Nomenclature of the desmosomal cadherins

Recombinant desmoglein 3 has the necessary epitopes to adsorb and induce blister-causing antibodies

The development of an animal model for studying the pathogenesis of pemphigus vulgaris (PV) has been hampered by the unavailability of the purified full-length autoantigen desmoglein 3 (Dsg 3).Therefore, we expressed Dsg 3 using a baculovirus expressed system. The expressed protein was identified as Dgs 3 by its reactivity with a pan-cadherin anti-serum, an anti-serum to a Dsg 3 synthetic peptide, or patient serum, and by amino-terminal sequencing. Carbohydrate analysis showed that recombinant Dsg 3 was glycosylated. While a majority of the recombinant protein was cell associated, by immunoprecipitation, some Dsg 3 was demonstrated in the medium. The Dgs 3 could adsorb out blister-causing antibodies from patient sera. Rabbit anti- Dsg 3 antibodies induced by the recombinant Dsg 3 showed specific binding to intercellular spaces of monkeys esophagus by indirect immunofluorescence. Moreover, these antibodies induced PV-like blisters in neonatal mice and weakly bound perilesional epidermis. Availability of large quantities of relatively pure Dsg 3 should now facilitate studies aimed at understanding Dsg 3 structure and pathogenesis of PV, with implications for developing specific immunotherapies.

Overexpression of occludin, a tight junction-associated integral membrane protein, induces the formation of intracellular multilamellar bodies bearing tight junction-like structures

Occludin is an integral membrane protein localizing at tight junctions with four transmembrane domains. When chicken occludin was overexpressed in insect cells by recombinant baculovirus infection, peculiar multilamellar structures accumulated in the cytoplasm. Partial isolation of these structures indicated that the introduced chicken occludin was highly enriched in these structures. Thin section electron microscopy revealed that each lamella was transformed from intracellular membranous cisternae whose luminal space was completely collapsed, and that in each lamella, outer leaflets of opposing membranes appeared to be fused with no gaps, like tight junctions. Furthermore, in the freeze-fracture replicas of these multilamellar structures, short tight junction-like intramembranous particle strands were occasionally observed, which were specifically labeled by anti-occludin mAb. These observations favor the idea that occludin plays a key role in the formation of tight junctions.

Mechanisms identified in the transcriptional control of epithelial gene expression

Epithelium-specific gene expression is fundamental in both embryogenesis and the maintenance of adult tissues, and impairment of epithelial characteristics contributes to diseases such as cancer. We have here analyzed the 5'-region of the epithelial (E-) cadherin gene in order to understand mechanisms of epithelium-specific transcription and loss of expression during epithelial-mesenchymal transitions. The regulatory region of the mouse epithelial cadherin gene is composed of a promoter (from position -94 to the transcription start site) and a 150-base pair enhancer located in the first intron. The 5'-promoter consists of positive regulatory elements (a CCAAT-box and two AP-2 binding sites in a GC-rich region) and the palindromic element E-Pal that activates and represses transcription in epithelial and mesenchymal cells, respectively. The enhancer of the first intron stimulates the activity of heterologous promoters exclusively in epithelial cells. This epithelium-specific enhancer consists of three elements (E I to E III; E II and E III bind AP-2) that are necessary and sufficient for activity. We thus propose two regulatory mechanisms by which epithelial specificity of epithelial cadherin expression is determined: suppression of promoter activity in mesenchymal cells by E-Pal and enhancement of activity in epithelial cells by both E-Pal and the epithelium-specific enhancer.

Pemphigus herpetiformis is a rare clinical expression of nonendemic pemphigus foliaceus, fogo selvagem, and pemphigus vulgaris. Cooperative Group on Fogo Selvagem Research

BACKGROUND

Pemphigus herpetiformis is a rare and atypical variant of pemphigus that resembles dermatitis herpetiformis. Most patients show antiepidermal autoantibodies that stain the epidermal intercellular spaces by immunofluorescence, similar to pemphigus autoantibodies, and lack the immunopathologic features of dermatitis herpetiformis.

OBJECTIVE

The study was aimed at characterizing the specificity of the antiepidermal autoantibodies in seven patients with pemphigus herpetiformis.

METHODS

The antiepidermal autoantibodies were characterized by immunofluorescence, immunoblotting, and immunoprecipitation studies in seven patients who fulfilled the clinical, histologic, and immunofluorescence diagnostic criteria for pemphigus herpetiformis.

RESULTS

Five patients with features of pemphigus herpetiformis either had classic pemphigus foliaceus, or their disease evolved into classic pemphigus foliaceus. One of these patients had fogo selvagem. Two of the seven patients showed features of or had disease that evolved into pemphigus vulgaris. The antiepidermal autoantibodies present in all seven patients recognized desmoglein 1.

CONCLUSION

Pemphigus herpetiformis is a rare clinical and histologic expression of nonendemic pemphigus foliaceus, fogo selvagem, and pemphigus vulgaris.

Cadherin cell adhesion molecules in differentiation and embryogenesis

The cadherin gene superfamily of calcium-dependent cell-cell adhesion molecules contains more than 40 members. We summarize functions attributed to these proteins, especially their roles in cellular differentiation and embryogenesis. We also describe hierarchies of protein-protein interactions between cadherins and cadherin-associated proteins (catenins). Several signal transduction pathways converge on, and diverge from, the cadherin/catenin complex to regulate its function; we speculate on roles of these signaling processes for cell structure and function. This review provides a framework for interpretation of developmental functions of cadherin cell adhesion molecules.

Continual assembly of half-desmosomal structures in the absence of cell contacts and their frustrated endocytosis: a coordinated Sisyphus cycle

It is widely assumed that the coordinate assembly of desmosomal cadherins and plaque proteins into desmosome-typical plaque-coated membrane domains, capable of anchoring intermediate-sized filaments (IF), requires cell-to-cell contacts and a critical extracellular Ca2+ concentration. To test this hypothesis we studied several cell lines grown for years in media with less than 0.1 mM Ca2+ to steady-state low Ca2+ medium (LCM) conditions, particularly the human keratinocyte line HaCaT devoid of any junctional cell contact (HaCaT-L cells). Using immunolocalization and vesicle fractionation techniques, we found that the transmembrane glycoprotein, desmoglein (Dsg), colocalized with the plaque proteins, desmoplakin and plakoglobin. The sites of coassembly of desmosomal molecules in HaCaT-L cells as well as in HaCaT cells directly brought into LCM were identified as asymmetric plaque-coated plasma membrane domains (half-desmosomes) or as special plaque-associated cytoplasmic vesicles, most of which had formed endocytotically. The surface exposure of Dsg in these half-desmosomes was demonstrated by the binding, in vivo, of antibodies specific for an extracellular Dsg segment which also could cross-bridge them into symmetric quasi-desmosomes. Otherwise, these half-desmosomes were shown in LCM to be taken up endocytotically. Half-desmosomal assemblies were also seen in uncoupled cells in normal Ca2+ medium. We conclude that, in the absence of intercellular contacts, assembly of desmosomal proteins at the cell surface takes place, resulting in transient half-desmosomes which then, in LCM and without a stable partner connection to the adjacent cell, can be endocytotically resumed. This frustrated cycle of synthesis and assembly maintains an ensemble of molecules characteristic of epithelial differentiation and the potential to form desmosomes, even when the final junctional structure cannot be formed. We propose that these half-desmosomal structures are general cell structures of epithelial and other desmosome-forming cells.

