The coxsackievirus and adenovirus receptor is a transmembrane component of the tight junction.
18 Dec 2001-Proceedings of the National Academy of Sciences of the United States of America (National Academy of Sciences)-Vol. 98, Iss: 26, pp 15191-15196
TL;DR: Results indicate that CAR is a component of the tight junction and of the functional barrier to paracellular solute movement and thatquestration of CAR in tight junctions may limit virus infection across epithelial surfaces.
Abstract: The coxsackievirus and adenovirus receptor (CAR) mediates viral attachment and infection, but its physiologic functions have not been described. In nonpolarized cells, CAR localized to homotypic intercellular contacts, mediated homotypic cell aggregation, and recruited the tight junction protein ZO-1 to sites of cell–cell contact. In polarized epithelial cells, CAR and ZO-1 colocalized to tight junctions and could be coprecipitated from cell lysates. CAR expression led to reduced passage of macromolecules and ions across cell monolayers, and soluble CAR inhibited the formation of functional tight junctions. Virus entry into polarized epithelium required disruption of tight junctions. These results indicate that CAR is a component of the tight junction and of the functional barrier to paracellular solute movement. Sequestration of CAR in tight junctions may limit virus infection across epithelial surfaces.
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TL;DR: A group of integral membrane proteins-occludin, claudins, and junction adhesion molecules-interact with an increasingly complex array of tight junction plaque proteins not only to regulate paracellular solute and water flux but also to integrate such diverse processes as gene transcription, tumor suppression, cell proliferation, and cell polarity.
Abstract: Multicellular organisms are separated from the external environment by a layer of epithelial cells whose integrity is maintained by intercellular junctional complexes composed of tight junctions, adherens junctions, and desmosomes, whereas gap junctions provide for intercellular communication. The aim of this review is to present an updated overview of recent developments in the area of tight junction biology. In a relatively short time, our knowledge of the tight junction has evolved from a relatively simple view of it being a permeability barrier in the paracellular space and a fence in the plane of the plasma membrane to one of it acting as a multicomponent, multifunctional complex that is involved in regulating numerous and diverse cell functions. A group of integral membrane proteins-occludin, claudins, and junction adhesion molecules-interact with an increasingly complex array of tight junction plaque proteins not only to regulate paracellular solute and water flux but also to integrate such diverse processes as gene transcription, tumor suppression, cell proliferation, and cell polarity.
1,332 citations
Cites background from "The coxsackievirus and adenovirus r..."
...It is noteworthy that overexpression of a recently identified TJassociated Rho GTPase-specific guanine nucleotide exchange factor (GEF/H1) increased the paracellular permeability to hydrophilic solutes without affecting TER (ion permeability) (20)....
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...Although its precise relationship to the TJ is somewhat controversial (31, 147), CAR coimmunoprecipitates with ZO-1....
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...Findings that the number of parallel strands and the complexity of the TJ network varies greatly among different pithelia led to the suggestion that there is a direct relationship between these and the measured transepithelial electrical resistance (TER) (30)....
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...By contrast, expression of claudin-4 chimeras, in which one or both extracellular domains of claudin-2 replaced those of claudin-4, increased the number of TJ strands, but alterations in TER and charge selectivity were only modest....
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...Cingulin JAM-1, ZO-1, ZO-2, ZO-3 Cross-linking TJ proteins to the actin cytoskeleton, bundling of F-actin filaments 18, 36 Symplekin Colocalizes with ZO-1 at TJ; also present in nucleus Processing of pre-mRNA and its polyadenylation 69, 83 ZONAB ZO-1, CDK4 Y-box transcription factor; by binding CDK4, ZONAB may regulate cell proliferation, may also regulate ErbB2 expression 11, 14 HuASH1 Transcription factor 108 GEF-H1 TJ-associated guanine nucleotide exchange factor; regulation of paracellular permeability but not TER 20 aPKC PAR-3, PAR-6 Establishment of cell polarity 40 PP2A TJ-associated protein phosphatase that regulates phosphorylation of aPKC, ZO-1, occludin, and claudin-1 110 Heterotrimeric G proteins ZO-1, ZO-2 Signaling molecules that participate in the regulation of TJ barrier function 100 Rab3b, Rab13 Recruited to junctional complexes following cell-cell contact, may be involved in vesicle targeting to cell-cell adhesion sites 94, 152, 166 Sec6/Sec8 Vesicle targeting to sites of cell-cell adhesion 58 PTEN MAGI-2, MAGI-3 Tumor suppressor; dephosphorylates phosphatidyl phosphates 160, 161 7H6 Not known Not known 167 TJ, tight junction....
