ADHESION MOLECULES,DERMAL-EPIDERMAL JUNCTION:ANATOMY &CLINICAL RELEVANCE, Cell Adhesion Molecules (CAMs)

1. MODERATOR
DR. SAROJ PUROHIT

2. INTRODUCTION
Cell Adhesion Molecules (CAMs)
 Proteins located on cell surface involved in binding with other
cells or with the extracellular matrix (ECM)
 Provides resistance against environmental influences
 Epidermal integrity is required for protection of the entire
organism against
- mechanical
- physical
- microbial insult.

3.  Are typically transmembrane receptors and are composed of
three domains:1. Intracellular domain that interacts with the cytoskeleton
2. Transmembrane domain
3. Extracellular domain that interacts either with other CAMs of
the same kind (homophilic binding) or with other CAMs or
the extracellular matrix (heterophilic binding)
 Regulates tissue :
- growth
- differentiation
- repair

4. CLASSIFICATION

Classified as:
1.calcium-dependent CAMs
2.calcium-independent CAMs

5. 
calcium-dependent CAMs
1.integrin
2.cadherin
3. selectin

calcium-independent CAMs
1. immunoglobulin superfamily

7. INTEGRINS
 Large family of heterodimeric transmembrane glycoproteins that
attach cells to extracellular matrix proteins of the basement
membrane or to ligands on other cells.
 Key to:
- embryogenesis
- tissue development and differentiation
- immune responses
- leukocyte trafficking
- cancer metastasis
- tissue homeostasis.
 Integrins contain large (α) and small (β) subunits of sizes 120-170
kDa and 90-100 kDa, respectively

8.  The α subunit of the integrin heterodimer especially the αI domain
determines the ligand specificity for cell-ECM adhesion.
 Contain binding sites for divalent cations Mg2+ and Ca2+, which are
necessary for their adhesive function.
 Common ECM components that are bound by integrins (with
respective recognition sequence) are
- Fibronectin (RGD, LDV)
- Collagen (triple helical GFOGER)
- Laminin
- Vitronectin (RGD)
- Fibrinogen(RGD)
- Thrombospondin
- Glycoproteins (e.g. tenascin C, osteopontin, nefronectin)

10.  Ligation of integrins initiates a plethora of signal transduction
events which serve to modulate cell behaviour including :
- proliferation
- apoptosis
- up-regulation of genes Involved in inflammation
cell polarity and migration
 Many integrin stimulated cell signalling pathways are similar
to those triggered by growth factor receptors and
cytokine/chemokine receptors
 Upon activation, integrins are capable of triggering a variety of
signal transduction cascades based on the context, ligand
(matrix components/growth factors) and substrate stiffness that
result in a variety of short-term and long-term responses

12. Cellular responses elicited by integrin signaling. In response to physical/chemical properties of the
matrix and growth factors in the environment (outside-in signaling), integrins bind ligands and get
activated. Accordingly, a variety of signaling pathways can be triggered mainly through the different
kinases as mentioned above. These can bring about changes in one or more cellular events (short term
responses) that eventually result in global (long term) responses in cellular behavior

13. Integrin type
In vivo function
β1 integrins
Development
αV
Vasculogenesis
α9β1
Lymphangiogenesis
αIIbβ3
Thrombus formation
α6β4
Integrity of skin
αVβ3
β2 integrins
Suppresses tumorigenesis, angiogenesis,
wound healing, inflammation and
atherosclerosis
Immune responses

14. SELECTINS
 Calcium-dependent transmembrane glycoproteins with an
amino-group terminal portion that binds to sialylated
carbohydrate counter-receptors on other cells.
 Key transient link between leukocytes and vascular
endothelium thereby mediating the initial steps of leukocyte
rolling and tethering
 There are three subsets of selectins:
- P-Selectin
- E-Selectin
- L-Selectin

17.  P-selectin and E- selectins plays an essential role in the initial
recruitment of leukocytes to the site of injury during
inflammation
 Following stimulation of TNF-α, IL-1 LPS and substance P
peak expression of E-selectin occurs within 4 h unlike Pselectin which takes minutes on being stimulated by histamine,
IL-4, IL-13, oncostatin M or thrombin.
 L-selectin is unique in that it is the only selectin known to be
involved in trafficking of lymphocytes into lymphatic tissue.

