1. Cell Adhesion Molecules
(CAM)
Medical Biology
Müjgan Cengiz

2. Cellular Junctions and Adhesion
• In multi-cellular cells have
junctions that occur with:
• 1- Other cells
• 2- The Extra-Cellular Matrix
(ECM):
•
a network of secreted
macromolecular
complexes

3. Two main ways in which animal cells are bound together:
•Connective tissue
•Epithelial cells.
Figure 19-1 Molecular Biology of the Cell (© Garland Science 2008)

4. Selective Adhesion Determines Specificity
of Tissue and Cellular Associations
• Townes
&
Holtfreter
(1950)
separated
embryonic cells of frogs
and
combined
them
together again. To be
able to identify the
different cell types, they
mixed together cells from
normal (pigmented) frogs
with cells from albino
frogs
Identification of CAM through
experiment:

5. Selective Adhesion Determines Specificity
of Tissue and Cellular Associations

6. Identification of CAM through
experiment:
Antibodies were developed
against specific types of
CAM.
Antibody treatment of the
target cells was found to
disturb the cell aggregation.

7. • What are the factors
that keep the cells
together?
• how do the same type
of cells recognize
each other?

8. Adhesion
Adhesion = molecules sticking to
a substrate

9. CELL ADESİON MOLECULES
• Cell-cell interactions
• Embryogenesis
• Immunity(migration of immun cells to the
inflamation center)
• Cell tissue organ development
• wound healing
• Cancer metastasis

10. Cell adhesion molecules
• 1-Holding cells together
• 2-Cells detect their extracellular
environment through interaction
employing a variety of cell adhesion
molecules (CAMs)

11. Cells adhere to each other and to the extracellular
matrix through cell-surface proteins called cell
adhesion molecules (CAMs)
• Many adhesion molecules are
mosaics of multiple distinct domains
• (1) extracellular domain:
– Mediate adhesion
(2) transmembrane domain
•
•
•
•
(3) cytosolic domain:
-recruit sets of multifunctional adaptor
proteins
--adaptor proteins: link to cytoskeleton/
signaling molecules
* outside-in and inside-out effects: connectivity
and communication

12. Cell adhesion molecules (CAM)
--Many adhesion molecules are mosaics of multiple distinct domains
(1) extracellular domain: mediate adhesion
*homotypic adhesion—adhesive interactions between cells of the same
type
*homophilic adhesion—a CAM on one cell can directly bind to the same
kind of CAM on an adjacent cell.
(2) cytosolic domain:
--recruit sets of multifunctional adaptor proteins
--adaptor proteins: link to cytoskeleton or signaling molecules
* outside-in and inside-out effects: connectivity and communication

13. Heterophilic Binding- Binding to a different kind
1) extracellular domain of molecule on adjacent cells
Homophilic Binding- Binding of
same kind of molecules in
adjacent cells
Linker-dependent BindingBinding through a
secreted linker molecules
to other molecules.
The binding of a cell-surface receptor to a secreted
ECM molecule immobilized on the substrate.

14. cell adhesion molecules
↑
1- cell adhesion molecules : glicoproteins
↓
2- linker-protein
connects the junction to (micro- or intermediate)
filaments

15. Cell-cell adhesions can be
• A- tight and long
junctions
•
e.g. nerve cells in the nerve cells/
the metabolic cells in the liver
• B- relatively weak and
transient
•
e.g. immune –system cells in the
blood

16. Cell Adhesion Molecules
What are they?
Cell adhesion molecules (CAMS) are cell surface proteins involved in
the binding of cells, usually leukocytes, to each other, to
endothelial cells, or to the extracellular matrix.
Most CAMS can be placed into one of four general families of proteins:
1) Cadherins
2) Integrins
3) Immunoglobulin (Ig) super family
4) Selectins

17. epithelial cells
non-epithelial cells
tight
junctions
actin
adhesion belt
(CADHERINS)
CELL CELL
ADHESION
desmosomes
(CADHERINS)
Gap junctions
(connexins)
CELL MATRIX
ADHESION
hemidesm.
(integrins)
focal
contacts
(integrins)
basal lamina
JUNCTIONAL ADHESION MECHANISMS
CADHERINS
IG-LIKE CAMS
INTEGRINS
SELECTINS
integrins
NO
attachment
plague
Non-JUNCTIONAL CONTACTS

18. • Cell Adhesion also occurs
in the blood
• Under most
circumstances, all blood
cells try to keep from
sticking to the wall.
• When a Leukocyte goes
on the hunt…
– Cell Rolling
– Cell Adhesion