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TL;DR: How the molecular architectures and interactions may represent a mechanistic basis for the function and regulation of junctions, focusing on junction assembly and permeability regulation, is emphasized.
Abstract: Intercellular junctions mediate adhesion and communication between adjoining endothelial and epithelial cells. In the endothelium, junctional complexes comprise tight junctions, adherens junctions, and gap junctions. The expression and organization of these complexes depend on the type of vessels and the permeability requirements of perfused organs. Gap junctions are communication structures, which allow the passage of small molecular weight solutes between neighboring cells. Tight junctions serve the major functional purpose of providing a "barrier" and a "fence" within the membrane, by regulating paracellular permeability and maintaining cell polarity. Adherens junctions play an important role in contact inhibition of endothelial cell growth, paracellular permeability to circulating leukocytes and solutes. In addition, they are required for a correct organization of new vessels in angiogenesis. Extensive research in the past decade has identified several molecular components of the tight and adherens junctions, including integral membrane and intracellular proteins. These proteins interact both among themselves and with other molecules. Here, we review the individual molecules of junctions and their complex network of interactions. We also emphasize how the molecular architectures and interactions may represent a mechanistic basis for the function and regulation of junctions, focusing on junction assembly and permeability regulation. Finally, we analyze in vivo studies and highlight information that specifically relates to the role of junctions in vascular endothelial cells.
1,185 citations
Cites background from "The coxsackievirus and adenovirus r..."
...The latter molecule is CAR (Coxsackie- and adeno-virus receptor), which also participates in TJ assembly and in the regulation of paracellular permeability (65)....
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TL;DR: Advances in the knowledge of the molecular structure of TJ support previous physiological models that exhibited TJ as dynamic structures that present distinct permeability and morphological characteristics in different tissues and in response to changing natural, pathological or experimental conditions.
Abstract: A fundamental function of epithelia and endothelia is to separate different compartments within the organism and to regulate the exchange of substances between them. The tight junction (TJ) constitutes the barrier both to the passage of ions and molecules through the paracellular pathway and to the movement of proteins and lipids between the apical and the basolateral domains of the plasma membrane. In recent years more than 40 different proteins have been discovered to be located at the TJs of epithelia, endothelia and myelinated cells. This unprecedented expansion of information has changed our view of TJs from merely a paracellular barrier to a complex structure involved in signaling cascades that control cell growth and differentiation. Both cortical and transmembrane proteins integrate TJs. Among the former are scaffolding proteins containing PDZ domains, tumor suppressors, transcription factors and proteins involved in vesicle transport. To date two components of the TJ filaments have been identified: occludin and claudin. The latter is a protein family with more than 20 members. Both occludin and claudins are integral proteins capable of interacting adhesively with complementary molecules on adjacent cells and of co-polymerizing laterally. These advancements in the knowledge of the molecular structure of TJ support previous physiological models that exhibited TJ as dynamic structures that present distinct permeability and morphological characteristics in different tissues and in response to changing natural, pathological or experimental conditions.
1,096 citations
TL;DR: The human intestinal epithelium is formed by a single layer of epithelial cells that separates the intestinal lumen from the underlying lamina propria, which is sealed by tight junctions (TJ), which regulate the permeability of the intestinal barrier.
Abstract: The human intestinal epithelium is formed by a single layer of epithelial cells that separates the intestinal lumen from the underlying lamina propria. The space between these cells is sealed by tight junctions (TJ), which regulate the permeability of the intestinal barrier. TJ are complex protein structures comprised of transmembrane proteins, which interact with the actin cytoskeleton via plaque proteins. Signaling pathways involved in the assembly, disassembly, and maintenance of TJ are controlled by a number of signaling molecules, such as protein kinase C, mitogen-activated protein kinases, myosin light chain kinase, and Rho GTPases. The intestinal barrier is a complex environment exposed to many dietary components and many commensal bacteria. Studies have shown that the intestinal bacteria target various intracellular pathways, change the expression and distribution of TJ proteins, and thereby regulate intestinal barrier function. The presence of some commensal and probiotic strains leads to an increase in TJ proteins at the cell boundaries and in some cases prevents or reverses the adverse effects of pathogens. Various dietary components are also known to regulate epithelial permeability by modifying expression and localization of TJ proteins.
920 citations
Cites background from "The coxsackievirus and adenovirus r..."
