Cell Junctions

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Epithelial Cell Junction Types

Introduction

Lets stick together!

This lecture introduces the concept of cell adhesion. Unicellular organisms use to adhere to the environment, nutrition or pathogenesis. Multicellular organisms require adhesion for cells to adhere to each other and the extracellular matrix. Cell adhesion occurs through specific cellular specializations and molecules and has both static and dynamic functions. This topic will be revisited in lectures on extracellular matrix, cell cytoskeleton and signalling.



Archive

MH - note that content listed below will not match exactly current lecture structure and has been selected as having similar content. 2010 | 2009


See also ANAT3231 Projects 2011 Junctions

Objectives

Desmosome
  • Broad understanding of cell adhesion with other cells and extracellular matrix
  • Understanding of different adhesion proteins
  • Understanding of different forms of adhesion junctions
  • Understanding of biological role of adhesion
  • Brief understanding of adhesion abnormalities

History

Below are some example historical research finding related to cell junctions from the JCB Archive.

1963 Defining junctional complexes A mess of nomenclature is sorted out by Marilyn Farquhar and George Palade, who use superb microscopy to define three of the four major types of cell–cell junctions in the polarized epithelial cells of vertebrates.

Epithelial Cell Junctions

1967 Defining gap junctions Jean-Paul Revel and Morris Karnovsky unite the fields of adhesion and intercellular current transfer around a distinct, structural correlate called the gap junction.

1967 Endothelial tight junctions form the blood–brain barrier What is the cellular correlate of the so called blood-brain barrier? Thomas Reese and Morris Karnovsky find that it is the junctions between endothelial cells in the brain vasculature. Their discovery comes thanks to three factors: high resolution electron microscopy; the development of sensitive tracer methods; and a fortuitous lunch date.

1977 The sticky business of discovering cadherins A change in the recipe for a trypsin solution allows Masatoshi Takeichi to distinguish calcium-dependent adhesion.

1984 Sticking it out with tight junctions With persistence and a species change, tight junction proteins are isolated.


Why Adhesion?

  • Adhesion refers to “stickiness”
  • Evolution of multicellular organisms developed specialized cells and tissues
  • Embryonic development also allows differentiation of different cell/tissue types
  • Interaction between cell-cell and cell-extracellular matrix by specific contacts
  • Note the Cell Biology definition is different from the Clinical term
    • Clinical term “adhesions” bands of scar-like tissue forming between two surfaces inside the body

Types of Junctions

Epithelia jns1.jpg

Prokaryotes

Bacteria adhesin.gif

  • Prokaryotes adhesion molecules usually termed "adhesins"
  • occur on pili (fimbriae), flagellae, or the cell surface
  • adhesion first step in colonization


Unicellular Eukaryotes

  • express multiple adhesion molecules for nutrition, migration and pathogenesis
  • malarial parasite (Plasmodium falciparum) uses circumsporozoite protein, an adhesion molecule, to bind to liver cells
  • merozoite surface protein, to bind to red blood cells

Multicellular Eukaryotes

  • Maintains body form and structure
  • Tissues organized during development
  • Can be used for cell migration
  • Cell signalling alteration in disease

Types of Adhesion

  • Cell-cell
  • Cell-extracellular matrix

Cell adhesion summary.png

Adhesive Functions

  • Basal lamina assemble and organize epithelia
  • Smooth muscle
    • Maintains integrity during contraction
  • Binds growth factors
    • Neurons growth cone guidance, fasiculation
  • Cell Migration
    • Development - migration, cell sorting, tissue development
    • Transmigration, wound healing, macrophages

Tem transmigration1.jpg Transmigration1.jpg


Links: Transmigration Movie - Part 1 Links: Transmigration Movie - Part 2

Adhesion Characteristics

Transmembrane glycoproteins

Normally permanent

Except migrating cells and embryonic

Changes with development

Loose adhesion when mature or disease (Erythrocytes, cancer)

Types of Adhesion Molecules

Each type of junction involves specific adhesion molecules embedded in the cell plasma membrane.

