EPIDERMAL ADHESION and CLINICAL CORRELATIONS
DESMOSOMES HEMIDESMOSOMES/BMZ CONNEXINS/GAP JCTS
Rich Nichols OVERVIEW
4 Main types of cellular junctions between keratinocytes Mechanical, biochemical and signalling interactions Desmosomes—coupled with IFs Adherens junctions—coupled with actin— movement Gap junctions—clusters of connexons; connections between cytoplasm Tight junctions—barrier integrity and permeability OVERVIEW
Desmosomes Present throughout epidermis Increase in size and number as keratinocytes migrate upward Link IFs to cell membrane Function in signal transduction Assembly occurs in Ca++-dependent and phosphorylation-dependent fashion OVERVIEW
Adherens
Bind actin instead of keratin Ifs
PLAKOGLOBIN is the only protein found in both desmosomes and adherens jcts
Establishment of adherens jcts is essential for desmosome assembly OVERVIEW
Tight Jcts Mediate cell adhesion, paracellular communication Play role in epidermal differentiation, barrier function, and proliferation Barrier and fenceÆrestricts solutes, proteins and lipids to certain tissues Major proteins Claudins Occludin and Zo-1 interact with connexins OVERVIEW
Gap Jcts
Connect cytoplasm of opposing cells
More later OVERVIEW
Cell-cell interactionsÆimportant in develop and maintenance of tissue structure and function Desmosomes most prominent in tissues subject to mechanical stress Desmosomes also found in myocytes, lymph system, meninges DESMOSOMES
Intercellular adhesive junctions Anchor IF cytoskeleton network to plasma membrane Maintain tissue integrity Function in cell adhesion and transduction of intracellular signals DESMOSOMES
Abnormal desmosomal structure or disruption causes:
Cells to round
Separate (acantholysis)
Form blisters and vesicles in the epidermis
Exfoliation of several epidermal layers DESMOSOMES Inner Plaque Attachment site of cytokeratin filaments to Desmosomal proteins (Desmoplakin). IFs loop thru plaque Outer Plaque (close to plasma membrane) Site of interaction between plakoglobin, desmoplakin I and II, keratocalmin, desmoyokin, (desmogleins, and desmocollins). Also Plectin and IFAP (Int. Fil. Ass. Prot.) Extracellular or Core Transmembrane proteins (cadherins): Desmogleins 1 & 3 and Desmocollin. Core includes plasma membranes
DESMOPLAKINS I & II
I—250kd protein (plakin); completely intracellular; dumbbell shaped. The head is within the outer plaque while the tail is within the inner plaque Associated diseases Paraneoplastic pemphigus Ag: 250, 230, 210, 190, 170, 160, 130 • All members of plakin family as well as desmogleins are targeted in paraneoplastic pemphigus EM Major (Desmoplakins I and II) Carvajal Desmoplakin II—210 kDa
PLAKOGLOBIN
83kd protein associated with the cytoplasmic portion of cadherins (desmoglein and desmocollin) Plakoglobin and plakophilin are members of armadillo family of nuclear and jct proteins (also β-catenin)
DESMOSOMAL CADHERINS
Six transmembrane glycoprotiens needed for cell adhesion. Six Proteins
Desmogleins 1-3
Dsg 1 & 3 in stratified squamous epithelia
Dsg2 in all desmosome-containing tissue
Desmocollins 1-3 DESMOSOMES
Cadherins are calcium-dependent cell-cell adhesion molecules—adhesive glycoproteins (Dsg1 Dsg3 Dsc1) Classic cadherins (E-,P-,N-cadherins) are present in adherens junctions Again, the big difference:
Adherens jcts—coupled with actin cytoskeleton
Desmosomes—coupled with intermediate filament network DESMOSOMES
All cadherins have extracellular conserved AA sequences (calcium-binding) Intracellular parts are different Desmosomes always have pairs of Dsg and Dsc “Cell Adhesion Zipper theory” Adherens—quick but weak cellular adhesion Desmosomes—slow but strong cellular adhesion
DESMOGLEIN 1
Desmoglein 1 is a 160kD protein Primarily expressed in the upper dermis But present throughout epidermis Very low level in mucous membranes Disease Associations Pemphigus Foliaceus and erythematosus: Have IgG to extracellular epitope of Desmoglein 1. Pemphigus Herpetiformis Penicillamine induced blisters.
