Gamma 2 chain of laminin-5 is recognized by monoclonal antibody GB3

Genotype-Phenotype Correlation in Junctional Epidermolysis Bullosa: Signposts to Severity

Junctional epidermolysis bullosa (JEB) is a rare autosomal recessive genodermatosis with a broad spectrum of phenotypes. Current genotype-phenotype paradigms are insufficient to accurately predict JEB subtype and characteristics from genotype, particularly for splice site variants, which account for over a fifth of disease-causing variants in JEB. This study evaluated the genetic and clinical findings from a JEB cohort, investigating genotype-phenotype correlations through bioinformatic analyses and comparison with previously reported variants. Eighteen unique variants in LAMB3, LAMA3, LAMC2, or COL17A1 were identified from 17 individuals. Seven had severe JEB, 9 had intermediate JEB, and 1 had laryngo-onycho-cutaneous syndrome. Seven variants were previously unreported. Deep phenotyping was completed for all intermediate JEB cases and demonstrated substantial variation between individuals. Splice site variants underwent analysis with SpliceAI, a state-of-the-art artificial intelligence tool, to predict resultant transcripts. Predicted functional effects included exon skipping and cryptic splice site activation, which provided potential explanations for disease severity and in most cases correlated with laminin-332 immunofluorescence. RT-PCR was performed for 1 case to investigate resultant transcripts produced from the splice site variant. This study expands the JEB genomic and phenotypic landscape. Artificial intelligence tools show potential for predicting the functional effects of splice site variants and may identify candidates for confirmatory laboratory investigation. Investigation of RNA transcripts will help to further elucidate genotype-phenotype correlations for novel variants.

Potential Therapeutic Significance of Laminin in Head and Neck Squamous Carcinomas

Simple Summary

Head and neck cancers (HNC) account for approximately 500,000 new cases of tumors annually worldwide and are represented by upper aerodigestive tract malignant neoplasms, which particularly arise in oral cavity, larynx, and pharynx tissues. Thus, due to the biological diversity between the upper aerodigestive organs, and to the heterogeneity of risk factors associated with their malignant transformation, HNC behavior, and prognosis seem to strongly vary according to the tumor site. However, despite to the heterogeneity which characterizes head and neck tumors, squamous cell carcinomas (SCC) represent the predominant histopathologic HNC subtype. In this sense, it has been reported that SCC tumor biology is strongly associated with deregulations within the extracellular matrix compartment. Accordingly, it has been shown that laminin plays a remarkable role in the regulation of crucial events associated with head and neck squamous cell carcinomas (HNSCC) progression, which opens the possibility that laminin may represent a convergence point in HNSCC natural history.

Abstract

Head and neck squamous cell carcinomas (HNSCC) are among the most common and lethal tumors worldwide, occurring mostly in oral cavity, pharynx, and larynx tissues. The squamous epithelia homeostasis is supported by the extracellular matrix (ECM), and alterations in this compartment are crucial for cancer development and progression. Laminin is a fundamental component of ECM, where it represents one of the main components of basement membrane (BM), and data supporting its contribution to HNSCC genesis and progression has been vastly explored in oral cavity squamous cell carcinoma. Laminin subtypes 111 (LN-111) and 332 (LN-332) are the main isoforms associated with malignant transformation, contributing to proliferation, adhesion, migration, invasion, and metastasis, due to its involvement in the regulation of several pathways associated with HNSCC carcinogenesis, including the activation of the EGFR/MAPK signaling pathway. Therefore, it draws attention to the possibility that laminin may represent a convergence point in HNSCC natural history, and an attractive potential therapeutic target for these tumors.

Expression of Laminin γ2 Proteolytic Fragments in Murine Skin Following Exposure to Sulfur Mustard

Laminin-332 is a basement membrane protein composed of three genetically distinct polypeptide chains that actively promote both skin epidermal cell adhesion and migration. Proteolytic fragments of the laminin γ2 chain stimulate migration and scattering of keratinocytes and cancer cells. Sulfur mustard (SM) is a bifunctional alkylating agent that induces separation of basal keratinocytes from the dermal-epidermal junction and invokes a strong inflammatory response leading to delayed wound repair. In the present studies, the role of laminin γ2 in SM-induced skin injury and wound repair was investigated using the mouse ear vesicant model. We found that laminin γ2 chain mRNA was preferentially upregulated in mouse ear skin exposed to SM. In situ hybridization confirmed overexpression of laminin γ2 transcript. Western blot analysis showed increased protein expression of the full-length proform of laminin γ2 and smaller processed fragments of laminin γ2 in skin exposed to SM. Dual immunofluorescence labeling indicated that laminin γ2 fragments are prevalent in suprabasal keratinocytes behind the leading edge in areas of hyperplasia in injured skin. In addition, co-expression of laminin γ2 and the senescent marker, p16^-INK4a was found to overlap with the hyperplastic migratory epithelial sheet. This observation is similar to hypermotile keratinocytes reported in invasive carcinoma cells. Overall, our studies indicate that laminin γ2 is preferentially expressed in skin post SM exposure and that protein expression appears to become progressively more fragmented. The laminin γ2 fragments may play a role in regulating SM-induced skin wound repair. Anat Rec, 2020. © 2020 American Association for Anatomy.

Sulfur mustard induces an endoplasmic reticulum stress response in the mouse ear vesicant model

The endoplasmic reticulum (ER) stress response is a cell survival pathway upregulated when cells are under severe stress. Severely damaged mouse ear skin exposed to the vesicant, sulfur mustard (bis-2-chloroethyl sulfide, SM), resulted in increased expression of ER chaperone proteins that accompany misfolded and incorrectly made proteins targeted for degradation. Time course studies with SM using the mouse ear vesicant model (MEVM) showed progressive histopathologic changes including edema, separation of the epidermis from the dermis, persistent inflammation, upregulation of laminin γ2 (one of the chains of laminin-332, a heterotrimeric skin glycoprotein required for wound repair), and delayed wound healing from 24h to 168h post exposure. This was associated with time related increased expression of the cell survival ER stress marker, GRP78/BiP, and the ER stress apoptosis marker, GADD153/CHOP, suggesting simultaneous activation of both cell survival and non-mitochondrial apoptosis pathways. Dual immunofluorescence labeling of a keratinocyte migration promoting protein, laminin γ2 and GRP78/BIP, showed colocalization of the two molecules 72h post exposure indicating that the laminin γ2 was misfolded after SM exposure and trapped within the ER. Taken together, these data show that ER stress is induced in mouse skin within 24h of vesicant exposure in a defensive response to promote cell survival; however, it appears that this response is rapidly overwhelmed by the apoptotic pathway as a consequence of severe SM-induced injury.

Laminin 332 in junctional epidermolysis bullosa

Laminin 332 is an essential component of the dermal-epidermal junction, a highly specialized basement membrane zone that attaches the epidermis to the dermis and thereby provides skin integrity and resistance to external mechanical forces. Mutations in the LAMA3, LAMB3 and LAMC2 genes that encode the three constituent polypeptide chains, α3, β3 and γ2, abrogate or perturb the functions of laminin 332. The phenotypic consequences are diminished dermal-epidermal adhesion and, as clinical symptoms, skin fragility and mechanically induced blistering. The disorder is designated as junctional epidermolysis bullosa (JEB). This article delineates the signs and symptoms of the different forms of JEB, the mutational spectrum, genotype-phenotype correlations as well as perspectives for future molecular therapies.

