Endothelial adherens junctions and the actin cytoskeleton: an 'infinity net'?

In vascular endothelium, adherens junctions between endothelial cells are composed of VE-cadherin (vascular endothelial cadherin), an adhesive receptor that is crucial for the proper assembly of vascular structures and the maintenance of vascular integrity. As a classical cadherin, VE-cadherin links endothelial cells together by homophilic interactions mediated by its extracellular part and associates intracellularly with the actin cytoskeleton via catenins. Although, from structural crystallographic data, a dimeric structure arranged in a trans orientation has emerged as a potential mechanism of cell–cell adhesion, the cadherin organization within adherens junctions remains controversial. Concerning VE-cadherin, its extracellular part possesses the capacity to self-associate in solution as hexamers consisting of three antiparallel cadherin dimers. VE-cadherin-based adherens junctions were reconstituted in vitro by assembly of a VE-cadherin EC (extracellular repeat) 1–EC4 hexamer at the surfaces of liposomes. The artificial adherens junctions revealed by cryoelectron microscopy appear as a two-dimensional self-assembly of hexameric structures. This cadherin organization is reminiscent of that found in native desmosomal junctions. Further structural studies performed on native VE-cadherin junctions would provide a better understanding of the cadherin organization within adherens junctions. Homophilic interactions between cadherins are strengthened intracellularly by connection to the actin cytoskeleton. Recently, we have discovered that annexin 2, an actin-binding protein connects the VE-cadherin–catenin complex to the actin cytoskeleton. This novel link is labile and promotes the endothelial cell switch from a quiescent to an angiogenic 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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Cadherin controls nectin recruitment into adherens junctions by remodeling the actin cytoskeleton

Journal of Cell Science ◽

10.1242/jcs.161588 ◽

2014 ◽

Vol 128 (1) ◽

pp. 140-149 ◽

Cited By ~ 13

Author(s):

R. B. Troyanovsky ◽

I. Indra ◽

C.-S. Chen ◽

S. Hong ◽

S. M. Troyanovsky

Keyword(s):

Actin Cytoskeleton ◽

Adherens Junctions

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

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1168128.793481722 ◽

2013 ◽

Cited By ~ 1

Author(s):

Alpha Yap

Keyword(s):

Actin Cytoskeleton ◽

Adherens Junctions ◽

Apical Constriction

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Tyrosine phosphorylation regulates the adhesions of ras-transformed breast epithelia.

The Journal of Cell Biology ◽

10.1083/jcb.130.2.461 ◽

1995 ◽

Vol 130 (2) ◽

pp. 461-471 ◽

Cited By ~ 209

Author(s):

M S Kinch ◽

G J Clark ◽

C J Der ◽

K Burridge

Keyword(s):

