Herlitz's junctional epidermolysis bullosa is linked to mutations in the gene (LAMC2) for the gamma 2 subunit of nicein/kalinin (LAMININ-5)

Developmental expression of laminin-5 and HD1 in the intestine: epithelial to mesenchymal shift for the laminin gamma-2 chain subunit deposition

We report the expression pattern of hemidesmosome-associated proteins laminin-5, composed of alpha 3 beta 3 gamma 2 chains, and HD1 in the developing mouse and human intestine, an organ in which variations in structure and function parallel morphogenesis and differentiation. Immunocytochemistry analysis revealed the coexpression of laminin-5 and HD1 at the basal pole of differentiating epithelial cells. Distinct noticeable variations occurring in the location of laminin alpha 3 chain in development of mouse gut were stressed by the reverse transcriptase-polymerase chain reaction data. A peculiar finding was also the location of laminin gamma 2 chain in the intestinal muscle coat. The cellular origin of laminin gamma 2 chain was examined by immunocytochemistry on interspecies hybrid intestines with specific antibodies recognizing mouse antigens. Complementary and sequential production of laminin gamma 2 chain was observed, by epithelial cells as establishment of the basement membrane occurs and by mesenchymal cells in the more differentiated organ. These results support the concept of mesenchymal involvement in deposition of basement membrane molecules, a crucial process for intestinal differentiation. Taken together these data provide the first evidence for the coexpression of hemidesmosome-associated proteins in the gut, a non-stratified tissue.

A homozygous deletion mutation in the gene encoding the 180-kDa bullous pemphigoid antigen (BPAG2) in a family with generalized atrophic benign epidermolysis bullosa

The 180-kDa bullous pemphigoid antigen (BPAG2) is a candidate gene/protein for mutations in some forms of junctional epidermolysis bullosa. In this study, we searched for mutations in BPAG2 in a large Austrian pedigree with generalized atrophic benign epidermolysis bullosa, a distinct nonlethal form of junctional epidermolysis bullosa, using polymerase chain reaction amplification of genomic DNA, heteroduplex analysis of the polymerase chain reaction products, and direct nucleotide sequencing. We identified a homozygous 2-bp deletion within the coding region of BPAG2 in the affected individuals. This mutation results in a frameshift and downstream stop codons on both alleles, predicting an absence of functional protein. These findings illustrate the molecular basis of the skin fragility in this family and attest to the importance of the 180-kDa bullous pemphigoid antigen in the attachment of the epidermis to the underlying dermoepidermal basement membrane.

Compound heterozygosity for nonsense and missense mutations in the LAMB3 gene in nonlethal junctional epidermolysis bullosa

Mutations in the genes encoding laminin 5 (LAMA3, LAMB3, and LAMC2) have been delineated in the autosomal recessive blistering skin disorder, junctional epidermolysis bullosa, particularly in the lethal (Herlitz) variant. In this study, we searched for mutations in these genes in two patients with nonlethal forms of junctional epidermolysis bullosa using polymerase chain reaction amplification of genomic DNA, followed by heteroduplex analysis and direct automated nucleotide sequencing. Both patients were found to be compound heterozygotes for the same nonsense mutation on one LAMB3 allele, and different missense mutations on the other LAMB3 allele. The combination of nonsense and a missense mutation in the LAMB3 gene appears to be important in determining the milder clinical phenotype in some cases of the nonlethal forms of junctional epidermolysis bullosa involving abnormalities in laminin 5.

Management of patients with epidermolysis bullosa

Epidermolysis bullosa is a group of systemic disorders whose management requires familiarity with its many extracutaneous complications. These include gastrointestinal, ophthalmologic, laryngeal, dental, and hematologic problems. This article reviews wound care and management of systemic complications seen in patients with epidermolysis bullosa.

A recurrent homozygous nonsense mutation within the LAMA3 gene as a cause of Herlitz junctional epidermolysis bullosa in patients of Pakistani ancestry: evidence for a founder effect

The anchoring filament protein laminin 5 is abnormally expressed in the skin of patients with Herlitz junctional epidermolysis bullosa (H-JEB). In this study, we performed mutational analysis on genomic DNA from a H-JEB child of first-cousin Pakistani parents, and identified a homozygous C-to-T transition in the LAMA3 gene of laminin 5 resulting in a premature termination codon (CGA-TGA) on both alleles. This mutation, R650X, has been previously reported in two other seemingly unrelated H-JEB individuals of Pakistani ancestry. Although this mutation may represent a mutational hotspot within the LAMA3 gene, haplotype analysis based on a silent intragenic polymorphism (GCC/GCG, alanine 429; GenBank no. L34155), and on three flanking microsatellite polymorphism (D18S45, D18S478, and D18S480), suggests that a common ancestral allele may be present in all three cases.

Human amnion contains a novel laminin variant, laminin 7, which like laminin 6, covalently associates with laminin 5 to promote stable epithelial-stromal attachment

Stable attachment of external epithelia to the basement membrane and underlying stroma is mediated by transmembrane proteins such as the integrin alpha6beta4 and bullous pemphigoid antigen 2 within the hemidesmosomes along the basolateral surface of the epithelial cell and their ligands that include a specialized subfamily of laminins. The laminin 5 molecule (previously termed kalinin/nicein/epiligrin) is a member of this epithelial-specific subfamily. Laminin 5 chains are not only considerably truncated within domains III-VI, but are also extensively proteolytically processed in vitro and in vivo. As a result, the domains expected to be required for the association of laminins with other basement membrane components are lacking in the mature laminin 5 molecule. Therefore, the tight binding of laminin 5 to the basement membrane may occur by a unique mechanism. To examine laminin 5 in tissue, we chose human amnion as the source, because of its availability and the similarity of the amniotic epithelial basement membrane with that of skin. We isolated the laminin 5 contained within the basement membrane of human amnion. In addition to monomeric laminin 5, we find that much of the laminin 5 isolated is covalently adducted with laminin 6 (alpha3beta1gamma1) and a novel laminin isotype we have termed laminin 7 (alpha3beta2gamma1). We propose that the association between laminin 5 and laminins 6 and 7 is a mechanism used in amnion to allow stable association of laminin 5 with the basement membrane. The beta2 chain is seen at the human amniotic epithelial-stromal interface and at the dermal-epidermal junction of fetal and adult bovine skin by immunofluorescence, but is not present, or only weakly present, in neonatal human skin.

