Adhesion%20%20Cell%20junctions

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Adhesion Cell junctions
Dr. habil. Kohidai László Assoc. Professor Dept.
Genetics, Cell- and Immunobiology Semelweis
University
Chemotaxis - Elective Course 2012 EM-ED
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Significance of cell-adhesion formation of cell
layers
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Significance of cell-adhesion Formation of
multiple layers of cells
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Lymphocytes cross the endothel
Rolling
Entry
Adhesion
Migration
homing receptor
vascular addressin
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Main groups of cell adhesion molecules
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Main adhesion molecules expressed on the cells
during adhesion

• Cadhedrins homophil
• Selectins heterophil
• Integrins heterophil
• Adh. mol. with immunoglobulin homophil domai
  n

Ca2
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i.e. cadherin
cyto- skele- ton
i.c. linker prot.
i.e. integrin
ECM
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Cadherin
Ca2
Ca2

• Homophil connection
• Cell-cell
• Ca2-dependent binding
• I.c. anchored to actin or
• intermedier filamentum
• Significant role in
• development
• of vertebrates

Ca2
catenin

• Tissue-specificity
• N - nerve
• P - placenta
• E - epithelial

actin or IF
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CAM Cell Adhesion Molecules

• 5 pcs. Ig-type domain
• Ca 2 indep. adhesion
• Homophi connection - typical
• Heterophil connection - rare
• More than 20 variations
• Expressed in the critical phase of
• development

Ig-like domains

• Tissue-specificity
• N-CAM - neuron
• L-CAM - liver

In melanoma relation between ICAM-1 density
and the Metastatic activity of the tumour
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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 (?!)
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Integrin
b

• Ca2-dependent binding
• Heterophil connection
• Focal contacts
• Its i.c. linker proteins are
• i.e.. talin, a-actinin, vinculin
• RGD sequ. Is significant in
• e.c. binding
• Partner molecules
• fibronectin
• laminin
• collagen

a
S
S
Deficiency (b) the adhesion of leukocytes
affected, results the increase of inflammations
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Cell-cell junctions
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Junctional complexes

• Tight junction
• Zonula adherens
• Desmosome
• Gap junction
• Hemidesmosome
• Interdigitation

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Tight junction zonula occludens
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Negative staining to detect insulating effect
of tight junction
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Transport accross tight junction
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System of occludin lines
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Role of tight junction

• Mechanical connection
• Barrier
• Inhibits
• entry of water-soluble molecules
• lateral diffusion of membrane-components
• Ca2 is required for the connections of
  occludins
• Permeability inorganic small substances
• amino acids
• monosaccharides

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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

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Desmosome macula adherens
Cell to cell, snap-like junction
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cytoplasmatic plaque desmoplaquin, plactoglobin
Desmosome
actin
intermedier filaments
desmosomal cadherins i.e. desmoglein, desmocollin
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Components of desmosomes
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TEM structure of desmosome
Cytoplasmatic plaque
Intermedier filaments (i.e. keratin)
cadherins
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Submembraneous network connecting desmosomes
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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

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Gap junction
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Gap junction
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Role of gap junction

• Transport of neurotransmitters, cAMP,
• Ca 2
• Signaling in early embryo

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Plasmodesmata
sER
cytoplasm
desmotubule
cellwall
membrane
plasmodesmata
Gap junction-like function Viral infection
results in the increase of pore diameter
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Plasmodesmata
ER
membrane
desmotubule
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Hemidesmosome
Fixing of epithelial cells to the basal membrane
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Basal striation
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Interdigitation
Characteristic between epithelial cells
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Structure of focal contact
actin filament
a actinin
vinculin
paxillin
talin
integrin
fibronectin
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Focal contacts
actin
vinculin
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Extracellular Matrix
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Extracellular matrix - Function

• Influence on migration of the cells
• Regulation of activity of molecules released
• Co-receptors

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Extracellular matrix Building blocks

• Glycosaminoglycans (GAG-s)
• heparan sulfate - basal membr., cell surface
• keratan sulfate - cornea, bone
• chondroitin sulfate cartilage, bone, heart
• hyaluronate - synovial fluid
• dermatan sulfate - blood vessels, heart
• Core-proteins aggrecan decorin
• collagen elastin - structure
• fibronectin laminin - adhesion

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Fibronectins
collagen
cell
RGD
Dimer composed by different channels
alternative splicing
heparin
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Fibronectins
Gly
Arg

• Glycoproteins
• Dimer-structure
• RGD (Arg-Gly-Asp)
• Plasma fibronectins
• Gene K.O. experiments

Asp
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Basal lamina
Cell Connective tissue
Layers lamina lucida lamina densa lamina
fibroreticularis
Components IV. collagen laminin perlecan
entactin
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SEM image of basal lamina
epithelial cells
basal membrane
collagen fibrils
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Main proteins composing the basal lamina
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Collagen IV
Entactin
Perlecan
Laminin
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Collagen

• 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

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Synthesis and association of collagen filament
synthesis of a-chain
Pro, Lys hydroxilation
glycosylation
assembly
organization into a fiber
formation of triple helix
secretion
splitting of procollagen
building into fibrill
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Negative staining of collagen fibrils
gaps between collagen molecules
collagen
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SEM image of collagen fibrils
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Laminin

• each chain has more types
• 18 isoforms of laminin
• diversities in tissues

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Elastin
fibre of elastin
cross-links
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Aggrecan

• One complex of aggrecan
• M.W. about 108
• Volume 2x10-12 ml
• ( bacterium)

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Complex of aggrecan
1 mm
Core prot.
Hyaluronan
Linker proteins
Keratin sulfate
Chondroitin sulfate
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Matrix types produced by vertebrate cells
Abbr. ChS chondroitin sulfate DS dermatan
sulfate HS heparan sulfate Hep -
heparin
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Clinical approaches
hydroxy-Pro ? hydroxy-Lys ? cross-linking
? N-term. propeptide
- poor wound healing - hyperextensibility -
musculo-skeletal deformities
Collagen
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Complexity of cell adhesion
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Interactions in focal contact
Fimbrin Nexilin Tensin A-Actinin Talin Paxillin
Caveolin Zyxin Palladin Vinexin Ponsin Integrin
, Syndecan-4, Leukocyte common antigen
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Protein associated to actin filaments
Zonula adherens E cadherin Catetin
Vinculin a-actinin Plactoglobin Adhesion
plaque Integrin a -actinin Vinculin Talin
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Induction of integrins
Binding site in matrix
e.c. matrix
active integrin
Binding site in cytoskeleton
P
P
P
P
actin