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

Mutant collagen COL11A1 enhances cancerous invasion

Collagens are the most abundant proteins in the body and comprise the basement membranes and stroma through which cancerous invasion occurs; however, a pro-neoplastic function for mutant collagens is undefined. Here we identify COL11A1 mutations in 66 of 100 cutaneous squamous cell carcinomas (cSCCs), the second most common U.S. cancer, concentrated in a triple helical region known to produce trans-dominant collagens. Analysis of COL11A1 and other collagen genes found that they are mutated across common epithelial malignancies. Knockout of mutant COL11A1 impairs cSCC tumorigenesis in vivo. Compared to otherwise genetically identical COL11A1 wild-type tissue, gene-edited mutant COL11A1 skin is characterized by induction of β1 integrin targets and accelerated neoplastic invasion. In mosaic tissue, mutant COL11A1 cells enhanced invasion by neighboring wild-type cells. These results suggest that specific collagens are commonly mutated in cancer and that mutant collagens may accelerate this process.

Gene editing in dermatology: Harnessing CRISPR for the treatment of cutaneous disease

The discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system has revolutionized gene editing research. Through the repurposing of programmable RNA-guided CRISPR-associated (Cas) nucleases, CRISPR-based genome editing systems allow for the precise modification of specific sites in the human genome and inspire novel approaches for the study and treatment of inherited and acquired human diseases. Here, we review how CRISPR technologies have stimulated key advances in dermatologic research.  We discuss the role of CRISPR in genome editing for cutaneous disease and highlight studies on the use of CRISPR-Cas technologies for genodermatoses, cutaneous viruses and bacteria, and melanoma. Additionally, we examine key limitations of current CRISPR technologies, including the challenges these limitations pose for the widespread therapeutic application of CRISPR-based therapeutics.

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.

Gene editing in dermatology: Harnessing CRISPR for the treatment of cutaneous disease

The discovery of the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) system has revolutionized gene editing research. Through the repurposing of programmable RNA-guided CRISPR-associated (Cas) nucleases, CRISPR-based genome editing systems allow for the precise modification of specific sites in the human genome and inspire novel approaches for the study and treatment of inherited and acquired human diseases. Here, we review how CRISPR technologies have stimulated key advances in dermatologic research.  We discuss the role of CRISPR in genome editing for cutaneous disease and highlight studies on the use of CRISPR-Cas technologies for genodermatoses, cutaneous viruses and bacteria, and melanoma. Additionally, we examine key limitations of current CRISPR technologies, including the challenges these limitations pose for the widespread therapeutic application of CRISPR-based therapeutics.

The genetics of human skin disease

The skin is composed of a variety of cell types expressing specific molecules and possessing different properties that facilitate the complex interactions and intercellular communication essential for maintaining the structural integrity of the skin. Importantly, a single mutation in one of these molecules can disrupt the entire organization and function of these essential networks, leading to cell separation, blistering, and other striking phenotypes observed in inherited skin diseases. Over the past several decades, the genetic basis of many monogenic skin diseases has been elucidated using classical genetic techniques. Importantly, the findings from these studies has shed light onto the many classes of molecules and essential genetic as well as molecular interactions that lend the skin its rigid, yet flexible properties. With the advent of the human genome project, next-generation sequencing techniques, as well as several other recently developed methods, tremendous progress has been made in dissecting the genetic architecture of complex, non-Mendelian skin diseases.

Gene therapy for skin diseases

The skin possesses qualities that make it desirable for gene therapy, and studies have focused on gene therapy for multiple cutaneous diseases. Gene therapy uses a vector to introduce genetic material into cells to alter gene expression, negating a pathological process. This can be accomplished with a variety of viral vectors or nonviral administrations. Although results are promising, there are several potential pitfalls that must be addressed to improve the safety profile to make gene therapy widely available clinically.