DESMOGLEINS
Abs in pemphigus possibly:
Interfere with desmoglein adherence via steric hindrance
Disruption via signal transduction Exfoliative toxin in SSSS specifically cleaves desmoglein 1
DESMOGLEIN 3
Desmoglein 3 (130kD), is expressed primarily in the lower epidermis. Cell-Cell adhesion mediated primarily by Dsg3 in Mucous Membranes Disease Associations P. vulgaris: Polyclonal IgG4 to extracellular component. P. vegetans IgA Pemphigus Intraepidermal Neutrophilic type DESMOGLEIN COMPENSATION
Abs to Dsg 1—superficial epidermis, no mucous membranes Abs to Dsg3—mucous membranes, no or limited skin blisters Abs to Dsg1 and Dsg3—skin and mucous membranesÆsplit suprabasal???
DESMOCOLLIN 1
Desmocollin 1 is associated with IgA pemphigus Subcorneal Pustular Dermatosis type. Left: How do you distinguish from other clinical entity?
QUESTION
Name a disease with a defect in plakoglobin? ANSWER
Naxos Disease
AR
Diffuse NEPPK
Wooly Hair
RVCM QUESTION
What is disease and defect of: Striate PPK, Wooly Hair and LVCM? ANSWER
Carvajal Syndrome Desmoplakin CONNEXINS/GAP JCTS
Gap Jcts Gap jcts directly connect cytoplasm of opposing cells 6 Connexins form annular hemichannel named a Connexon Max diameter of central pore in hemichannel is 2 nm Connexons cluster together and dock with connexons on opposing cells to form gap jcts Gap Jct channels can be homotypic, heterotypic, or heteromeric (see pic)
CONNEXINS/GAP JCTS
Gap Jcts essential for cell-cell communication and skin integrity Half-life of each connexin is short (hours) Thus, constant assembly and degradation Tissue distribution is distinct Particularly important in cardiovascular, GI, reproductive, and immune systems Also nerves, skin, ears, eyes CONNEXINS/GAP JCTS
Gap jcts allow passage of small molecules <1 kDa in size Aqueous channels allow passage of metabolites, ions Open/Closed channels depends on pH, voltage, Ca++ concentration, & phosphorylation Defects result in deafness, cataracts, neuropathy, and skin disease Mediates differentiation (keratinocyte) and tissue repair Defect? Defect? Defect? CONNEXINS/GAP JCTS Cx 26 mutationsÆnon-syndromic hearing impairment Ionic environment of inner ear sensory epithelia Cell death in cochlear epithelial network and sensory hair cells Charcot-Marie ToothÆCx 32 results in impaired diffusion of nutrients and signalling molecules into peripheral nerves EKVÆCx31 (GJB 3) and Cx 30.3 (GJB4) Vohwinkel’s with hearing impairmentÆCx26 Hidrotic Ectodermal DysplasiaÆCx30
BASEMENT MEMBRANE ZONE
Attachment of Keratinocytes to Basement membrane via Hemidesmosome and basement membrane proteins. BASEMENT MEMBRANE ZONE MAJOR COMPONENTS
Cytoskeleton
Inner Plaque
Outer Plaque
Lamina Lucida
Anchoring Fibrils
Dermis
ORIGIN OF BMZ
From Keratinocytes (ectodermal)
Proteins in HDs:
Plectin, BPAG1, BPAG2, integrins α6β4
IV and VII collagen
Laminins 5 and 6
Heparan Sulfate Proteoglycans (HSPG) ORIGIN OF BMZ
From Dermal Fibroblasts (mesodermal)
Nidogen (entactin)
Types IV and VII collagen Plasma membrane of basal keratinocytes, via integrins, provides localization and organizational cues CYTOSKELETON
Major components of cytoskeleton include Keratin 5 (basic) and Keratin 14 (acidic). They form heterodimers that combine into 10nm intermediate filaments that insert into the inner plaque. Associated Disease
Epidermolysis Bullosa Simplex
INNER PLAQUE
BP antigen 1 (230kDa; plakin) Main protein of inner plaque Connects plaque to cytoskeleton K5-14 via C- terminus Also connects inner plaque to outer plaque via N- terminus, which binds BP180 and β4 integrin, and ERBIN (Erb-B2 tyrosine kinase receptor) Completely intracellular Associated Disease Bullous pemphigoid Paraneoplastic pemhigus INNER PLAQUE
Other Components Plectin: 500 kDa Is an IFAP in the Plakin family Works with BPAG1 (230) to attach cytoskeleton to inner plaque Also attaches to β4 integrin, BPAG2 to connect to outer plaque (also to actin) Associated Disease EBS with muscular dystrophy
OUTER PLAQUE
Transmembrane proteins link to inner plaque and extend to the lamina lucida. Components
BP Ag 2 (180kDa) aka type XVII collagen:
Transmembrane prot. with extracellular C- terminus