Clinical and immunological heterogeneity of canine subepidermal blistering dermatoses with anti-laminin-332 (laminin-5) auto-antibodies

Laminin-332 (laminin-5) is a basement membrane heterotrimeric protein composed of alpha-3, beta-3 and gamma-2 laminin chains. Laminin-332 polypeptides are targeted by auto-antibodies in human patients with mucous membrane (cicatricial) pemphigoid or, more rarely, subepidermal vesicular diseases that resemble epidermolysis bullosa acquisita (EBA) or bullous pemphigoid (BP). The objectives of this report were to characterize the clinical, histopathological and immunological characteristics of nine dogs with auto-antibodies targeting laminin-332. Immunological investigations consisted of direct immunofluorescence (IF), indirect IF with intact and salt-split canine gingival, and salt-split normal or laminin-332-deficient human skin, immunoblotting with purified human laminin-332 and immunoblotting with recombinant NC1 domain of human collagen VII. All dogs exhibited varying degrees of skin blistering and ulceration associated with microscopic subepidermal vesiculation with or without inflammatory cells. Indirect IF established that circulating IgG auto-antibodies bound the dermal side of salt-split canine lip and human skin. In five dogs, IgG variably recognized the basement membrane of laminin-332-deficient human skin (three dogs negative, two dogs positive). In all nine dogs, IgG auto-antibodies detected purified human laminin-332 by immunoblotting. In two dogs, additional targeting of collagen VII-NC1 was present. These observations establish laminin-332 as a novel basement membrane antigen in dogs with autoimmune blistering diseases with variable clinical phenotypes. The names 'acquired junctional epidermolysis bullosa', 'anti-laminin-332 mucous membrane pemphigoid (MMP)' and 'mixed auto-immune subepidermal blistering dermatosis' are proposed for dogs with clinical signs reminiscent of EBA, MMP or BP respectively.

Identification of a novel family of laminin N-terminal alternate splice isoforms: structural and functional characterization

The laminins are a family of heterotrimeric basement membrane proteins that play roles in cellular adhesion, migration, and tissue morphogenesis. Through in silico analysis of the laminin-encoding genes, we identified a novel family of alternate splice isoforms derived from the 5'-end of the LAMA3 and LAMA5 genes. These isoforms resemble the netrins in that they contain a laminin N-terminal domain followed by a short stretch of laminin-type epidermal growth factor-like repeats. We suggest the terms LaNt (laminin N terminus) alpha3 and LaNt alpha5, for the predicted protein products of these mRNAs. RT-PCR confirmed the presence of these transcripts at the mRNA level. Moreover, they exhibit differential, tissue-specific, expression profiles. To confirm the existence of LaNt alpha3 protein, we generated an antibody to a unique domain within the putative polypeptide. This antibody recognizes a protein at the predicted molecular mass of 64 kDa by immunoblotting. Furthermore, immunofluorescence analyses revealed a basement membrane staining in epithelial tissue for LaNt alpha3 and LaNt alpha3 localized along the substratum-associated surface of cultured keratinocytes. We have also tested the functionality LaNt alpha3 through RNAi-mediated knockdown. Keratinocytes exhibiting specific knockdown of LaNt alpha3 displayed impaired adhesion, stress resistance, and reduced ability to close scratch wounds in vitro.

Regulated laminin-332 expression in human islets of Langerhans

Laminin-332 (LN-332) is a basement membrane component known to exert a beneficial effect on rat pancreatic beta cells in vitro. In this work, we analyzed the expression of LN-332 in human islets, its expression after inflammatory insults by cytokines, and the molecular mechanisms responsible for this effect. By Western blotting and RT-PCR, we showed that LN-332 was expressed in isolated human islets. By immunofluorescence on pancreas sections, we observed that labeling was confined to endocrine cells in islets. Confocal microscopy analysis on isolated islet cells revealed that labeling was granular but did not colocalize with hormone secretory granules. LN-332 was most abundant in cultured islets compared to freshly isolated islets and was found in culture medium, which suggests that it was secreted by islets. When islets were exposed to interleukin (IL)-1beta, expression and secretion of LN-332 increased as compared to control. No effect was observed with tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma. LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K) activity, inhibited culture- and IL-1beta-induced LN-332 expression in islets. These results show that LN-332, known to have some beneficial effect on beta cells in vitro, is produced and secreted by endocrine islet cells and is up-regulated by stressing conditions such as culture and IL-1beta-exposure.

Self-assembling peptide nanofiber scaffolds accelerate wound healing

Cutaneous wound repair regenerates skin integrity, but a chronic failure to heal results in compromised tissue function and increased morbidity. To address this, we have used an integrated approach, using nanobiotechnology to augment the rate of wound reepithelialization by combining self-assembling peptide (SAP) nanofiber scaffold and Epidermal Growth Factor (EGF). This SAP bioscaffold was tested in a bioengineered Human Skin Equivalent (HSE) tissue model that enabled wound reepithelialization to be monitored in a tissue that recapitulates molecular and cellular mechanisms of repair known to occur in human skin. We found that SAP underwent molecular self-assembly to form unique 3D structures that stably covered the surface of the wound, suggesting that this scaffold may serve as a viable wound dressing. We measured the rates of release of EGF from the SAP scaffold and determined that EGF was only released when the scaffold was in direct contact with the HSE. By measuring the length of the epithelial tongue during wound reepithelialization, we found that SAP scaffolds containing EGF accelerated the rate of wound coverage by 5 fold when compared to controls without scaffolds and by 3.5 fold when compared to the scaffold without EGF. In conclusion, our experiments demonstrated that biomaterials composed of a biofunctionalized peptidic scaffold have many properties that are well-suited for the treatment of cutaneous wounds including wound coverage, functionalization with bioactive molecules, localized growth factor release and activation of wound repair.

Protein therapeutics for junctional epidermolysis bullosa: incorporation of recombinant beta3 chain into laminin 332 in beta3-/- keratinocytes in vitro

Junctional epidermolysis bullosa (JEB) is an inherited mechanobullous disease characterized by reduced adherence of the epidermal keratinocytes to the underlying dermis, and is often caused by the absence of functional laminin 332 due to the lack or dysfunction of its beta3 chain. As there are no specific therapies for JEB, we tested whether a protein replacement strategy could be applicable for the restoration of the laminin 332 assembly and reversion of the JEB phenotype in human keratinocytes that lack beta3 subunit. Here, we developed the protocol for production and purification of the biologically active recombinant beta3 chain. Next, we demonstrated that delivery of recombinant beta3 polypeptide into the endoplasmic reticulum of the immortalized beta3-null keratinocytes led to the restoration of the laminin 332 assembly, secretion, and deposition into the basement membrane zone, as confirmed by Western blot analysis, confocal immunofluorescent microscopy in vitro, and on cultured organotypic human JEB skin reconstructs. Although the amount of laminin 332 produced by protein-treated beta3-null keratinocytes is lower than that in normal human keratinocytes, our results demonstrate the applicability of the recombinant proteins for JEB treatment and open new perspectives for the development of novel therapeutics for this inherited, currently intractable, skin disorder.

A quantitative co-localization analysis of large unspliced tenascin-C(L) and laminin-5/gamma2-chain in basement membranes of oral squamous cell carcinoma by confocal laser scanning microscopy

BACKGROUND

A structural interaction of the oncofetal large tenascin-C splice variants (Tn-C(L)) and the gamma2-chain of laminin-5 (Ln-5/gamma2) was recently demonstrated in oral squamous cell carcinoma (OSCC). In situ different patterns of co-localization and co-deposition of both proteins could be detected. Especially the co-localization in re-established basement membrane (BM) structures seemed to be biologically meaningful within the process of tumour progression.

METHODS

The amount of Tn-C(L) incorporated in reorganized OSCC BM structures at the tumour margins was investigated by a laser scanning microscopy-based quantitative co-localization analysis.