Laminins: a family of diverse multifunctional molecules of basement membranes

Laminins represent a growing family of disulfide-linked heterotrimers constituted by the association of three genetically different polypeptides, the alpha, beta, and gamma chains. Laminins are endowed with structural and biological functions. They play a direct critical role in the control of cellular behavior by providing cells with specific information through interactions with cell surface receptors. Because of their structural properties, they represent crucial building blocks for tissue assembly, architecture, and stability. The expression of laminin chain variants is spatio-temporally regulated, which suggests that laminin isoforms might have different functions responsible for the biological and morphological polymorphism of basement membranes. The different cells present in the skin express several laminin chains, which lead to the deposition of various laminin isoforms, whose mechanical and biological functions are likely to be adapted to the properties of the dermo-epidermal junction. Recently, defective laminin isoforms have been shown to be associated with several inborn and acquired diseases, illustrating a major structural function for laminins in skin integrity.

Molecular complexity of the cutaneous basement membrane zone. Revelations from the paradigms of epidermolysis bullosa

Spectacular success has recently been made towards elucidation of the molecular basis of various forms of epidermolysis bullosa (EB), a group of heritable blistering skin diseases. The information derived from these studies has already had a profound impact in terms of precise diagnosis and classification, early prenatal prediction of the phenotype and genetic counseling in families at risk for recurrence. This review highlights recent progress made in defining the molecular basis of junctional and dystrophic forms of EB and the genotype/phenotype relationships established from these studies. Extensive molecular studies, such as the ones captured in this review, form a foundation for the rational design of gene therapies to counteract these conditions in the future.

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.

Stimulation of endothelial cell migration in culture by ladsin, a laminin-5-like cell adhesion protein

Ladsin is a laminin-like cell-adhesive scatter factor with potent cell motility-stimulating ability and was purified from serum-free conditioned medium of a malignant human gastric adenocarcinoma cell line STKM-1. To test its possible role in tumor angiogenesis, we investigated its effect on primary culture of endothelial cells (human umbilical vein endothelial cells) and endothelial cell line ECV304 in this study. Cell adhesion and motility effects of ladsin were observed in both types of endothelial cells. In cell-attachment assay, ladsin interacted with integrin alpha 3 beta 1 that was expressed on the endothelial cell surface. In Boyden chambers, ladsin stimulated both directed and random migration of ECV304 cells. Ladsin induced repair of artificial wounds generated in ECV304 cell monolayers by stimulating cell migration. Ladsin did not affect the growth rate of ECV304 cells at a low cell density but significantly increased the saturation cell density. These results suggest that ladsin may be involved in the adhesion and migration of endothelial cells under some physiological and pathological conditions.

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

Herlitz junctional epidermolysis bullosa is an autosomal recessive disorder characterized by generalized blistering at the lamina lucida of the cutaneous basement membrane. The monoclonal antibody GB3 has been used as a diagnostic probe because of its lack of reactivity in patient skin. The antigen recognized by GB3 has been identified as laminin-5, a glycoprotein consisting of three subunits (alpha 3, beta 3 and gamma 2). To identify the laminin-5 protein chain that contains the epitope recognized by GB3 and to determine if chain assembly is required for antibody recognition, we expressed a gamma 2 protein constructed from a full-length gamma 2 cDNA. Radioimmunoprecipitation of the culture medium from 293 cells revealed that both GB3 and anti-gamma 2 polyclonal antibodies were capable of directly precipitating recombinant gamma 2 without coprecipitation of other proteins. In immunodepletion experiments, each antibody removed most of the protein that was reactive with the other antibody. The epitope recognized by GB3 is present only when the complex is in the native conformation because GB3 reacted only with the non-reduced laminin-5, but not the reduced laminin-5 in immunoblots. Moreover, because GB3 reacted with laminin-5 of SCC25 cells (gamma 2 in the heterotrimer) but not recombinant gamma 2 in 293 cells (gamma 2 alone) during indirect immunofluorescence staining, this epitope may be dependent upon a less stable conformation of gamma 2. We conclude that GB3 recognizes the gamma 2 chain of laminin-5 and that the epitope is entirely contained in the native form of the gamma 2 chain.

Junctional epidermolysis bullosa and pyloric atresia: a distinct entity. Clinical and pathological studies in five patients

Junctional epidermolysis bullosa (JEB) associated with pyloric atresia (PA) is a distinct entity which is inherited as an autosomal recessive disorder. We describe five patients with this association; four died in the neonatal period and one is still alive at 4 years of age. The cutaneous lesions in these patients are identical or similar to those in other JEB subtypes. Urinary tract involvement is part of the syndrome and presents a problem for long-term survival. Using the monoclonal antibody GB3 we investigated skin biopsies from three of our patients and showed normal expression in all of them, unrelated to the outcome of their disease. This indicates that the GB3 monoclonal antibody is without prognostic significance in this syndrome. It is clear that JEB with PA is a distinct entity. The molecular basis as yet is unknown.

Prenatal diagnosis of Herlitz junctional epidermolysis bullosa by amniocentesis

Herlitz junctional epidermolysis bullosa (HJEB) is a severe blistering disorder which usually results in death during infancy. We have previously shown that the anchoring filament protein laminin-5 (kalinin/nicein), which mediates keratinocyte attachment and dermal-epidermal cohesion, is abnormally expressed in individuals with HJEB. Laminin-5 was detected by Western blot analysis in amniotic fluid from 44 consecutive normal second-trimester control pregnancies, but was undetectable in second-trimester amniotic fluid from four pregnancies with fetuses affected by HJEB. In one case of severe non-Herlitz JEB, laminin-5 was detected in both amniotic fluid and skin. In human amniotic fluid, the laminin-5 a3 subunit was processed to a major 165 kD species and a minor 145 kD species and the beta 2 subunit was partially processed to 105 kD. Although laminin-5 was covalently associated with laminin-6 (K-laminin) in amniotic membrane, no covalent interaction was detected in amniotic fluid. Laminin-5 from amniotic fluid strongly supported keratinocyte attachment. These results suggest that Western blot analysis of second-trimester amniotic fluid is useful in determining the prenatal diagnosis of HJEB and that laminin-5 may serve a physiologically important function in amniotic fluid.