Links lamina densa to anchoring filaments (BP230 and α6β4 integrin)
Associated diseases
BP, Pemphigoid Gestationis, CP, GABEB BPAG2 (180 kDa)
BP, PG, CP, LABD, GABEB
Auto-Abs target NC16A in:
BP, PG, and LABD
In CP, target is most distal carboxy terminus
Thought to increase likelihood of scar OUTER PLAQUE
α6β4-Integrin All integrins are heterodimeric transmembrane proteins, most bind actin unlike α6β4-Integrin Links cytoskeleton with laminin 5&1 in lamina lucida. β4 subunit interacts with BP230 and plectin in the inner plaque. C-Terminus binds to BP180 Associated Disease JEB-PA Ocular CP (β4)
LAMINA LUCIDA
Contains the Anchoring Filaments Major Components
Laminin 5 (epiligrin)
Uncein
LAD-1
Laminin 6-7-10 (3 above are more important) LAMINA LUCIDA
Laminin 5 Heterodimer α3β3γ2 Links α6β4-Integrin to lamina densa and type VII collagen. Binds NC1 region of type VII collagen Associated diseases Cicatricial Pemphigoid (antiepiligrin CP): IgG to α3 portion Herlitz-JEB: Point mutation causes stop codon in laminin 5, all subunits have been involved. LAMINA LUCIDA
Uncein
Related to Laminin 5, with a similar function. Associated Diseases
Recessive-JEB
Cicatricial Pemphigoid (EBA Like) LAMINA LUCIDA
LAD-1 (ladinin; LAD97): 97kD, very basic protein that holds BMZ together via ionic bonds
Cleaved ectodomain of BPAG2 (BP180) Associated Diseases
Linear IgA disease (lamina lucida type)
Chronic Bullous Disease of Childhood
Drug Induced Linear IgA, Vancomycin, Lithium and Captopril.
LAMINA DENSA
Basement membrane proper Lamina Densa links lamina lucida to the Anchoring Fibrils. Components
Type IV Collagen
Nidogen
Laminin 1 LAMINA DENSA
Type IV Collagen: Provides the meshwork (“chickenwire”) for attachment of other BMZ proteinS Forms a triple helix Looks like a procollagen with globular heads “Hockey stick” 4 blades overlapÆspiderÆmeshwork Possibly important biological activities: antitumor, antiangiogenesis
LAMINA DENSA
Nidogen (entactin): Binds to Laminin 1,6,7, connecting laminin to type IV Collagen Laminin 1 (α1β1γ1): linked to Nidogen via α1 segment Heparan Sulfate Proteoglycans (HSPGs): Central core lined with GAGs in a bottle-brush configuration Interactions with type IV collagen Contribute to overall negative charge of BMs ANCHORING FIBRILS
Anchoring Fibrils connect the Lamina Densa to the Dermis. Type VII Collagen is the main component. The NC-1 domain binds to type IV collagen and Laminin 5 Associated Diseases
EBA, Bullous SLE, Dystrophic-EB
IgG from most EBA pts bound to NC1 domain DERMIS
The Dermis contains types I and III Collagen and Elastin, which intertwine with the Anchoring Fibrils as the final anchor. BMZ REMODELING
BMZ is constantly being remodeled Penetrated by Langerhans cells, lymphs Metalloproteases play role in alterations
REFERENCES
Bolognia, Jorizzo, Rapini Dermatology 2003 Fitzpatrick’s Dermatology in General Medicine 6th ed. Rook’s Textbook of Dermatology 7th ed. Saez JC. Berthoud VM. Branes MC. Martinez AD. Beyer EC. Plasma membrane channels formed by connexins: their regulation and functions. [Review] [682 refs] [Journal Article. Review] Physiological Reviews. 83(4):1359-400, 2003 diseases. [Review] [74 refs] [Journal Article. Review. Review, Tutorial] Current Opinion in Cell Biology. 8(5):647- 56, 1996 Oct. Amagai M. Desmoglein as a target in autoimmunity and infection. [Review] [61 refs] [Journal Article. Review. Review, Tutorial] Journal of the American Academy of Dermatology. 48(2):244-52, 2003 Feb. Kowalczyk AP. Bornslaeger EA. Norvell SM. Palka HL. Green KJ. Desmosomes: intercellular adhesive junctions specialized for attachment of intermediate filaments. [Review] [373 refs] [Journal Article. Review. Review, Academic] International Review of Cytology. 185:237-302, 1999. Burgeson RE. Christiano AM. The dermal-epidermal junction. [Review] [49 refs] [Journal Article. Review. Review, Tutorial] Current Opinion in Cell Biology. 9(5):651-8, 1997 Oct. Lin MS. Mascaro JM Jr. Liu Z. Espana A. Diaz LA. The desmosome and hemidesmosome in cutaneous autoimmunity. [Review] [55 refs] [Journal Article. Review. Review, Tutorial] Clinical & Experimental Immunology. 107 Suppl 1:9-15, 1997 Jan.