Chapter 7 Cell Adhesion and the Extracellular Matrix

Home , Adherens junction, Desmosome, Tight junction, Tight junction proteins

© 2020 Elsevier Inc. All rights reserved. 2 Figure 7–2. Structural features of selectins and PSGL-1. (Adapted from Kappelmayer, Nagy. Biomed Res Int 2017, https://doi.org/10.1155/2017/6138145, by permission with added colors.)

© 2020 Elsevier Inc. All rights reserved. 4 Figure 7–4. Hierarchical organization of integrin clusters in migrating cell. Image of a mouse embryonic fibroblast spread on fibronectin-coated substrate for 30 min. dSTORM imaging of endogenous paxillin conjugated (labeled with paxillin antibody, BD biosciences) to antibody tagged with AlexaFlour-647 (antimouse secondary antibody conjugated to AlexaFlour-647). Gray scale shows the TIRF image, whereas false color image shows the reconstructed superresolution image. Color code (top left corner, from left to right) indicates increasing intensity of molecules. Encircled in dotted lines from left- to right-cell edge, nascent adhesions, maturing adhesions, mature adhesions. Scale bar 2 μm. (Adapted from Changede, Sheetz. BioEssays 2016;39:1, 1600123, by permission.)

© 2020 Elsevier Inc. All rights reserved. 5 Figure 7–5. Intercellular junctions and the junctional complex. Simple epithelial cells have a junctional complex at their apicolateral borders. The components are the tight junction, the adherens junction, and the desmosome. The tight and adherens junctions are zonular, extending right around the cells, whereas desmosomes are punctate. Desmosomes are also present beneath the junctional complex, as is another punctate junction, the gap junction.

© 2020 Elsevier Inc. All rights reserved. 6 Figure 7–6. Tight junctions are anastomosing strands of multiprotein complexes. (A) The close relationship between the organization of the junctional complex, and that of the terminal web in the small intestine is illustrated in this thin-section electron micrograph. In the cytoplasm at the level of the tight junction (TJ), the core microfilaments appear as compact bundles enmeshed in a matrix of 70 Å filaments. Mats of 70 Å filaments line the membranes of the zonula adherens (ZA) or intermediate junction, and the bundles of core microfilaments became more diffuse in the adherens zone. Numerous tonofilaments course through the plaque of the spot desmosome (SD); some of these tonofilaments enter the adherens zone, while others form the basal zone. 80,000 ×. The inset image is a higher magnification of TJ region showing the “kisses.” (B) An evenly cross-linked tight junction network found between the absorptive cells of the small intestine of a Xenopus laevis, stage 57. Short ridges or grooves on the protoplasmic (PF) or extracellular (EF) faces, respectively, intersect at acute angles to form a series of adjoining, similarly shaped polygons, which display no predominant orientation relative to the cell surface. Bar denotes 0.25 μm in the electron micrographs unless marked otherwise. 60,000 ×. (C) Line drawing of the apical junctional complex of an intestinal epithelial cell. Tight junction proteins include claudins, occluding, junctional adhesion molecule (JAM), and zonula occludens-1 (ZO-1), whereas E-cadherin, α-catenin, and β-catenin interact to form the adherens junction. Myosin light chain kinase (MLCK) is associated with the perijunctional actomyosin ring. Gap junctions are tubelike connections between adjacent cells formed by assembly of connexins. Desmosomes are formed by interactions between desmoglein, desmocollin, desmoplakin, and keratin filaments. (D) Occludin has four transmembrane domains with two extracellular loops. The first loop is characterized by a high content (~ 60%) of glycine and tyrosine residues. Claudin-1 also has four transmembrane domains but shows no sequence similarity to occludin. Note that the cytoplasmic tail of claudin-1 is shorter than that of occludin. Junctional adhesion molecule (JAM) has a single transmembrane domain, and its extracellular portion bears two immunoglobulin-like loops that are formed by disulfide bonds. ([A] Adapted from Hull, Staelin. J Cell Biol 1979;81:67–82, by permission; Tsukita, Furose, Itoh. Nat Rev 2001;2:285, by permission; [B] Adapted from Hull, Staelin. J Cell Biol 1976;68:688–704, by permission; [C] From Turner JR. Intestinal mucosal barrier function in health and disease. Nat Rev Immunol 2009;9:799–809, by permission; [D] Adapted from Tsukita, Furose, Itoh. Nat Rev 2001;2:285, by permission.) © 2020 Elsevier Inc. All rights reserved. 7 Figure 7–7. Disrupted tight junction strands in intestinal disease. Freeze-fracture electron microscopy of epithelial tight junctions from the jejunum of control subject and acute celiac disease patient. The jejunum from celiac disease patient shows significant reduction in the number or horizontally oriented strands and the depth of the tight junctional strand network. Additionally, strand discontinuities appeared in celiac disease. (Adapted from Rosenthal, Barmeyer, Schulzke. Tissue Barriers 2015;3:1–2, e977176, by permission.)