Studies of patients with anti-epiligrin cicatricial pemphigoid

We have recently identified patients with a form of cicatricial pemphigoid who have IgG anti-basement membrane autoantibodies directed against epiligrin, a laminin isoform closely related if not identical to laminin 5. These patients' autoantibodies bind the lower lamina lucida of human epidermal basement membrane and immunoprecipitate this laminin isoform from extracts and media of biosynthetically radiolabeled human keratinocytes. Immunoblot studies show that these patients' autoantibodies specifically bind the alpha subunit of this laminin (i.e., laminin subunit alpha 3). We have found no evidence of these autoantibodies in normal volunteers or patients with other bullous skin diseases (including those with other forms of CP). These studies have identified a group of patients with an acquired, autoimmune, subepidermal bullous disorder who have disease-specific autoantibodies directed against the alpha subunit of epiligrin/laminin 5. These findings correlate with prior reports showing that a monoclonal antibody directed against this laminin subunit induces detachment of keratinocytes from extracellular matrix in vitro as well as epidermis from human skin in situ. Together, these findings suggest that this laminin mediates attachment of basal keratinocytes to epidermal basement membrane and that autoantibodies directed against it may be pathogenic. Moreover, recent studies showing that subunits of this laminin isoform are mutated in some patients with Herlitz's junctional epidermolysis bullosa indicate that acquired or inherited abnormalities in this adhesion ligand are associated with skin diseases characterized by separation of epidermis from epidermal BM.

The assembly of laminin-5 subunits

Laminin-5 is a heterotrimer composed of alpha 3, beta 3, and gamma 2 chains, produced by keratinocytes and the human squamous cell carcinoma line (SCC-25), and is one of the candidate proteins for the genetic lesion in junctional epidermolysis bullosa. Two-dimensional SDS-polyacrylamide gel electrophoresis (first dimension, nonreducing conditions; second dimension, reducing conditions) revealed that the immunoprecipitated laminin-5 from a SCC-25 cell fraction consisted of alpha 3, beta 3, and gamma 2 monomers, a beta 3 gamma 2 heterodimer, and an alpha 3 beta 3 gamma 2 heterotrimer. The presence of the beta 3 gamma 2 heterodimer, but not heterodimers containing an alpha 3 chain and any of the other chains, was suggestive of assembly of laminin-5 proceeding from a beta 3 gamma 2 heterodimer to an alpha 3 beta 3 gamma 2 heterotrimer. We showed, by cotransfection experiments using full-length recombinant beta 3 and gamma 2 chains in a human cell line devoid of endogenous laminin-5, that stable heterodimers can be formed in the absence of alpha 3 chain expression. In the SCC-25 cell fraction, the alpha 3 monomer pool was the smallest of the monomers. Pulse-chase experiments using the cell fraction also indicated that the heterotrimer was assembled after a 10-min pulse and was nearly absent after a 24-h chase. These results are consistent with the synthesis of alpha 3 being limiting for heterotrimer assembly, with rapid association of the alpha 3 chain with beta 3 gamma 2 heterodimers to form complete heterotrimers. Treatment with tunicamycin reduced the size of each of the laminin-5 subunits, indicating that all chains are glycosylated, but that N-linked glycosylation is not necessary for chain assembly and secretion.

Rapid spreading and mature hemidesmosome formation in HaCaT keratinocytes induced by incubation with soluble laminin-5r

HaCaT cells, an immortalized keratinocyte line, incubated in plastic wells in the presence of conditioned medium from 804G cells adhered and spread rapidly in less than 30 min. In contrast, cells plated in fibroblast or keratinocyte conditioned medium adhered poorly and remained rounded at 30 min. Immunodepletion of 804G conditioned medium with polyclonal antisera to laminin-5r, but not control antisera, abolished rapid cell spreading. Electron microscopy of HaCaT cells spread by incubation in 804G conditioned medium, but not control medium, revealed mature hemidesmosomes after 24 h. Rapid spreading was also observed in wells precoated with 804G conditioned medium or 804G cell-deposited matrix, but not with fibronectin, vitronectin, or laminin-1. Immunoblotting of 804G conditioned medium with anti-laminin-5r antibodies unveiled polypeptides of 150, 140, 135, and 100 kDa, identical by electrophoretic mobility to immunoreactive polypeptides in 804G deposited matrix. Our results suggest that addition of laminin-5r in a soluble form is sufficient to promote rapid spreading and hemidesmosome assembly in keratinocytes. The mechanism of soluble laminin-5r action may include efficient surface "priming" for cell adhesion. Soluble laminin-5r may have a physiologic role in morphogenesis and repair of the epidermis and may be of use for therapeutic applications.

Anti-basement membrane autoantibodies in patients with anti-epiligrin cicatricial pemphigoid bind the alpha subunit of laminin 5

Recent studies have identified a group of cicatricial pemphigoid patients who have IgG anti-basement membrane autoantibodies that recognize epiligrin, a set of disulfide-linked polypeptides closely related if not identical to laminin 5 (formerly called kalinin, nicein, or BM600). To further understand the pathophysiology of blister formation in these patients, we have sought to identify the specific polypeptide(s) targeted by their autoantibodies. Comparative studies show that sera from these patients (nine of nine), P1E1 monoclonal anti-epiligrin antibody, and polyclonal as well as monoclonal anti-laminin 5 antibodies immunoprecipitate the same set of disulfide-linked polypeptides from media of biosynthetically radiolabeled human keratinocytes. Moreover, sera from eight of nine patients with anti-epiligrin cicatricial pemphigoid immunoblot the alpha subunit of laminin 5 but show no reactivity to its beta or gamma subunits. In addition, circulating IgG from a representative patient was affinity-purified against the alpha subunit of laminin 5 and shown to bind the dermal side of 1 M NaC1 split skin in the same manner as autoantibodies from all patients with anti-epiligrin cicatricial pemphigoid. Sera from patients with bullous pemphigoid (n = 5), other forms of cicatricial pemphigoid (n = 5), epidermolysis bullosa acquisita (n = 4), or bullous systemic lupus erythematosus (n = 1) show no reactivity against any subunit of this laminin isoform in immunoprecipitation or immunoblot experiments. These findings correlate with prior reports showing that a monoclonal antibody directed against the alpha subunit of laminin 5 (i.e., laminin subunit alpha 3) induces detachment of human keratinocytes from extracellular matrix in vitro as well as epidermis from human skin in situ. Together, these studies suggest that laminin subunit alpha 3 mediates attachment of basal keratinocytes to epidermal basement membrane and that autoantibodies directed against it may be pathogenic.