Extracellular matrix molecules: potential targets in pharmacotherapy

The extracellular matrix (ECM) consists of numerous macromolecules classified traditionally into collagens, elastin, and microfibrillar proteins, proteoglycans including hyaluronan, and noncollagenous glycoproteins. In addition to being necessary structural components, ECM molecules exhibit important functional roles in the control of key cellular events such as adhesion, migration, proliferation, differentiation, and survival. Any structural inherited or acquired defect and/or metabolic disturbance in the ECM may cause cellular and tissue alterations that can lead to the development or progression of disease. Consequently, ECM molecules are important targets for pharmacotherapy. Specific agents that prevent the excess accumulation of ECM molecules in the vascular system, liver, kidney, skin, and lung; alternatively, agents that inhibit the degradation of the ECM in degenerative diseases such as osteoarthritis would be clinically beneficial. Unfortunately, until recently, the ECM in drug discovery has been largely ignored. However, several of today's drugs that act on various primary targets affect the ECM as a byproduct of the drugs' actions, and this activity may in part be beneficial to the drugs' disease-modifying properties. In the future, agents and compounds targeting directly the ECM will significantly advance the treatment of various human diseases, even those for which efficient therapies are not yet available.

Oral manifestations in the epidermolysis bullosa spectrum

The craniofacial and oral manifestations of the different epidermolysis bullosa (EB) types vary markedly in character and severity depending largely on the EB type. The tissues affected and the phenotypes displayed are closely related to the specific abnormal or absent proteins resulting from the causative genetic mutations for these disorders. In this article, the major oral manifestations are reviewed for different EB subtypes and are related to the causative genetic mutations and gene expression.

Extracutaneous manifestations and complications of inherited epidermolysis bullosa: part I. Epithelial associated tissues

Based upon case reports and small case series, it has been known for many years that some types and subtypes of inherited epidermolysis bullosa (EB) may be at risk for developing one or more extracutaneous complications. Many of these are associated with considerable morbidity; some may result in death. Only over the past few years have there been data generated from large, well characterized cohorts. However, these data, to date, have been published almost exclusively in the nondermatologic literature. Our objective is to provide dermatologists with a comprehensive review of each major extracutaneous complication with a summary of the pertinent literature and recommendations for evaluation and optimal management. Part I highlights epithelial associated tissues, and part II addresses other organs. Based on these reviews, the readership should gain a greater understanding of the types of complications that may occur, when they are most likely to develop, and the range of medical and surgical interventions that are currently available. It should also be possible for the reader to develop surveillance strategies based on an understanding of the published evidence-based data. The breadth and range of severity of complications that arise in some EB types and subtypes within the external eye, ear, nose, upper airway, and gastrointestinal and genitourinary tracts suggest that optimal management must be multidisciplinary. Given the unique knowledge that dermatologists have of this disease, we believe that the care of the EB patient should be under the direction of his or her dermatologist, who can best assist in timely referrals to those specialists who are most experienced in the care of specific extracutaneous problems.

Type VII collagen gene mutations (c.8569G>T and c.4879G>A) result in the moderately severe phenotype of recessive dystrophic epidermolysis bullosa in a Korean patient

Dystrophic epidermolysis bullosa (DEB) are caused by mutations in the COL7A1 gene, which encodes type VII collagen. Even though more than 500 different COL7A1 mutations have been identified in DEB, it still remains to be under-investigated. To investigate the mutation of COL7A1 in moderately severe phenotype of recessive DEB (RDEB) in a Korean patient, the mutation detection strategy was consisted of polymerase chain reaction (PCR) amplification of genomic DNA, followed by heteroduplex analysis, nucleotide sequencing of the PCR products demonstrating altered mobility. In this study, we found that one mutation (c.8569G>T) was detected within exon 116. The mutation of c.8569G>T in exon 116 changed the GAG (Glu) to TAG, eventually resulted in premature termination of type VII collagen polypeptide. Furthermore the mother did not have the mutation c.8569G>T in exon 116. The other novel mutation (c.4879G>A) was detected within exon 51 of both patient and mother, thereby resulting in changing valine (Val) to isoleucine (Ile) in type VII collagen polypeptide. Taken together, in this study we identified compound heterozygosity for COL7A1 mutations (c.8569G>T and c.4879G>A) in moderately severe RDEB in a Korean patient. We hope that this data contribute to the expanding database on COL7A1 mutations in DEB.