RESULTS

In the BM of normal oral mucosa no Tn-C(L) could be detected. In dysplastic and neoplastic oral mucosa a distinct co-localization of Tn-C(L) and Ln-5/gamma2 in the BM region could be observed. The extent of Tn-C(L) arrangement into reorganized BM structures correlated with malignancy grade.

CONCLUSIONS

The results suggest at first, a modulation of carcinomatous BM structures by the inclusion of oncofetal matrix proteins during tumour progression and secondly, the BM incorporation of the adhesion-modulating molecule Tn-C(L) as a pre-invasive structural phenomenon in OSCC.

A comparative study between transmission electron microscopy and immunofluorescence mapping in the diagnosis of epidermolysis bullosa

The classification of epidermolysis bullosa (EB) into 3 main subtypes has been based on transmission electron microscopy (TEM) that is able to directly visualize and quantify specific ultrastructural features. Immunofluorescence antigenic mapping (IFM) is a technique that determines the precise level of skin cleavage by determining binding sites for a series of antibodies. To date, no study has compared the accuracy of these two techniques in diagnosing the major types of EB. A prospective cohort of 33 patients thought to have EB on clinical grounds had TEM, IFM, and genetic testing performed. The sensitivities and specificities of TEM and IFM were calculated compared with the genetic results. Of 33 cases, 30 had a positive EB diagnosis. TEM subclassified EB into its three major forms in 24/30 cases (80%) and IFM in 29/30 cases (97%). Overall, TEM sensitivities and specificities when compared with genetic results were 71% and 81%, respectively. IFM sensitivities and specificities when compared with genetic results were 97% and 100%, respectively. If a patient tested positive for EB by IFM, the likelihood ratio of having a particular type of EB was consistently greater than 20 against the reference standard (compared with a likelihood ratio less than 10 for TEM). Our results indicate that the diagnosis of EB is improved (sometimes substantially) by the use of IFM compared with TEM.

Snail-dependent and -independent Epithelial-Mesenchymal Transition in Oral Squamous Carcinoma Cells

Disappearance of E-cadherin is a milestone for epithelial-mesenchymal transition (EMT), found both in carcinomas and in some fibrotic diseases. We have studied the mechanisms of EMT in oral squamous cell carcinoma (SCC) cells isolated from primary tumor (43A) and its recurrent tumor (43B). Whereas the cells from primary carcinoma displayed a typical phenotype of squamous epithelial cells including E-cadherin and laminin-332 (laminin-5), cells from recurrent tumor expressed characteristics of dedifferentiated, EMT-experienced tumors. 43B cells expressed E-cadherin repressors ZEB-1/δEF1 and especially ZEB-2/SIP1, which therefore appear as candidates for endogenous EMT in these cells. Differences between endogenous and exogenous EMT were assessed by transfecting 43A cells with SNAIL cDNA. SNAIL-transfected cells showed complete EMT phenotype with fibroblastoid appearance, vimentin filaments, E-cadherin/N-cadherin switch, lack of hemidesmosomes and, as a new feature of EMT, lack of laminin-332 synthesis. Upregulation of ZEB-1 and ZEB-2 was evident in these cells, suggesting that SNAIL can regulate these E-cadherin repressors. New monoclonal antibodies against SNAIL showed nuclear immunoreactivity not only in the SNAIL-transfected cells but also in carcinoma cells lacking production of Lm-332 and showing signs of EMT. These results suggest that changes in the epithelial cell differentiation program and EMT in SCC cells can result from the interplay among several E-cadherin repressors; however, SNAIL alone is able to accomplish a complete EMT. (J Histochem Cytochem 54:1263-1275, 2006)

Characterization of the Initial Response of Engineered Human Skin to Sulfur Mustard

We have used a new approach to identify early events in sulfur mustard-induced, cutaneous injury by exposing human, bioengineered tissues that mimic human skin to this agent to determine the morphologic, apoptotic, inflammatory, ultrastructural, and basement membrane alterations that lead to dermal-epidermal separation. We found distinct prevesication and post-vesication phases of tissue damage that were identified 6 and 24 h after sulfur mustard (SM) exposure, respectively. Prevesication (6 h) injury was restricted to small groups of basal keratinocytes that underwent apoptotic cell death independent of SM dose. Immunoreactivity for basement membrane proteins was preserved and basement membrane ultrastructure was intact 6 h after exposure. Dermal-epidermal separation was seen by the presence of microvesicles 24 h after SM exposure. This change was accompanied by the dose-dependent induction of apoptosis, focal loss of basement membrane immunoreactivity, increase in acute inflammatory cell infiltration, and ultrastructural evidence of altered basement membrane integrity. These studies provide important proof of concept that bioengineered, human skin demonstrates many alterations previously found in animal models of cutaneous SM injury. These findings further our understanding of mechanisms of SM-induced damage and can help development of new countermeasures designed to limit the morbidity and mortality caused by this chemical agent.

Increased risk of squamous cell carcinoma in junctional epidermolysis bullosa

Non-Herlitz junctional epidermolysis bullosa (JEB) is an autosomal recessive genodermatosis characterized by skin fragility and blistering. It is usually caused by mutations in the genes encoding the basement membrane proteins laminin 5 or type XVII collagen. Clinically, impaired wound healing and chronic erosions cause major morbidity in affected patients. Previously it was thought that these individuals, unlike patients with dystrophic EB, did not have an increased risk of developing skin cancer. However, we describe three patients with non-Herlitz JEB (aged 42, 56 and 75 years) who developed cutaneous squamous cell carcinomas (SCCs). The tumours were well-differentiated in two cases, but one patient had multiple primary SCCs that were either well- or moderately differentiated. Most cases of SCC in non-Herlitz JEB described have occurred in those with laminin 5 defects and on the lower limbs. These clinicopathological observations have important implications for the management of patients with this mechanobullous disorder as well as providing further insight into the biology of skin cancer associated with chronic inflammation and scarring.

Basement membrane proteins promote progression of intraepithelial neoplasia in 3-dimensional models of human stratified epithelium

We have developed novel 3-dimensional in vitro and in vivo tissue models that mimic premalignant disease of human stratified epithelium in order to analyze the stromal contribution of extracellular matrix and basement membrane proteins to the progression of intraepithelial neoplasia. Three-dimensional, organotypic cultures were grown either on a de-epidermalized human dermis with pre-existing basement membrane components on its surface (AlloDerm), on a Type I collagen gel that lacked basement membrane proteins or on polycarbonate membranes coated with purified extracellular matrix proteins. When tumor cells (HaCaT-II4) were mixed with normal keratinocytes (4:1/normals:HaCaT-II4), tumor cells selectively attached, persisted and proliferated at the dermal-epidermal interface in vitro and generated dysplastic tissues when transplanted to nude mice only when grown in the presence of the AlloDerm substrate. This stromal interface was permissive for tumor cell attachment due to the rapid assembly of structured basement membrane. When tumor cells were mixed with normal keratinocytes and grown on polycarbonate membranes coated with individual extracellular matrix or basement membrane components, selective attachment and significant intraepithelial expansion occurred only on laminin 1 and Type IV collagen-coated membranes. This preferential adhesion of tumor cells restricted the synthesis of laminin 5 to basal cells where it was deposited in a polarized distribution. Western blot analysis revealed that tumor cell attachment was not due to differences in the synthesis or processing of laminin 5. Thus, intraepithelial progression towards premalignant disease is dependent on the selective adhesion of cells with malignant potential to basement membrane proteins that provide a permissive template for their persistence and expansion.