  • Cadherins
  • Immunoglobulin Superfamily
  • Selectins
  • Connexins
  • Integrins


Cadherins

Cadherin2.gif
  • The cadherin superfamily comprises classical and non-classical cadherins
  • present in all multicellular animals
  • mediate calcium ion (Ca2+) dependent cell-cell adhesions
  • more than 180 members in humans
  • Classical cadherins
    • (e.g.: E-cadherin, N-cadherin and P-cadherin) contain 5 cadherin repeats
  • Require calcium ions to bind
  • Homophilic binding through end element
  • Like with like
  • Functional unit a dimer
  • Non-classical cadherins
    • (e.g. desmosomal cadherin, protocadherins and T-cadherins) are more distantly related in sequence
  • Varying number of cadherin repeats
  • Some non-classical cadherins have primarily a signalling function

Immunoglobulin Superfamily

Igsuperfamily.gif
  • Vertebrates have 100+
  • In addition to adhesion they also have role in immune system
  • Contain varying number of Ig-related domains
  • G. Edelman - Nobel Prize in Physiology or Medicine in 1972
    • "for their discoveries concerning the chemical structure of antibodies"
    • studying the nervous system
    • Cell Adhesion Molecules (CAMs) family - Neuronal cell adhesion molecules (N-CAM) N-CAM, Ng-CAM L-CAM, I-CAM (Review - PMID 15550947)

Selectins

White blood cell migrating out of a blood vessel (EM)
Transmigration1.jpg
  • Cell Surface carbohydrate-binding proteins
  • Vertebrates have only in circulatory system
  • Role in inflammatory response: adhesion of leukocytes (blood cells) to endothelium (vessel wall)
  • Cooperate with integrins and Ig-SF receptors
  • Selectins 2 Heterophilic interactions
  • Bind counterreceptors
    • L-selectin on white blood cells
    • P-selectin on blood platelets and on endothelial cells that have been locally activated
    • E-selectin on activated endothelial cells

Integrins

Integrin.gif
  • Mammals have genes for 18 alpha and 8 beta integrins
  • Role in cell adhesion to extracellular matrix (ECM) basement membranes
  • Induction of cell polarization by adhesion
  • Cell migration through ECM will discuss in ECM lecture
  • Glycosylated proteins
  • Bind through C terminal lectin domain of selectin
  • Comprising sandwich of beta sheets
  • Held together by hydrophobic interactions


  • Mainly receptors for ECM proteins
  • Fibronectin, laminin, collagen
  • Some heterotypic binding Ig superfamily
  • Interact with cell cytoskeleton
  • key component in signalling

See additional information on interns below.

Cell Junction Types

Metazoan intercellular junctions

The above adhesion molecules, along with other associated proteins and cytoskeleton elements, cluster on the plasma membrane to form identifiable cell junctions.

  • Desmosomes (macula adherens)
  • Adherens Junctions (zonula adherens)
  • Septate Junctions
  • Tight Junctions
  • Gap Junctions
  • Tunneling nanotubes


Desmosomes

Desmosome1.jpg
  • Discovered by K.R. Porter in 1954
  • intermediate filaments anchor the dense plaque that occurs under the membrane of each cell
  • desmos = bond
  • skin, lining of internal body cavity surfaces
  • disappear when cells are transformed

Hemi-Desmosome

cell anchored to extracellular matrix

Present in tissues subject to shear or lateral stress

Hemi=half

Adherens Junctions

microfilaments anchor the plaque that occurs under the membrane of each cell

plaques not as dense also occur as hemiform

heart muscle, layers covering body organs, digestive tract

transmembrane proteins

Cadherin

Septate Junctions

  • Discovered by R.L. Wood 1959
  • found in invertebrate tissues - adhesion, sealing, communication
  • septa = walls, regularly spaced cross bars 15-17 nm