Plasmin induces degradation and dysfunction of laminin 332 (laminin 5) and impaired assembly of basement membrane at the dermal-epidermal junction

BACKGROUND

The epidermal basement membrane (BM), located at the dermal-epidermal junction (DEJ), plays important roles not only in adhesion between epidermis and dermis, but also in controlling skin functions. In sun-exposed skin, the BM becomes disrupted and multilayered. In order to explore the impairment of BM assembly, we have used a skin-equivalent (SE) as a model of BM damage and previously clarified the involvement of matrix metalloproteinases (MMPs) in impairment of BM assembly.

OBJECTIVES

In this work, we examined the role of urokinase-type plasminogen activator (uPA) and plasmin in impairment of BM assembly at the DEJ by using the SE, as ultraviolet irradiation to the skin increases uPA as well as MMPs.

METHODS

SEs were used as a model of formation and damage of BM. Human uPA was detected by enzyme-linked immunosorbent assay and zymography, and gelatinases such as MMP-2 and MMP-9 were detected by zymography. Human plasminogen was added at 0.06 micromol L(-1) (about 3% of plasma level) to increase plasmin to a pathological level. N-terminal peptide sequence analysis of plasmin-treated laminin 332 was carried out to identify alpha3, beta3 and gamma2 chains of laminin 332 and their cleavage sites of each chain. Plasmin-treated laminin 332 was analysed in keratinocyte adhesion activity and binding to type VII collagen.

RESULTS

Human uPA was detected in addition to MMP-2 and MMP-9, in conditioned medium of SE. Although the BM was well organized in the presence of an MMP inhibitor alone, the activated plasmin disorganized the BM even in the presence of the inhibitor. The impairment of BM assembly made the epidermis thinner as compared with that of a control cultured in the presence of MMP inhibitor, indicating that the BM affects the polarity and differentiation of the epidermis. The addition of aprotinin, a serine proteinase inhibitor, and tranexamic acid, a uPA-plasmin inhibitor, inhibited the plasmin-induced impairment of BM assembly and facilitated BM reorganization, thereby improving the epidermal structure. N-terminal peptide sequence analysis of plasmin-treated laminin 332 revealed the removal of a 5- or 10-kDa fragment, including the cell adhesion region, from the G3 domain of the alpha3 chain, and the LN domain, which binds to the noncollagenous 1 domain in type VII collagen, from the beta3 chain. Plasmin-treated laminin 332 showed lower keratinocyte adhesion activity and reduced binding to type VII collagen.

CONCLUSIONS

These results suggest that uPA and plasmin are involved in the impairment of BM assembly and epidermal differentiation, and that these effects arise at least partly through direct degradation of laminin 332.

Transformation-specific matrix metalloproteinases (MMP)-7 and MMP-13 are expressed by tumour cells in epidermolysis bullosa-associated squamous cell carcinomas

BACKGROUND

Patients with recessive dystrophic epidermolysis bullosa (RDEB) have an increased risk of developing rapidly progressive and metastatic cutaneous squamous cell carcinomas (SCC). It is unclear why these SCC behave more aggressively than sporadic SCC. Matrix metalloproteinases (MMP) are a family of endopeptidases that contribute to growth, invasion and metastasis of SCC. The role of MMP in RDEB-associated SCC is not known.

OBJECTIVES

To investigate the expression of MMP-7, MMP-13 and MMP-9 in RDEB-associated SCC in comparison with sporadic SCC and Bowen's disease.

METHODS

Immunohistochemical analysis of 25 RDEB-associated SCC, 61 sporadic SCC and 28 sporadic lesions of Bowen's disease was carried out using monoclonal antibodies for MMP-7, MMP-9, MMP-13 and E-cadherin and syndecan-1.