Epithelial Cells ◽

Actin Cytoskeleton ◽

Tyrosine Phosphorylation ◽

Tyrosine Kinases ◽

Adherens Junctions ◽

Focal Adhesions ◽

Transformed Cells ◽

Beta Catenin ◽

Altered Cell ◽

E Cadherin

Transformed epithelial cells often are characterized by a fibroblastic or mesenchymal morphology. These cells exhibit altered cell-cell and cell-substrate interactions. Here we have identified changes in the adhesions and cytoskeletal interactions of transformed epithelial cells that contribute to their altered morphology. Using MCF-10A human breast epithelial cells as a model system, we have found that transformation by an activated form of ras is characterized by less developed adherens-type junctions between cells but increased focal adhesions. Contributing to the modified adherens junctions of the transformed cells are decreased interactions among beta-catenin, E-cadherin, and the actin cytoskeleton. The ras-transformed cells reveal elevated phosphotyrosine in many proteins, including beta-catenin and p120 Cas. Whereas in the normal cells beta-catenin is found in association with E-cadherin, p120 Cas is not. In the ras-transformed cells, the situation is reversed; tyrosine-phosphorylated p120 Cas, but not tyrosine-phosphorylated beta-catenin, now is detected in E-cadherin complexes. The tyrosine-phosphorylated beta-catenin also shows increased detergent solubility, suggesting a decreased association with the actin cytoskeleton. p120 Cas, whether tyrosine phosphorylated or not, partitions into the detergent soluble fraction, suggesting that it is not tightly bound to the actin cytoskeleton in either the normal or ras-transformed cells. Inhibitors of tyrosine kinases decrease the level of tyrosine phosphorylation and restore a normal epithelial morphology to the ras-transformed cells. In particular, decreased tyrosine phosphorylation of beta-catenin is accompanied by increased interaction with both E-cadherin and the detergent insoluble cytoskeletal fraction. These results suggest that elevated tyrosine phosphorylation of proteins such as beta-catenin and p120 Cas contribute to the altered adherens junctions of ras-transformed epithelia.

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Regulating polarity by directing traffic: Cdc42 prevents adherens junctions from Crumblin' aPart

The Journal of Cell Biology ◽

10.1083/jcb.200811057 ◽

2008 ◽

Vol 183 (6) ◽

pp. 971-974 ◽

Cited By ~ 8

Author(s):

Mara C. Duncan ◽

Mark Peifer

Keyword(s):

Cell Adhesion ◽

Actin Cytoskeleton ◽

Cell Polarity ◽

Adherens Junctions ◽

Vesicular Trafficking ◽

Cell Junction ◽

Par Proteins ◽

Cell Biol ◽

Embryonic Morphogenesis ◽

Junction Proteins

The GTPase Cdc42 was among the original genes identified with roles in cell polarity, and interest in its cellular roles from yeast to humans remains high. Cdc42 is a well-known regulator of the actin cytoskeleton, but also plays important roles in vesicular trafficking. In this issue, Harris and Tepass (Harris, K.P, and U. Tepass. 2008. J. Cell. Biol. 183:1129–1143) provide new insights into how Cdc42 and Par proteins work together to modulate cell adhesion and polarity during embryonic morphogenesis by regulating the traffic of key cell junction proteins.

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Branched actin networks push against each other at adherens junctions to maintain cell–cell adhesion

The Journal of Cell Biology ◽

10.1083/jcb.201708103 ◽

2018 ◽

Vol 217 (5) ◽

pp. 1827-1845 ◽

Cited By ~ 37

Author(s):

Nadia Efimova ◽

Tatyana M. Svitkina

Keyword(s):

Actin Cytoskeleton ◽

Actin Polymerization ◽

Mechanical Load ◽

Adherens Junctions ◽

Cell Junctions ◽

Pull System ◽

Actin Networks ◽

Pulling Forces ◽

Intercellular Adhesions ◽

Cell Cell

Adherens junctions (AJs) are mechanosensitive cadherin-based intercellular adhesions that interact with the actin cytoskeleton and carry most of the mechanical load at cell–cell junctions. Both Arp2/3 complex–dependent actin polymerization generating pushing force and nonmuscle myosin II (NMII)-dependent contraction producing pulling force are necessary for AJ morphogenesis. Which actin system directly interacts with AJs is unknown. Using platinum replica electron microscopy of endothelial cells, we show that vascular endothelial (VE)-cadherin colocalizes with Arp2/3 complex–positive actin networks at different AJ types and is positioned at the interface between two oppositely oriented branched networks from adjacent cells. In contrast, actin–NMII bundles are located more distally from the VE-cadherin–rich zone. After Arp2/3 complex inhibition, linear AJs split, leaving gaps between cells with detergent-insoluble VE-cadherin transiently associated with the gap edges. After NMII inhibition, VE-cadherin is lost from gap edges. We propose that the actin cytoskeleton at AJs acts as a dynamic push–pull system, wherein pushing forces maintain extracellular VE-cadherin transinteraction and pulling forces stabilize intracellular adhesion complexes.

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