Changes in the expression of integrins and basement membrane proteins in benign mucous membrane pemphigoid

OBJECTIVE

To determine the location of the subepithelial split in benign mucous membrane pemphigoid (BMMP) and its relationship to the anchoring filaments and their receptors.

MATERIALS AND METHODS

Frozen sections of lesional and perilesional oral mucosa from 10 cases of BMMP were stained, using an immunofluorescence method, for the beta-1, beta-4, alpha-3 and alpha-6 integrin subunits and for their ligands, laminin I and laminin V (kalinin). In all cases the diagnosis was confirmed by the demonstration of linear staining for IgG at the basement membrane zone. Six specimens of normal mucosa were stained for comparison.

RESULTS

Staining for integrins, laminin and kalinin in perilesional mucosa was similar to normals, although one case showed loss of alpha-6 and beta-4 . In lesional mucosa, laminin and kalinin showed strong linear staining localised to the floor of the bullae. The alpha-6 and beta-4 subunits were expressed only on the roof of the bullae but staining was weak and patchy with areas of loss. In some sections alpha-6 showed a punctate intracellular distribution similar to IgG. The distribution of alpha-3 and beta-1 was similar to that seen in normals.

CONCLUSIONS

In all cases kalinin was found on the connective tissue side of the lesions and alpha-6 beta-4 localised to the epithelial side. This shows that the split occurs at a location which separates anchoring filaments from the hemidesmosomes. Loss of the alpha-6 beta-4 integrin in the lesions and the similar intracellular staining of alpha-6 and IgG, suggest that disruption of hemidesmosomes may be a key event in the immunopathogenesis of the lesions and that the alpha-6 integrin subunit is a potential antigen in oral mucosal BMMP.

Mutations in the 180-kD bullous pemphigoid antigen (BPAG2), a hemidesmosomal transmembrane collagen (COL17A1), in generalized atrophic benign epidermolysis bullosa

Junctional epidermolysis bullosa (JEB) is a heterogeneous autosomal recessively inherited blistering skin disorder associated with fragility at the dermal-epidermal junction. Characteristic ultrastructural findings in JEB are abnormalities in the hemidesmosome-anchoring filament complexes. These focal attachment structures, which extend from the intracellular compartment of the basal keratinocytes to the underlying basement membrane, have been shown to be hypoplastic or rudimentary in different forms of JEB. Previously, in different JEB phenotypes, mutations have been found in the three genes for the anchoring filament component laminin 5 (LAMA3, LAMB3, and LAMC2) and in the gene for the hemidesmosome-associated integrin beta 4 subunit. Here, we describe the first mutations in the gene encoding the 180-kD bullous pemphigoid antigen (BPAG2), a transmembranous hemidesmosomal collagen, also known as type XVII collagen (COL17A1). The patient is affected with generalized atrophic benign epidermolysis bullosa (GABEB), a rare variant of JEB, and is a compound heterozygote for premature termination codons on both alleles. These novel findings emphasize the molecular heterogeneity of this group of genodermatoses, and attest to the importance of BPAG2 in maintaining adhesion between the epidermis and the dermis.

The renal glomerulus of mice lacking s-laminin/laminin beta 2: nephrosis despite molecular compensation by laminin beta 1

S-laminin/laminin beta 2, a homologue of the widely distributed laminin B1/beta 1 chain, is a major component of adult renal glomerular basement membrane (GBM). Immature GBM bears beta 1, which is replaced by beta 2 as development proceeds. In mutant mice that lack beta 2, the GBM remains rich in beta 1, suggesting that a feedback mechanism normally regulates GBM maturation. The beta 2-deficient GBM is structurally intact and contains normal complements of several collagenous and noncollagenous glycoproteins. However, mutant mice develop massive proteinuria due to failure of the glomerular filtration barrier. These results support the idea that laminin beta chains are functionally distinct although they assemble to form similar structures. Laminin beta 2-deficient mice may provide a model for human congenital or idiopathic nephrotic syndromes.

Diminished expression of the extracellular domain of bullous pemphigoid antigen 2 (BPAG2) in the epidermal basement membrane of patients with generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa (GABEB) is a nonlethal form of junctional epidermolysis bullosa characterized by generalized skin and mucosal blisters that heal with atrophy; other features include alopecia, nail dystrophy, large melanocytic nevi, and autosomal recessive inheritance. The specific aim of this study was to identify an abnormality in epidermal basement membrane adhesion molecules in well characterized GABEB patients that would explain why these subjects' epidermis separates from their epidermal basement membrane. Cryostat sections of nonlesional skin from 8 GABEB patients in 5 different families as well as skin from normal volunteers (controls) were studied by indirect immunofluorescence microscopy using rabbit antiserum directed against a BPAG1 fusion protein or monoclonal antibodies directed against the extracellular domain of BPAG2 (HD18 and 233), epiligrin (P1E1), laminin 5 (GB3), types IV and VII collagen, or integrin subunits alpha 2, alpha 3, beta 1, alpha 6, or beta 4. In these studies, monoclonal antibodies HD18 and 233 showed no reactivity and diminished reactivity, respectively, to the epidermal BM of all GABEB patients. Interestingly, in one patient, the absent or diminished reactivities of monoclonal anti-BPAG2 antibodies were limited to well demarcated portions of an otherwise intact epidermal basement membrane. Moreover, BPAG1, epiligrin, laminin 5, types IV and VII collagen, and all integrin subunits under study were expressed in the same manner in both GABEB and normal human skin. These findings identify an abnormality in the extracellular domain of BPAG2 in the skin of GABEB patients. BPAG2 (type XVII collagen) is a transmembrane, hemidesmosome-associated molecule whose extracellular domain resides at the exact level where blisters develop in the skin of patients with GABEB.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential cytokine modulation of the genes LAMA3, LAMB3, and LAMC2, encoding the constitutive polypeptides, alpha 3, beta 3, and gamma 2, of human laminin 5 in epidermal keratinocytes