RESULTS

MMP-7 was detected in all RDEB-associated SCC, in tumour cells within the invasive edge, where E-cadherin and syndecan-1 were markedly diminished or absent. MMP-7 expression was also observed in 98% of sporadic SCC and in 68% of Bowen's diseases. MMP-7 staining was significantly stronger in RDEB-associated SCC than in sporadic SCC, and was most abundant in poorly differentiated tumours. MMP-13 was detected in tumour cells in 96% of RDEB-associated SCC and in all sporadic cutaneous SCC. MMP-9 was detected in the inflammatory cells in all SCC examined.

CONCLUSIONS

These results identify MMP-7 and MMP-13 as tumour cell-specific markers for SCC progression and as potential therapeutic targets in RDEB-associated SCC. The pattern of immunolabelling suggests that MMP-7 may shed E-cadherin and syndecan-1 from the SCC cell surface.

Esophageal strictures in children with recessive dystrophic epidermolysis bullosa: an 11-year experience with fluoroscopically guided balloon dilatation

BACKGROUND

Recessive dystrophic epidermolysis bullosa (RDEB) is an inherited blistering skin disorder that is associated with significant esophageal strictures, resulting in dysphagia and nutritional failure. Although endoscopically guided balloon dilatation is a widely used treatment, the use of an endoscope carries the risk of oropharyngeal trauma. To minimize this risk, we have eliminated its use.

METHOD

We reviewed the charts of all RDEB patients who underwent balloon dilatation for esophageal strictures between August 1993 and March 2005. Balloon dilatation procedures were performed under anesthesia and with fluoroscopic control.

RESULTS

We performed 92 dilatations on 25 RDEB patients. Most patients reported immediate relief of symptoms, rapid recovery, and resumption of adequate food intake within 1 day. The mean interval between dilatations was 1 year. Six patients (24%) have required only 1 dilatation, and 1 of these 6 has had a dilatation-free interval of 25 months. One patient with a history of multiple dilatations has remained dilatation-free for 5 years. No procedure-related complications have occurred.

CONCLUSIONS

Fluoroscopically guided balloon dilatation is a gentle, safe, effective, and repeatable technique that should be considered as a first line of treatment.

Protective effect of matrix metalloproteinase inhibitors against epidermal basement membrane damage: skin equivalents partially mimic photoageing process

BACKGROUND

The epidermal basement membrane (BM) plays important roles in adhesion between epidermis and dermis, and in controlling epidermal differentiation. The BM has been reported to be damaged in sun-exposed skin. Although matrix metalloproteinases (MMPs) are believed to be involved in the BM damage, there is no good in vitro model for examining BM damage by MMPs or for exploring methods to protect the BM.

OBJECTIVES

To examine the involvement of MMPs in BM damage and approaches to protect the BM from such damage by using an in vitro skin-equivalent (SE) model.

METHOD

SE was prepared by culturing human keratinocytes on contracted collagen gel including human fibroblasts. MMP-1, -2, -3 and -9, laminin 5 and type IV and VII collagens were determined by specific sandwich ELISAs, and MMP-2 and MMP-9 were analysed by gelatin zymography. Histological examination of SE was also carried out.

RESULTS

Despite production of BM components such as laminin 5 and type IV and VII collagens in SEs, BM was rarely observed at the dermal-epidermal junction. Several MMPs, such as MMP-1, -2, -3 and -9, were observed to be present in conditioned media and some of them were in active forms. Tissue inhibitor of metalloproteinase (TIMP)-2 was not detected, although TIMP-1 was present. Synthetic MMP inhibitors, CGS27023A and MMP-inhibitor I, which inhibit MMP-1, -2, -3 and -9, markedly augmented deposition of laminin 5 and type IV and VII collagens at the dermal-epidermal junction, resulting in the formation of continuous epidermal BM.

CONCLUSIONS

Our results indicate that MMPs are involved in the degradation of BM in SEs, and that MMP inhibitors exert a protective effect against BM damage.