19. CELL-CELL adhesion
Cadh. repeats
CELL ADHESION MOLECULES
Cadherins
Ca 2+ -dep. homophilic adhesion
functional unit = dimer
Ig and Fn III
repeats
Immunoglobin superfamily
(CAMs)
homophilic or heterophilic
lectin repeats
Selectins
heterophilic
P selectin + counter-receptor
PSGL-1, glycosylated
I-CAM
Integrins
heterodimers, heterophilic
bind to ECM, Ig-CAMs, cadherins
adhesion, polarity, migration
Hynes: TiCB: 9:M33 1999

20. Immunobiology, 6th Edition, Janeway, Travers, Walport, and Shlomchik

21. Some CAMs are Ca2+-dependent,
some others are Ca2+-independent.
•
Ca2+-dependent
Cadherins,
Selectins,
İntegrins
•
Ca2+-independent
Ig superfamily

22. 1-CADHERINS
• A family of Ca2+dependent CAMs
• Ca2+ causes dimerization
of Cadherins
• The binding is
homophilic-hold cells of
one tissue type/subtype
together by binding to the
same cadherin on a
neighbouring cell
• greater the number of
cadherins, greater the
strength of adhesion

23. Compaction of an early mouse embryo.
At the 8-cell stage they start expressing E-cadherins
Figure 19-5 Molecular Biology of the Cell (© Garland Science 2008)

24. 1) CA-DEPENDENT CAMs (CELL ADHESION MOLECULES):
a) classic CADHERINS:
involved in both junctional and non junctional adhesions
E-, N- and P- cadherins (Epithelial, Nerve, Placenta)
single-pass transmembrane glycoproteins
(~700-750 AA s), 5 cadherin repeats
selective adhesion, homophilic
differential expression during development + morphogenesis
the extracellular side:
5 cadherin repeats of 100 AA,
(3 are Ca2+ -binding)
in the absence of Ca >>> rapid proteolysis
the cytoplasmic side:
the intracellular attachment proteins:
catenins α,β,γ (bind actin) (required for cell-cell adhesion)
Nonclassical cadherines cannot bind actin filaments .
They can bind to intermediate filaments and forms
desmosomes.

25. Cadherin structure
Extracellular domains of a classical cadherin (C-cadherin)
Figure 19-9a Molecular Biology of the Cell (© Garland Science 2008)

26. If Ca2+ is removed, the extracellular part of the
protein becomes floppy and is rapidly degraded by
proteolytic enzymes
Ca2+ causes dimerization of Cadherins

27. Cadherins
-Ca-dependent adhesion molecules
Extracellular domains adhere cells together
Participate in intracellular signalling
Link and help assemble the cytoskeleton via
actin or intermediate filaments

28. Cadherins Are Linked To Actin
Cytoskeleton
• The linkage of cadherins
to actin filaments.

29. Different CAMs function in different junctions

30. Zonula adherens- E-cadherin
•Cadherins interact with actin filaments by CATENINs.

31. Cadherin-containing junctions connect cells to
one another and are linked to either the actin
or IF cytoskeleton
α,β,γ, catenins
Figure 22-5

32. Localization of sub-types:
E-epithelial N-neuronal P-placental VE-endothelial
For instance: N-cadherin binds to other N-cadherins, but not
P or VE-cadherins
This keeps neurons attached to other neurons!
to E,

33. Table 19-3 Molecular Biology of the Cell (© Garland Science 2008)

34. Embryogenesis & Cadherins
• Expression of specific
cadherins accompanies
morphogenetic
movements during
embryogenesis

35. Embryogenesis & Cadherins
•
E-cadherin is the first cadherin
expressed during mammalian
development. It helps cause
compaction, an important
morphological change that
occurs at the eight-cell stage of
mouse embryo development.
•
During embryogenesis,
production of cadherins
promotes cells of similar type
to adhere when cells need to
migrate to newly growing
tissue (e.g. limbs), they lose
adhesive properties –
cadherins must be
endocytosed
•

36. Cadherins and Catenins participate in transduction of extracellular signals and Med
various cellular response.
interior
cell
Ca2+
external
interior
GTP
cell
Small GTPaz
GTP
effectors
Cell- cell
Adhesion
The changes in
cell shape
Cell differentation?