...and promote their localization at cell boundaries (32,33)....
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...JAM-A and coxsackie and adenovirus receptor, 2 examples of JAM proteins, have been shown to regulate epithelial barrier function, because expression of either protein leads to a reduction in paracellular permeability (31,32)....
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TL;DR: The regulation of the intestinal TJ barrier is discussed together with its implications for the pathogenesis of diseases.
Abstract: The gastrointestinal epithelium forms the boundary between the body and external environment. It effectively provides a selective permeable barrier that limits the permeation of luminal noxious molecules, such as pathogens, toxins, and antigens, while allowing the appropriate absorption of nutrients and water. This selective permeable barrier is achieved by intercellular tight junction (TJ) structures, which regulate paracellular permeability. Disruption of the intestinal TJ barrier, followed by permeation of luminal noxious molecules, induces a perturbation of the mucosal immune system and inflammation, and can act as a trigger for the development of intestinal and systemic diseases. In this context, much effort has been taken to understand the roles of extracellular factors, including cytokines, pathogens, and food factors, for the regulation of the intestinal TJ barrier. Here, I discuss the regulation of the intestinal TJ barrier together with its implications for the pathogenesis of diseases.
914 citations
Cites background from "The coxsackievirus and adenovirus r..."
...In CHO and MDCK cells, CAR overexpression decreases dextran permeability and increases TER [77]....
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...CAR is concentrated at cell-cell contacts and is co-localized with ZO-1 in intestinal T84 cells [77]....
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...The recombinant soluble CAR protein, which encodes the extracellular domain and inhibits the intercellular interaction of CAR, delays the recovery of TER after calcium repletion [77]....
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References
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TL;DR: The tight junction is impervious to concentrated protein solutions and appears to function as a diffusion barrier or "seal," and the desmosome and probably also the zonula adhaerens may represent intercellular attachment devices.
Abstract: The epithelia of a number of glands and cavitary organs of the rat and guinea pig have been surveyed, and in all cases investigated, a characteristic tripartite junctional complex has been found between adjacent cells. Although the complex differs in precise arrangement from one organ to another, it has been regularly encountered in the mucosal epithelia of the stomach, intestine, gall bladder, uterus, and oviduct; in the glandular epithelia of the liver, pancreas, parotid, stomach, and thyroid; in the epithelia of pancreatic, hepatic, and salivary ducts; and finally, between the epithelial cells of the nephron (proximal and distal convolution, collecting ducts). The elements of the complex, identified as zonula occludens (tight junction), zonula adhaerens (intermediary junction), and macula adhaerens (desmosome), occupy a juxtaluminal position and succeed each other in the order given in an apical-basal direction. The zonula occludens (tight junction) is characterized by fusion of the adjacent cell membranes resulting in obliteration of the intercellular space over variable distances. Within the obliterated zone, the dense outer leaflets of the adjoining cell membranes converge to form a single intermediate line. A diffuse band of dense cytoplasmic material is often associated with this junction, but its development varies from one epithelium to another. The zonula adhaerens (intermediate junction) is characterized by the presence of an intercellular space ( approximately 200 A) occupied by homogeneous, apparently amorphous material of low density; by strict parallelism of the adjoining cell membranes over distances of 0.2 to 0.5 micro; and by conspicuous bands of dense material located in the subjacent cytoplasmic matrix. The desmosome or macula adhaerens is also characterized by the presence of an intercellular space ( approximately 240 A) which, in this case, contains a central disc of dense material; by discrete cytoplasmic plaques disposed parallel to the inner leaflet of each cell membrane; and by the presence of bundles of cytoplasmic fibrils converging on the plaques. The zonula occludens appears to form a continuous belt-like attachment, whereas the desmosome is a discontinuous, button-like structure. The zomula adhaerens is continuous in most epithelia but discontinuous in some. Observations made during experimental hemoglobinuria in rats showed that the hemoglobin, which undergoes enough concentration in the nephron lumina to act as an electron-opaque mass tracer, does not penetrate the intercellular spaces beyond the zonula occludens. Similar observations were made in pancreatic acini and ducts where discharged zymogen served as a mass tracer. Hence the tight junction is impervious to concentrated protein solutions and appears to function as a diffusion barrier or "seal." The desmosome and probably also the zonula adhaerens may represent intercellular attachment devices.
3,388 citations
TL;DR: Identification of CAR as a receptor for these two unrelated and structurally distinct viral pathogens is important for understanding viral pathogenesis and has implications for therapeutic gene delivery with adenovirus vectors.