Kindler surprise: mutations in a novel actin-associated protein cause Kindler syndrome

Kindler syndrome is an autosomal recessive genodermatosis characterized by acral blistering in neonates and diffuse, progressive poikiloderma in later life. Other clinical features include photosensitivity, premature skin ageing and severe periodontal disease. Two groups have recently shown that the molecular basis of Kindler syndrome is loss of a novel epidermal protein, kindlin-1, encoded by the gene KIND1. Two additional kindlin proteins, kindlin-2 and kindlin-3, have also been described. Kindlin-1 is considered to be a component in the linkage of the actin cytoskeleton to the extracellular matrix and as such is proposed to have both structural and cell-signalling functions. Kindler syndrome is therefore the first skin fragility syndrome due to disruption of the actin-extracellular matrix system.

Characterization of mutations of the type VII collagen gene (COL7A1) in recessive dystrophic epidermolysis bullosa mitis (M-RDEB) from three Korean patients

In recent years, the molecular basis for the main subtypes of epidermolysis bullosa (EB) has been elucidated with pathogenetic mutations delineated in ten different genes encoding structural components of the dermal-epidermal junction. Both the autosomal dominant and recessive forms of dystrophic EB (DEB) is caused by mutations in the COL7A1 gene. Type VII collagen is a major component of anchoring fibrils, structural elements that stabilize the attachment of the basement membrane to underlying dermis. Recent delineation of the exon-intron organization of the COL7A1 gene provided the basis for the comprehensive design of PCR primer pairs that amplified exons in genomic DNA by placing the primers on the flanking introns. A number of COL7A1 mutations have been reported and some genotype-phenotype correlations are starting to emerge. In this study, we examined mutational analyses from three Korean patients with recessive dystrophic EB (RDEB) mitis. We designed and optimized primers according to the previously reported sequences. Such PCR amplification products can be examined by electrophoretic scanning technique, CSGE heteroduplex analyses. Utilizing heteroduplex analyses, we have identified a number of sequence variants in COL7A1 both in unaffected individuals and in patients with M-RDEB. Mutation detection of the COL7A1 gene revealed six allelic mutations (V6677E, P6685S, Y3749S, P6084S, P6695R and G6697C). We suggest that the full length of type VII collagen polypeptide are synthesized, but those missense mutations, that may affect a critical amino acid, can alter the conformation of the protein and interferes with the assembly and packing of type VII collagen molecules into anchoring fibrils. Immunohistochemical study of skin biopsies by use of anti-type VII collagen antibody showed markedly reduced staining and presence of a dermo/epidermal cleavage. This is the first report of a COL7A1 mutation study in DEB from Korean patients. We hope that these data contribute to the expanding database on COL7A1 mutations in dystrophic epidermolysis bullosa, and further illustrate the extensive diversity of mutational events that led to the RDEB phenotype.

Pediatric skin tumors

This article summarizes several malignant childhood neoplasms and benign tumors that can mimic malignancies. Because malignant skin tumors are rare in children, parents and physicians often are not sufficiently suspicious to ensure that an early diagnosis can be made. Many malignant skin tumors have features that suggest a vascular or hemangioma-like lesion. Because hemangiomas occur in 10% of infants, it is often considered prudent to adopt a wait-and-see attitude; however, if the lesion is too firm to be a hemangioma or its growth pattern does not follow that of a typical hemangioma, additional options should be considered. To manage childhood skin malignancies, one needs expert consultation, early biopsy, and correct histopathologic interpretation.

Update on inherited bullous dermatoses

Bullous diseases are becoming increasingly better understood owing to the active research which has taken place in this field over the past decade. Advances in understanding of bullous disease pathophysiology is translating into clinical applications for diagnosis and therapy that will greatly enhance the quality of care bullous disease patients may receive now and in the future. This review focuses on the progress which has been achieved in inherited bullous dermatoses.

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.

