being in close proximity to neurons. An unexpected fact was that the processes of microglia cells of the human brain substantia nigra have a sufficiently large thickness - 1.5-3 microns, which is not typical for a ramified microglia. Astrocytes of substantis nigra were characterized by the presence of very long processes (more than 100 microns) and the formation of the pericellular sheath around the nerve cells. These sheaths consisted of a dense interweaving of thin sparingly branched astrocyte processes. The processes of microglia were rarely present within such sheaths. The results obtained indicate moderate activation of microglia in substantia nigra and the special role of astrocytes in ensuring the compartmentalization of the pericellular zones in this nerve center.

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Spatial Actin Structure Does Not Correlate With Nuclear Organization

Volume 1A: Abdominal Aortic Aneurysms; Active and Reactive Soft Matter; Atherosclerosis; BioFluid Mechanics; Education; Biotransport Phenomena; Bone, Joint and Spine Mechanics; Brain Injury; Cardiac Mechanics; Cardiovascular Devices, Fluids and Imaging; Cartilage and Disc Mechanics; Cell and Tissue Engineering; Cerebral Aneurysms; Computational Biofluid Dynamics; Device Design, Human Dynamics, and Rehabilitation; Drug Delivery and Disease Treatment; Engineered Cellular Environments ◽

10.1115/sbc2013-14167 ◽

2013 ◽

Author(s):

Shin-Min Wen ◽

Pen-hsiu Grace Chao

Keyword(s):

Actin Cytoskeleton ◽

Chromatin Condensation ◽

Nuclear Shape ◽

Nuclear Deformation ◽

Linc Complex ◽

Mechanical Coupling ◽

Actin Structure ◽

Actomyosin Cytoskeleton ◽

Chromatin Density

Cells in situ exhibit a great variety of morphologies that intimately relates to phenotypic controls. Cell morphology regulates cytoskeletal organization, which in turn influences nuclear shape and organization [1–4]. The actomyosin cytoskeleton is connected to a structure known as the linker of nucleoskeleton and cytoskeleton (LINC) complex located on the nuclear membrane. LINC is believed to transmit deformation of the actin cytoskeleton into the nucleus and nucleoskeleton, change nuclear shape as well as chromatin conformation, and modulate gene expression [5, 6]. Khatau and coworkers reported a structure of apical actin dome, called the actin cap, that controls nuclear deformation through LINC [7]. In addition, actin stress fibers hves been shown to compress the nucleus laterally and increase chromatin condensation [4]. Based on these findings, we hypothesize that there is a spatial correlation between the actin cytoskeleton and chromatin density. In the current study, we investigated the role of actin cytoskeleton in nuclear deformation with respect to the z-axis. We found no spatial relationships between actin structure and nuclear deformation or chromatin condensation, suggesting that the actomyosin cytoskeleton acts globally to influence nuclear structure and additional structural components may contribute to the actin-nucleus mechanical coupling.

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The plant endoplasmic reticulum: a cell-wide web

Biochemical Journal ◽

10.1042/bj20091113 ◽

2009 ◽

Vol 423 (2) ◽

pp. 145-155 ◽

Cited By ~ 70

Author(s):

Imogen A. Sparkes ◽

Lorenzo Frigerio ◽

Nicholas Tolley ◽

Chris Hawes

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

Golgi Apparatus ◽

Actin Cytoskeleton ◽

Higher Plants ◽

Direct Interaction ◽

Present Review ◽

A Cell ◽

Myosin Motors

The ER (endoplasmic reticulum) in higher plants forms a pleomorphic web of membrane tubules and small cisternae that pervade the cytoplasm, but in particular form a polygonal network at the cortex of the cell which may be anchored to the plasma membrane. The network is associated with the actin cytoskeleton and demonstrates extensive mobility, which is most likely to be dependent on myosin motors. The ER is characterized by a number of domains which may be associated with specific functions such as protein storage, or with direct interaction with other organelles such as the Golgi apparatus, peroxisomes and plastids. In the present review we discuss the nature of the network, the role of shape-forming molecules such as the recently described reticulon family of proteins and the function of some of the major domains within the ER network.