Laminin 5, an anchoring filament protein previously known as nicein/kalinin/epiligrin, consists of three polypeptide chains, alpha 3, beta 3, and gamma 2, encoded by the genes LAMA3, LAMB3, and LAMC2, respectively. The expression of laminin 5 was detected by Northern hybridization with specific cDNA probes in various epidermal keratinocyte cultures, whereas no expression of any of the three genes could be detected in foreskin fibroblast cultures. Transforming growth factor-beta (TGF-beta) enhanced LAMA3, LAMB3, and LAMC2 gene expression in human epidermal keratinocytes, as well as in HaCaT and Balb/K cells in culture, although the extent of enhancement was greater for LAMA3 and LAMC2 genes than for LAMB3. Interestingly, tumor necrosis factor-alpha, (TNF-alpha) alone did not alter the expression of LAMB3 and LAMC2 genes in human epidermal keratinocytes, whereas it inhibited the expression of LAMA3. These results suggest that the expression of the three genes encoding the laminin 5 subunits is not coordinately regulated by the cytokines tested.

Genetic basis of lethal junctional epidermolysis bullosa in an affected fetus: implications for prenatal diagnosis in one family

Fetal skin biopsy at 20 weeks' gestation in a woman at risk for a child with the lethal skin-blistering disorder junctional epidermolysis bullosa (Herlitz) confirmed an affected fetus. Genomic DNA from the aborted fetus was examined for mutations in laminin 5, a macromolecule involved in adhesion at the dermal-epidermal junction, and a candidate protein in this condition. Polymerase chain reaction (PCR) amplification of exon 10 and parts of the flanking introns of the gene encoding the beta 3 chain of laminin 5 (LAMB3) and subsequent analysis by agarose gel electrophoresis showed a more slowly migrating band in the affected fetus compared with the normal control. Nucleotide sequencing of the abnormal PCR product revealed a homozygous 77 bp duplication within the exon, resulting in a premature termination codon 250 bp downstream from the 3' end of the duplication. Maternal DNA was heterozygous for the mutant and wild-type alleles. These findings illustrate the genetic basis of the skin disease in this case and also offer the prospects of a simple, rapid, and reliable first-trimester DNA-based prenatal, or even preimplantation, diagnostic test for future pregnancies in this family.

Structural requirement for cell adhesion to kalinin (laminin-5)

Laminin-5 (kalinin) was purified from spent cell culture media (SCC25 cells) by affinity chromatography on monoclonal antibody BM165. The protein was recovered as a mixture of the typical polypeptides of 165-155, 140, and 105 kDa as judged b SDS-polyacrylamide gel electrophoresis analysis under reducing conditions. The amino acid composition of purified laminin-5 was in agreement with that compiled from the recently published cDNA sequences of the alpha 3-, beta 3-, and gamma 2-laminin chains. Moreover, the content of half-cystine residues in laminin-5 was about two-thirds that in laminin-1, which confirms the prediction of a smaller number of epidermal growth factor-like repeats in the amino-terminal portion of the three chains. The content of coiled-coil alpha-helices (27%) determined by CD spectroscopy was comparable to that reported for laminin-1, which indicates that the long arm portion of laminin-5 is equivalent to that of other laminin isoforms. The melting temperature was recorded at 72 degrees C by CD monitoring of unfolding and refolding of the coiled-coil structures during thermal denaturation and renaturation, respectively. The thermal stability of laminin-5 is therefore significantly higher than that of laminin-1 or alpha 2-chain-containing laminins, which suggests higher ionic interactions between the three polypeptide chains of laminin-5. Cell adhesion-promoting activity of laminin-5 was found to be strictly and entirely dependent on the presence of coiled-coil structures. It decreased gradually after heat denaturation of the protein above 65 degrees C and was totally abrogated at 75 degrees C. This is in contrast to laminin-1, which contains both conformation-dependent and -independent cell-binding sites on the long and short arm domains, respectively.

Integrin beta 4 mutations associated with junctional epidermolysis bullosa with pyloric atresia

Pyloric atresia associated with junctional epidermolysis bullosa (PA-JEB), is a rare inherited disorder characterized by pyloric stenosis and blistering of the skin as primary manifestations. We demonstrate that in one PA-JEB patient the disease resulted from two distinct mutations in the beta 4 integrin gene alleles. The paternal mutation consists of a one base pair deletion causing a shift in the open reading frame, and a downstream premature termination codon. The maternal mutation occurs in a donor splice site, and results in in-frame exon skipping involving the cytoplasmic domain of the polypeptide. Our results implicate mutations in the beta 4 integrin gene in some forms of PA-JEB.

Gastric outlet obstruction and gastric infarct in junctional epidermolysis bullosa

A newborn boy had junctional epidermolysis bullosa, duodenal obstruction, and gastric infarction, a newly described combination that extends the spectrum of gastrointestinal findings associated with junctional epidermolysis bullosa. The infant underwent feeding jejunostomy, but died 16 days after birth. This report emphasizes the need for gastrointestinal assessment in any neonate suspected of having epidermolysis bullosa, especially if the pregnancy was complicated by polyhydramnios.

Primary structure and expression of a novel human laminin alpha 4 chain

The complete primary structure of a novel human laminin alpha 4 chain was derived from cDNA clones. The translation product contains a 24-residue signal peptide preceding the mature alpha 4 chain of 1792 residues. The domain structure is similar to that of the recently described alpha 3 chain [Ryan, Tizard, Van Devanter and Carter (1994) J. Biol. Chem. 269, 22779-22787]. Northern analysis of RNA from human fetal and adult tissues revealed developmental regulation of expression. In adult, strong expression was observed in heart as well as lung, ovary, small and large intestines, placenta and liver, whereas weak or no expression was detected in skeletal muscle, kidney, pancreas, testis, prostate or brain. In contrast, fetal lung and kidney revealed high expression. In situ hybridization analysis of human fetal and newborn tissues showed expression of the laminin in alpha 4 chain in certain mesenchymal cells in tissues such as smooth muscle and dermis.