Demonstration of antibodies to bovine desmocollin isoforms in certain pemphigus sera

We have shown previously that IgG antibodies in certain pemphigus sera, particularly endemic Brazilian pemphigus foliaceus (BPF) sera, react with bovine desmocollins (Dsc), which are transmembranous glycoproteins of desmosome junctions. Desmocollins occur as three different isoforms (Dsc 1, 2 and 3), all of which are represented in the epidermis. In this study, we examined sera of various pemphigus types by immunoblotting purified bovine desmosomes and bovine Dsc 1, 2 and 3 fusion proteins, expressed in pGEX expression vectors. Six of 15 (40.0%) BPF sera, two of 18 (11.1%) non-endemic pemphigus foliaceus sera, eight of 39 (20.5%) pemphigus vulgaris (PV) sera, and two of 11 (18.2%) normal sera, showed reactivity with Dsc from desmosomes. Experiments with fusion proteins showed that no Dsc isoform was specifically recognized by sera of any individual pemphigus type. Our results indicate that the pathogenesis of pemphigus might be more complex than previously believed.

Pharmacologic evidence for involvement of phospholipase C in pemphigus IgG-induced inositol 1,4,5-trisphosphate generation, intracellular calcium increase, and plasminogen activator secretion in DJM-1 cells, a squamous cell carcinoma line

The precise mechanism for acantholysis after pemphigus IgG binds to the cell surface is as yet unknown, although involvement of proteinases such as plasminogen activator (PA) has been suggested. We previously reported that pemphigus IgG, but not normal nor bullous pemphigoid IgGs, caused a transient increase in intracellular calcium ([Ca++]i) and inositol 1,4,5-trisphosphate (IP3) concentration in cultured DJM-1 cells (a squamous cell carcinoma line). To clarify whether phospholipase C is involved in this process after the antibody binds to the cell surface, we examined the effects of a specific phospholipase C inhibitor (U73122) on the pemphigus IgG-induced increase in [Ca++]i, IP3, PA secretion, and cell-cell detachment in DJM-1 cells. [Ca+2]i and IP3 contents were determined with or without 30-min pre-incubation with U73122 or an inactive analogue (U73343) with fura-2 acetoxymethylester and a specific IP3 binding protein, respectively. PA activity in the culture medium was measured after various incubation periods with pemphigus IgG by two-step amidolytic assay. The detachment of cell-cell contacts was examined by detecting the retraction of keratin filament bundle from cell-cell contact points to the perinuclear region by immunofluorescence microscopy using anti-keratin antibody. Pemphigus IgG immediately increased [Ca++]i and IP3 content. PA activity in the culture medium has also been increased at 24 h after pemphigus IgG was added in association with cell-cell detachment. However, pre-incubation with U73122 (1-10 microM), but not with U73343 (10 microM), dramatically reduced the pemphigus IgG-induced increases in [Ca++]i, IP3, and PA activity and inhibited the pemphigus IgG-induced cell-cell detachment. Both U73122 and U73343 caused no effects on cell viability and IgG binding to the cell surface. These results suggest that phospholipase C plays an important role in transmembrane signaling leading to cell-cell detachment exerted by pemphigus IgG binding to the cell surface.

The desmocollins of human foreskin epidermis: identification and chromosomal assignment of a third gene and expression patterns of the three isoforms

A third human desmocollin, designated DSC3, was identified in foreskin epidermis by reverse transcriptase-polymerase chain reaction (PCR) using degenerate desmocollin primers. cDNA clones covering the entire coding sequence of the longer DSC3 splice variant were isolated and sequenced. Sequence comparisons indicated that this new desmocollin showed greater homology (67% amino acid identity) with the original human desmocollin (now designated DSC2) than with DSC1 (52% amino acid identity) although it had a unique potential cell adhesion recognition site (YAS). DSC3 was assigned to chromosome 18 by PCR analysis of rodent-human somatic cell hybrids, where it appears to be closely linked to all the other desmosomal cadherin genes. The expression of the three human desmocollins was examined in foreskin epidermis by in situ hybridization with 3'-untranslated riboprobes and by immunofluorescence with isoform-specific anti-peptide antibodies. DSC1 was present in the upper spinous/granular layers but not in the basal/lower spinous layers of the tissue. DSC2 and DSC3 were present in most of the living layers of the epidermis. DSC1 was not detected in any of the nonkeratinizing human epithelia examined (buccal mucosa, cervix, esophagus), indicating that it is specific for the keratinizing epithelium of the epidermis. However, all these internal epithelia expressed DSC2 and DSC3, and both were present in most of the living layers of the tissues including the basal layers.

Maintenance of cell-type-specific cytoskeletal character in epithelial cells out of epithelial context: cytokeratins and other cytoskeletal proteins in the rests of Malassez of the periodontal ligament

We have determined the patterns of synthesis of cytokeratins and other epithelial marker proteins in the "rests of Malassez" of the periodontium of rabbits and humans, by immunofluorescence microscopy of cryosections prepared from fixed and decalcified rabbit teeth with attached ligament or from manually isolated human periodontal ligaments. Proteins of the major cell structures characterizing epithelial differentiation are present in Malassez cells: a complex set of cytokeratins as well as desmosomal, hemidesmosomal and basal lamina proteins. In addition, we have shown these cytoskeletal and extracellular matrix structures by electron microscopy. The cytokeratin complement of Malassez cells was found to be highly complex, as 8 of the total of 20 known epithelial cytokeratins were detected (nos. 5, 7, 8, 14, 15, 17, 18, 19). This pattern, together with the presence of the desmosomal cadherins Dsg2 and Dsc2 and the cytoplasmic desmosome plaque-associated protein plakophilin 1, indicates that the cells of the rests of Malassez are derived from the basal cell layer of a stratified squamous epithelium rather than from simple epithelial or neuroendocrine epithelial cells. Our observations show that Malassez cells retain the major characteristics of epithelial cells throughout their differentiation from the root sheath epithelium into the rests of Malassez, even though the surface location and the polar tissue architecture that typify epithelial are lost during this process. From this study we further conclude that the specific cytoskeletal complement of the Malassez cells represents an intrinsic gene expression program that neither depends on nor causes the formation of a stratified epithelium. We also compare the specific cytoskeletal features of Malassez cells with those of other persisting epithelial residues and discuss the potential value of these findings in relation to the histogenesis and diagnostic classification of dental and periodontal cysts and tumors.