18.  Levels of soluble E-selectin in plasma are increased in
- scleroderma
- polyarteritis nodosa
- SLE
- psoriasis
- atopic dermatitis
 Correlation between levels of soluble E-selectin and disease activity has
been observed in
- atopic and allergic dermatitis
- psoriasis and palmoplantar pustulosis
- eczema
- Kawasaki disease
 E-selectin may be of potential therapeutic value in inflammatory diseases
and cancer by virtue of its unique temporal and spatial expression profile

19.  Adhesion is a key step in the metastatic cascade
 E-selectin expressed on activated endothelium can facilitate
tumor cell seeding
 Expression of Lewis carbohydrates is often more pronounced
on the surface of metastatic tumor cells
 E-selectin expression is often enhanced on the surface of
endothelial vessels at the site proximal to or directly at tumor
metastases.

20. Schematic presentation of selectin- and integrin-mediated cancer cell interactions
with several blood constituents (e.g., platelets, leukocytes, and endothelial cells)
during hematogenous metastasis

21. The medical potential of antagonists to human
selectins
 Intravenous administration of the CDP850 humanized anti-E-
selectin antibody reduces levels of soluble E-selectin in plasma
and of E-selectin expressed on lesional psoriatic skin in
patients with moderate-to-severe chronic plaque psoriasis
 Pan selectin competitive inhibitors, including sLeX
oligosaccharide, sLeX mimetics , multivalent sLeX ligands or
diverse molecular weight species of heparin have been
developed.
 A few such carbohydrates have shown some success in the
treatment of psoriasis (Bimosiamose or TBC-1269 and
Efomycine M) or asthma (Bimosiamose)

22. IMMUNOGLOBULIN SUPERFAMILY
 Large group of cell surface and soluble proteins that are involved in
- recognition
- binding
- adhesion processes of cells
 These molecules have been associated with cancer progression and a
metastatic phenotype
 Includes members such as:
- vascular cell adhesion molecules (VCAM)
- neural cell adhesion molecules (NCAM)
- intercellular adhesion molecules (ICAM)
- nectin and nectin-like (Necl) family
- platelet endothelial cell adhesion molecules (PECAM)

24.  ICAM-1 contributes to leukocyte adhesion via the LFA-1 and Mac-1 β2
integrins
 The related VCAM-1 molecule expression is increased after cytokine
stimulation, and it binds the α4β1 integrin mediating extravascular
migration, principally of monocytes and eosinophils.
 Platelet–endothelial cell adhesion molecule (PECAM-1 or CD31), is found
in platelets and at the intercellular junctions of endothelium,where it
contributes to leukocyte passage from blood vessels
 sICAM-1 is significantly elevated in the serum of a number of
dermatological diseases including atopic dermatitis, psoriasis and metastatic
melanoma and correlates with clinical severity in untreated disease.
 sICAM-3 is increased in the sera of patients with psoriasis and atopic
dermatitis but is less relevant than sICAM-1 to disease activity

25.  sVCAM are elevated in advanced cutaneous melanoma,
localized scleroderma, systemic sclerosis and SLE
 CD99participates in the process of transendothelial migration
of monocytes and neutrophils, can be a potential therapeutic
target in skin inflammation
 Recent studies demonstrated L1CAM expression in various
types of cancer, predominantly at the invasive front of tumours
and in metastases

26. Neutrophil emigration. (a) Rolling: cells roll over the endothelium by brief non-adherent
contacts via the selectins,particularly L-selectin. The integrins are non-binding. (b) Arrest:
on contact with activated endothelium, selectin binding brieflyincreases, integrins become
avid and intercellular adhesion molecule1 (ICAM-1) increases on the endothelial surface.
(Monocytes and eosinophils also bind via α4β1 to vascular cell adhesion molecule 1
(VCAM-1).) (c) Adherence: the neutrophil fl attens on the endothelium, affinity increases
and motility response to chemokines is initiated. (d) Emigration: neutrophil leaves vessel
through interendothelial cell junction, regulated by integrins, platelet/endothelium cell
adhesion molecule 1 (PECAM-1) and chemokines

27. Pleiotropic anti-inflammatory effect of dPGS diminishes the inflammatory response and
reduces leukocyte extravasation. Molecular targets of dPGS are the adhesion
molecules L- and P-selectin. dPGS prevents leukocyte extravasation by shielding the
selectins. Binding to complement factors C3 and C5 inhibits the formation of the
proinflammatory anaphylatoxins. Reduction of the C5a level decreases vascular
permeability and further leukocyte extravasation. By addressing these inflammatory
targets simultaneously, dPGS promote the resolution of inflammation.