Low nidogen affinity of laminin-5 can be attributed to two serine residues in EGF-like motif gamma 2III4

High affinity nidogen binding of laminin-1 (chain composition alpha 1 beta 1 gamma 1) has been previously mapped to a single EGF-like motif gamma 1III4 of its gamma 1 chain. Two more isoforms, laminin-5 (alpha 3 beta 3 gamma 2) and laminin-7 (alpha 3 beta 2 gamma 1), show low and high binding activity, respectively, indicating that the gamma 2 chain is of low affinity. This was confirmed by recombinant production of the homologous EGF-like motif gamma 2III4 of the gamma 2 chain, which has a 100,000-fold lower binding activity than gamma 1III4. The crucial heptapeptide binding sequence Asn-Ile-Asp-Pro-Asn-Ala-Val of gamma 1III4 is modified in gamma 2III4 by replacing both the central Asn and Val by Ser. Changing these replacements to Asn and Val by site-directed mutagenesis enhanced the activity of gamma 2III4 to a level which was only 5-fold lower than that of gamma 1III4. Despite their high sequence identity (77%) motifs gamma 1III4 and gamma 2III4 were also shown to differ considerably in immunological epitopes. This indicates distinctly different functions for laminins which differ in the gamma chain isoform.

Identification of a homozygous one-basepair deletion in exon 14 of the LAMB3 gene in a patient with Herlitz junctional epidermolysis bullosa and prenatal diagnosis in a family at risk for recurrence

Herlitz junctional epidermolysis bullosa, a severe epidermal blistering disorder, is inherited in an autosomal recessive manner. It has recently been shown that, in kindreds with junctional epidermolysis bullosa, the disorder results from mutations in the gamma 2 chain of laminin-5, a basement membrane protein synthesized by the basal cells of stratifying squamous epithelia. In this report we describe a mutation identified in the beta 3 chain gene of laminin-5 in a family with Herlitz junctional epidermolysis bullosa. The disease is caused by a homozygous deletion of 1 bp that leads to a frameshift and premature termination codon. The segregation of the mutated allele in the family is consistent with the pathogenic role of the mutation. We also report a direct DNA-based prenatal exclusion of Herlitz junctional epidermolysis bullosa in a pregnancy at risk using a chorionic villus biopsy and allele-specific oligomer hybridization from polymerase chain reaction-amplified genomic DNA.

Altered laminin 5 expression due to mutations in the gene encoding the beta 3 chain (LAMB3) in generalized atrophic benign epidermolysis bullosa

The anchoring filament component laminin 5 (kalinin/nicein) is a candidate protein for mutations in some hereditary blistering skin disorders. In this study, laminin 5 expression was assessed in a family with generalized atrophic benign epidermolysis bullosa, a non-lethal variant of the junctional form of epidermolysis bullosa. Immunofluorescence microscopy of the skin basement-membrane zone with a monoclonal antibody (GB3) revealed reduced anti-laminin 5 staining compared to normal controls. The labeling, when examined by immunoelectron microscopy, was present within the lower lamina lucida, immediately below the plane of blister formation. Numerous hemidesmosomes and well-formed anchoring filaments were seen on transmission electron microscopy. Polymerase chain reaction amplification of genomic DNA encoding the beta 3 subunit (LAMB3) of laminin 5, heteroduplex analysis of the polymerase chain reaction products, and nucleotide sequencing of the heteroduplexes revealed two putative mutations within the LAMB3 gene; these consisted of a premature termination codon in exon 3 and a missense mutation in exon 7. Exons 3 and 7 encode part of domain VI of the laminin 5 beta 3 chain short arm. This globular domain of the protein has been postulated to have an important function in the interaction of laminin 5 with other structural components of the basement membrane zone, such as laminin 6 (K-laminin). Thus the mutations delineated in this family may have a critical pathogenetic significance in reducing adhesion between the epidermis and the dermis.

180-kD bullous pemphigoid antigen (BP180) is deficient in generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa (GABEB) is a form of nonlethal junctional epidermolysis bullosa characterized by universal alopecia and atrophy of the skin. We report a deficiency of the 180-kD bullous pemphigoid antigen in three patients with GABEB from unrelated families. We screened specimens of clinically normal skin from nine junctional epidermolysis bullosa patients (3 GABEB, 4 lethal, 1 cicatricial, 1 pretibial) by immunofluorescence using monoclonal antibodies to the 180-kD and 230-kD bullous pemphigoid antigens (BP180 and BP230). In the skin of the three GABEB patients there was no reactivity with antibodies to BP180, whereas staining for BP230 was normal. In the skin of the other six, non-GABEB patients, included in this study the expression of BP180 and BP230 was normal. Immunoblot analysis of cultured keratinocytes from one of the GABEB patients also failed to detect BP180 antigen, whereas BP230 was present in normal amounts. The deficient expression of BP180 is reflected in the RNA message, as in Northern blot analysis a reduced amount of BP180 transcripts, although of normal length, were detected. Interestingly, in another GABEB patient there were not-involved areas of skin, in which blistering could not be induced by rubbing. Biopsy material from these areas showed interrupted staining for BP180. There was no staining for BP180 in areas of clinically normal but involved skin of this patient. In conclusion, this study reveals that the BP180 antigen is deficient and the BP180 mRNA is reduced in generalized atrophic benign epidermolysis bullosa.