The epidermolytic (exfoliative) toxins of Staphylococcus aureus

Two epidermolytic toxins, produced by different strains of Staphylococcus aureus, split human skin at a site in the upper epidermis. Clinical effects are most common in infants, but adults are susceptible. Epidermolysis may also be observed in the mouse, in vivo and in vitro, and in a few other mammals. Recent in vitro experiments have demonstrated an inhibition by chelators and point to metal-ion, possibly Ca2+, involvement. The epidermolysis effect is insensitive to a wide range of other metabolic inhibitors. The toxin amino acid sequences are similar to that of staphylococcal proteinase, and new experiments by chemical modification and site-directed mutagenesis have shown that toxicity depends on 'active serine' residues of a catalytic triad similar to that found in serine proteases. Furthermore the toxins possess esterolytic activity, also dependent on the 'active serine' sites. However, the toxins have low or undetectable activity towards a range of peptide or protein substrates. In histological and related studies, the toxins bound selectively to an intracellular skin protein, profilaggrin, but there was no evidence that the toxin can enter intact epidermal cells. Therefore, although the circumstantial evidence that the toxins act by proteolysis is convincing, a specific skin proteolytic substrate for the toxin has not been identified.

Differences in the expression of pemphigus antigens during epidermal differentiation

Epidermal desmogleins with molecular weights of 130/140 kDa (Dsg3 or PVA) and 150/160 kDa (Dsg1 or DGI) are recognized by autoantibodies from patients with pemphigus vulgaris (PV) and pemphigus foliaceus (PF), respectively. In order to understand the histogenesis of both types of pemphigus, we studied the expression patterns of Dsg1 and Dsg3 during stratification of cultured keratinocytes. Monolayers of cultured normal human keratinocytes demonstrated uniform intercellular staining with PV sera. The staining pattern was distinct from the focal staining with PF sera observed only in the stratified areas. Both Dsg1 and Dsg3 proteins and their mRNA were expressed by the monolayers, whereas no production of Dsg2 (HDGC) mRNA was found. The relative ratio of Dsg3 to the total desmogleins, as determined by density on immunoblotting, decreased as the cultured keratinocytes stratified. In the completely stratified keratinocytes cultured on collagen membrane, Dsg1 became predominant, with subsequent reduction of PV antigen expression. The relative decrease of Dsg3 (PVA) during epidermal differentiation might be responsible for the induction of suprabasal acantholysis in PV.

Management of the immunobullous disorders. II. Pemphigus

In the second of our reviews on the management of the immunobullous disorders, we review the therapy of pemphigus disorders, including pemphigus vulgaris, pemphigus vegetans, pemphigus foliaceus, pemphigus erythematosus, pemphigus herpetiformis, drug-induced pemphigus, IgA pemphigus and paraneoplastic pemphigus.

Contactus adherens, a special type of plaque-bearing adhering junction containing M-cadherin, in the granule cell layer of the cerebellar glomerulus

In the glomeruli of the granule cell layer of mammalian cerebellum, neuronal extensions are interconnected by numerous small, nearly isodiametric (diameters up to 0.1 micron), junctions previously classified as puncta adherentia related to the vinculin-containing, actin microfilament-anchoring junctions of the zonula adherens of epithelial and certain other cells. Using immunofluorescence and immunoelectron microscopy, we have found, however, that these junctions are negative for E- and VE-cadherin, for desmosomal cadherins, and also for vinculin, alpha-actinin, and desmoplakin, but they do contain, in addition to the protein plakoglobin common to all forms of adhering junctions, the plaque proteins alpha- and beta-catenin and the transmembrane glycoprotein M-cadherin previously found as a spread--i.e., not junction bound--plasma membrane protein in certain fetal and regenerating muscle cells and in satellite cells of adult skeletal muscle. We conclude that these M-cadherin-containing junctions of the granule cell layer represent a special type of adhering junction, for which we propose the term contactus adherens (from the Latin contactus, for touch, site of bordering upon, also influence), and we discuss the differences between the various adhering junctions on the basis of their molecular constituents.

The human E48 antigen, highly homologous to the murine Ly-6 antigen ThB, is a GPI-anchored molecule apparently involved in keratinocyte cell-cell adhesion

The E48 antigen, a putative human homologue of the 20-kD protein present in desmosomal preparations of bovine muzzle, and formerly called desmoglein III (dg4), is a promising target antigen for antibody-based therapy of squamous cell carcinoma in man. To anticipate the effect of high antibody dose treatment, and to evaluate the possible biological involvement of the antigen in carcinogenesis, we set out to molecularly characterize the antigen. A cDNA clone encoding the E48 antigen was isolated by expression cloning in COS cells. Sequence analysis revealed that the clone contained an open reading frame of 128 amino acids, encoding a core protein of 13,286 kD. Database searching showed that the E48 antigen has a high level of sequence similarity with the mouse ThB antigen, a member of the Ly-6 antigen family. Phosphatidylinositol-specific (PI-specific) phospholipase-C treatment indicated that the E48 antigen is glycosylphosphatidylinositol-anchored (GPI-anchored) to the plasma membrane. The gene encoding the E48 antigen is a single copy gene, located on human chromosome 8 in the 8q24-qter region. The expression of the gene is confined to keratinocytes and squamous tumor cells. The putative mouse homologue, the ThB antigen, originally identified as an antigen on cells of the lymphocyte lineage, was shown to be highly expressed in squamous mouse epithelia. Moreover, the ThB expression level is in keratinocytes, in contrast to that in lymphocytes, not mouse strain related. Transfection of mouse SV40-polyoma transformed mouse NIH/3T3 cells with the E48 cDNA confirmed that the antigen is likely to be involved in cell-cell adhesion.

