EPIDERMAL ADHESION and CLINICAL CORRELATIONS

DESMOSOMES HEMIDESMOSOMES/BMZ CONNEXINS/GAP JCTS

Rich Nichols OVERVIEW

„ 4 Main types of cellular junctions between „ 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 ‹ 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 ƒ 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 ‹ 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

‹ 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 () 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 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.