© 2020 Elsevier Inc. All rights reserved. 8 Figure 7–8. Fluorescence labeling of epithelial tight junctions. (A) Frozen section of mouse colon was stained for occludin (green) and ZO-1 (red) by immunofluorescence method. Nucleus was stained by a DNA-binding fluorescent dye (blue). Confocal fluorescence microscopic image shows organization of tight junctions on the apical ends of colonic epithelial cells. (B) TNF-α induces redistribution of occludin from the junctions to cytoplasm. Mice were injected with vehicle or TNF-α. Cryosections of jejunum were stained for occludin (green) by immunofluorescence method. Filamentous actin (red) was stained by binding to fluorescently labeled phalloidin, and nucleus (blue) was stained by binding to fluorescent dye. The images show the TNF-α disrupts tight junctions. In one group of mice, the jejunum was perfused with divertin (MLCK inhibitor), which shows that divertin blocks TNF-α-mediated disruption of tight junctions. ([A] From Rao et al. Unpublished; [B] Adapted from Graham et al. Nat Med 2019, https://doi.org/10.1038/s41591-019-0393-7, by permission.)

© 2020 Elsevier Inc. All rights reserved. 9 Figure 7–9. Structure and function of tight junctions. (A) The “gate” function of the tight junction refers to its property of regulating the permeability of the paracellular channels, and the “fence” function maintains the separation of molecules in the apical and basolateral cell membranes. (B) The low permeability of tight junctions causes high electrical resistance across the epithelial cell layer between the apical and basal compartments. (C) Some of the molecules that contribute to the structure and function of the tight junction are shown.

© 2020 Elsevier Inc. All rights reserved. 10 Figure 7–10. Fluorescence labeling of epithelial adherens junctions. Frozen section of mouse ileum was stained for E-cadherin (green) and β-catenin (red) by immunofluorescence method. Nucleus was stained by a DNA-binding fluorescent dye (blue). Confocal fluorescence microscopic image shows organization of adherens junctions along the lateral membranes of colonic epithelial cells. (Adapted from Shukla, Meena, et al. Am J Physiol (GI&Liv) 2016;310: G705, by permission.)

© 2020 Elsevier Inc. All rights reserved. 11 Figure 7–11. Functions of the adherens junction. (A) Initial cell contact is made by filopodia. These interdigitate and punctate adherens junctions are formed to constitute an adhesion zipper. The adhesion is then expanded and stabilized by the formation of desmosomes. (B) Bending of epithelial cell sheets during embryonic development is accomplished by contraction of the actin filament ring underlying the apicolateral adherens junctions. This acts like a purse-string to narrow the apices of the cells. This process can result in tube formation as in generation of the neural tube.

© 2020 Elsevier Inc. All rights reserved. 12 Figure 7–12. Molecular structure of the adherens junction. Two types of adhesion molecule are involved, E-cadherin and the immunoglobulin (Ig) family protein nectin. The cytoplasmic domain of E-cadherin binds β-catenin, which, in turn, binds α-catenin. This complex may link E-cadherin to the cytoskeleton, but an alternative view (inset) suggests that the whole complex cannot form simultaneously. Nectin is linked to actin by afadin.

© 2020 Elsevier Inc. All rights reserved. 13 Figure 7–13. Wnt signaling pathway. In the absence of Wnt (left), cytosolic β-catenin is continually phosphorylated by casein kinase-1α (CK1) and glycogen synthase kinase-3β (GSK3β) within an APC-axin scaffold complex. This phosphorylation allows β-catenin to be ubiquitylated and rapidly degraded by proteasome. During Wnt activation (right), GSK3β activity is inhibited directly by Lrp5/6, which allows β-catenin to accumulate, enter the nucleus, interact with LEF/TCF family members, and promote transcription. (Adapted from McEwen, Escobar, Gottardi. Subcell Biochem 2012;60:171. https://doi.org/10.1007/978-94-007-4186-7_8, by permission.)