Antigen-specific immunoadsorption of pathogenic autoantibodies in pemphigus foliaceus

Patients with the autoimmune blistering disease pemphigus foliaceus (PF) have circulating autoantibodies directed against the desmosomal cadherin desmoglein 1 (Dsg1). Based on the fact that purified IgG fractions from PF patients induce loss of cell adhesion in organ culture and in a neonatal mouse model, it has been proposed that these anti-Dsg1 antibodies play a pathogenic role in blister formation. To directly address whether antibodies in PF sera specific for the Dsg1 extracellular domain are indeed pathogenic in the disease, PFIg, a chimeric protein containing the entire extracellular domain of human Dsg1 and the constant region of human IgG1, was produced by baculovirus expression. Incubation of PF patients' sera with the PFIg baculoprotein removed the immunoreactivity of autoantibodies against keratinocyte cell surfaces in all 20 PF and eight Brazilian PF patients' sera tested. This adsorption was conformation dependent, because PFIg protein denatured by low pH or heat was no longer able to adsorb the immunoreactivity of PF sera. Furthermore, the incubation with the PFIg baculoprotein eliminated the pathogenic activity of PF patients' sera and prevented gross blister formation in a neonatal mouse model of pemphigus. Anti-Dsg1 antibodies eluted from the PFIg protein column were pathogenic as they resulted in the appearance of gross blisters in neonatal mice with typical histologic findings of PF. These observations indicate that the extracellular domain of Dsg1 expressed by baculovirus is capable of specifically immunoadsorbing pathogenic autoantibodies from PF patients' sera and provide direct evidence that the anti-Dsg1 autoantibodies in PF sera are indeed pathogenic. The availability of this Dsg1 recombinant protein may facilitate the development of antigen-specific plasmapheresis as a novel therapeutic strategy in pemphigus.

Characterisation of a desmocollin isoform (bovine DSC3) exclusively expressed in lower layers of stratified epithelia

Desmocollins are cadherin-like glycoproteins involved in cell adhesion and plaque formation in desmosome junctions. Three distinct isoforms, the products of different genes, have been found in bovine tissues. We have reported previously that one of these, DSC3, is expressed only in basal and lower suprabasal layers of stratified epithelia. Using RT-PCR we have now obtained the complete cDNA coding sequence of mature bovine DSC3. It has alternatively spliced ‘a’ and ‘b’ forms found in other desmocollins but is unique in having a 43 instead of a 46 base pair exon. We have characterised a monoclonal antibody, 07–4G, which is specific for the Dsc3 protein, recognising an epitope in the extracellular domain. Immunofluorescent staining with 07–4G confirms that this isoform is found only in stratified epithelia, being strongly expressed in the basal cell layers of these tissues. The intensity of expression fades gradually in the suprabasal layers and disappears completely below the upper limit of desmosome expression. These results suggest that Dsc3 plays an important role in cell epithelial differentiation.

Desmoyokin/AHNAK protein localizes to the non-desmosomal keratinocyte cell surface of human epidermis

Desmoyokin, a high-molecular-weight protein of 680 kD with a 170-nm-long dumbbell shape, was originally thought to be localized to the desmosomal attachment plaque and to work as a kind of stabilizer of desmosomes. Recently, desmoyokin was shown to be widely detected in many types of cells that do not possess desmosomes. The purpose of the present study was to elucidate the precise localization and possible function of desmoyokin in human epidermis. In 0.2-micron ultrathin cryosections of human skin for immunofluorescence, anti-desmoyokin antibody showed a ladder-like staining pattern along the cell surface, whereas anti-desmocollin and anti-desmoplakin antibodies as controls showed a discontinuous dotted staining pattern, indicating their distinct localization. Post-embedding immunoelectron microscopy with cryofixation and cryosubstitution revealed that desmoyokin was localized mainly along the non-desmosomal and non-hemidesmosomal plasma membrane, but not to the desmosomes and hemidesmosomes themselves. This localization was further confirmed by double-labeling immunoelectron microscopy with antibodies against desmocollin, desmoplakin, or bullous pemphigoid antigen. Results indicate that desmoyokin was not localized to the desmosomes themselves as previously considered. Desmoyokin was localized to the non-desmosomal and non-hemidesmosomal epidermal keratinocyte cell surface as a plasma membrane-associated protein, and might play a role in cell adhesion that is not directly associated with desmosomes or hemidesmosomes.

Endemic pemphigus foliaceus (fogo selvagem) in native Americans from Brazil

BACKGROUND

Fogo selvagem (FS) is an autoimmune disease that is endemic in certain regions of Brazil and appears to be precipitated by an environmental factor.

OBJECTIVE

Our purpose was to confirm the occurrence and prevalence of FS in a population of Xavante Indians living in an endemic region of central Brazil.

METHODS

Clinical, anthropologic, and immunologic studies were carried out in patients and in normal inhabitants of the Pimentel Barbosa Indian Reservation, Mato Grosso, Brazil.

RESULTS

FS was identified and confirmed in 10 patients from a patient pool of 295 with various skin diseases. The Xavante settlement has a total population of 746. Anti-desmoglein 1 autoantibodies were detected in all patients with FS and were absent from more than 300 serum samples collected from randomly selected unaffected persons.

CONCLUSION

FS is strongly linked to outdoor activities and is largely restricted to immunogenetically predisposed persons. FS appears to have been endemic in certain regions of South America for several centuries.

Immunolocalization of desmoglein and intermediate filaments in human oral squamous cell carcinomas

BACKGROUND

Information is limited as to how to predict the malignant behavior of the oral squamous cell carcinomas. The invasive and metastatic phenotype of the carcinoma cells may be related to changes in the expression of desmosomal and cytoskeletal proteins.

METHODS

To investigate the expression of desmoglein, cytokeratins, and vimentin, 22 biopsy specimens of oral squamous cell carcinomas were examined by immunohistochemistry. The data were analyzed by morphometry with reference to the cell differentiation, mode of invasion, and cervical lymph node metastasis.

RESULTS

The expression of desmoglein, a major desmosomal glycoprotein, was remarkably reduced in the poorly differentiated, highly invasive, and metastatic carcinomas. Although the immunohistochemical expression of cytokeratins in the carcinoma cells was a good marker for the differentiation status of the carcinomas, the level of expression demonstrated no correlation with tumor invasiveness or lymph node metastasis. On the other hand, the vimentin expression was inversely correlated to the differentiation and mode of invasion, and carcinomas in the metastatic group had significantly higher levels of vimentin expression than the nonmetastatic group.

CONCLUSION

The results suggest that immunohistochemical examination of desmoglein and vimentin in oral squamous cell carcinomas is valuable in evaluating the malignant behavior of tumors.

A case of pemphigus vulgaris showing reactivity with pemphigus antigens (Dsg1 and Dsg3) and desmocollins

Both pemphigus vulgaris antigen (PVA; Dsg3) and pemphigus foliaceus antigen (PFA; Dsg1) are members of the desmoglein subfamily of the cadherin supergene family. Another desmosomal cadherin, desmocollin, is occasionally recognized by certain pemphigus sera. We present a 38-year-old Japanese male who showed clinically and histopathologically typical features of pemphigus vulgaris, whose sera reacted with all PVA, PFA, and desmocollins using immunoblotting of both human epidermis and bovine snout epidermis. Studies using domain-specific fusion proteins of PFA and PVA suggested that this patient's serum reacted with the intracellular domain of PFA and the extracellular domain of PVA, the latter of which seems to be responsible for initiating the skin lesion. The patient's serum showed reactivity with human desmocollin and was shown to react with bovine Dsc2 fusion protein, further suggesting the significance of anti-desmocollin autoantibodies in pemphigus. These results indicate that certain pemphigus cases may produce antibodies against multiple antigen molecules, although the complex mechanism of the production of autoantibodies remains to be elucidated.