Laminin alpha-1, alpha-3, and alpha-5 chain expression in human prepubertal [correction of prepubetal] benign prostate glands and adult benign and malignant prostate glands

BACKGROUND

Laminins (Lns) are a family of extracellular matrix glycoproteins located in the basement membrane (BM) of epithelial cells. They exist as heterotrimers composed of an alpha, beta, and gamma chain. Presently, five alpha (alpha1-5), three beta (beta1-3), and three gamma (gamma1-3) chains have been identified with different combinations of these chains resulting in 14 laminin heterotrimers thus far identified (1, 3-5).

METHODS

In this study, using immunohistochemistry with chain-specific antibodies, we characterized the expression of the alpha1 (Lns-1/3), alpha3 (Lns 5,6,7), and alpha5 (Lns 10/11) chains in fetal, newborn, infant, prepubertal, and adult benign and malignant prostate glands.

RESULTS

In general, alpha1 expression was higher in normal fetal prostate glands and declined by full-term birth, whereas the alpha3 and alpha5 chains remained highly expressed in the adult normal glands. In carcinoma alpha1 (Lns 1/3) and alpha5 (Lns 5,6,7) are lost, whereas alpha5 (Lns 10/11) persists.

CONCLUSIONS

Alpha 1 (Lns 1/3) is prominent in BM, but is replaced by a laminin matrix rich in alpha3 (Lns 5,6,7) and alpha5 (Lns 10/11) in benign adult prostate glands. In carcinoma, both alpha1 (Lns-1/3) and alpha3 (Lns 5,6,7) are not expressed with persistence of a BM rich in alpha5 (Lns 10/11).

The expression of nectin-1alpha in normal human skin and various skin tumours

BACKGROUND

A novel cell-cell adhesion system that consists of nectin and afadin has been identified at cadherin-based cell-cell adherens junctions. Nectin is a Ca2+-independent homophilic and heterophilic cell adhesion molecule that belongs to the immunoglobulin superfamily. Nectin has recently been shown to serve as an alpha-herpesvirus entry and cell-cell spread mediator. In spite of the ubiquitous expression of nectin-1alpha, its detailed localization in human skin has not been examined so far.

OBJECTIVES

To investigate the localization of nectin-1alpha in normal human skin and the alteration of its expression in malignant skin tumours.

METHODS

Immunohistochemistry was employed to determine the expression of nectin-1alpha and other adhesion molecules.

RESULTS

We detected nectin-1alpha in normal human epidermis, follicles and eccrine ducts. Nectin-1alpha was colocalized with E-cadherin at cell-cell adherens junctions of the epidermis. The concentration of the nectin-afadin system at cell-cell adherens junctions was reduced in the early stage of malignant transformation of keratinocytes, such as in basal cell carcinomas and squamous cell carcinomas, where the cadherin-catenin system was preserved. Nectin-1alpha at cell-cell adherens junctions was reduced in human epithelial cancer cells located at the advancing border of the tumour.

CONCLUSIONS

Our results showed that nectin-1alpha is located at cell-cell adherens junctions in human skin and that reduction of nectin-1alpha at cell-cell adherens junctions may be involved in the invasion of squamous cell tumours.

Animal models for skin blistering conditions: absence of laminin 5 causes hereditary junctional mechanobullous disease in the Belgian horse

Recent achievements in the genetic correction of keratinocytes isolated from patients with junctional epidermolysis bullosa have paved the way to a gene therapy approach for the disease. Because gene therapy protocols require preclinical validation in animals, we have characterized spontaneous animal models of junctional epidermolysis bullosa. In this study we have elucidated the genetic basis of the hereditary junctional mechanobullous disease in the Belgian horse, a condition characterized by blistering of the skin and mouth epithelia, and exungulation (loss of the hoof). Immunofluorescence analysis associated the condition to the absent expression of the gamma2 chain of laminin 5 and designated Lamc2 as the candidate gene. Comparative analysis of the nucleotide sequence of the full-length gamma2 cDNA isolated by reverse transcription polymerase chain reaction amplification of total RNA purified from the epithelium of a junctional epidermolysis bullosa foal and a healthy control disclosed a homozygous basepair insertion (1368insC) in the affected animal. Mutation 1368insC results in a downstream premature termination codon and is predicted to cause absent expression of the laminin gamma2 polypeptide. Our results also show that: (i) the horse junctional epidermolysis bullosa genetically corresponds to the severe Herlitz form of junctional epidermolysis bullosa in man; (ii) the amino acid sequence and structure of the horse laminin gamma2 chain are virtually identical to the human counterpart; (iii) the moderate eruption of skin blisters in the affected animals with respect to the human Herlitz junctional epidermolysis bullosa patients correlates with the protection provided by hair. Our observations suggest that the affected foals are a convenient source of epithelial cells from tissues that cannot be obtained from human junctional epidermolysis bullosa patients, and imply that hairless strains of animals with recessive skin disorders would be the best models for in vivo gene therapy approaches to skin blistering diseases.

Function of laminins and laminin-binding integrins in gingival epithelial cell adhesion

BACKGROUND

In human gingiva, epithelial cells attach to their adjacent tissues by means of specialized molecular adhesion complexes and a basement membrane. Little is known about the synthesis of adhesion proteins by gingival keratinocytes; we, therefore, studied how cultured immortalized gingival epithelial cells produce laminins and express laminin-binding integrins. We presumed that different laminins and integrins would be involved in the adhesion of gingival epithelial cells.

METHODS

We cultured gingival keratinocytes and studied their production of laminins and expression of integrins using immunofluorescence microscopy, immunoprecipitation, and immunoblotting methods and by quantitative cell adhesion experiments. We also studied how gingival tissue expresses these adhesion proteins in vivo by using immunofluorescence microscopy.

RESULTS

In immunofluorescence microscopy, the cells were seen to organize chains of laminin-5 (alpha3beta03gamma2) to extracellular patches, whereas the alpha5 chain of laminin-10 (alpha5betalgamma1) could only be seen intracellularly. Of the laminin-binding integrin subunits, integrin a6 subunit was organized to dotted arrays, typical of prehemidesmosomal adhesions, whereas integrin alpha3 subunit was located at cell-cell junctions, in prehemidesmosomal structures, and at some locations also in small focal-contact like patches. Integrin beta1 subunit was found at cell-cell junctions and in focal contacts. Immunoprecipitation experiments showed that the cells synthesize and secrete chains of laminin-5 and laminin-10. In quantitative cell adhesion experiments, the cells adhered efficiently to these laminins by using cooperatively integrin alpha3beta1 and alpha6beta1 integrin complexes. None of the other known laminin-binding integrin subunits appeared to be significantly involved in cell adhesion to these laminin isoforms.

CONCLUSIONS

Our results provide new information on gingival epithelial cell adhesion and extracellular matrix production and may thus aid in the understanding of periodontal physiology.

Laminin-5 in the progression of carcinomas

The basement membrane (BM) separates epithelial elements from the surrounding stroma. BM is dynamic in regulation of epithelial cells differentiation as well as their organization into 3-dimensional tissues. In these functions, among the molecules of the BM, laminins are especially dynamic. Laminins are distributed in a spatially and temporally regulated manner in various epithelial tissues. Various changes in the laminin distribution accompany the malignant transformation of epithelia. The role of the BM and laminins in the progression of carcinomas is not well understood. The BM has been suggested to act as a mechanical barrier against carcinoma cell invasion. BM laminins may play an active role in regulating the migration and proliferation of the carcinoma cells. Laminin isoform laminin-5 expression is typical for some invasive carcinomas and it may act as a ligand for invading carcinoma cells. Neoexpression of laminin-5 has also been associated to proliferative activity of the carcinoma cells. Integrins alpha(3)beta(1) and alpha(6)beta(4) are probable cell surface receptors acting with laminin-5 in the regulation of carcoma cell invasion and proliferation.