Septate junction EM.jpg

Tight Junctions

Tight junction3.jpg
  • Discovered by M.G. Farquhar and G.E. Palade in 1963
  • zonula occludens
  • Fusion of 2 plasma membranes acts as a “seal”
  • located on epithelia linings - digestive system gut, ducts, cavities of glands, liver, pancreas capillary walls urinary bladder

Schematic representation of tight junctions between two adjacent cells..jpg

Gap Junctions

Gap junction1.jpg
  • Discovered by J.P. Revel & M.J. Karnovsky in 1967
  • allowing direct communication between cells (open & close)
    • ATP, cyclic adenosine monophosphate (cAMP), inositol triphosphate (IP3), glucose, glutathione, glutamate, sodium, potassium and calcium ions.
  • close membranes 2 - 3 nm apart
  • connexins form hollow 1.5 nm diameter cylinders
  • heart muscle, smooth muscle, embryo blastocyst cells, electrical and chemical integration as a single functional unit
  • Also in embryonic development
  • two hemichannels (connexons)
  • each formed from 6 connexin molecules
  • rapidly turned over
Electron Micrograph Filtered Image of Two Connexons.jpg

Electron Micrograph Filtered Image of Two Connexons

Gap junction5.jpg

Tunneling nanotubes

  • Discovered by A. Rustom and H.-H. Gerdes in 2004
  • allowing direct communication between cells
  • connecting cells at a distance of up to several cell diameters
  • tubes with a diameter of 50-200 nm

Junctions Overview - Typical Epithelia

  • Tight Junction - seals neighbouring cells.
  • Adherens Junction - joins actin bundles between cells.
  • Desmosome - joins intermediate filaments between cells.
    • Hemidesmosome - anchors cell intermediate filaments to ECM (basal lamina in epithelia, ECM CT)
  • Gap Junction - cell-cell communication (signalling), passage of small molecules.
  • Tunneling nanotubes - cell-cell communication, passage of organelles.

Extracellular Matrix

Adhesion cell ecm2.jpg
  • Substances secreted (exocytosis) by cells lying outside the cell membrane
  • When cell junctions bind to ECM rather than a cell they form a "hemi" or half junction.
  • Specific ECM glycoproteins interact with these cell adhesion proteins.

Integrins

Mammals have genes for 18 alpha and eight beta integrins Role in cell adhesion to extracellular matrix (ECM) basement membranes Induction of cell polarization by adhesion Cell migration through ECM Mainly receptors for ECM proteins Fibronectin, laminin, collagen Some heterotypic binding Ig superfamily Interact with cell cytoskeleton signalling


Fl focaladhesion.jpg

focal adhesions

  • links the outside of the cell (ECM) through transmembrane proteins (integrins) with the cell cytoskeleton (actin microfilaments)
  • (or inside the cell outward) actin cytoskeleton - integrins - extracellular matrix
  • Important for tissue integrity and cell migration.

Adhesion cell ecm2.jpg


Focal adhesion migrating cell.jpg

Focal adhesion migrating cell

  • Adhesion is closely coupled with the protrusions of the leading edge of the cell (filopodia and lamellipodia).
  • Adhesions (nascent adhesions) initially form in the lamellipodium (although adhesions may also be associated with filopodia) and the rate of nascent adhesion assembly correlates with the rate of protrusion.
  • Nascent adhesions either disassemble or elongate at the convergence of the lamellipodium and lamellum (the transition zone).
  • Adhesion maturation to focal complexes and focal adhesions is accompanied by the bundling and cross-bridging of actin filaments, and actomyosin-induced contractility stabilizes adhesion formation and increases adhesion size.