37. 2-Integrins:
• Mediates Ca+2 dependent
adhesion
Integrin makes cell-substrate
interaction
• Ligands: ECM molecules,
soluble ligands, CAMs
• ( fibronectin, fibrinogen, ICAM,
laminin)
• Two transmembrane glycoprotein
subunits: α and β
• both required for matrix binding

38. D
R
transmembrane linkers of the ECM and the cytoskeleton
G
β
chain
bind ligands with low affinity
present at very high concentration on the cell surface
α
chain
Cys-rich
Cells both bind to and respond to the ECM via integrins.
3-4 Ca2+ or Mg2+ binding domains on the α chain
Diversity of integrins:
9 types of β, 14 types of α
~ 20 different heterodimers identified so far
Integrins are modulated by additional cell-specific factors
RGD” sequence is the specific substrate

39. Integrins
On the extracellular side integrins bind
to the sequence Arg-Gly-Asp found in
adhesion
molecules
including
fibronectins
On the intracellular side they bind
Vinculin and a-Actinin, these proteins
bind to Actin filaments
This dual binding allow cells to move by
contracting Actin filaments against the
EM

40. integrin plays a major role in assembly of the hemidesmosome, or stable
stable anchoring contact.

41. 2007 TUS
• Hücrenin, hücreler arası matriks ile
etkileşimini sağlayan transmembran
yapıdaki adezyon reseptörleri
aşağıdakilerden hangisidir?
A) Kateninler
B) Selektinler
C) Kaderinler
D) İntegrinler
E) Vinkülinler

42. Aralık 2010
• Asagıdaki hücre baglantılarından
̧ ̆
̆
hangisinin yapısında hücre adezyon
molekülü olan integrin yogun olarak
̆
bulunur?
A) Zonula occludens
B) Zonula adherens
C) Macula adherens
D) Konnekson
E) Hemidesmozom

43. Integrins Interact with The
Cytoskeleton
Integrins are linkers
between cytoskeleton
and extracellular matrix.
Bind to actin filaments
Need intracellular anchor
proteins for bindig to
actins.
These intracellular anchor
proteins are:
1. Talin
2. α –actinin
3. Filamin

44. Integrins Are TM Heterodimers
(αβ Combinations) That Mediate Weak
Cell-Matrix and Cell-Cell Interactions
Cell-matrix adhesion is modulated by
changes in the activity and number of
integrins
De-adhesion factors promote cell
migration and can remodel the
cell surface

45. interactions and the three binding modes
of various integrins
Adherent Cell
PMN
Platelet
1
2
3
Fibrinogen
ECM
Vasc. Endo. Cell
1. Integrins bind to ECM proteins via specific
amino acid recognition sites
2. Integrins bind to other cell adhesion molecules
3. Integrins promote platelet aggregation through
soluble miltivalent mediator molecules
Platelet

46. 2. Integrins bind to other cell adhesion molecules

47. 2-
Integrins promote platelet aggregation through soluble miltivalent mediator molecules
Integrin and platelet aggregation
(Karp, 2001)

48. Activation of some integrins may require to bind their ligand
Ex: Platelet aggregation
Leukocyte migration

49. Fibrinojen
Trombin
thrombin activation of platelets causes an
induction of platelet agregation mediated by
fibrinogen binding to the integrin

50. Disintegrins
• Disintegrins are
peptides isolated from
the venom of various
snakes of the viper
family. They interact
with the beta 1 and
beta 3 families of
integrin proteins.
• They cause the
bleeding.

51. Disintegrin drugs
Drug
Function
Bitistatin
platelet aggregation inhibitor, which
binds with high affinity to the
alphaIIbbeta3 integrin
Kistrin
Kistrin has an RGD site that competes
for the platelet IIb/IIIa integrin
Barbourin
that function as potent inhibitors of
both platelet aggregation and integrindependent cell adhesion
Batroxostatin
They were first identified as inhibitors
of platelet aggregation and were
subsequently shown to bind with high
affinity to integrins and to block the
interaction of integrins with RGD
containing proteins for example they
block the binding of the platelet
integrin _IIb_3 to fibrinogen

52. Integrins and Signal Transduction:
• Integrins play an
important role not
only in structure &
architecture of
tissues, but also for
signal transduction
leading to regulation
of functions in cell.

53. 3-Immunoglobulin (Ig) Superfamily:
•Mediate Ca2+-independent Cell-Cell Adhesion
•
•
•
Contain one or more Ig-like domains
that are characteristic of antibody
molecules
a homophilic mechanism (between
N-CAM molecules on adjacent
cells). Some Ig-like cell-cell
adhesion proteins, however, use a
heterophilic mechanism
Function: ICAM and VCAM
molecules play an important role
in T cell interactions and binding of
leukocytes to activated or resting
endothelial cells

54. 3-Immunoglobulin (Ig) Superfamily :
members
• Intercellular adhesion
molecules (ICAMs)on endothelial cells
Vasculer adesion
molecules: VCAM
• the neural cell
adhesion molecule
(N-CAM),
• Platelet-endotel..:
PECAM