A comparative quantitative analysis of laminin-5 in the basement membrane of normal, hyperplastic, and malignant oral mucosa by confocal immunofluorescence imaging

Laminin-5 (Ln-5) is a heterotrimeric basement membrane (BM) molecule (alpha3beta3gamma2). It is a principal protein constituent of the anchoring filaments, which connect the BM with the hemidesmosomes of the basal keratinocytes and possess a crucial function in keratinocyte adhesion. Confocal immunofluorescence imaging is introduced for a quantitative evaluation of the Ln-5 content in the BM of oral squamous epithelium. The BM of normal oral mucosa was used as a reference (100%) for comparative analysis and showed a nearly uniform Ln-5 immunofluorescence intensity (99-100%). In all hyperplastic lesions of oral mucosa, the Ln-5 immunofluorescence intensity was increased (107-141%). The increased Ln-5 content in the BM of hyperplastic lesions suggests an increased keratinocyte-BM adhesion, possibly resulting in a higher stability of the oral mucosa. In contrast, in the oral squamous cell carcinoma (OSCC) invasive front, the remaining BM segments were characterized by a decrease in Ln-5 immunofluorescence intensity (35-74%). A stronger decrease of Ln-5-linked kerationocyte-BM adhesion correlates with a higher tumor grade. Because in central areas of carcinoma BM segments with a normal Ln-5 content could be demonstrated, the fundamental Ln-5 diminution in BM segments of the invasive front should be considered as an invasion-associated phenomenon.

Basement membrane laminin-5 is deposited in colorectal adenomas and carcinomas and serves as a ligand for alpha3beta1 integrin

Interplay between laminin-5 (Ln-5) and its integrin (Int) receptors alpha2beta1, alpha3beta1 and alpha6beta4 has been implicated in the progression and invasion of carcinomas. In this study we found abundant immunoreactivity for chains of Ln-5 (alpha3-beta3-gamma2) and Ln-10 (alpha5-beta1-gamma1), as well as for type VII collagen, in basement membranes (BM) of colorectal adenomas. In carcinomas of all differentiation grades, Lns were seen in tumor BMs, whereas type VII collagen was almost absent. Ln-5 appeared to accumulate along the invading edges of carcinomas, while Ln-10 was mostly absent. Immunoreactivity for Ln al chain, a component of Lns-1 and -3, was not seen in adenomas or carcinomas. Immunoreactivity for alpha2, alpha6, beta1 and beta4 Ints was found in all tumors and that for alpha3 Int in all adenomas and most of the carcinomas, often in colocalization with Ln-5. Immunoblotting of carcinoma tissues showed that the gamma2 chain of Ln-5 was present as typical Mr 105000 and 155000 isoforms. Immunoprecipitation experiments showed production of Ln-5 by cultured colon carcinoma cells. In quantitative cell adhesion experiments, function-blocking MAbs to alpha3 and beta1 Int subunits, but not those to Int alpha2 or alpha6 subunits, significantly inhibited the adhesion of cells to Ln-5. Our results suggest that BM composition in colorectal adenomas reflects the properties of surface epithelial BM of colorectal mucosa. In invading carcinomas, trimeric Ln-5, produced by carcinoma cells, is a major BM component and the cells use the alpha3beta1 Int complex for adhesion to Ln-5.

The alpha3 laminin subunit, alpha6beta4 and alpha3beta1 integrin coordinately regulate wound healing in cultured epithelial cells and in the skin

Previously, we demonstrated that proteolytic processing within the globular domain of the alpha3 subunit of laminin-5 (LN5) converts LN5 from a cell motility-inducing factor to a protein complex that can trigger the formation of hemidesmosomes, certain cell-matrix attachment sites found in epithelial cells. We have prepared a monoclonal antibody (12C4) whose epitope is located toward the carboxy terminus of the globular domain of the alpha3 laminin subunit. This epitope is lost from the alpha3 subunit as a consequence of proteolytic processing. Antibody 12C4 stains throughout the matrix of cells that fail to process the alpha3 laminin subunit, but does not recognize the matrix of confluent cultures of MCF-10A cells, which efficiently process their alpha3 laminin chain. In subconfluent populations of MCF-10A cells, 12C4 only stains matrix deposited at the outer edges of cell colonies. In these cells, integrin alpha3beta1 occasionally colocalizes with the staining generated by the 12C4 antibody but alpha6beta4 integrin does not. In wounded MCF-10A cell cultures, the 12C4 antibody stains the extracellular matrix beneath those cells at the very edge of the cellular sheet that moves to cover the wound site. A similar phenomenon is observed in human skin wounds, since we also detect expression of the unprocessed alpha3 laminin subunit at the leading tip of the sheet of epidermal cells that epithelializes skin wounds in vivo. In addition, using alpha3 laminin subunit and integrin function-inhibiting antibodies, we provide evidence that LN5 and its two integrin receptors (alpha6beta4 and alpha3beta1) appear necessary for wound healing to occur in MCF-10A cell culture wounds. We propose a model for healing of wounded epithelial tissues based on these results.

Melanocytes adhere to and synthesize laminin-5 in vitro

Melanocytes arise from the neural crest, migrate to the skin, and can be detected in the basal layer of the epidermis in skin biopsies of human fetuses as early as 11 weeks gestational age. During post-natal life, melanocytes reside at the basal layer of the epidermis, but the ligands to which they attach are unknown. Laminin-5 is a component of anchoring filaments of the lamina lucida of the epidermal basement membrane. In this report we show that human melanocytes adhere to purified laminin-5 to a level comparable with normal human keratinocytes. Blocking antibodies to the 165 kDa subunit of laminin-5 significantly inhibited fetal and neonatal melanocyte attachment to the surface of salt-split skin, which exposes laminin-5 on its surface, suggesting that laminin-5 is a ligand for melanocyte attachment to the basement membrane in vivo. Western blotting of concentrated culture supernatant of fetal and neonatal melanocytes with anti-laminin-5 antibodies demonstrated a single immunoreactive band of the expected size of laminin-5. In contrast, 3 human metastatic melanoma cell lines did not produce laminin-5. Immunofluorescence microscopy with antibodies to each of the three chains of laminin-5 confirmed the presence of laminin-5 in a peri-cellular distribution around melanocytes, but not melanoma cells. Our results suggest that laminin-5 may be a ligand for normal human melanocytes in the basement membrane, and that loss of laminin-5 production by melanoma cells may be a marker for malignant transformation.

Immunohistopathologic diagnosis of epidermolysis bullosa

Routine histologic study usually is insufficient to subclassify epidermolysis bullosa (EB); currently, electron microscopic evaluation has been the gold standard. A major advance recently has been made in elucidating the molecular basis of several major forms of EB. Concomitantly, immunoreagents have been developed to map antigens in the basement membrane zone. Some of these reagents facilitate the classification of EB into types and subtypes and can be used as an adjunct informative screening procedure to direct mutation identification efforts using DNA technologies. The current review provides an overview of these recent developments and a more detailed account of the immunohistopathologic diagnosis of EB.

Loss of laminin-5 in the epithelium-stroma interface: an immunohistochemical marker of malignancy in epithelial lesions of the breast

AIMS

To demonstrate immunohistochemically the alpha3 and gamma2 chain of laminin-5 in benign epithelial and malignant lesions of the human breast.