Prenatal diagnosis as a test for genodermatoses: its past, present and future

The prenatal diagnosis (PND) of severe hereditary skin diseases started in the early 1980s using fetal skin biopsy techniques based on ultrastructural and immunohistochemical abnormalities of the fetal skin. Recent success in identifying responsible genes and demonstrating mutations in such genes has set the stage for DNA-based PND in the 1990s. Common examples of skin conditions which can be prenatally diagnosed include epidermolysis bullosa, oculocutaneous albinism and Harlequin ichthyosis in which the severity of the clinical phenotype appears to justify PND in families at risk. More recently, preimplantation diagnoses of inherited diseases have become possible using in vitro fertilization techniques. The diagnosis consists of a blastomere biopsy of the six to ten-cell embryo and a DNA analysis of single blastomeres. Disease-free embryos are selected for transfer to the uterus, thereby avoiding the need for termination of a fetus found to be affected by conventional PND. Furthermore, carrying out a PND using a single fetal cell from the maternal blood, such as nucleated erythrocytes, has become technically feasible. Although there are many questions that remain unanswered, the outlook for further development of noninvasive PND in the future appears optimistic.

Informativeness of polymorphic markers for prenatal diagnosis of recessive dystrophic epidermolysis bullosa in Spanish families at risk

DNA polymorphic markers are useful for the prenatal diagnosis of generalized recessive dystrophic epidermolysis bullosa (GRDEB) in families with at least one child affected with the disease. It is our policy to investigate families at risk using DNA polymorphic markers before a new pregnancy is intended, to inform about the real chances of offering an accurate prenatal diagnosis based on such DNA markers. We have analysed 10 Spanish families with at least one child affected with GRDEB with three different markers linked to the type VII collagen gene: the intragenic PvuII RFLP, and two markers mapped close to the COL7A1 gene, an MspI polymorphism belonging to the anonymous marker D3S2, and the microsatellite D3S1100. The PvuII marker was partially informative in two of 10 families, and was fully informative in three additional families; The MspI marker was partially informative in two of 10 families, and was fully informative in three additional families; it was not informative in five families. The D3S1100 microsatellite was partially informative in two out of 10 families, and fully informative in the other eight families. Combination of all three markers was shown to be partially informative in one family and fully informative in the remaining nine families. Using this combination of markers, we have inferred an accurate linkage-based prenatal diagnosis of GRDEB in four pregnancies. Surprisingly, the intragenic marker PvuII had a very limited usefulness, despite the results of previous studies; the microsatellite D3S1100 offered the best results for an eventual prenatal diagnosis of GRDEB. However, families at risk should be informed that extragenic markers may fail due to the possibility of recombination, estimated as 5% for D3S1100.

Histopathologic and immunohistochemical features in human skin after exposure to nitrogen and sulfur mustard

N-methyl-2,2'-dichlorodiethylamine (HN2)is a topical chemotherapeutic agent used as therapy for cutaneous T-cell lymphomas (CTCL). Di(2-chloroethyl)sulfide (SM), and less often HN2, have been used as chemical weapons, with the skin being a principle target. The mechanisms by which these chemicals produce their therapeutic and toxic effects in skin, however, are not clearly defined. We exposed human skin explants to two doses of HN2 and SM. At 18 hours after exposure, histopathologic features were compared. In addition, immunohistochemical markers to basement membrane proteins were used to evaluate the effects of both chemicals on the basement membrane zone. Gross vesication was not seen. Pyknotic nuclei with or without dyskeratotic changes within epidermal keratinocytes were present at both doses. These changes varied more between skin specimens than they did between doses. Ballooning degeneration was more marked after SM exposures. Diffuse dermal-epidermal separation was present only at high-dose exposures and did not appear to correlate with the degree of changes locally in the overlying epidermis. Antibodies to laminin-5 showed decreased immunoreactivity after exposure to HN2 and SM. Immunoreactivity for laminin- was decreased to a lesser extent, and immunoreactivity for collagen IV and VII was unchanged. HN2 and SM produce similar histopathologic and immunohistochemical features after cutaneous exposure. These features suggest that part of mechanism of action of HN2 and SM is a direct effect on the basement membrane zone. Understanding the effects of HN2 and SM separate from their effect on DNA may be important in designing therapies and in advancing our understanding of the pathophysiologic changes induced by these chemicals when delivered topically.

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.