28. EPIDERMAL, DERMO-EPIDERMAL
ATTACHMENT COMPLEX
 The basement membrane between the epidermis and the dermis
contains unique structures that maintains the attachment of the
epithelium.
 The components of the attachment complex provide links to the
intracellular intermediate filament network of basal
keratinocytes and to the extracellular matrix of the papillary
dermis.
 Can be divided into :
1. Epidermal attachment complex
2. Dermo-epidermal attachment complex

29.  Epidermal attachment complex includes:
1. Desmosomes
2. Adherens Junctions
3. Tight Junctions
4. Gap Junctions
 Dermo-epidermal attachment complex includes:
1. Intermediate filaments
2. Hemidesmosomes
3. Anchoring Filaments
4. Anchoring Fibrils

30. DESMOSOMES
 Desmosomes are small, electron-dense structures that link
the intermediate filament within cells to the plasma
membrane and to adjacent cells
 Found in Epidermis, myocardium, meninges and cortex of
lymph nodes
 Characteristic ultrastructural appearance, in which the cell
membrane of two adjacent cells forms a symmetrical
junction with a central intercellular space of 30 nm
containing a dense line

31. COMPONENTS OF DESMOSOMES
 Transmembranous cadherins - heterophilic associations of
desmogleins and desmocolins
There are Four main epidermis-specific desmogleins
(Dsg1–4) and Three desmocollins (Dsc1–3), which show
differentiation-specific expression.
 Desmoglein-3 is expressed only in the basal and suprabasal
layers of the epidermis
 Desmoglein-1 is found throughout the epidermis, particularly
in the upper layers
 In mucosae, desmoglein-3 is strongly expressed throughout
whereas desmoglein-1 is expressed only weakly

32.  Plaque components-
Intracellular parts of desmosomal cadherins attached to KF
network via-Desmoplakin
-Plakoglobin
-Armadillo protein: plakophilin
-Enovaplakin
-Periplakin

33. Molecular model of the desmosome. The desmosomal cadherins desmoglein and desmocollin
undergo homophilic and heterophilic binding via interaction with the amino-terminal
extracellular (EC) 1 domain of partner molecules on the same (cis) as well as on the
neighbouring cell (trans). The cytoplasmic domains are largely embedded in the outer dense
plaque (ODP) where they are associated with plakoglobin and plakophilin. In the inner dense
plaque (IDP), desmoplakin links these adaptor molecules to the intermediate filament
cytoskeleton

34. Autosomal dominant and autosomal recessive mutations in human
desmosome genes resulting in skin, hair and cardiac abnormalities

35. Desmosomal components as targets for immunobullous diseases.
Antibodies to these proteins may directly lead to blistering skin and mucous
membrane disorders.

36.  Disruption of extracellular domain of Dsg1
by bacterial toxin:
 Staphylococcal scalded skin syndrome
 Bullous impetigo

37. ADHERENS JUNCTIONS
 Electron dense,transmembrane structures
 Adhesion site that links Actin cytoskeletal components of two
cells
 Contribute to:
- epithelial assembly
- adhesion
- barrier formation
- cell motility
- changes in cell shape
 Transmembrane component: Cadherins, Nectin
 Plaque component : Catenin,Afadin

38.  Charaterized by two opposing membranes separated by
approximately 20 nm space and are 0.2–0.5 μm in
diameter
 Two basic adhesive units:
1. Nectin–afadin complex
2.Cadherin-catenins (α, β,p120 catenin)complex
both attach to Actin cytoskeleton.
 Cell signalling via β-catenin can activate several Wnt
pathways which implicates adherens junctions in coordinating morphogenetic movements with cell fate
determination.

39.  Associated with a variety of actin-binding molecules,
suggesting multiple dynamic interactions with the
cytoskeleton
 Spatially coordinate :
a.signalling molecules
b.polarity cues
c.serve as docking sites for vesicle release

41. CLINICAL RELEVANCE OF
ADHERENS JUNCTIONS
 Mutation in CDH3 gene, which encodes P-cadherin :-
Autosomal recessive hypotrichosis with juvenile macular
dystrophy.

42. TIGHT JUNCTIONS
 Form at the apical end of lateral membranes
 Regulate the paracellular flux of water-soluble molecules
between adjacent cells
 Transmembranous components:
1.Junctional adhesion molecules (JAM)
2.Claudins
3.Occludins
 Claudins and occludins bind to the intracellular zonula
occudens proteins ZO-1, ZO-2, ZO-3; these proteins can
also interact with actin thus providing a direct link with
the cytoskeleton.