METHODS AND RESULTS

The alpha3 chain was identified by the monoclonal antibody BM165 and the gamma2 chain by GB3 in shock frozen samples using APAAP (alkaline phosphatase monoclonal anti-alkaline phosphatase) technique. The pre-existing breast epithelium, the 12 benign ductal and lobular proliferations and the three fibroadenomas showed a continuous immunostaining in the basement membrane region. In contrast to benign epithelial lesions, the 44 cases of invasive breast carcinoma showed a loss of the laminin-5 chains in more than 50% of the carcinoma stroma interface. Twenty-four out of the 44 invasive carcinomas revealed a complete loss of laminin-5 immunostaining. Focal defects of the laminin-5 immunostaining were also found in ductal carcinoma in situ in its pure form.

CONCLUSIONS

As recently described, the malignant transformation of breast epithelium with expression of an invasive phenotype is associated with a decrease of hemidesmosomes. The reduced immunostaining of laminin-5 is in line with this finding because laminin-5 represents the major component of the anchoring filaments attaching hemidesmosomes to the basement membrane. We feel that immunohistochemical demonstration of laminin-5 may serve as a marker of benignity in epithelial breast lesions. While other carcinoma types exhibit an increased laminin-5 deposition, which has been suggested as an invasion promoting factor, the loss of laminin-5 in breast cancer supports the view that breast carcinomas do not utilize laminin-5 for invasion.

Laminin 5 in the human thymus: control of T cell proliferation via alpha6beta4 integrins

Laminin 5 (alpha3beta3gamma2) distribution in the human thymus was investigated by immunofluorescence on frozen sections with anti-alpha3, -beta3, and -gamma2 mAbs. In addition to a linear staining of subcapsular basal laminae, the three mAbs give a disperse staining in the parenchyma restricted to the medullary area on a subset of stellate epithelial cells and vessel structures. We also found that laminin 5 may influence mature human thymocyte expansion; while bulk laminin and laminin 2, when cross-linked, are comitogenic with a TCR signal, cross-linked laminin 5 has no effect. By contrast, soluble laminin 5 inhibits thymocyte proliferation induced by a TCR signal. This is accompanied by a particular pattern of inhibition of early tyrosine kinases, including Zap 70 and p59(fyn) inhibition, but not overall inhibition of p56(lck). Using a mAb specific for alpha6beta4 integrins, we observed that while alpha3beta1 are known to be uniformly present on all thymocytes, alpha6beta4 expression parallels thymocyte maturation; thus a correspondence exists between laminin 5 in the thymic medulla and alpha6beta4 on mature thymocytes. Moreover, the soluble Ab against alpha6beta4 inhibits thymocyte proliferation and reproduces the same pattern of tyrosine kinase phosphorylation suggesting that alpha6beta4 is involved in laminin 5-induced modulation of T cell activation.

Extent of laminin-5 assembly and secretion effect junctional epidermolysis bullosa phenotype

Junctional epidermolysis bullosa (JEB) is an autosomal recessive skin blistering disease with both lethal and nonlethal forms, with most patients shown to have defects in laminin-5. We analyzed the location of mutations, gene expression levels, and protein chain assembly of the laminin-5 heterotrimer in six JEB patients to determine how the type of genetic lesion influences the pathophysiology of JEB. Mutations within laminin-5 genes were diversely located, with the most severe forms of JEB correlating best with premature termination codons, rather than mapping to any particular protein domain. In all six JEB patients, the laminin-5 assembly intermediates we observed were as predicted by our previous work indicating that the alpha3beta3gamma2 heterotrimer assembles intracellularly via a beta3gamma2 heterodimer intermediate. Since assembly precedes secretion, mutations that disrupt protein-protein interactions needed for assembly are predicted to limit the secretion of laminin-5, and likely to interfere with function. However, our data indicate that typically the most severe mutations diminish mRNA stability, and serve as functional null alleles that block chain assembly by resulting in either a deficiency (in the nonlethal mitis variety) or a complete absence (in lethal Herlitz-JEB) of one of the chains needed for laminin-5 heterotrimer assembly.

Processing of laminin-5 and its functional consequences: role of plasmin and tissue-type plasminogen activator

The laminin-5 component of the extracellular matrices of certain cultured cells such as the rat epithelial cell line 804G and the human breast epithelial cell MCF-10A is capable of nucleating assembly of cell- matrix adhesive devices called hemidesmosomes when other cells are plated upon them. These matrices also impede cell motility. In contrast, cells plated onto the laminin-5-rich matrices of pp126 epithelial cells fail to assemble hemidesmosomes and are motile. To understand these contradictory phenomena, we have compared the forms of heterotrimeric laminin-5 secreted by 804G and MCF-10A cells with those secreted by pp126 cells, using a panel of laminin-5 subunit-specific antibodies. The alpha3 subunit of laminin-5 secreted by pp126 cells migrates at 190 kD, whereas that secreted by 804G and MCF-10A cells migrates at 160 kD. The pp126 cell 190-kD alpha3 chain of laminin-5 can be specifically proteolyzed by plasmin to a 160-kD species at enzyme concentrations that do not apparently effect the laminin-5 beta and gamma chains. After plasmin treatment, pp126 cell laminin-5 not only impedes cell motility but also becomes competent to nucleate assembly of hemidesmosomes. The possibility that plasmin may play an important role in processing laminin-5 subunits is supported by immunofluorescence analyses that demonstrate colocalization of laminin-5 and plasminogen in the extracellular matrix of MCF-10A and pp126 cells. Whereas tissue-type plasminogen activator (tPA), which converts plasminogen to plasmin, codistributes with laminin-5 in MCF-10A matrix, tPA is not present in pp126 extracellular matrix. Treatment of pp126 laminin-5-rich extracellular matrix with exogenous tPA results in proteolysis of the laminin-5 alpha3 chain from 190 to 160 kD. In addition, plasminogen and tPA bind laminin-5 in vitro. In summary, we provide evidence that laminin-5 is a multifunctional protein that can act under certain circumstances as a motility and at other times as an adhesive factor. In cells in culture, this functional conversion appears dependent upon and is regulated by tPA and plasminogen.

Neoexpression of the epithelial adhesion complex antigens in thyroid tumours is associated with proliferation and squamous differentiation markers

Integrin dimer alpha 6 beta 4 is a transmembrane component of an epithelial cell adhesion complex that consists of hemidesmosomes (HDs), basement membrane (BM)-associated laminin-5 (Ln-5), and anchoring filaments/type VII collagen, all of which are absent from normal thyroid follicular epithelium. In the present study, the expression of epithelial cell adhesion complex antigens in thyroid tumours was investigated using immunohistochemistry. In addition to integrin subunits alpha 6 and beta 4, immunoreactivity was found for all chains of Ln-5, alpha 3, beta 3 and gamma 2, type VII collagen and hemidesmosomal antigen, HD1, in most thyroid carcinomas associated with tumour anaplasia and papillary growth pattern and located at the border of parenchymal cells and connective tissue or blood vessel walls. In addition, a more restricted expression of bullous pemphigoid antigens 180 and 230 (BP180 and BP230), constituents of HDs, was found in some papillary and anaplastic carcinomas and atypical adenomas. Adhesion complex antigens were located to regions of cells which were immunoreactive for cytokeratin (ck)-5 and proliferating cell nuclear antigen Ki-67. The results suggest that in thyroid carcinomas, the emergence of adhesion complex antigens is associated with squamous differentiation and high proliferative activity.