Identification of a homozygous exon-skipping mutation in the LAMC2 gene in a patient with Herlitz's junctional epidermolysis bullosa

We describe a family with the Herlitz type of junctional epidermolysis bullosa, in which the disease is associated with a homozygous splice-site mutation in the gamma 2-chain gene (LAMC2) of laminin-5. The mutation consists of a G-to-T substitution resulting in the out-of-frame skipping of exon 7, a frame shift, and premature stop codon accompanied by a severe reduction in the level of mRNA from the mutant allele. The distribution of the wild-type and mutated gamma 2-chain alleles in family members implicates the mutation in the pathology and confirms the haplotypes of the healthy carriers previously determined by genetic linkage analysis. Our results confirm that the lethal Herlitz junctional epidermolysis bullosa phenotype is caused by mutations resulting in an altered synthesis of laminin-5.

Premature termination codons on both alleles of the type VII collagen gene (COL7A1) in three brothers with recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa (EB) is a group of heritable mechano-bullous skin diseases classified into three major categories on the basis of the level of tissue separation within the dermal-epidermal basement membrane zone. In the most severe, dystrophic (scarring) forms of EB, blisters form below the cutaneous basement membrane at the level of the anchoring fibrils, which are composed of type VII collagen. Ultrastructural observations of altered anchoring fibrils and genetic linkage to the type VII collagen locus (COL7A1) have implicated COL7A1 as the candidate gene in the dystrophic forms of EB. We have recently cloned the entire cDNA and the gene for human COL7A1. In this study, we describe distinct mutations in both COL7A1 alleles in three brothers with severe, mutilating recessive dystrophic EB (the Hallopeau-Siemens type, HS-RDEB). The patients are compound heterozygotes for two different mutations, both of which result in a premature termination codon in COL7A1, and the parents were shown to be clinically heterozygous carries of the respective mutations. Premature termination codons in both alleles of COL7A1 appear to be the underlying cause of severe, recessive dystrophic EB in this family.

Nail changes in epidermolysis bullosa: clinical and pathogenetic considerations

Nail changes in epidermolysis bullosa (EB) are common, but although they are highly suggestive of the disease, they are not pathognomonic. They are the result of abnormalities of the nail matrix and nail bed, associated with the pathogenetic alterations of the dermo-epidermal junction which occur in EB. In addition, secondary trauma in the areas of epidermal-dermal separation, and chronic inflammation of the nail matrix, are probable contributory factors, even in non-scarring forms of EB. Recent developments in the molecular and cell biology of the cutaneous basement membrane zone have greatly advanced our understanding of the pathomechanisms underlying different subtypes of EB. Defects in genes coding for the structural proteins of the basement membrane zone have been defined in some EB subtypes, and abnormal expression of structural proteins in others. The data accumulated from study of these genetic disorders will contribute to knowledge of the role of the dermo-epidermal junction in the normal physiology and differentiation of the nails, and be of value in discerning the aetiopathogenesis of acquired nail diseases.

Altered expression of a new antigen of the dermal-epidermal junction (NU-T2 DEJ Ag) in junctional epidermolysis bullosa

NU-T2 antigen (Ag) is a new and recently described antigen of the dermal-epidermal junction, recognized by an anti-CD1b monoclonal antibody denominated NU-T2. We studied NU-T2 Ag expression in junctional epidermolysis bullosa (13 patients) and in other forms of hereditary epidermolysis bullosa (23 patients), comparing the results with nicein expression. In junctional epidermolysis bullosa gravis type no differences were found between the expression of NU-T2 and nicein, both being negative in bullous as well as in non-bullous skin. Interestingly, in mitis type junctional epidermolysis bullosa, NU-T2 Ag was found to be absent or reduced in five of six patients both in lesional and in uncleaved skin. When compared with nicein expression, clearcut differences were found, further suggesting that these two antigens are different. These data confirm that NU-T2 Ag is a novel epitope of the dermal-epidermal junction, probably relevant in dermal-epidermal cohesion, and it could be responsible, together with nicein, 19-DEJ-1 and other adhesion molecules, for the different subtypes of junctional epidermolysis bullosa. Finally, NU-T2 monoclonal antibody is a new relevant tool for the diagnosis, classification, and prenatal diagnosis of junctional epidermolysis bullosa.

Detection of sequence variants in the gene encoding the beta 3 chain of laminin 5 (LAMB3)

Laminin 5, a candidate gene/protein system for mutations in the junctional forms of epidermolysis bullosa (JEB), consists of three polypeptides encoded by the LAMA3, LAMB3, and LAMC2 genes. In this study, primer pairs for the amplification of the complete cDNA as well as 22 exons of the LAMB3 gene encoding the entire beta 3 chain of laminin 5, were established. The primers for amplification of individual exons from genomic DNA were placed at least 50 bp away from the exon-intron borders in the flanking intronic sequences. For amplification of cDNA generated by RT-PCR, eight primer pairs covering overlapping segments of mRNA were used. The amplified sequences were used to study sequence variations of the LAMB3 gene in patients with JEB and unrelated individuals using heteroduplex analysis. Nine out of 13 JEB patients examined showed heteroduplexes in at least one of the PCR products, indicating the existence of two variable alleles in their DNA. Sequence analyses revealed putative pathogenetic mutations in seven of the JEB patients, while four of the heteroduplexes resulted from polymorphisms, reflecting a single basepair substitution. The results demonstrate that this method is useful in the detection of JEB mutations, as well as polymorphisms in the LAMB3 gene.

Cloning of the beta 3 chain gene (LAMB3) of human laminin 5, a candidate gene in junctional epidermolysis bullosa

Laminin 5 consists of three polypeptides, alpha 3, beta 3, and gamma 2, encoded by the genes LAMA3, LAMB3, and LAMC2, respectively. In this study, we have elucidated the exon-intron organization of the human LAMB3 gene. Characterization of five overlapping lambda phage DNA clones revealed that the gene was approximately 29 kb in size. Subsequent sequence data revealed that the gene consisted of 23 exons that varied from 64 to 379 bp in size, accounting for the full-length cDNA with an open reading frame of 3516 bp encoding 1172 amino acids. Comparison of the LAMB3 gene structure with the previously characterized LAMB1 gene revealed that LAMB3 was considerably more compact. Knowledge of the exon-intron organization of the LAMB3 gene will facilitate elucidation of mutations in patients with the junctional forms of epidermolysis bullosa, some of which have been associated with mutations in the laminin 5 genes.