A simple epithelial cell line (MDCK) shows heterogeneity of desmoglein isoforms, one resembling pemphigus vulgaris antigen

The epidermal blistering disease, pemphigus vulgaris (PV), is caused by circulating autoantibodies that react with a desmosomal glycoprotein desmoglein (Dsg3). This antigen is expressed only in stratified epithelial tissues. Here we show that the simple epithelial canine kidney cell line, MDCK, expresses at least two desmoglein isoforms recognised by different monoclonal antibodies. One of these isoforms is a 130 × 10(3) M(r) polypeptide that is recognised by both PV autoantisera and a monoclonal antibody reactive with a cytoplasmic domain of human Dsg3. Antibodies in PV sera bind to the surface of MDCK cells but not cause loss of intercellular adhesion. This is the first demonstration of the expression of a polypeptide related to human PV antigen by a simple epithelial cell type.

Pemphigus foliaceus and pemphigus vulgaris autoantibodies react with the extracellular domain of desmoglein-1

Pemphigus foliaceus is associated with an autoimmune response against desmoglein-1; however, the fine specificity of these autoantibodies and the role that they play in pathogenesis have not yet been elucidated. In an attempt to develop a system to facilitate the detection and characterization of this antigen/antibody system, recombinant human desmoglein-1 was expressed in COS-1 cells, a mammalian epithelial cell line. The desmoglein-1 transgene product was shown to be expressed on the surface of the COS-1 cells in the appropriate transmembrane orientation. All pemphigus foliaceus sera (endemic form, n = 24; nonendemic form, n = 7) reacted strongly with nonpermeabilized desmoglein-1-transfected cells, exhibiting a punctate cell-surface staining pattern. This reactivity against the desmoglein-1 ectodomain was predominantly an IgG4-restricted response and was calcium dependent. Ten of 18 pemphigus vulgaris sera also reacted with the extra-cellular domain of recombinant desmoglein-1. Use of this eukaryotic expression system should greatly facilitate further characterization of the anti-desmoglein-1 autoimmune response associated with pemphigus foliaceus and pemphigus vulgaris and may aid in determining its pathogenic relevance.

Regulation of desmocollin transcription in mouse preimplantation embryos

The molecular mechanisms regulating the biogenesis of the first desmosomes to form during mouse embryogenesis have been studied. A sensitive modification of a reverse transcriptase-cDNA amplification procedure has been used to detect transcripts of the desmosomal adhesive cadherin, desmocollin. Sequencing of cDNA amplification products confirmed that two splice variants, a and b, of the DSC2 gene are transcribed coordinately. Transcripts were identified in unfertilized eggs and cumulus cells and in cleavage stages up to the early 8-cell stage, were never detected in compact 8-cell embryos, but were evident again either from the 16-cell morula or very early blastocyst (approx 32-cells) stages onwards. These two phases of transcript detection indicate DSC2 is encoded by maternal and embryonic genomes. Previously, we have shown that desmocollin protein synthesis is undetectable in eggs and cleavage stages but initiates at the early blastocyst stage when desmocollin localises at, and appears to regulate assembly of, nascent desmosomes that form in the trophectoderm but not in the inner cell mass (Fleming, T. P., Garrod, D. R. and Elsmore, A. J. (1991), Development 112, 527–539). Maternal DSC2 mRNA is therefore not translated and presumably is inherited by blastomeres before complete degradation. Our results suggest, however, that initiation of embryonic DSC2 transcription regulates desmocollin protein expression and thereby desmosome formation. Moreover, data from blastocyst single cell analyses suggest that embryonic DSC2 transcription is specific to the trophectoderm lineage. Inhibition of E-cadherin-mediated cell-cell adhesion did not influence the timing of DSC2 embryonic transcription and protein expression. However, isolation and culture of inner cell masses induced an increase in the amount of DSC2 mRNA and protein detected. Taken together, these results suggest that the presence of a contact-free cell surface activates DSC2 transcription in the mouse early embryo.

Modulation of epidermal differentiation by epiligrin and integrin alpha 3 beta 1

We previously reported that integrin alpha 3 beta 1 mediates epidermal intercellular adhesion as well as cell-substrate adhesion. P1B5, an anti-alpha 3 beta 1 specific monoclonal antibody, is a potent in vitro trigger of epidermal cell-cell adhesion and an inhibitor of cell-substrate adhesion. We now show that P1B5 specifically induces the intercellular localization of integrins alpha 2 beta 1 and alpha 3 beta 1, consistent with its role in inducing intercellular adhesion via these two integrins. P1F2, another anti-alpha 3 beta 1 antibody, does not induce either intercellular adhesion or intercellular accumulation of alpha 3 beta 1 and alpha 2 beta 1. Growth of epidermal cells in high calcium, known to induce epidermal differentiation, also induces intercellular accumulation of alpha 3 beta 1 and alpha 2 beta 1 and increased cell-cell adhesion. We therefore asked whether P1B5 treatment induces epidermal differentiation. P1B5 treatment induces changes consistent with epidermal differentiation, including increased involucrin expression, stratification, and production of squames. P1F2 treatment has none of these effects. In vivo, epidermal basal cells are in close contact with the epithelial basement membrane component epiligrin. Growth of keratinocytes on purified epiligrin but not other matrix components specifically reduces involucrin expression by P1B5-treated keratinocytes. These results suggest that integrin alpha 3 beta 1 has a unique role in epidermal differentiation, that the epitope recognized by P1B5 is involved in triggering this differentiation, and that keratinocyte adhesion to epiligrin inhibits alpha 3 beta 1-mediated differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Atypical pemphigus associated with monoclonal IgA gammopathy

We describe a 60-year-old woman with atypical pemphigus and IgA-lambda monoclonal gammopathy. Histopathologic study of vesiculopustular lesions showed intraepidermal acantholytic and neutrophilic blisters. Direct immunofluorescence revealed intercellular IgG deposition with concurrent deposits of IgA and C3. Indirect immunofluorescence and immunoblotting studies revealed that the patient had circulating IgG anti-intercellular antibodies that recognized the 150 kd desmoglein (pemphigus foliaceus antigen) in bovine desmosome preparation. Immunoblot studies with human epidermal extract showed that the IgG of this patient exclusively reacted with the 140 kd protein (between the 150 kd human desmoglein and the 130 kd human pemphigus vulgaris antigen), the nature of which is currently unknown. The patient also had IgA anti-intercellular autoantibodies, which reacted with the desmoglein in the bovine desmosome sample but did not show any reactivity in human epidermal extract.

