Cell adhesion

www.dgci.sote.huLecture EPh 2014

Láng, Orsolya MD, PhDDept. Genetics, Cell & Immunobiology, Semmelweis University

Cell adhesion

Contact with other cells and extracellular matrix

Role:

- embryonic development: formation of layers, tubes

- connection and communication between cells

- barrier, membrane polarity, mechanical attachment

- cell motility

- signal transduction

- cancer progression

Cell-cell adhesion molecules1. Cadherins

2. CAMs or Ig like adhesion molecules

3. selectins

Cell-ECM adhesion Molecules4. Integrins

5. Proteoglycans (dystroglycan)

Homophyl or heterophyl

Ion dependency :Ca++, Mg++

Cytoskeletal component

Junctional complex

Cadherins

Homophil connection Cell – cell

Ca++ - dependent binding

I.c. anchored to actin or intermedier filamentum

Significant role in developmentof vertebrates

Cell specificity

N – neuralP – placentalE - epithelial

Cadherin superfamily

Type Localisation Adherent

cla

ssic

al

E Epithelial Adherens junction

N Neuronal, muscle, fibroblast

Adherens junction

Synapsism

P Placenta, epidermis, mammary gland

Adherens junction

VE Endothelial Adherens junction

Non

-cl

Desmocollin Skin Desmosomes

Desmoglein Skin Desmosomes

T cadherin Neuronal, muscle -

Cadherin 23 Inner ear Stereocilia

Cadherins allow cells to sort themselves

Ig-like adhesion molecules Homophil connection - typical Heterophil connection - rare

5 pcs. Ig-type domain Ca 2+ indep. adhesion

Linked to actin filaments

More than 20 variations Expressed in the critical phase of development

Tissue-specificity:N-CAM - neuronL-CAM – liverV-CAM1- vascular

In melanoma – relation between In melanoma – relation between ICAM-1 density and theICAM-1 density and themetastatic activity of the tumormetastatic activity of the tumorIntracellul

ar

Lectin type proteins,Carbohydrate specificity

Tissue-specificity:E - epithelialL - lymphoidP - placenta

L selectin: it has role in the initial phase of adhesion;

in newborns the level of L sel. is low – the low number of inflammations (?!)

Selectin molecules

Heterophil connection

Ca2+-dependent binding

Focal contacts Its i.c. linker proteins arei.e.. talin, -actinin, vinculin RGD sequ. is significant in ECM binding

Partner molecules: fibronectin

laminincollagen

Deficiency (Deficiency () – the adhesion of ) – the adhesion of leukocytes affected, resultsleukocytes affected, resultsthe increase of inflammations the increase of inflammations

Integrin molecules

Type of integrins

Integrin Ligand Localisation Mutation of α or ß subunit

α5ß1 fibronectin ubiquitous Early death of the embryo,

α6ß1 laminin ubiquitous Early death of the embryo, severe skin blistering

α7ß1 laminin muscle Musclar dystrophy

αLß2 ICAM leukocytes Impaired recruitment of leukocytes, LAD, recurrent infections

αIIbß3 fibrinogen thrombocyte bleeding, no platelet aggregation, (osteoporosis)

α6ß4 laminin Hemidesmosomeepithelial cells

severe skin blistering

Role of adhesion molecule in extravasation of leukocytes

Adhesion molecules

www.cbrinstitute.org/.../media/image1.html

Functional classification of cell junction

Anchoring – mechanical junction

Barrier formation - separation

Channel like (gap junction) – communication

Signal relaying junctions sinapsm

immunological sinapsism

transmembrane proteins

Functional classification of cell junction

Anchoring junctions

Junctional complexes

Tight junction

Zonula adherens

Desmosome

Gap junction

Interdigitation

Hemidesmosome

Isolate parts of plasma membrane (apical and basolateral) Completely encircle polarized cells Look like honey comb

Tight junction(TJ) = zonula occludens

Claudins and occludins (membrane proteins) zip two membranes together

Molecular structure of tight junction

Stabilized by spectrinConnected to spectrin by adapter proteins ZO1 and ZO2

Regulation of tight junctions

BeltsBelts of proteins that close extracellular space between cells Prevent passagePrevent passage of water and water-soluble substances Account for electrical resistance across epithelia

Leaky epithelia where there is need for some trafficHormonesVasopressinCytokinesLack of ATP causes “leak”Extravasating leukocytes open tight junctions

Tight junctions separate components of the plasma membrane as well

Mechanical juncion: zonula adherens - adhesion belt

Adherent junctionsHold cells tightly togetherConfer mechanical strengthCommon in tissue that are subject to severestress such as skin and cardiac muscle

Molecular structure of zonula adherens

Belt like junctions located just below tight junction Simple points of attachment, do not contain channels connecting the interiors of the two attached cells

Adhesion molecule -cadherin (E)

Linker proteins - α, and catenin, vinculin

Cytoskeletal component - microfilament (actin)

Desmosome = macula adherens

Cytoskeletal componentIntermedier filaments

(i.e. keratin)

Cytoplasmatic plaque

Adhesion moleculecadherins

Components of desmosomes

The expression pattern of DSGs and DSC is tissue-specific and may even vary within one tissue, like in the different layers of the epidermis

Spinous layer desmosome

Focal adhesion

Hemidesmosome – Cell-ECM junction

Fixing of epithelial cells to the basal membrane

Adhesion molecule - integrins

/Linker proteins – plectin, dystonin/

Cytoskeletal component – intermediate filament (keratin)

