Download Ca 2+ - Chemotaxis Group

Adhesion
Cell junctions
Dr. habil. Kőhidai László
Assoc. Professor
Dept. Genetics, Cell- and Immunobiology
Semelweis University
Chemotaxis - Elective Course
2015 – 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
homophil
heterophil
heterophil
homophil
{
Cadhedrins
 Selectins
 Integrins
 Adh. mol. with
immunoglobulin
domain

Ca2+
i.e. cadherin
cytoskeleton
i.c. linker prot.
ECM
i.e. integrin
Ca2+
Cadherin
Ca2+
Homophil connection
 Cell-cell
 Ca2+-dependent binding
 I.c. anchored to actin or
intermedier filamentum
 Significant role in
development
of vertebrates

Ca2+
catenin
actin or
IF

Tissue-specificity:
N - nerve
P - placenta
E - epithelial
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 o
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
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
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

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
• Ca2+ 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, cAMP,
Ca 2+
• Signaling in early embryo
Plasmodesmata
sER
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
molecules released
• Co-receptors
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
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
Arg
Gly
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., II., 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
B1 chain
B2 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 2x10-12 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
ChS, DS
ChS
HS, Hep.
fibrobl.
chondrocyte
hepatocyte
epithel
integrin
IV
laminin
HS, Hep.
laminin rec.
epithel,
endothel,
regenerating
hepatocyte
V
VI
fibronectin
fibronectin
HS, Hep.
HS
integrin
integrin
resting fibrobl.
resting fibrobl.
Abbr.: ChS – 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
P
actin
P
P
P