© 2020 Elsevier Inc. All rights reserved. 14 Figure 7–14. The desmosome-intermediate filament complex strengthens epithelia, particularly the epidermis. (A) Fluorescence micrograph showing desmosome-intermediate filament complex in cultured epithelial cells. Desmosomes stained by anti-desmoplakin antibody (magenta), intermediate filament stained by anti-keratin antibody (green), and nuclei (blue). (B) Diagram showing the desmosome-intermediate-hemidesmosome complex in the basal epidermis. ([A] From Moch M, Schwarz N, Windoffer R, Leube RE. Keratin-desmosome scaffold: pivotal role of desmosomes for keratin network morphogenesis. Cell Mol Life Sci 2019;77:543–558, by permission; [B] modified from Ellison JE, Garrod DR. J Cell Sci 1984;72:163–172, with permission.)

© 2020 Elsevier Inc. All rights reserved. 15 Figure 7–15. Electron micrograph of a desmosome from bovine tongue. IDP, inner dense plaque; ODP, outer dense plaque; and P, plasma membrane. The desmosome is about 0.5 μm wide. (From Yin T, Green K. Regulation of Desmosome Assembly and Adhesion. Semin Cell Dev Biol 2004;18:665–667, by permission.)

© 2020 Elsevier Inc. All rights reserved. 18 Figure 7–17. Molecular structure and function of the gap junctions. (A) Electron micrograph of a gap junction showing the close (2 nm) approach of the cell membranes. Scale bar = 0.6 μm. (B) Electron micrograph of surface view of an isolated gap junction showing connexons with central pores. Scale bar = 33 nm. (C) Connexin has four transmembrane domains. (D) Six connexin molecules form the channel of the connexon. (E) Docking of two hemichannels between adjacent cells establishes intercellular communication. (F) Adjacent cells are coupled electrically by gap junctions. ([A] and [B] From Gilula NB. Gap junctional contact between cells. In: Edelman GM, Thiery J-P, eds. The Cell in Contact: Adhesions and Junctions as Morphogenetic Determinants. New York: John Wiley & Sons, 1985, pp. 395– 405, by permission.)

© 2020 Elsevier Inc. All rights reserved. 19 Figure 7–18. Structure of the hemidesmosome as observed by electron microscopy. A Fib, anchoring fibril; A Fil, anchoring filaments; IF, intermediate filaments; LD, lamina densa of basement membrane; and P, plaque. Scale bar = 0.4 μm. (From Ellison JE, Garrod DR. J Cell Sci 1984;72:163–172, by permission.)

© 2020 Elsevier Inc. All rights reserved. 21 Figure 7–20. Fluorescence micrograph showing fibronectin produced by cells in culture. (From Mattey DL, Garrod DR. J Cell Sci 1984;67:171–188, by permission.)

© 2020 Elsevier Inc. All rights reserved. 22 Figure 7–21. Focal contacts and stress fibers of cells in culture. (A) Micrograph of cells under interference reflection microscopy showing focal contacts. (B) Fluorescence micrograph showing actin stress fibers. Note how each stress fiber terminates at a focal contact. (From Morgan J, Garrod DR. J Cell Sci 1984;66:133–145, by permission.)

© 2020 Elsevier Inc. All rights reserved. 23 Figure 7–22. Molecular composition of focal contact and mechanotransduction. ECM stiffness increases the loading rate of focal adhesions (ECM-integrin-actin cytoskeleton machinery), while compliant ECM reduces its loading. The extracellular integrin head domain binds the ECM, and the intracellular tail of integrins binds the F-actin through adaptor proteins, such as talin and vinculin. Actin protein polymerization and extension of F-actin at the leading edge of a cell lead to retrograde flow of the actin filaments and directional migration, which is also facilitated by myosin II-mediated pulling forces in the cells. Besides cell motility, mechanotransduction also regulates cell response to ECM mechanical property by regulating GTPases, Rho/Rac activity, and nuclear translocation of transcriptional factor YAP/TAZ.

© 2020 Elsevier Inc. All rights reserved. 25 Figure 7–24 . Model of collective migration. Leader cells (A, one or several cells at the front of the migrating group) determine the direction of migration by forming protrusions or a leading edge in response to environmental cues. The front-rear polarity of leader cells was determined by asymmetric environment of lateral and rear cell-cell adhesions and ECM contact at the front. Inner follower cells (B, behind leader cells inside of the cluster) and peripheral follower cells (C, locate at the outside of the cluster) also contribute to the front- rear polarity of the leader cells and directional movement of the group. Supracellular actomyosin cables formed in peripheral follower cells at the outer surface of the cluster maintain cohesion of the migrating group.