Epidermolysis bullosa: hereditary skin fragility diseases as paradigms in cell biology

Recent research into the molecular basis of epidermolysis bullosa has provided a unique insight into a variety of mechanisms in normal cell biology, such as cell-matrix interactions, and has uncovered an excellent model for studies on keratin intermediate filaments. The simplex forms of epidermolysis bullosa are caused by mutations in the genes for the basal epidermal keratins, K5 and K14. Most mutations affect highly conserved parts of the molecules, illustrating their importance in normal keratin filament assembly and integrity. Mutations in corresponding regions of the differentiation-associated keratins, K1 and K10 can also occur in epidermolytic ichthyosis. Both recessive and dominant forms of dystrophic epidermolysis bullosa result from mutations in an anchoring fibril collagen gene, COL7A1. Junctional epidermolysis bullosa is caused by mutations in the genes encoding different chains of the novel laminin isoform, nicein/kalinin, also known as laminin 5, which is associated with the anchoring filament-hemidesmosome complex of the basement membrane zone. These recent findings strengthen the evidence for the role of nicein/kalinin and type VII collagen in adherence and stabilization of the dermo-epidermal junction.

Ultrastructural identification of basic abnormalities as clues to genetic disorders of the epidermis

The present article discusses specific, directly gene-dependent ultrastructural markers of dominantly inherited epidermal disorders that serve as clues to their underlying molecular genetic abnormalities. These are epidermolysis bullosa simplex Koebner and Weber-Cockayne with rupture or non-assembly of basal cell keratins and point mutations in keratins 5 and 14. Clumping of basal cell keratins is pathognomonic of EB Dowling-Meara and caused by mutations in hot spots of the rod domain of K5 and K 14. Clumps and aggregates of basal keratins occur side by side in the same cell and thus do not indicate specific different types of mutations. Similar clumping of suprabasal keratins in bullous CIE Brocq and in palmoplantar keratoderma Voerner have been assigned to identical types of mutations in the same critical position of the rod domain in K 1, K 10, and K 9, respectively. Highly unusual tubular keratins are pathognomonic of another dominant palmoplantar keratoderma type the genetic basis of which still awaits elucidation. Shell formation of (low molecular weight?) keratins in ichthyosis hystrix Curth-Macklin is not linked to the keratin gene clusters on chromosomes 12 and 17 and might be related to regulatory genes of keratin expression. Suprabasal shells in congenital reticular ichthyosiform erythroderma do not consist of keratins but resemble glycoprotein networks. Finally, the keratohyalin abnormality in ichthyosis vulgaris was the clue for the identification of a filaggrin deficiency, at the same time giving evidence to the heterogeneity of keratohyalin proteins.

Murine muscular dystrophy caused by a mutation in the laminin alpha 2 (Lama2) gene

The classic murine muscular dystrophy strain, dy, was first described almost 40 years ago. We have identified the molecular basis of an allele of dy, called dy2J, by detecting a mutation in the laminin alpha 2 chain gene--the first identified mutation in laminin-2. The G to A mutation in a splice site consensus sequence causes abnormal splicing and expression of multiple mRNAs. One mRNA is translated into an alpha 2 polypeptide with a deletion in domain VI. The truncated protein apparently lacks important qualities of the wild type protein and is unable to provide sufficient muscle stability.

Molecular basis of the dystrophic and junctional forms of epidermolysis bullosa: mutations in the type VII collagen and kalinin (laminin 5) genes

Epidermolysis bullosa (EB) is a group of heritable mechano-bullous skin diseases classified into three major categories, the simplex, junctional, and dystrophic forms, on the basis of the level of tissue separation within the dermal-epidermal basement membrane zone. Approaches of molecular biology have demonstrated that these three different forms of EB result from mutations in distinct genes: the simplex forms are due to mutations in the genes encoding keratins 5 and 14 expressed in basal keratinocytes; the junctional forms are associated with mutations in the kalinin/laminin 5 genes; and the dystrophic forms result from mutations in the type VII collagen gene (COL7A1). In this overview, we summarize our recent discoveries of pathogenic mutations in COL7A1, including premature termination codons that result in the severe, mutilating (Hallopeau-Siemens) type of recessive dystrophic EB and a glycine substitution in the collagenous region resulting in dominant dystrophic EB. Furthermore, we present evidence that implicates mutations in the kalinin/laminin 5 gamma 2 chain gene (LAMC2) in some forms of junctional EB. This information has provided the basis for DNA-based prenatal diagnosis during the first trimester of gestation, and sets the stage for the application of gene therapy to these devastating skin diseases in the future.

Mutations of keratin 9 in two families with palmoplantar epidermolytic hyperkeratosis

The hereditary palmoplantar keratodermas are a heterogeneous group of diseases unified by thickening of the stratum corneum of the palms and soles with consequent painful fissuring, discomfort on pressure, and resultant disability. One of the histologic patterns underlying palmoplantar hyperkeratosis is that of epidermolytic hyperkeratosis. Because that histologic pattern has been found in its generalized form to be due to keratin gene mutations, we assessed the inheritance of the form localized to the palms and soles. In each of two families studied, the mutant gene causing the disease is linked strongly to the chromosome 17 cluster of genes encoding type I keratins, and mutations are present in the conserved helix initiation region of keratin 9 in affected members of both kindreds. These data, as well as those generated recently by others, indicate that keratin gene mutations may underlie not only the generalized phenotype but also this more localized phenotype of epidermolytic hyperkeratosis and suggest one mechanism by which skin diseases can achieve their characteristic localization.

The epidermis: rising to the surface

At the skin surface, the epidermis serves an important protective function which it manifests by building an extensive cytoskeletal architecture of keratin filaments, spanning from the nuclear envelope to hemidesmosomes and desmosomes. Recent studies on epidermal proteins and their interactions have provided insights into human skin diseases, including genetic disorders of keratins, laminins, and collagen. Explorations into the regulatory mechanisms underlying epidermal genes have underscored the importance of transcription factors AP-1 and AP-2, retinoic acid receptors, and POU proteins. Transgenic and gene ablation experiments on TGF-alpha and TGF-beta genes have yielded clues as to how the epidermis maintains a balance of growing and differentiating cells.