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Disruption of F-actin stimulates hypertonic activation of the BGT1 transporter in MDCK cells

AJP Renal Physiology ◽

10.1152/ajprenal.00289.2002 ◽

2003 ◽

Vol 284 (5) ◽

pp. F930-F937 ◽

Cited By ~ 13

Author(s):

Jeremy L. Bricker ◽

Shaoyou Chu ◽

Stephen A. Kempson

Keyword(s):

Actin Cytoskeleton ◽

Mdck Cells ◽

Major Change ◽

Cytochalasin D ◽

Transport Systems ◽

Microtubule Network ◽

Cell Monolayers ◽

Latrunculin A ◽

Membrane Transport Systems

Many membrane transport systems are altered by changes in the state of the actin cytoskeleton. Although an intact microtubule network is required for hypertonic activation of the betaine transporter (BGT1), the possible role of the actin cytoskeleton is unknown. BGT1 function in Madin-Darby canine kidney cell monolayers was assessed as Na+-dependent uptake of GABA, following disassembly of F-actin by cytochalasin D (1.0 μM) or latrunculin A (0.6 μM). Both drugs significantly increased ( P < 0.001) the activation of BGT1 transport by 24-h hypertonicity (500 mosmol/kgH2O). In contrast, the hypertonic upregulation of Na+-dependent alanine uptake remained unaltered by cytochalasin D. Disruption of F-actin did not interfere with downregulation of BGT1 transport when cells were transferred from hypertonic to isotonic medium. Immunofluorescence staining revealed colocalization of BGT1 and F-actin at the plasma membrane of hypertonic cells. Surface biotinylation revealed no major change in BGT1 protein abundance after cytochalasin D action, suggesting that stimulation of hypertonic activation of BGT1 transport is due to increased activity of existing BGT1 transporters.

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Drebrin Regulates Acetylcholine Receptor Clustering and Organization of Microtubules at the Postsynaptic Machinery

International Journal of Molecular Sciences ◽

10.3390/ijms22179387 ◽

2021 ◽

Vol 22 (17) ◽

pp. 9387

Author(s):

Paloma Alvarez-Suarez ◽

Natalia Nowak ◽

Anna Protasiuk-Filipunas ◽

Hiroyuki Yamazaki ◽

Tomasz J. Prószyński ◽

...

Keyword(s):

Actin Cytoskeleton ◽

Acetylcholine Receptors ◽

Neuromuscular Junctions ◽

Microtubule Network ◽

Postsynaptic Protein ◽

Cultured Myotubes ◽

The Brain

Proper muscle function depends on the neuromuscular junctions (NMJs), which mature postnatally to complex “pretzel-like” structures, allowing for effective synaptic transmission. Postsynaptic acetylcholine receptors (AChRs) at NMJs are anchored in the actin cytoskeleton and clustered by the scaffold protein rapsyn, recruiting various actin-organizing proteins. Mechanisms driving the maturation of the postsynaptic machinery and regulating rapsyn interactions with the cytoskeleton are still poorly understood. Drebrin is an actin and microtubule cross-linker essential for the functioning of the synapses in the brain, but its role at NMJs remains elusive. We used immunohistochemistry, RNA interference, drebrin inhibitor 3,5-bis-trifluoromethyl pyrazole (BTP2) and co-immunopreciptation to explore the role of this protein at the postsynaptic machinery. We identify drebrin as a postsynaptic protein colocalizing with the AChRs both in vitro and in vivo. We also show that drebrin is enriched at synaptic podosomes. Downregulation of drebrin or blocking its interaction with actin in cultured myotubes impairs the organization of AChR clusters and the cluster-associated microtubule network. Finally, we demonstrate that drebrin interacts with rapsyn and a drebrin interactor, plus-end-tracking protein EB3. Our results reveal an interplay between drebrin and cluster-stabilizing machinery involving rapsyn, actin cytoskeleton, and microtubules.

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