Laminin 5 binds the NC-1 domain of type VII collagen

Mutational analyses of genes that encode components of the anchoring complex underlying the basolateral surface of external epithelia indicate that this structure is the major element providing for resistance to external friction. Ultrastructurally, laminin 5 (alpha3beta3gamma2; a component of the anchoring filament) appears as a thin filament bridging the hemidesmosome with the anchoring fibrils. Laminin 5 binds the cell surface through hemidesmosomal integrin alpha6beta4. However, the interaction of laminin 5 with the anchoring fibril (type VII collagen) has not been elucidated. In this study we demonstrate that monomeric laminin 5 binds the NH2-terminal NC-1 domain of type VII collagen. The binding is dependent upon the native conformation of both laminin 5 and type VII collagen NC-1. Laminin 6 (alpha3beta1gamma1) has no detectable affinity for type VII collagen NC-1, indicating that the binding is mediated by the beta3 and/or gamma2 chains of laminin 5. Approximately half of the laminin 5 solubilized from human amnion or skin is covalently complexed with laminins 6 or 7 (alpha3beta2gamma1). The adduction occurs between the NH2 terminus of laminin 5 and the branch point of the short arms of laminins 6 or 7. The results are consistent with the presumed orientation of laminin 5, having the COOH-terminal G domain apposed to the hemidesmosomal integrin, and the NH2-terminal domains within the lamina densa. The results also support a model predicting that monomeric laminin 5 constitutes the anchoring filaments and bridges integrin alpha6beta4 with type VII collagen, and the laminin 5-6/7 complexes are present within the interhemidesmosomal spaces bound at least by integrin alpha3beta1 where they may mediate basement membrane assembly or stability, but contribute less significantly to epithelial friction resistance.

alpha3beta1 Integrin is required for normal development of the epidermal basement membrane

Integrins alpha3beta1 and alpha6beta4 are abundant receptors on keratinocytes for laminin-5, a major component of the basement membrane between the epidermis and the dermis in skin. These integrins are recruited to distinct adhesion structures within keratinocytes; alpha6beta4 is present in hemidesmosomes, while alpha3beta1 is recruited into focal contacts in cultured cells. To determine whether differences in localization reflect distinct functions of these integrins in the epidermis, we studied skin development in alpha3beta1-deficient mice. Examination of extracellular matrix by immunofluorescence microscopy and electron microscopy revealed regions of disorganized basement membrane in alpha3beta1-deficient skin. Disorganized matrix was first detected by day 15.5 of embryonic development and became progressively more extensive as development proceeded. In neonatal skin, matrix disorganization was frequently accompanied by blistering at the dermal-epidermal junction. Laminin-5 and other matrix proteins remained associated with both the dermal and epidermal sides of blisters, suggesting rupture of the basement membrane itself, rather than detachment of the epidermis from the basement membrane as occurs in some blistering disorders such as epidermolysis bullosa. Consistent with this notion, primary keratinocytes from alpha3beta1-deficient skin adhered to laminin-5 through alpha6 integrins. However, alpha3beta1-deficient keratinocytes spread poorly compared with wild-type cells on laminin-5, demonstrating a postattachment requirement for alpha3beta1 and indicating distinct roles for alpha3beta1 and alpha6beta4. Our findings support a novel role for alpha3beta1 in establishment and/or maintenance of basement membrane integrity, while alpha6beta4 is required for stable adhesion of the epidermis to the basement membrane through hemidesmosomes.

Coating of titanium alloy with soluble laminin-5 promotes cell attachment and hemidesmosome assembly in gingival epithelial cells: potential application to dental implants

The formation of a biological seal around the transmucosal portion of dental implants may be crucial for the long-term success of these therapies. Data to date suggest that the gingival epithelium attaches to dental implants through the formation of hemidesmosomes. Biochemical and genetic data indicate that the laminin isoform, laminin-5, a component of basement membranes, plays a crucial role in the assembly and maintenance of hemidesmosomes. We report the use of soluble laminin-5 as a biological coating of titanium-alloy to promote cell attachment of the gingival epithelial cell line, IHGK. Monoclonal antibodies reactive with laminin-5 depleted the coating solution of all cell attachment activity and blocked cell attachment to laminin-5-coated disks. Immunodepletion with antibodies to fibronectin had no effect. Finally, we demonstrate that IHGK cells assembled hemidesmosomes within 24 h of attachment to laminin-5-coated titanium alloy but not to the titanium alloy alone. These results suggest that soluble laminin-5 may have clinical applications as a dental implant coating to promote the formation of a biological seal.