© 2020 Elsevier Inc. All rights reserved. 26 Figure 7–25. Adhesion of blood platelets. (A) The adhesive environment. Diagram summarizing the molecular adhesive components in blood plasma, platelets, and the endothelial cell basement membrane. (B) The adhesion receptors of platelets and their ligands. PSGL- 1, P-selectin glycoprotein ligand-1.

© 2020 Elsevier Inc. All rights reserved. 27 Figure 7–26. Cell adhesion in embryonic development. (A) Compaction in the mammalian embryo. (i) At the early eight-cell stage, the embryonic cells, the blastomeres, are loosely attached. (ii) Without further cell division, they “zip up” their adhesive contacts. (B) At the blastocyst stage the first epithelium, the trophectoderm, is formed. This contains the inner cell mass and the fluid-filled blastocoel cavity. (C) Gastrulation is shown in the amphibian embryo because it is easier to visualize than in the mammal where gastrulation is more complex because of the presence of extraembryonic tissue that forms the placenta. (i) Longitudinal and (ii) transverse sections of the early gastrula. Cell invagination is just beginning with the formation of the blastopore lip (arrow). (iii, iv) Comparable sections of the late gastrula where invagination is almost complete though the blastopore (arrow) is not quite closed. Ectoderm (blue), mesoderm (red), and endoderm (yellow). A, archenteron, the future gut cavity; B, blastocoel. Vertical lines indicate the relationship between the sections. (D) Formation of the neural tube, the future central nervous system, involves expression of different adhesion molecules.

© 2020 Elsevier Inc. All rights reserved. 28 Figure 7–27. Neural crest and its derivatives in the trunk. Arrows indicate paths of migration of neural crest cells. The ventral pathway gives rise to ganglia and their associated nerves. The dorsal pathway gives rise to pigment cells of the skin. Cell adhesion plays a crucial role in guiding the migration and final positioning.

© 2020 Elsevier Inc. All rights reserved. 29 Figure 7–28. Contact inhibition of cell movement. Cell 1 moving in the direction of the arrow makes contact with and adheres to cell 2 (shown completely stationary for the purpose of illustration). Movement in the initial direction is inhibited. Cell 1 forms a new leading lamella or lamellipodium and moves off in a different direction.

© 2020 Elsevier Inc. All rights reserved. 30 Figure 7–29. Cell attachment, division, and death. (A) Normal cells are anchorage dependent requiring attachment to the substratum to proliferate. (B) Cells that become detached from the substratum undergo anoikis, a form of programmed cell death or apoptosis. (C) Many tumor cells both survive and proliferate in suspension.

© 2020 Elsevier Inc. All rights reserved. 32 Figure 7–31. Molecular structure of fibrillar collagen. (A) Electron micrograph showing the banded appearance of a type I collagen fiber from tendon. (Courtesy Drs. Helen Graham and Karl Kadler.) (B) Diagram showing the fiber assembly. The N- and C-propeptides of procollagen are cleaved to give a collagen monomer that is triple-helical with nonhelical telopeptides at each end. Monomers assemble in a regular manner to cause the banded collagen fibril.

© 2020 Elsevier Inc. All rights reserved. 36 Figure 7–35. Elastic fibers. (A) Elastic fibers are composed of a central core of elastin surrounded by microfibrils of fibrillin. The whole is cross-linked by γ-glutamyl-lysine bonds. (B) Elastin molecules consist of tandem repeats of hydrophilic (purple) and hydrophobic (pink) domains. (C) The hydrophobic domains are responsible for elasticity.

© 2020 Elsevier Inc. All rights reserved. 41 Figure 7–40. Normal and abnormal adhesion of blood platelets. (i) von Willebrand factor (vWF) (blue) attaches to exposed endothelial basement membrane collagen (green), and platelets adhere loosely, rolling under the force of blood flow. (ii) Platelets form stable adhesions to collagen and more plates attach by aggregation mediated by vWF and fibrinogen (brown). The thrombus then continues to grow. (iii) Platelets may adhere to the surfaces of endothelial cells initiating the formation of a thrombus by recruitment of other plates and leukocytes and, eventually, development of atherosclerotic plaque.