56. 4- Selectins
• Integral proteins
• Extracellular domain bind
specific carbohydrates on
other cells
• Most commonly found on
epithelial cells, used to
mediate interactions with
leukocytes (white blood
cells/immune cells)

57. P-selectin glycoprotein
ligand-1

58. 4- Selectins
• 3 types:
- P-selectin- blood platelets,endothelial
cells
-L-selectin- white blood cells
-E-selectin- endothelial cells

60. Selectins are calcium-dependent (C-type)
lectins (carbohydrate binding proteins)
•
L-selectin – on lymphocytes (neutrophils)
– binds specialized sulfated mucins (‘peripheral node
addressins’ or PNAd) made by high endothelial venules
(HEV)
– Can be shed upon lymphocyte activation
•
P-selectin - early role in entry to site of
inflammation
– in Weibel-Palade bodies in endothelial cells and α-granules
of platelets
– translocates to membrane in response to thrombin,
histamine, C5a, etc
– binds PSGL-1, a tyrosine sulfated mucin - on neutrophils,
some effector T cells
•
E-selectin - delayed role in entry to site of
inflammation
– cytokine inducible on endothelial cells (especially
cutaneous)
– binds carbohydrate ligand (sialyl-Lex) on neutrophil
glycoproteins /glycolipids and cutaneous leukocyte
antigen (CLA) on effector T cells
L = C-type lectin domain
E = EGF-like domain
C = complement regulatory domain

61. Lymphocyte Extravasation

62. Selectins are involved in
extravasation
Inflammatory signals activate
endothelial cells making PSelectin undergo exocytosis
P-Selectin on the surface of
endothelial cells binds a specific
carbohydrate ligand (Sialyl Lewis
-x) on leukocytes
The leukocytes attach to the
endothelial wall and roll slowly on
it
PAF and integrins are then activated
and the leukocytes start to
extravasate

63. Selectins

64. functions of selectins
animation
Figure 19-19b Molecular Biology of the Cell (© Garland Science 2008)

65. Lökosit
Endotel
1-K.H
P-selektin
2- İntegrin
ICAM
3-İntegrin
ECM

68. Diseases of cell adhesion
molecules

69. Integrin diseases-1
•
Leukocyte adhesion deficiency
(LAD) type I:
–
–
•
•
defects in β2 integrin -> defective
neutrophil migration to inflammed skin,
peritoneum; lymphocytes less affected
due to continued use of α4β1, α4β7
LAD patients have recurrent bacterial
infections
Other types of LAD involve defects in
expression of glycosyltransferases
needed to make selectin ligands and
defects in intracellular signaling
molecules needed for chemokinemediated integrin activation
EX: LAD 2 results from a lack of sialyl
LewisX (defect of carbohydrate
fucosylation). Interaction with
endothelial E-and P-selectins is
impaired

70. Integrin diseases-2
• Glanzmann
Thrombasthenia
• : is an inherited
bleeding disorder
fibrinojen
– IIbß3 integrin
expression deficieny
– ↓
• adequate formation of
the platelet plug
» ↓
Susceptibility of bleeding
trombin

71. Immunoglobulins
• One Ig cell adhesion
protein known as L1,
assists in growth of nerve
cells – mutants can have
severe neural problems:
– Mental retardation
– Hydrocephaly (fluid
accumulation in ventricles of
brain - arrows)

72. Cancer Metastasis and adhesion
Alteration in expression of adhesion molecules
cell- cell a recognition- adhesion system breaks down in cancer

73. 6 basic steps for metastasis
For metastasis
1. Detachment
No need for cell to cell interaction
2. Invasion and intravasation
3. Circulation
4. Stasis
5. Extravasation and invasion
6. proliferation

74. Cancer
Metastasis and
adhesion
cell- cell a recognition- adhesion system breaks down in cancer

75. •
A loss-of-function allele of a
Cadherin, a Desmocollin, or a Ca++independent CAM can lead a cell to a
lose its adhesion to proper neighbors
and start to wander(tour)
•
About 85% of cancers are epithelial in nature
(due to high replication rate), metastasis is
linked to a loss of E-cadherins
E (Cadherins is down regulated in most
carcinomas and is therefore a tumor
suppressor

76. E (Cadherins:
•.
Loss of cadherin is accompanied by a loss of zonula adherens junctions
and a dramatic reduction in cell-cell adhesion.
•Experimentally increasing the levels of E-cadherin can restore many of the normal
•epithelial properties of carcinoma cells including loss of their ability to cause tumors
• when injected into animals.
cadherins

77. Circulation
Stasis
Extravasation and invasion
Changes in cell adhesion behavior