Tandem arrangement of the closely linked desmoglein genes on human chromosome 18

The desmogleins, together with the desmocollins, both members of the cadherin superfamily, are the adhesive proteins of the desmosome type of cell junction, characteristically found in epithelial cells. Three different human desmoglein isoforms are encoded by separate genes (DSG1, DSG2, and DSG3) located on chromosome 18q12.1. DSG2 has been shown to be the most widely expressed in all desmosome-containing tissues, whereas DSG1 and DSG3 are expressed only in certain tissues, mostly stratified squamous epithelia. The desmoglein isoforms are expressed in a stratification-related manner in human epidermis, DSG1 being suprabasally expressed and DSG3 at a lower level, while DSG2 expression is weak and basal. Yeast artificial chromosome clones carrying all three known human desmoglein genes have now been isolated. The smallest clone containing all three DSG genes was 275 kb, and the three desmoglein genes were clustered within a region of less than 150 kb. From the types of clone obtained and from restriction enzyme analysis the order of the DSG genes and their orientation was deduced to be 5'-DSG1-DSG3-DSG2-3'. There thus appears to be some correspondence between the order of DSG genes and their expression within tissues, raising the intriguing possibility that the organization of the desmoglein gene cluster is required for properly regulated gene expression.

Characterization of a novel human IgG antibody reactive with a Ca(2+)-sensitive cell-cell adhesion epitope of PtK2 epithelial cells

We have characterized a human IgG antibody present in the serum of a patient with an autoimmune undifferentiated connective tissue disease and reactive with PtK2 epithelial cell-cell adhesions. The fluorescent staining pattern is observed only at cell-cell contacts whether cells are permeabilized or not. The serum reacts with polypeptides of 90, 48 and 45 kD by immunoblotting. IgG affinity-purified from these bands failed to reproduce the original immunofluorescence staining pattern. Treatment with cycloheximide did not abolish the staining pattern suggesting that the recognized antigen is not a newly expressed protein. However, when EGTA was used for chelating calcium ions in the culture medium the original staining pattern observed at cell-cell adhesions was affected although some fluorescence was still present at cell periphery. This was reversible when cells were reincubated with fresh medium containing Ca2+. The recognized antigen colocalizes at cell-cell adhesions with actin, the microfilament-associated proteins vinculin, alpha-actinin and myosin light chain, and with Triton-insoluble uvomorulin (E-cadherin) material. We conclude that the antibody reacts with, at least, an extracellular portion of a Ca(2+)-dependent PtK2 antigen. The characterization of this antibody based on (1) its localization at cell-cell adhesions, (2) its sensitivity to EGTA-treatment and (3) its colocalization with the epithelial cellular adhesion molecule (CAM) uvomorulin, strongly suggest that the recognized Ag is a CAM or a CAM-associated protein.

Delayed assembly of desmosomes in keratinocytes with disrupted classic-cadherin-mediated cell adhesion by a dominant negative mutant

We examined whether classic cadherins play a role in the formation of desmosomes using a mouse keratinocyte, PAMcN390 delta cell, which shows disrupted classic-cadherin-mediated cell adhesion by introduction of a dominant-negative mutant of N-cadherin. The expression of the mutant did not alter that of endogenous E-cadherin or desmoplakin. In control cells with functional classic cadherins, we observed redistribution of desmoplakin to cell-cell borders with insertions of keratin filaments at the contact sites as soon as 2 h after calcium elevation, after an earlier event of E-cadherin translocation to the cell-cell contact sites. In contrast, in the PAMcN390 delta cells, which showed retarded translocation of E-cadherin, the redistribution of desmoplakin and the rearrangement of keratin filaments were delayed as late as 24 h after the calcium elevation. The acquisition of Nonidet P-40 insolubility of desmoplakins also was found to be delayed in the PAMcN390 delta cells. These findings indicate that the disruption of classic cadherin affected the organization of desmosomes upon calcium elevation and suggest that the proper function of classic cadherins is a prerequisite for desmosome assembly in keratinocytes.

Desmosome assembly and disassembly are regulated by reversible protein phosphorylation in cultured epithelial cells

Desmosomes are one component of the intercellular junctional complex in epithelia. In cultures of epithelial cells, desmosome assembly can be regulated by modulating the calcium concentrations of the growth media. At present, very little is known about the intracellular signal transduction mechanisms that regulate desmosome assembly and disassembly in response to changing extracellular calcium concentrations. We have used inhibitors of protein kinases and phosphatases in a combined biochemical and morphological approach to analyze the role of protein phosphorylation in the assembly and disassembly of desmosomes in Madin-Darby canine kidney epithelial cells. Our results suggest that desmosomal proteins (desmoplakins I/II and desmoglein 1) are primarily phosphorylated on serine residues. Electron microscopic analyses of desmosome assembly upon induction of cell-cell contact, in the presence of protein kinase inhibitor, H-7, revealed an apparently normal assembly of desmosomes. However, complete disassembly of desmosomes was inhibited by H-7 upon removal of extracellular calcium. Under these conditions, although desmosomes split, desmosomal plaques and their associated cytokeratin filaments can not be internalized. In contrast, treatment of the cultures with okadaic acid (OA), an inhibitor of protein phosphatases, inhibited desmosome assembly but had no effect on disassembly. In addition, the inhibitory effect of okadaic acid on desmosome assembly was specific to this junction since we observed apparently normal tight junction and adherens junction in okadaic acid-treated cultures. These results suggest that assembly and disassembly of desmosomes may be regulated by extracellular Ca2+ via reversible protein phosphorylation involving both protein kinase and protein phosphatases.

Structure and turnover of junctional complexes between principal cells of the rat epididymis

The epididymal junctional complex between adjacent principal cells is composed of apically located gap, adherens and tight junctions. Tight junctions between adjacent epithelial cells lead to the formation of the blood-epididymal barrier. The objectives of this study were to examine the structure of the epididymal junctional complex in the different regions of the epididymis and to review the regulation of epithelial cadherin in the rat epididymis. Changes in the structure of the junctional complex, at the level of the electron microscope, were evident when comparing the initial segment to other regions of the epididymis. In the initial segment, the tight junction spanned a considerable length of the apical plasma membrane but had few desmosomes. In the other regions of the epididymis, the span of merging plasma membranes was considerably reduced, but in these regions, numerous desmosomes were present in the apical region. Several examples of what appeared to be a loss of portions of the plasma membrane of adjacent principal cells were evident along the entire epididymis. Such images as the invagination of a portion of the lateral plasma membrane of one principal cell into another, constriction of the invaginated area and eventual detachment leading to the formation of annular junctions suggest that there is a turnover of plasma membranes. The formation of cellular junctions involves the interactions of cell adhesion proteins followed by the addition of junctional proteins which assemble into tight and gap junctions. Epithelial cadherin (E-Cad), a calcium-dependent cell adhesion protein, was localized to the principal cells of the epididymis. Immunocytochemistry at the level of the electron microscope showed that E-Cad was present between the lateral plasma membranes of adjacent principal cells, both in the region of the junctional complex and in the deeper lying areas. E-Cad was also present in annular junctions located in close proximity to the junctional complex, indicating that these structures were related to the plasma membrane. E-Cad mRNA levels are regulated during postnatal epididymal development. In the caput-corpus epididymidis, E-Cad mRNA concentrations increase to peak at 42 days of age. This is well correlated with the conversion of testosterone to dihydrotestosterone in the epididymis. In the cauda epididymidis, however, E-Cad mRNA concentrations do not increase as a function of age, indicating that this protein is regulated in a segment-specific manner.(ABSTRACT TRUNCATED AT 400 WORDS)