Desmosomes and hemidesmosomes both link to

intermediate filaments

Gap junction – channel forming junction

Communicating junction

100-1000 connexon

protein: connexin

homomeric-heteromeric combinations

Gap junction TEM SEM

In plant cells plasmodesmata perform many of the same functions as gap junctions

Interdigitation

Wave-like plasma membrane extensions + desmosomes

Characteristic of epithelial cell

Basal striationnucleus

mitochondria

Basement

membrane

Basa

l st

riati

on

Increases the surface of the basal membraen for molecular transport

ECM- Extracellular matrix

• Mechanical

• Influence on migration of the cells

• Regulation of activity of molecules released

• Co-receptors

Main components of ECM

Protein componentGlycan

Molecular Biology of the Cell (© Garland Science 2008)

LNs are cross-shaped proteins.All LN isoforms contain α, β1 and β2 chains that are connected by disulfide bonds (18 isoform of laminin- diverse in tissue)LN binds to membrane receptors (integrins) of the overlying cells.LN attaches cells to the basal lamina.

LN contains binding sites for other components of the basal lamina: type IV collagen, heparin,

Laminin (LN)

Collagens

Provide strength of ECMmaintains form of tissue

Most abundant protein in vertebrates Found as bundles throughout ECM Structure:

Rigid triple helix of 3 intertwined polypeptide chains Unusual aa compositionn (hydroxilation) Collagen fiber consists of numerous fibrils (molecules,

polypeptides)

Structure and synthesis of collagene ER/Golgi: Pro-a-chains are produced, hydroxylated and glycosylated at selected Lys and Pro residues. The lack of vitamin C prevents hydroxylation → impaired fibril formation (scurvy).Processed pro-peptides assemble into triple-helical pro-collagen. Golgi: Disulphide bonds form between the N- and C-termini of procollagen. After exocytosis, N- and C-termini are trimmed, allowing fibril assembly

Fibrils (diam.10-300 nm) More than 15 types I., II., III., V., XI. – formation of fibrils IV., VII. – network IX., XII. – association of fibrils

Collagen Assembly

Matrix types produced by vertebrate cells

COLLAGENE

I ChS, DS fibroblastII fibronectin ChS integrin chondrocyteIII HS, Hep. hepatocyte

epithel

IV laminin HS, Hep. laminin rec. epithel,endothel,regenerating hepatocyte

V fibronectin HS, Hep. integrin resting fibrobl.VI fibronectin HS integrin resting fibrobl.

Anchor Proteogly.Receptor Cells

Abbr.: ChS – chondroitin sulfate; DS – dermatan sulfate; HS – heparan sulfate; Hep - heparin

Fibroblast surrounded by collagen fibrils

Osteogenesis imperfecta – clinical manifestation

Tissue elasticity

Elastic fibers permit long-range deformability and passive recoil. Elastic modulus is ~0.1 MPa. This function is crucial for arteries, lung, skin and other dynamic connective tissues that undergo cycles of extension and recoil.

The major component of elastic fibers is the thread-like protein elastin Fibrillins provide an outer structure for amorphous, cross-linked elastin.

During ageing, elastin is degraded and becomes inflexible.

Elastin

Tropoelastine→ cross link→ functional elastin

Fibronectin

Glycoproteins Fibronectin is a dimer of two identical 250 kDa subunits Alternative splicing of one gene produces ~20 human FNs RGD (Arg-Gly-Asp) component is recognised by integrines Mediate the connection between the ECM and the cell membrane. FN exists as a soluble form (plasma FN) and cellular FN.

Plasma FN is predominantly produced in the liver.Cellular FN is deposited into the ECM by a cell-mediated

process, FN binds a variety of other proteins like integrins, heparin, collagen, fibrin.

Molecular Biology of the Cell (© Garland Science 2008)

TEM structure of basal lamina ~ basement membrane

In epithelial membrane – prevent cancer cell invasionKidney – serves as a filtration barrier

Molecular Biology of the Cell (© Garland Science 2008)

Molecular structure of basal lamina

Transmembrane

HA is a large, unbranched and negatively charged polymer of repeating (2-25K) disaccharides.

it is synthesized freely at the plasma membrane by hyaluronan synthases.

Free HA is found in the ECM of migrating cells.

HA binds to cell surface receptors (CD44) HA binds proteoglycans.

Structure of Hyaluronan

Structure of aggrecan aggregate

In cartilage the key proteoglycan is aggrecan (MW: 2 x 108)

At 40 nm intervals aggrecan core proteins are attached (assisted by a linker protein) to a decasaccharide sequence in hyaluronan

Attached to the aggrecan core protein are multiple GAGs

The major GAGs in aggrecan are chondroitin sulphate and keratin sulphate

Aggrecan

Rheumatoid artritis

Synovial fluidSerum

Molecular structure of the focal contactMolecular structure of the focal contactFimbrinFimbrinNexilinNexilin

TensinTensinαα-Actinin-ActininTalinTalin

PaxillinPaxillinCaveolinCaveolin

ZyxinZyxinPalladinPalladinVinexinVinexinPonsinPonsin

Integrin, Syndecan-4, Leukocyte common antigenIntegrin, Syndecan-4, Leukocyte common antigen

Function of the adhesion molecules

Adhesion molecule

Summary I.

Molecular Biology of the Cell (© Garland Science 2008)

Summary II.