44. CLINICAL RELEVANCE OF TIGHT
JUNCTIONS
 Key role in skin barrier integrity and maintaining cell
polarity
 Mutations in Claudin 1 – Autosomal recessive disease
with clinical features of
- diffuse ichthyosis with large scales
- hypotrichosis
- scarring alopecia
- sclerosing cholangitis.

45. GAP JUNCTIONS
 Clusters of intercellular channels, known as connexons,
that directly form connections between the cytoplasm of
adjacent keratinocytes
 Connexons - assembly of six connexin subunits within the
Golgi network that are then transported to plasma
membrane, where they associate with other connexons to
form a gap junction.

46.  Essential for
 Cell synchronization
 Differentiation
 Cell growth and
 Metabolic coordination of avascular organs, including
epidermis.
 Functions are:
1. sharing of low-molecular-mass metabolites
2. ion exchange between neighbouring cells
3. intercellular coordination
4. tissue/organ homeostasis

47. CLINICAL RELEVANCE OF GAP
JUNCTIONS
 Inherited abnormalities in genes encoding four different
connexins (Cx 26, 30, 30.3 and 31) leads to several forms
of keratoderma and/or hearing loss.

49. DERMO-EPIDERMAL JUNCTION
 The functions and homeostasis of skin critically depend on
stable organization
cohesion between epidermis and dermis
 The suprastructural entity affording pivotal mechanical stability is
the anchoring complex sequentially consists of :
1. hemidesmosomes at the basal surface of the keratinocytes
2. anchoring filaments linking the hemidesmosomes to the
basement membrane
3. anchoring fibrils connecting the basement membrane with
the underlying dermal stroma

50. MOLECULAR COMPONENTS OF EPIDERMAL
BASEMENT MEMBRANE ZONE
 Intermediate filament (IF) components
- Keratin 5
- Keratin 14
 Hemidesmosomal plaque components
- 230-kDa bullous pemphigoid antigen(BP230/BPAG1)
- Plectin

51.  Transmembrane components
- α6β4 integrin
- Type XVII collagen (180-kDa bullous pemphigoid
antigen/BPAG2)
- α3β1 integrin
- Type XIII collagen
- Syndecans 1 and 4
 Lamina lucida/lamina densa components
- Laminin 332 (laminin 5)
- Laminin 311 (laminin 6)
- Laminin 511 (laminin 10)

52.  Lamina densa components
- Type IV collagen
- Laminin 111 (laminin 1)
- Nidogen
- Perlecan
 Anchoring fibril components
- Type VII collagen

53. Fig. - The dermal–epidermal junction. , The structure of
the adhesion complex of the basement-membrane zone

54. INTERMEDIATE FILAMENTS
 Proteins which form building blocks of cytoskeletal filaments




of cells along with Actin and Tubulin.
IF proteins are expressed in a tissue and cell compartment
specific manner.
Subdivided into 5 major types Types I–IV : Cytoplasmic IFs,
Type V(lamins) : Nuclear IFs.

55.  Keratins are the largest subgroup of IF proteins .
 54 functional human keratin genes have been recognised
 Classified as
Epithelial keratins : Encoded by 37 genes
Hair keratins : Encoded by 17 genes
 Genes encoding individual keratins fall into Two families:
Type I ( basic )
Type II (acidic)

56.  Intermediate Filament proteins have a conserved central
rod domain of helical coiled-coil segments
 Keratins heterodimerize with specific pairing partners:
One Type I family
One Type II family
 Heterodimers then oligomerize into longer fibrils
 Fibrils continue to assemble untill Intermediate Filament
is 10-12 nm in diameter

57.  Keratin filaments extends from the nuclear membrane to
desmosomal plaques at the cell membrane
 Keratins enable keratinocytes to sustain mechanical and
non-mechanical stress

58. CLINICAL RELEVANCE
Disease associations with Mutation in keratin genes:
 Palmoplantar keratoderma,epidermolytic: K1,K9
 Palmoplantar keratoderma,diffuse nonepidermolytic: K1
 Palmoplantar keratoderma,focal nonepidermolytic: K16
 Epidermolysis Bullosa Simplex: K5, K14
 Epidermolytic Hyperkeratosis: K1, K10
 Ichthyosis hystrix type Curth-Macklin: K1