Plakoglobin: kinetics of synthesis, phosphorylation, stability, and interactions with desmoglein and E-cadherin

We have analyzed the kinetics of synthesis, phosphorylation, and stability of the soluble and insoluble plakoglobin (PG) and their interactions with Dsg1 and E-cadherin in Madin-Darby canine kidney (MDCK) epithelial cells in the absence of cell adhesion and after the induction of cell-cell contact. Using a combination of biochemical and morphological approaches, we show that newly synthesized PG enters a soluble:insoluble pool of proteins in a 60:40 ratio regardless of cell-cell contact. Following synthesis, PG is increasingly found in the insoluble pool. Although cell-cell contact does not effect either the size of each pool or the rate or efficiency of the transfer from the soluble into the insoluble pool, it results in a significant increase in the metabolic stability of the newly synthesized insoluble PG. The soluble PG initially forms separate complexes with E-cadherin and Dsg1. PG-Dsg1 complexes become insoluble and localize to the desmosome. PG-E-cadherin complexes remain soluble and are distributed intracellularly. The insoluble PG and E-cadherin detected at the cell periphery remain distinctly separate, as demonstrated previously [Hinck et al., 1994: J. Cell Biol. 125:1327-1340; Nathke et al., 1994: J. Cell Biol. 125:1341-1352]. In addition, we detected a separate pool of PG which is not associated with either Dsg1 or E-cadherin and after the induction of cell-cell contact becomes primarily insoluble and is distributed along the lateral membrane. Phosphorylation analysis showed that there is a significantly greater amount of phosphorylated PG in the soluble pool than in the insoluble pool. In addition the soluble pool is both serine and threonine phosphorylated, whereas the insoluble PG is primarily phosphorylated on serine residues.

Adhesion molecules. I: Keratinocyte-keratinocyte interactions; cadherins and pemphigus

During the last few years, considerable progress has been made in our understanding of the structure and function of cadherins and of the pathophysiology of pemphigus. Cadherins are a multiple gene family of Ca(++)-dependent cell adhesion molecules with a typical single-spanning transmembrane structure. Cadherins have two major subfamilies, classic cadherin and desmosomal cadherin. Classic cadherins, including E-, P-, and N-cadherins, are characterized by a homophilic binding specificity. They localize at adherens junctions and mediate physiologic interaction with the involvement of cytoplasmic anchoring molecules, catenins, and the actin-based cytoskeleton network. Desmosomal cadherins, the desmocollins and desmogleins, localize at desmosomes and are linked to the intermediate keratin filaments network via plakoglobin and desmoplakin. Molecular cloning has demonstrated that the autoantigens of both pemphigus vulgaris and pemphigus foliaceus are members of the desmoglein subfamily of the cadherin supergene family. Thus, pemphigus is characterized as an anti-cadherin autoimmune disease. Furthermore, a baculovirus recombinant protein of pemphigus vulgaris antigen was capable of absorbing out the pathogenic autoantibodies from patients' sera, providing a possibility of antigen-specific therapeutic strategies for pemphigus.

Cell type-specific desmosomal plaque proteins of the plakoglobin family: plakophilin 1 (band 6 protein)

Desmosomes represent a special type of the plaque-bearing adhering junctions, characteristic of certain pathways of cell differentiation, which compositionally are not identical in the various kinds of desmosome-forming cells. While all desmosomes contain the cytoplasmic plaque proteins desmoplakin I and plakoglobin, they can vary in their specific complement of desmosomal cadherins and by the presence of additional plaque proteins. We have raised monoclonal antibodies recognizing one such 'accessory' plaque protein, the cytokeratin-binding, basic protein plakophilin 1, originally introduced as 'band 6 protein' or 'polypeptide D6', which is an abundant desmosomal component in certain epithelia. Using such antibodies, we have isolated cDNA clones encoding the bovine and the human protein and determined their complete amino acid sequences. The mRNAs, which on Northern blot tests appear as two bands corresponding to approximately 4 and 2.4 kb (bovine) or 5 and 2.6 kb (human), code for 727 amino acids (calculated mol. wt. 80,180; IEP 9.25) in bovine and 726 amino acids (mol. wt. 80,496; IEP 9.34) in human plakophilin. Sequence analyses have revealed the presence of 9.2 repeated units of the arm-motif sequence, confirming our previous conclusion that this protein is a member of a larger family of proteins including, inter alia, several membrane-associated plaque proteins such as vertebrate plakoglobin and beta-catenin as well as the product of the armadillo gene of Drosophila. The plakophilin antibodies and cDNA probes have also allowed us to examine its synthesis in various tissues and cell cultures. While we confirm the occurrence of the protein in cytoskeletal fractions from various stratified squamous, complex, glandular duct and bladder epithelia, where it can be localized to desmosomes, we have, surprisingly, also identified the protein, although at lower amounts, in cytoskeletal fractions from several cultured cell lines in which the protein has not been consistently localized to desmosomes by immunofluorescence microscopy. Examples include cultured cells derived from certain simple epithelia such as the kidney-derived line MDBK and cultured calf lens cells. We have also found that, in all plakophilin 1-positive cells examined, a pool of diffusible ('soluble') cytoplasmic plakophilin exists, including cell lines such as human mammary carcinoma MCF-7 cells in which this soluble plakophilin seems to be the only detectable form. In addition, we have identified some soluble proteins conspicuously cross-reacting with plakophilin 1. Possible functions of plakophilin and its potential value as a marker for specific states of cell differentiation are discussed, particularly with respect to tumor diagnosis.