Neuronal laminins and their cellular receptors

The laminins are a family of extracellular matrix glycoproteins expressed throughout developing neural tissues. The laminins are potent stimulators of neurite outgrowth in vitro for a variety of cell types, presumably reflecting an in vivo role in stimulating axon outgrowth. In recent years, the laminins have been shown to occur in several distinct isoforms; currently, the precise functional differences between the laminin variants are not well understood. A variety of neuronal surface receptors have been identified for one laminin isoform, laminin-1. These receptors include several members of the integrin family, as well as non-integrin laminin-binding proteins such as LBP-110, the 67 kDa laminin-receptor, alpha-dystroglycan, and beta 1,4 galactosyltransferase. Little is currently known about receptors for other laminin isoforms.

The role of immunohistochemistry in the diagnosis of the non-lethal forms of junctional epidermolysis bullosa

Skin biopsies from four patients with similar clinical phenotypes of non-lethal junctional epidermolysis bullosa (JEB) were investigated by electron microscopy and immunohistochemistry. Electron microscopy revealed cleavage within the lamina lucida in each case, but in addition, there was considerable variability in the number and ultrastructure of hemidesmosome-anchoring filament complexes. Immunohistochemical staining of the dermal-epidermal junction, using monoclonal antibodies to laminin 5 and the 180-kDa bullous pemphigoid antigen, showed reduced laminin 5 staining with normal 180-kDa bullous pemphigoid antigen labelling in two cases, and reduced or absent 180-kDa bullous pemphigoid antigen staining with normal laminin 5 labelling in the other two cases. Whereas electron microscopy is invaluable for the diagnosis of JEB as a group of diseases, immunohistochemistry is able to provide insight into the molecular pathology of non-lethal JEB and reveal abnormalities in candidate genes and proteins underlying this group of genetic blistering disorders.

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.

Immunohistochemical and mutation analyses demonstrate that procollagen VII is processed to collagen VII through removal of the NC-2 domain

Collagen VII is the major structural constituent of anchoring fibrils in the skin. It is synthesized as a procollagen that is larger than the collagen deposited in the tissue. In this study, we investigated the conversion of procollagen VII to collagen VII in human skin and in cutaneous cells in vitro and identified the propeptide using domain-specific antibodies. For this purpose, two bacterial fusion proteins containing unique sequences of the carboxy-terminal globular NC-2 domain of procollagen VII were prepared, and polyclonal antibodies raised against them. Immunoblotting showed that the anti-NC2 antibodies reacted with procollagen VII isolated from cultured keratinocytes, but not with collagen VII extracted from the skin. Immunohistochemical experiments with the NC-2 antibodies revealed a strong reaction in cultured keratinocytes, but the basement membrane zone of normal skin remained negative. The staining could not be rendered positive by chemical or enzymatic unmasking of potential hidden epitopes in the skin, indicating that most of the NC-2 domain is absent from normal skin. In contrast, a positive staining with NC-2 antibodies was observed in the skin of a patient with NC-2 antibodies was observed in the skin of a patient with dystrophic epidermolysis bullosa, who carried a 14-bp deletion at one of the intro-exon junctions of the collagen VII gene. This aberration led to an in-frame skipping of exon 115 from the mRNA and eliminated 29 amino acids from the NC-2 domain which include the putative cleavage site for the physiological processing enzyme, procollagen C-proteinase. The results indicate that in normal human skin, the removal of the NC-2 domain from procollagen VII precedes its deposition at the dermal-epidermal junction. Furthermore, they suggest that an aberration in the procollagen VII cleavage interferes with the normal fibrillogenesis of the anchoring fibrils.

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.