Abstract: A complementary DNA clone has been isolated that encodes a coxsackievirus and adenovirus receptor (CAR). When transfected with CAR complementary DNA, nonpermissive hamster cells became susceptible to coxsackie B virus attachment and infection. Furthermore, consistent with previous studies demonstrating that adenovirus infection depends on attachment of a viral fiber to the target cell, CAR-transfected hamster cells bound adenovirus in a fiber-dependent fashion and showed a 100-fold increase in susceptibility to virus-mediated gene transfer. Identification of CAR as a receptor for these two unrelated and structurally distinct viral pathogens is important for understanding viral pathogenesis and has implications for therapeutic gene delivery with adenovirus vectors.
3,128 citations
TL;DR: An integral membrane protein localizing at tight junctions is now identified, which is designated as "occludin," which was revealed by a hydrophilicity plot that was very similar to that of connexin, an integral membraneprotein in gap junctions.
Abstract: Recently, we found that ZO-1, a tight junction-associated protein, was concentrated in the so called isolated adherens junction fraction from the liver (Itoh, M., A. Nagafuchi, S. Yonemura, T. Kitani-Yasuda, Sa. Tsukita, and Sh. Tsukita. 1993. J. Cell Biol. 121:491-502). Using this fraction derived from chick liver as an antigen, we obtained three monoclonal antibodies specific for a approximately 65-kD protein in rats. This antigen was not extractable from plasma membranes without detergent, suggesting that it is an integral membrane protein. Immunofluorescence and immunoelectron microscopy with these mAbs showed that this approximately 65-kD membrane protein was exclusively localized at tight junctions of both epithelial and endothelial cells: at the electron microscopic level, the labels were detected directly over the points of membrane contact in tight junctions. To further clarify the nature and structure of this membrane protein, we cloned and sequenced its cDNA. We found that the cDNA encoded a 504-amino acid polypeptide with 55.9 kDa. A search of the data base identified no proteins with significant homology to this membrane protein. A most striking feature of its primary structure was revealed by a hydrophilicity plot: four putative membrane-spanning segments were included in the NH2-terminal half. This hydrophilicity plot was very similar to that of connexin, an integral membrane protein in gap junctions. These findings revealed that an integral membrane protein localizing at tight junctions is now identified, which we designated as "occludin."
2,469 citations
TL;DR: The role of scaffold, anchoring, and adaptor proteins that contribute to the specificity of signal transduction events by recruiting active enzymes into signaling networks or by placing enzymes close to their substrates is discussed.
Abstract: The process by which extracellular signals are relayed from the plasma membrane to specific intracellular sites is an essential facet of cellular regulation. Many signaling pathways do so by altering the phosphorylation state of tyrosine, serine, or threonine residues of target proteins. Recently, it has become apparent that regulatory mechanisms exist to influence where and when protein kinases and phosphatases are activated in the cell. The role of scaffold, anchoring, and adaptor proteins that contribute to the specificity of signal transduction events by recruiting active enzymes into signaling networks or by placing enzymes close to their substrates is discussed.
2,237 citations
TL;DR: It is indicated that multiple integral membrane proteins with four putative transmembrane domains, occludin and claudins, constitute TJ strands.
Abstract: Occludin is the only known integral membrane protein localizing at tight junctions (TJ), but recent targeted disruption analysis of the occludin gene indicated the existence of as yet unidentified integral membrane proteins in TJ. We therefore re-examined the isolated junction fraction from chicken liver, from which occludin was first identified. Among numerous components of this fraction, only a broad silver-stained band ∼22 kD was detected with the occludin band through 4 M guanidine-HCl extraction as well as sonication followed by stepwise sucrose density gradient centrifugation. Two distinct peptide sequences were obtained from the lower and upper halves of the broad band, and similarity searches of databases allowed us to isolate two full-length cDNAs encoding related mouse 22-kD proteins consisting of 211 and 230 amino acids, respectively. Hydrophilicity analysis suggested that both bore four transmembrane domains, although they did not show any sequence similarity to occludin. Immunofluorescence and immunoelectron microscopy revealed that both proteins tagged with FLAG or GFP were targeted to and incorporated into the TJ strand itself. We designated them as “claudin-1” and “claudin-2”, respectively. Although the precise structure/function relationship of the claudins to TJ still remains elusive, these findings indicated that multiple integral membrane proteins with four putative transmembrane domains, occludin and claudins, constitute TJ strands.
2,017 citations