Adhesion Cell junctions Dr habil Khidai Lszl Assoc
Adhesion Cell junctions Dr. habil. Kőhidai László Assoc. Professor Dept. Genetics, Cell- and Immunobiology Semelweis University Chemotaxis - Elective Course 2019 – EM-ED
Significance of cell-adhesion: formation of cell layers
Significance of cell-adhesion: Formation of multiple layers of cells
Lymphocytes cross the endothel „Rolling” Entry Adhesion homing receptor vascular addressin Migration
Main groups of cell adhesion molecules
Main adhesion molecules expressed on the cells during adhesion { Cadhedrins homophil l Selectins heterophil l Integrins heterophil l Adh. mol. with immunoglobulin homophil domain l Ca 2+
i. e. cadherin cytoskeleton i. c. linker prot. ECM i. e. integrin
Cadherin Ca 2+ Homophil connection l Cell-cell l Ca 2+-dependent binding l I. c. anchored to actin or intermedier filamentum § Significant role in development of vertebrates l Ca 2+ catenin actin or IF l Tissue-specificity: N - nerve P - placenta E - epithelial
CAM = Cell Adhesion Molecules Ig-like domains 5 pcs. Ig-type domain l Ca 2+ indep. adhesion l Homophi connection - typical l Heterophil connection - rare l More than 20 variations l Expressed in the critical phase o development l Tissue-specificity: N-CAM - neuron L-CAM - liver In melanoma – relation between ICAM-1 density and the Metastatic activity of the tumour l
Selectins Lectin type proteins, Carbohydrate specificity Tissue-specificity: E - epithelial L - lymphoid P - 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 (? !)
Integrin b a S S Ca 2+-dependent binding l Heterophil connection l Focal contacts l Its i. c. linker proteins are i. e. . talin, a-actinin, vinculin l RGD sequ. Is significant in e. c. binding l Partner molecules: fibronectin laminin collagen l Deficiency (b) – the adhesion of leukocytes affected, results the increase of inflammations
Cell-cell junctions
Junctional complexes • Tight junction • Zonula adherens • Desmosome • Gap junction • Hemidesmosome • Interdigitation
Tight junction = zonula occludens Intercellular space 0. 6 mm Transmembrane proteins occludin Lipid bilayer Cytoplasmic face
Negative staining to detect „insulating” effect of tight junction
Transport accross tight junction
System of occludin – lines
Role of tight junction • Mechanical connection • Barrier • Inhibits: entry of water-soluble molecules lateral diffusion of membrane-components • Ca 2+ is required for the connections of occludins • Permeability: inorganic small substances amino acids monosaccharides
Septate junction • on the apical part of the cells • they form a continous belt (like z. adherens) • promote to stick together the cells • actin is anchored in this junction
Desmosome = macula adherens Cell to cell, snap-like junction
cytoplasmatic plaque desmoplaquin, plactoglobin Desmosome actin intermedier filaments desmosomal cadherins i. e. desmoglein, desmocollin
Components of desmosomes
TEM structure of desmosome Cytoplasmatic plaque Intermedier filaments (i. e. keratin) cadherins
Submembraneous network connecting desmosomes
Gap junction (1958, 1968) • Bridges the 2 -4 nm gap between the neighbour cells • Hexagonal channel is formed (connexon) • The wall of the channel is composed by 6 connexins (4 helical components) • The distribution of channels is tissue- or cell-specific due to the difference of connexins • Accross channels substances are transmitted (max MW. 1000) by a regulated mechanism
Gap junction
Gap junction
Role of gap junction • Transport of neurotransmitters, c. AMP, Ca 2+ • Signaling in early embryo
Plasmodesmata s. ER cytoplasm desmotubule cellwall plasmodesmata membrane Gap junction-like function Viral infection results in the increase of pore diameter
Plasmodesmata ER membrane desmotubule
Hemidesmosome Fixing of epithelial cells to the basal membrane
Basal striation
Interdigitation Characteristic between epithelial cells
Structure of focal contact actin filament a actinin vinculin paxillin talin integrin fibronectin
Focal contacts actin vinculin
Extracellular Matrix
Extracellular matrix - Function • Influence on migration of the cells • Regulation of activity of released • Co-receptors molecules
Extracellular matrix – Building blocks • Glycosaminoglycans (GAG-s) Ø heparan sulfate - basal membr. , cell surface Ø keratan sulfate - cornea, bone Ø chondroitin sulfate – cartilage, bone, heart Ø hyaluronate - synovial fluid Ø dermatan sulfate - blood vessels, heart • „Core-proteins” aggrecan – decorin Ø collagen – elastin - structure Ø fibronectin – laminin - adhesion
Fibronectins collagen cell RGD heparin Dimer composed by different channels – alternative splicing
Fibronectins • Glycoproteins • Dimer-structure • RGD (Arg-Gly-Asp) • Plasma fibronectins • Gene „K. O. ” experiments Gly Arg Asp
Basal lamina Cell Layers: lamina lucida lamina densa lamina fibroreticularis Components: IV. collagen laminin perlecan entactin Connective tissue
SEM image of basal lamina epithelial cells basal membrane collagen fibrils
Main proteins composing the basal lamina
Collagen IV Entactin Perlecan Laminin
Collagen • Fibrils (diam. 10 -300 nm) • More than 15 types • I. , III. , V. , XI. – formation of fibrils • IV. , VII. – network • IX. , XII. – association of fibrils
Synthesis and association of collagen filament synthesis of a-chain Pro, Lys hydroxilation glycosylation assembly formation of triple helix secretion splitting of procollagen building into fibrill organization into a fiber
Negative staining of collagen fibrils gaps between collagen molecules collagen
SEM image of collagen fibrils
Laminin A chain Globular domains B 1 chain B 2 chain a-helix • each chain has more types • 18 isoforms of laminin • diversities in tissues
Elastin fibre of elastin strech relax cross-links
Aggrecan One complex of aggrecan: • • M. W. about 108 Volume 2 x 10 -12 ml (= bacterium)
1 mm Complex of aggrecan Core Hyaluronan prot. Linker proteins Keratin sulfate Chondroitin sulfate
Matrix types produced by vertebrate cells Anchor C O L L A G E N E I II III Proteogly. Receptor Cells fibronectin Ch. S, DS Ch. S HS, Hep. fibrobl. chondrocyte hepatocyte epithel integrin IV laminin HS, Hep. laminin rec. epithel, endothel, regenerating hepatocyte V VI fibronectin HS, Hep. HS integrin resting fibrobl. Abbr. : Ch. S – chondroitin sulfate; DS – dermatan sulfate; HS – heparan sulfate; Hep - heparin
Clinical approaches Collagen hydroxy-Pro hydroxy-Lys cross-linking N-term. propeptide - poor wound healing - hyperextensibility - musculo-skeletal deformities
Complexity of cell adhesion
Fimbrin Nexilin Interactions in focal contact Tensin A-Actinin Talin Paxillin Caveolin Zyxin Palladin Vinexin Ponsin Integrin, Syndecan-4, Leukocyte common antigen
Protein associated to actin filaments Zonula adherens: E – cadherin Catetin Vinculin a-actinin Plactoglobin Adhesion plaque Integrin a -actinin Vinculin Talin
Induction of integrins Binding site in matrix e. c. matrix active integrin Binding site in cytoskeleton actin P P
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