Postnatal reorganization of actin filaments and differentiation of intercellular boundaries in the rat aortic endothelial cells

Postnatal change in the distribution of actin filaments in endothelial cells was studied in the rat aorta by use of rhodamine-phalloidin staining and confocal laser scanning microscopy. Endothelial cells of the rat aorta possessed two populations of actin filament bundles, namely, peripheral bands at the cell border and stress fibers running longitudinally in the cytoplasm. Aortic endothelial cells of the neonatal rat contained only stress fibers, whereas those of the 10-day-old rat developed both peripheral bands and stress fibers. After 20 days of age, aortic endothelial cells had predominantly peripheral bands with occasional stress fibers around the branch orifices. During postnatal development the length density of stress fibers in aortic endothelial cells decreased, whereas individual stress fibers in endothelial cells were shortened. Electron-microscopic observation revealed that the high intercellular boundaries of aortic endothelial cells at birth decreased in height and developed cytoplasmic interdigitations after 20 days of age. The occurrence of peripheral bands at the cell border is thought to be closely related to formation of cytoplasmic interdigitation which strengthens the mechanical connection between endothelial cells against increasing transmural pressure. Expression of stress fibers in aortic endothelial cells of the neonatal rat is supposed to be affected by longitudinal elongation of the developing aorta, whereas their postnatal decrease is thought to be correlated with the change of fluid shear stress loaded on the aortic endothelium.

Identification of amino acid sequence motifs in desmocollin, a desmosomal glycoprotein, that are required for plakoglobin binding and plaque formation

By transfecting epithelial cells with gene constructs encoding chimeric proteins of the transmembrane part of the gap junction protein connexin 32 in combination with various segments of the cytoplasmic part of the desmosomal cadherin desmocollin 1a, we have determined that a relatively short sequence element is necessary for the formation of desmosome-like plaques and for the specific anchorage of bundles of intermediate-sized filaments (IFs). Deletion of as little as the carboxyl-terminal 37 aa resulted in a lack of IF anchorage and binding of the plaque protein plakoglobin, as shown by immunolocalization and immunoprecipitation experiments. In addition, we show that the sequence requirements for the recruitment of desmoplakin, another desmosomal plaque protein, differ and that a short (10 aa) segment of the desmocollin 1a tail, located close to the plasma membrane, is also required for the binding of plakoglobin, as well as of desmoplakin, and also for IF anchorage. The importance of the carboxyl-terminal domain, homologous in diverse types of cadherins, is emphasized, as it must harbor, in a mutually exclusive pattern, the information for assembly of the IF-anchoring desmosomal plaque in desmocollins and for formation of the alpha-/beta-catenin- and vinculin-containing, actin filament-anchoring plaque in E- and N-cadherin.

E1a induces the expression of epithelial characteristics

Cells closely resembling epithelia constitute the first specific cell type in a mammalian embryo. Many other cell types emerge via epithelial-mesenchymal differentiation. The transcription factors and signal transduction pathways involved in this differentiation are being elucidated. I have previously reported (Frisch, 1991) that adenovirus E1a is a tumor suppressor gene in certain human cell lines. In the present report, I demonstrate that E1a expression caused diverse human tumor cells (rhabdomyosarcoma, fibrosarcoma, melanoma, osteosarcoma) and fibroblasts to assume at least two of the following epithelial characteristics: (a) epithelioid morphology; (b) epithelial-type intercellular adhesion proteins localized to newly formed junctional complexes; (c) keratin-containing intermediate filaments; and (d) down-regulation of non-epithelial genes. E1a thus appeared to partially convert diverse human tumor cells into an epithelial phenotype. This provides a new system for molecular analysis of epithelial-mesenchymal interconversions. This effect may also contribute to E1a's tumor suppression activity, possibly through sensitization to anoikis (Frisch, S.M., and H. Francis, 1994. J. Cell Biol. 124:619-626).

Autoantibodies against cell adhesion molecules in pemphigus

cDNA cloning has demonstrated that pemphigus autoantigens of both pemphigus vulgaris (PV) and pemphigus foliaceus are members of the desmoglein subfamily of the cadherin supergene family. The availability of these cDNAs allowed us to utilize molecular engineering to attempt to understand the pathophysiology of pemphigus. Transfection study with a chimeric molecule containing the extracellular domain of PV antigen (PVA) and the cytoplasmic domain of E-cadherin demonstrated that the extracellular domain of PVA mediates weak homophilic cell adhesion. Bacterial fusion proteins representing different parts of PVA showed that the major immunogenic domains are EC1, EC2, and EC4 and that at least one pathogenic epitope is located on the amino-terminal region of PVA, an area thought to be important for classic cadherin homophilic interaction. Further, a secreted form of PVA recombinant protein, PVIg, was produced by baculovirus expression. Immunoabsorption assay has demonstrated that PVIg is capable of absorbing pathogenic autoantibodies from patients' sera and preventing blister formation in neonatal mice.

Epican, a heparan/chondroitin sulfate proteoglycan form of CD44, mediates cell-cell adhesion

Epican is a heparan/chondroitin sulfate proteoglycan form of CD44 and is expressed on the surface of keratinocytes from the basal layer to the granular layer of the epidermis. To analyze the adhesive properties of epican apart from the influence of other adhesive molecules found on keratinocytes, mouse L cell fibroblasts were transfected with CD44Epican cDNA. The epican expressed on the surface of transfected L cells was predominantly a heparan or chondroitin sulfate proteoglycan. The CD44Epican-transfected L cells acquired: (a) a self-aggregating phenotype that required hyaluronan but was calcium-independent; and (b) a new capacity to adhere to keratinocytes, a property that was blocked by an anti-epican antibody. Both aggregation and adhesion of CD44Epican-transfected cells were completely prevented by pretreatment with hyaluronidase, but were totally restored by the addition of exogenous hyaluronan. Aggregation of transfected L cells was minimally influenced by other glycosaminoglycans, but adhesion of transfected L cells to keratinocytes was substantially inhibited by heparin.

Visualisation by electron microscopy of the unique part of the cytoplasmic domain of a desmoglein, a cadherin-like protein of the desmosome type of cell junction

Part of the cytoplasmic domain of a human desmoglein, Dsg1, a cadherin-like protein found in desmosomes of epithelial cells, has been visualised by electron microscopy. The cloned fragment contains five repeats of a 29 +/- 4 residue sequence unique to desmogleins, followed by a glycine-rich region. In rotary shadowed preparations the molecule consists of a globular head attached to a thin tail, the latter perhaps corresponding to the glycine-rich region. This portion of the molecule is thought to span the width of the inner dense plaque. The structure and dimensions concur well to the configuration deduced from the protein sequence.

Purification and spectroscopic characterization of a recombinant amino-terminal polypeptide fragment of mouse epithelial cadherin

Cadherins are a family of Ca(2+)-dependent cell adhesion molecules containing four extracellular tandem repeats each of 110 amino acids. The most amino-terminal repeat is believed to confer the specificity of cell adhesion. A polypeptide containing the amino-terminal repeat of mouse epithelial cadherin has been over-expressed in E. coli and purified to homogeneity. This polypeptide binds Ca2+ with a dissociation constant of 1.6 x 10(-4) M. CD and NMR experiments indicate that the polypeptide adopts a predominantly beta-sheet conformation and that binding of Ca2+ induces only small conformational changes.