59. HEMIDESMOSOMES-ANCHORING
FILAMENT COMPLEX
 Electron dense attachment complexes, extend from
intracellular compartment of basal keratinocytes to lamina
lucida in upper portion of D-E BMZ.
 Intracellular component of a hemidesmosome attaches to
the keratin IF network
 Within the lamina lucida ,HD contiguous with anchoring
filaments,which are thread-like structures that traverse the
lamina lucida and tend to concentrate below the
hemidesmosomes

60.  Five components of hemidesmosomes, originally
designated as HD1–HD5
 HD2 and HD4:- 230-kDa and 180-kDa bullous
pemphigoid antigens (BPAG1 and BPAG2), respectively
 HD3 and HD5:- β4 and α6 integrin subunit polypeptides,
respectively;
 HD1 corresponds to plectin

61.  The 180-kDa BP Ag, a transmembrane collagenous
protein, also known as type XVII collagen,
 It interacts with α6β4 integrin and extends from the
intracellular compartment of basal cells to the
extracellular space
 stabilizes the association of basal keratinocytes to the
underlying basement membrane

62. CLINICAL RELEVANCE
 Mutations in the BPAG2 gene result in a relatively mild,
non-Herlitz type of junctional EB
 Mutations in the α6β4 integrin genes (ITGA6, ITGB4)
cause skin fragility associated with congenital pyloric
atresia
 Mutations in the plectin gene (PLEC1) result in skin
blistering disorder frequently associated with late-onset
muscular dystrophy

63. BASEMENT MEMBRANE
 Interface between the lower part of the epidermis and the
top layer of the dermis comprises D-E BMZ, consist of
various extracellular matrix macromolecules
 BMZ by transmission electron microscopy shows two
distinct layers with different optical densities:
1) Upper layer- Lamina lucida
2) Lower layer- Lamina densa

64.  Major biochemical components of the BMZ are type IV
collagen and a number of collagenous glycoproteins,
including laminin 322.
 Component of BMZ distributed in LL and LD
 Major Laminin in skin
Laminin 332 - α3β3γ2
Laminin 311 - α3β1γ1
Laminin 511 - α5β1γ1
 Cell binding of Laminins is mediated by Integrins –family
of cellular receptors

65.  Laminin 332 is a disulphide-bonded complex of α3, β3,
and γ2 chains which associate into a trimeric, cruciform
structure
 Complete absence of any of the three subunit polypeptides
of laminin 332, due to loss-of-function mutations in both
alleles of the corresponding gene, results in Herlitz
junctional EB

66. In the absence of laminin 332, affected
individuals develop erosions and blisters at the
level of lamina lucida, manifesting with the
Herlitz form of junctional EB

67. Type IV collagen

major component of Lamina densa
 Consist of 3 polypeptide subunits (α-chains)
 Autoantibodies against α5 and α6 chain epitopes glomerulonephritis and subepidermal blistering

68. ANCHORING FIBRILS
 Ultrastructurally recognizable, U-shaped structures,
extends from the lower part of lamina densa to upper
reticular dermis
 Type VII collagen is major component of anchoring fibrils
 Synthesized by both dermal fibroblasts and epidermal
keratinocytes
 The anchoring fibril network forms a scaffold that entraps
large numbers of dermal fibrils, securing the lamina densa
to the subjacent dermis

69. CLINICAL RELAVANCE
 In the acquired form of epidermolysis bullosa,
epidermolysis bullosa acquisita and in bullous systemic
lupus erythematosus, autoantibodies target mainly the
NC-1 domain of coliagen VII.
 Mutation causing complete absence of type VII collagen
results in severe, generalized, recessive dystrophic EB
 Missense mutations, particularly glycine substitution
mutations, can result in somewhat milder, dominantly
inherited dystrophic EB

70. Schematic representation of the gene/protein systems within the cutaneous basement
membrane zone that can harbour mutations

71. Subepidermal immunobullous disorders
Autoantibodies to molecules within the anchoring
complex of the Basement-membrane zone






Bullous pemphigoid- 230-kDa BP Ag &180-kDa BP Ag
Mucous Membrane pemphigoid- all components of BMZ
Pemphigoid gestationis- 180-kDa BP Ag & 230 kDaBPAg
Linear IgA disease - BP180/ collagen XVII
Epidermolysis bullosa acquisita- Type VII collagen
Bullous SLE - Type VII collagen