Hemidesmosomes show abnormal association with the keratin filament network in junctional forms of epidermolysis bullosa

Junctional epidermolysis bullosa is a group of hereditary bullous disorders resulting from defects in several hemidesmosome-anchoring filament components. Because hemidesmosomes are involved not only in keratinocyte-extracellular matrix adherence, but also in normal anchorage of keratin intermediate filaments to the basal keratinocyte membrane, we questioned whether this intracellular function of hemidesmosomes was also perturbed in junctional epidermolysis bullosa. We used quantitative electron microscopic methods to assess certain morphologic features of hemidesmosome-keratin intermediate filaments interactions in skin from normal subjects (n = 11) and from patients with different forms of junctional epidermolysis bullosa (n = 13). In addition, skin from patients with autosomal recessive epidermolysis bullosa simplex with plectin defects (n = 3) or with autosomal recessive dystrophic epidermolysis bullosa (n = 4) were included as controls. Values were expressed as a percentage of the total number of hemidesmosomes counted. In normal skin 83.3% +/- 3.3 (SEM) hemidesmosomes were associated with keratin intermediate filaments and 90.1% +/- 1.9 had inner plaques. In Herlitz junctional epidermolysis bullosa (laminin 5 abnormalities, n = 4) these values were reduced to 45.3% +/- 11.5 (p < 0.001; analysis of variance) and 50.3% +/- 12.8 (p < 0.001), respectively. In junctional epidermolysis bullosa with pyloric atresia (alpha6beta4 abnormalities, n = 3) the values were also reduced [41.8% +/- 7.0 (p < 0.001) and 44.5% +/- 5.7 (p < 0.001), respectively]. In the non-Herlitz group (laminin 5 mutations, n = 3) the counts were 66.7% +/- 7.1 (p > 0.05) and 70.5% +/- 8.5 (p < 0.05), and in skin from patients with bullous pemphigoid antigen 2 mutations (n = 3) the counts were 54.3% +/- 13.8 (p < 0.01) and 57.1% +/- 13.9 (p < 0.01). In epidermolysis bullosa simplex associated with plectin mutations the values were 31.9% +/- 8.9 (p < 0.001) for keratin intermediate filaments association and 39.9% +/- 7.1 (p < 0.001) for inner plaques. Findings in recessive dystrophic epidermolysis bullosa patients' skin were indistinguishable from normal control skin with inner plaques (90.5% +/- 2.5) and keratin intermediate filaments attachment (86.3% +/- 2.1). These findings suggest that the molecular abnormalities underlying different forms of junctional epidermolysis bullosa appear to affect certain critical intracellular functions of hemidesmosomes, such as the normal connections with keratin intermediate filaments. This may have important implications for the maintenance of basal keratinocyte integrity and resilience in junctional epidermolysis bullosa.

Differential expression of laminin chains in the human major salivary gland

Laminin represents a macromolecule family. The heterotrimeric isoforms of laminin can be determined by immunohistochemical demonstration of the single chains. The laminin chain heterogeneity of the basement membrane in adult human major salivary glands was evaluated in relation to cellular differentiation of the epithelia and the stromal compartment. Monoclonal antibodies to the laminin alpha1, alpha3 (BM165) chains and epiligrin reacted with the basement membranes of serous and mucous acini and of intercalated, striated and excretory ducts. As evidenced by a double-labelling technique, the alpha2 chain showed a spatial association with the myoepithelium of the acini, whereas the ductal basement membranes containing no myoepithelial cells were negative. Almost exclusively, beta1 chain was detected in acinar basement membrane, beta2 chain whereas in ductal basement membrane. Gamma2 chain is a unique chain belonging to the laminin-5 isoform. It was restricted to the ductal basement membrane. Alpha1, alpha2, beta1, beta2 and gamma1 chains were detected in nerves of salivary tissue and alpha1, alpha3, beta1, beta2 and gamma1 chains and epiligrin in blood vessels. Our results indicate that the acinar ductal unit contains basement membranes with different isoforms, which relate to cell differentiation and cell function.

Acquired junctional epidermolysis bullosa associated with IgG autoantibodies to the beta subunit of laminin-5

We report the case of a 72-year-old man with clinical features resembling those of non-lethal junctional epidermolysis bullosa associated with IgG autoantibodies to the beta chain of laminin-5. The patient presented with a sudden onset of blistering and severe fragility of the skin and mucous membranes resulting in atrophic scars. Electron microscopy showed that the blistering arose in the lamina lucida. Indirect immunofluorescence indicated that the autoantibodies bound to the dermal side of 1 mol/L NaCl-split skin, and both direct and indirect immunoelectron microscopy demonstrated antibody binding to the lamina densa. Postembedding immunogold electron microscopy also revealed labelling in the lamina lucida beneath the hemidesmosomes. On immunoblotting, we found the autoantibodies to comigrate with the beta chain of laminin-5. Following the nomenclature of inherited junctional epidermolysis bullosa with mutations of the laminin-5 gene, we propose the name acquired junctional epidermolysis bullosa for this newly recognized disease.

LAD-1 is absent in a subset of junctional epidermolysis bullosa patients

The anchoring filament protein LAD-1 has been recently identified as the target of autoantibodies in the acquired blistering disorder linear IgA bullous dermatosis. Because this protein appears to be involved in the process of dermal-epidermal cohesion, this study sought to determine the involvement of LAD-1 in the pathology of junctional epidermolysis bullosa (JEB). To this end, 44 patients with a variety of subtypes of JEB were analyzed by indirect immunofluorescence microscopy with antibodies to LAD-1, BP180, and laminin-5. We found that only patients with generalized atrophic benign epidermolysis bullosa (GABEB) contained LAD-1 defects. Of the 16 GABEB patients studied, 13 showed absent or greatly reduced expression of LAD-1 (including 2 patients with a peculiar interrupted staining pattern) and 3 patients showed defects of laminin-5 expression with normal LAD-1 expression. Patients who showed LAD-1 defects also showed abnormal expression of BP180. Keratinocytes were cultured from the skin of two GABEB patients and analyzed by indirect immunofluorescent microscopy. One culture demonstrated defects of BP180 and LAD-1 expression (which was also verified by radioimmunoprecipitation assay), and one culture showed decreased laminin-5 expression but normal BP180 and LAD-1 expression. Thus, these studies demonstrate that: (i) LAD-1 and BP180 are normally expressed in all subtypes of JEB except GABEB, (ii) the majority of GABEB patients show absent or near absent expression of both LAD-1 and BP180 but normal expression of laminin-5, and (iii) a smaller subset of GABEB patients show normal LAD-1 and BP180 expression but express persistent but reduced levels of laminin-5.

Laminin-6 and laminin-5 are recognized by autoantibodies in a subset of cicatricial pemphigoid

We characterized basement membrane zone (BMZ) autoantigens targeted by autoantibodies (AAb) from patients with cicatricial pemphigoid. Serum from a patient with severe oral cicatricial pemphigoid contained IgG anti-BMZ AAb. The AAb labeled a lower BMZ component on salt-split skin and localized to the lower lamina lucida/lamina densa by direct and indirect immunoelectron microscopy (IEM) but did not label blood vessels. The AAb did not react with EHS laminin-1 and type IV collagen, pepsinized human type IV collagen, recombinant entactin, or NC1 domain of type VII collagen by dot blotting and western blotting. We focused our studies on the laminin family, as laminin-5 was identified as an autoantigen in cicatricial pemphigoid. Culture-conditioned media from normal keratinocytes (containing laminin-6 and laminin-5) and JEB keratinocytes (containing laminin-6 but not laminin-5) were studied by western blotting. Under nonreducing conditions, the patient's AAb recognized a 600-kDa protein (laminin-6) intensely and a 400-kDa protein (laminin-5) weakly in normal keratinocyte medium even though abundant laminin-5 was present. InJEB keratinocyte medium, however, the 600-kDa protein (laminin-6) alone was recognized by the patient's AAb. The AAb also immunolabeled BMZ of JEB skin that lacked laminin-5. The AAb from this patient and two other patients with anti-laminin-5 cicatricial pemphigoid immunoprecipitated both laminin-6 and laminin-5. Taken together, the results of IEM, non-reducing western blotting, immunoprecipitation, and JEB skin BMZ immunolabeling indicate that laminin-6, as well as laminin-5, is identified by the AAb from a subset of cicatricial pemphigoid patients. We propose the name "anti-laminin cicatricial pemphigoid" for this subset.