Proteins linking integrins to actin cytoskeleton

  • Talin - actin-binding protein that forms antiparallel homodimers. The amino-terminal FERM (protein 4.1, ezrin, radixin and moesin) domain binds β-integrin tails and is sufficient to activate integrins. The carboxy-terminal rod domain interacts with vinculin and filamentous actin.
  • Vinculin - actin-binding protein associated with cell–cell and cell–extracellular matrix junctions. A globular head domain linked to a tail domain by a short Pro-rich sequence. The intramolecular interaction between the head and tail masks binding sites for talin, actin and other effectors.
  • α-actinin - actin cross-linking protein of the spectrin superfamily. Forms antiparallel homodimers in a rod-like structure, with one actin-binding domain on each side of the rod. It can therefore cross link two filaments of actin.
  • Kindlins - members of a family of conserved FERM domain–containing proteins named after the gene mutated in Kindler syndrome, a rare skin blistering disease. Not clear how kindlins activate integrins, they seem to act synergistically with talins to do so.

Abnormalities

Desmosomes

  • pemphigus and bullous impetigo - antibodies made against one of their own desmosomal cadherin proteins
  • antibodies bind to and disrupt the desmosomes that hold together skin epithelial cells
  • severe skin blistering, leakage of body fluids

palmoplantar keratoderma

Arrhythmogenic right-ventricular cardiomyopathy (ARVC)

Oncogenesis

  • not the cause but transformed cells loose adhesion, able to "break away" and spread (metastasis).

References

Textbooks

Essential Cell Biology

  • Chapter 19 Tissues Epithelial sheets and Cell-Cell Junctions p606

Molecular Biology of the Cell

Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter New York and London: Garland Science; c2002

  • Molecular Biology of the Cell 4th ed. - V. Cells in Their Social Context Chapter 19. Cell Junctions, Cell Adhesion, and the Extracellular Matrix
  • Cell Junctions


Molecular Cell Biology

Lodish, Harvey; Berk, Arnold; Zipursky, S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E. New York: W. H. Freeman & Co.; c1999

The Cell- A Molecular Approach

Cooper, Geoffrey M. Sunderland (MA): Sinauer Associates, Inc.; c2000

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Books

PubMed

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Reviews

  • Tight junctions/adherens junctions: basic structure and function. Niessen CM. J Invest Dermatol. 2007 Nov;127(11):2525-32. Review.. PMID: 17934504
  • The desmosome and pemphigus. Waschke J. Histochem Cell Biol. 2008 Jul;130(1):21-54. Epub 2008 Apr 3. Review. PMID: 18386043
  • Tunneling Nanotubes. Rustom A. Ann N Y Acad Sci. 2009 Oct;1178:126-39. Review. PMID: 19845633


Articles

Working Area

Adhesion Images

A series of micrographs showing adhesion junction images. Adhesion Junction Images | Cell Biology Images | New Images

There is also a gallery of all images added sorted by date New Images (the search option will only search by image file name).


2015 Course Content

Lectures: Cell Biology Introduction | Cells Eukaryotes and Prokaryotes | Cell Membranes and Compartments | Cell Nucleus | Cell Export - Exocytosis | Cell Import - Endocytosis | Cytoskeleton Introduction | Cytoskeleton - Microfilaments | Cytoskeleton - Microtubules | Cytoskeleton - Intermediate Filaments | Cell Mitochondria | Cell Junctions | Extracellular Matrix 1 | Extracellular Matrix 2 | Cell Cycle | Cell Division | Cell Death 1 | Cell Death 2 | Signal 1 | Signal 2 | Stem Cells 1 | Stem Cells 2 | Development | 2015 Revision


Laboratories: Introduction to Lab | Microscopy Methods | Preparation/Fixation | Cell Knockout Methods | Cytoskeleton Exercise | Immunochemistry | Project Work | Confocal Microscopy | Tissue Culture | Stem Cells Lab | Microarray Visit

2015 Projects: Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6 | Group 7

Dr Mark Hill 2015, UNSW Cell Biology - UNSW CRICOS Provider Code No. 00098G