1. Dept. Genetics, Cell & Immunobiology, Semmelweis University
Cell adhesion
Láng, Orsolya MD, PhD
Dept. Genetics, Cell & Immunobiology, Semmelweis University
Lecture EPh 2014

2. 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

3. Cell-cell adhesion molecules Cell-ECM adhesion Molecules
Cadherins
CAMs or Ig like adhesion molecules
selectins
4. Integrins
5. Proteoglycans (dystroglycan)
Homophyl or heterophyl
Ion dependency :Ca++, Mg++
Cytoskeletal component
Junctional complex

4. Cadherins Homophil connection Cell – cell Ca++ - dependent binding
I.c. anchored to actin or intermedier filamentum
Significant role in development
of vertebrates
Cell specificity
N – neural P – placental E - epithelial

5. Neuronal, muscle, fibroblast Placenta, epidermis, mammary gland
Cadherin superfamily
Type
Localisation
Adherent
classical E
Epithelial
Adherens junction N
Neuronal, muscle, fibroblast
Synapsism P
Placenta, epidermis, mammary gland VE
Endothelial
Non-cl
Desmocollin
Skin
Desmosomes
Desmoglein
T cadherin
Neuronal, muscle -
Cadherin 23
Inner ear
Stereocilia

6. Cadherins allow cells to sort themselves

7. 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 - neuron
L-CAM – liver
V-CAM1- vascular
In melanoma – relation between
ICAM-1 density and the
metastatic activity of the tumor
Intracellular

8. Selectin molecules 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 (?!)

9. Integrin molecules Heterophil connection Ca2+-dependent binding
Focal contacts
Its i.c. linker proteins are
i.e.. talin, a-actinin, vinculin
RGD sequ. is significant in ECM binding
Partner molecules:
fibronectin
laminin
collagen
Deficiency (b) – the adhesion of leukocytes affected, results
the increase of inflammations

11. Type of integrins Integrin Ligand Localisation
Mutation of α or ß subunit
α5ß1
fibronectin
ubiquitous
Early death of the embryo,
α6ß1
laminin
Early death of the embryo, severe skin blistering
α7ß1
muscle
Musclar dystrophy
αLß2
ICAM
leukocytes
Impaired recruitment of leukocytes, LAD, recurrent infections
αIIbß3
fibrinogen
thrombocyte
bleeding, no platelet aggregation, (osteoporosis)
α6ß4
Hemidesmosomeepithelial cells
severe skin blistering

12. Role of adhesion molecule in extravasation of leukocytes

14. Adhesion molecules

15. Functional classification of cell junction

16. Functional classification of cell junction
Anchoring – mechanical junction
Barrier formation - separation
Channel like (gap junction) – communication
Signal relaying junctions sinapsm
immunological sinapsism
transmembrane proteins 16

17. Anchoring junctions

18. Junctional complexes Tight junction Zonula adherens Desmosome
Gap junction
Interdigitation
Hemidesmosome

19. Tight junction(TJ) = zonula occludens
Isolate parts of plasma membrane (apical and basolateral)
Completely encircle polarized cells
Look like honey comb

20. Molecular structure of tight junction
Claudins and occludins (membrane proteins) zip two membranes together
Stabilized by spectrin
Connected to spectrin by adapter proteins ZO1 and ZO2

21. Regulation of tight junctions
Belts of proteins that close extracellular space between cells
Prevent passage of water and water-soluble substances
Account for electrical resistance across epithelia
Leaky epithelia where there is need for some traffic
Hormones
Vasopressin
Cytokines
Lack of ATP causes “leak”
Extravasating leukocytes open tight junctions

22. Tight junctions separate components of the plasma membrane as well

23. Mechanical juncion: zonula adherens - adhesion belt
Adherent junctions
Hold cells tightly together
Confer mechanical strength
Common in tissue that are subject to severe
stress such as skin and cardiac muscle

24. 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)

25. Cytoskeletal component Intermedier filaments
Desmosome = macula adherens
Cytoskeletal component
Intermedier filaments
(i.e. keratin)
Cytoplasmatic
plaque
Adhesion molecule
cadherins

26. 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

27. Spinous layer
desmosome

28. Hemidesmosome – Cell-ECM junction
Fixing of epithelial cells
to the basal membrane
Focal adhesion
Adhesion molecule - integrins
/Linker proteins – plectin, dystonin/
Cytoskeletal component – intermediate filament (keratin)

29. Desmosomes and hemidesmosomes both link to intermediate filaments

30. Gap junction – channel forming junction
Communicating junction
connexon
protein: connexin
homomeric-heteromeric combinations

31. Gap junction
TEM
SEM

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

33. Interdigitation Wave-like plasma membrane extensions + desmosomes
Characteristic of epithelial cell

34. Increases the surface of the basal membraen for molecular transport
Basal striation
nucleus
Increases the surface of the basal membraen for molecular transport
mitochondria
Basal striation
Basement membrane

35. ECM- Extracellular matrix
Mechanical
Influence on migration of the cells
Regulation of activity of molecules released
Co-receptors

36. Main components of ECM
Protein component
Glycan

37. Laminin (LN) 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,
Molecular Biology of the Cell (© Garland Science 2008)

38. Collagens Provide strength of ECM maintains 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)

39. 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 nm)
More than 15 types
I., II., III., V., XI. – formation of fibrils
IV., VII. – network
IX., XII. – association of fibrils

40. Collagen Assembly

41. Matrix types produced by vertebrate cellsG E N
I ChS, DS fibroblast
II fibronectin ChS integrin chondrocyte
III 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

42. Fibroblast surrounded by collagen fibrils

43. Osteogenesis imperfecta – clinical manifestation

44. Tissue elasticity

45. Elastin
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.
Tropoelastine→ cross link→ functional elastin

46. 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.

47. TEM structure of basal lamina ~ basement membrane
In epithelial membrane – prevent cancer cell invasion
Kidney – serves as a filtration barrier
Molecular Biology of the Cell (© Garland Science 2008)

48. Molecular structure of basal lamina
Transmembrane
Molecular Biology of the Cell (© Garland Science 2008)

49. Structure of Hyaluronan
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.

50. 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

51. Aggrecan

52. Rheumatoid artritis
Synovial fluid
Serum

53. Molecular structure of the focal contact
Fimbrin
Nexilin
Tensin
α-Actinin
Talin
Paxillin
Caveolin
Zyxin
Palladin
Vinexin
Ponsin
Integrin, Syndecan-4, Leukocyte common antigen
Molecular structure of the focal contact

54. Function of the adhesion molecules

55. Summary I.

56. Summary II.
Molecular Biology of the Cell (© Garland Science 2008)