Immunomapping of basement membrane zone macromolecules in canine salt-split skin

Certain macromolecules of human and canine cutaneous basement membrane zone (BMZ) have shown to have responsibilities for pathogenesis of mechanobullous skin diseases. Salt-split skin by 1 M NaCl have been used for diagnosis of human mechanobullous diseases. However, there have been no studies to characterize canine salt-split skin. Electron microscopy of canine salt-split skin showed the separation within lamina lucida. Indirect immunofluorescence revealed the roof of the cleft was labeled by human patient serum with bullous pemphigoid, whereas laminin, laminin 5, type IV and type VII collagen were labeled at the bottom of the cleft. It is suggested that immunomapping of salt-split skin may be useful for the differential diagnosis of canine mechanobullous diseases.

The role of laminin-5 and its receptors in mammary epithelial cell branching morphogenesis

In vivo, normal mammary epithelial cells utilize hemidesmosome attachment devices to adhere to stroma. However, analyses of a potential role for hemidesmosomes and their components in mammary epithelial tissue morphogenesis have never been attempted. MCF-10A cells are a spontaneously immortalized line derived from mammary epithelium and possess a number of characteristics of normal mammary epithelial cells including expression of hemidesmosomal associated proteins such as the two bullous pemphigoid antigens, alpha 6 beta 4 integrin and its ligand laminin-5. More importantly, MCF-10A cells readily assemble mature hemidesmosomes when plated onto uncoated substrates. When maintained on matrigel, like their normal breast epithelial cell counterparts, MCF-10A cells undergo a branching morphogenesis and assemble hemidesmosomes at sites of cell-matrigel interaction. Function blocking antibodies specific for human laminin-5 and the alpha subunits of its two known receptors (alpha 3 beta 1 and alpha 6 beta 4 integrin) not only inhibit hemidesmosome assembly by MCF-10A cells but also impede branching morphogenesis induced by matrigel. Our results imply that the hemidesmosome, in particular those subunits comprising its laminin-5/integrin 'backbone', play an important role in morphogenetic events. We discuss these results in light of recent evidence that hemidesmosomes are sites involved in signal transduction.

Defective integrin alpha 6 beta 4 expression in the skin of patients with junctional epidermolysis bullosa and pyloric atresia

Junctional epidermolysis bullosa (JEB) is a heterogeneous group of rare inherited skin disorders in which defects in cell adhesion components cause incomplete formation of hemidesmosomes. We have immunohistochemically examined the skin from ten JEB patients (JEB gravis, n = 4; JEB mitis, n = 3; JEB plus pyloric atresia [JEB/PA], n = 3) using monoclonal antibodies specific for the integrin adhesion receptors alpha 3 beta 1 and alpha 6 beta 4, and for the alpha 3, beta 3, and gamma 2 subunits of the basement membrane ligand, laminin 5. Consistent with our previous reports, only the JEB gravis patients without associated pyloric atresia expressed reduced or absent epitopes for laminin-5 subunits in their epidermal basement membrane. In contrast, all three JEB/PA cases showed abnormalities in integrin alpha 6 beta 4, but not in laminin 5, expression in their basal epidermal cells. Integrin beta 4 subunit was undetectable in the biopsied epidermis of these JEB/PA individuals using five different monoclonal antibodies that recognize both intra- and extracellular epitopes. The absence of the beta 4 subunit in the epidermis of JEB/PA specimens was confirmed by Western blot analysis of tissue extracts. Epidermal expression of the integrin alpha 6 subunit was variable in the JEB/PA patients. Abnormal integrin alpha 6 beta 4 expression may define the subset of JEB cases with pyloric atresia. These results strongly implicate a functional role for alpha 6 beta 4 in the formation of complete hemidesmosomes and in stable adhesion of basal keratinocytes to the basement membrane in vivo.

Functional Re-expression of laminin-5 in laminin-gamma2-deficient human keratinocytes modifies cell morphology, motility, and adhesion

Herlitz junctional epidermolysis bullosa (H-JEB) is characterized by a reduced adherence of keratinocytes consequent to deficient expression of the extracellular adhesive ligand laminin-5. To complement the genetic defect causing H-JEB, we transferred an eukaryotic cassette expressing the cDNA for the gamma2 chain of laminin-5 into H-JEB keratinocytes in which the expression of the polypeptide is hampered by a homozygous mutation generating a premature termination codon. Transfection using adenovirus-polylysin-transferrin-DNA complexes resulted in a transient synthesis of the recombinant laminin gamma2 chain that associated with the endogenous alpha3 and beta3 chains to form laminin-5 molecules readily deposited on the tissue culture substrate. Furthermore, retroviral-mediated transduction of the gamma2 cDNA yielded persistent expression and polarized secretion of laminin-5. The protein incorporated into the basement membrane produced by the revertant cells inoculated subcutaneously in nude mice. In these transfectants, re-expression of laminin-5 induced changes in cell morphology and reorganization of focal adhesions that assumed the shape and distribution of the counterparts detected in normal keratinocytes. These observations correlated with an enhanced cell-substrate adhesion and a reduced motility of the transfected cells. Our results demonstrate that a restored expression of laminin-5 induces a phenotypic reversion of genetically altered H-JEB keratinocytes and open new perspectives to the analysis of the mechanisms regulating adhesion of epithelial cells.

Plectin deficiency results in muscular dystrophy with epidermolysis bullosa

We report that mutation in the gene for plectin, a cytoskeleton-membrane anchorage protein, is a cause of autosomal recessive muscular dystrophy associated with skin blistering (epidermolysis bullosa simplex). The evidence comes from absence of plectin by antibody staining in affected individuals from four families, supportive genetic analysis (localization of the human plectin gene to chromosome 8q24.13-qter and evidence for disease segregation with markers in this region) and finally the identification of a homozygous frameshift mutation detected in plectin cDNA. Absence of the large multifunctional cytoskeleton protein plectin can simultaneously account for structural failure in both muscle and skin.

Mutational hotspots in the LAMB3 gene in the lethal (Herlitz) type of junctional epidermolysis bullosa

The Herlitz type of junctional epidermolysis bullosa (H-JEB) is a severe blistering disease affecting the skin and mucous membranes, and laminin 5 has been implicated as the candidate gene/protein system for most patients with H-JEB. In this study, we have examined a cohort of 14 families with H-JEB for mutations in the LAMB3 gene. Premature termination codon mutations were delineated in both alleles of each proband in all pedigrees. Interestingly, two recurrent mutations, R42X and R635X, were noted in over 50% of the mutant LAMB3 alleles. These nonsense mutations occurred at CpG dinucleotide sequences, suggesting hypermutability of 5-methylcytosine to thymine. Additional evidence suggested that R42X and R635X represent mutational hotspots. First, the inheritance of R635X in a homozygous individual on two different genetic backgrounds was demonstrated by haplotype analysis. Furthermore, in one family, R42X was shown to be inherited on the maternal allele which lacked this mutation, suggesting that it arose as a result of maternal germline mutation. Elucidation of these two hotspot mutations will facilitate screening of additional JEB patients for the underlying mutations.