NC1 domain of type VII collagen binds to the beta3 chain of laminin 5 via a unique subdomain within the fibronectin-like repeats

Dystrophic epidermolysis bullosa - From biochemistry to interventions

The skin, as a barrier organ meeting constant mechanical challenges, is equipped with multiple adhesive structures that collectively support resilient, yet flexible attachment of its epithelium -the epidermis to its mesenchyme - the dermis. One such structure is the collagen VII-composed anchoring fibril, which provides firm anchorage of the epidermal basement membrane to the underlying interstitial extracellular matrix. Blistering and wider tissue fragility in the genetic disease dystrophic epidermolysis bullosa (DEB) caused by collagen VII deficiency illustrate the essential function of collagen VII in supporting skin integrity. DEB is also a progressive inflammatory fibrotic disease with multi-organ involvement, indicating that collagen VII has broader functions than simply providing epithelial anchorage. This review explores the reciprocal relationship between collagen VII biology and DEB pathophysiology. A deeper understanding of collagen VII biology - spanning its synthesis, assembly into suprastructures, and regulatory roles - enhances our understanding of DEB. Conversely, detailed insights into DEB through analysis of disease progression or therapeutic interventions offer valuable information on the broader tissue and organismal roles of collagen VII in maintaining homeostasis. This review focuses on such knowledge exchange in advancing our understanding of collagen VII, the extracellular matrix in general, and inspiring potential strategies for treatment of DEB. Importantly, in a broader sense, the discussed themes are applicable to other conditions driven by compromised extracellular matrix instruction and integrity, leading to progressive damage and inflammation.

Autoimmunity against laminin 332

Laminin 332 is a heterotrimeric structural protein of the basal membrane zone (BMZ) of the skin and adjacent mucosal tissues. The importance of laminin 332 for the structural integrity of the BMZ is demonstrated by mutations in any of the three genes encoding for its three chains causing variants of junctional epidermolysis bullosa. Autoimmunity against laminin 332 is observed in mucous membrane pemphigoid (MMP) and in the rare patients with orf-induced pemphigoid. MMP is an autoimmune blistering disease with predominant mucosal manifestations and autoantibodies against the BMZ of the skin and orifice-close mucous membranes. The main autoantigens of MMP are type XVII collagen (BP180) and laminin 332 targeted in about 80% and 10-20% of patients, respectively. An increasing number of studies has highlighted the association of anti-laminin 332 MMP and malignancies that can be revealed in about a quarter of these patients. This data has led to the recommendation of current guidelines to assay for anti-laminin 332 reactivity in all MMP patients. The present review focuses on anti-laminin 332 MMP describing clinical features, its pathophysiology, and detection of serum anti-laminin 332 IgG. In addition, the available data about the occurrence of malignancies in anti-laminin 332 MMP, the underlying tumor entities, and its biology are detailed.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Dystrophic Epidermolysis Bullosa: Secondary Disease Mechanisms and Disease Modifiers

The phenotypic presentation of monogenetic diseases is determined not only by the nature of the causative mutations but also is influenced by manifold cellular, microenvironmental, and external factors. Here, heritable extracellular matrix diseases, including dystrophic epidermolysis bullosa (DEB), are no exceptions. Dystrophic epidermolysis bullosa is caused by mutations in the COL7A1 gene encoding collagen VII. Deficiency of collagen VII leads to skin and mucosal fragility, which progresses from skin blistering to severe fibrosis and cancer. Clinical and pre-clinical studies suggest that targeting of secondary disease mechanisms or employment of natural disease modifiers can alleviate DEB severity and progression. However, since many of these mechanisms are needed for tissue homeostasis, informed, selective targeting is essential for safe and efficacious treatment. Here, we discuss a selection of key disease modifiers and modifying processes active in DEB, summarize the still scattered knowledge of them, and reflect on ways forward toward their utilization for symptom-relief or enhancement of curative therapies.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Laminins and interaction partners in the architecture of the basement membrane at the dermal-epidermal junction

The basement membrane at the dermal-epidermal junction keeps the epidermis attached to the dermis. This anatomical barrier is made up of four categories of extracellular matrix proteins: collagen IV, laminin, nidogen and perlecan. These proteins are precisely arranged in a well-defined architecture through specific interactions between the structural domains of the individual components. Some of the molecular constituents are provided by both fibroblasts and keratinocytes, while others are synthesized exclusively by fibroblasts or keratinocytes. It remains to be determined how the components from the fibroblasts are targeted to the dermal-epidermal junction and correctly organized and integrated with the proteins from the adjacent keratinocytes to form the basement membrane.

The Human Epidermal Basement Membrane: A Shaped and Cell Instructive Platform That Aging Slowly Alters

One of the most important functions of skin is to act as a protective barrier. To fulfill this role, the structural integrity of the skin depends on the dermal-epidermal junction-a complex network of extracellular matrix macromolecules that connect the outer epidermal layer to the underlying dermis. This junction provides both a structural support to keratinocytes and a specific niche that mediates signals influencing their behavior. It displays a distinctive microarchitecture characterized by an undulating pattern, strengthening dermal-epidermal connectivity and crosstalk. The optimal stiffness arising from the overall molecular organization, together with characteristic anchoring complexes, keeps the dermis and epidermis layers extremely well connected and capable of proper epidermal renewal and regeneration. Due to intrinsic and extrinsic factors, a large number of structural and biological changes accompany skin aging. These changes progressively weaken the dermal-epidermal junction substructure and affect its functions, contributing to the gradual decline in overall skin physiology. Most changes involve reduced turnover or altered enzymatic or non-enzymatic post-translational modifications, compromising the mechanical properties of matrix components and cells. This review combines recent and older data on organization of the dermal-epidermal junction, its mechanical properties and role in mechanotransduction, its involvement in regeneration, and its fate during the aging process.

LAMB3 Missense Variant in Australian Shepherd Dogs with Junctional Epidermolysis Bullosa

In a highly inbred Australian Shepherd litter, three of the five puppies developed widespread ulcers of the skin, footpads, and oral mucosa within the first weeks of life. Histopathological examinations demonstrated clefting of the epidermis from the underlying dermis within or just below the basement membrane, which led to a tentative diagnosis of junctional epidermolysis bullosa (JEB) with autosomal recessive inheritance. Endoscopy in one affected dog also demonstrated separation between the epithelium and underlying tissue in the gastrointestinal tract. As a result of the severity of the clinical signs, all three dogs had to be euthanized. We sequenced the genome of one affected puppy and compared the data to 73 control genomes. A search for private variants in 37 known candidate genes for skin fragility phenotypes revealed a single protein-changing variant, LAMB3:c.1174T>C, or p.Cys392Arg. The variant was predicted to change a conserved cysteine in the laminin β3 subunit of the heterotrimeric laminin-322, which mediates the binding of the epidermal basement membrane to the underlying dermis. Loss-of-function variants in the human LAMB3 gene lead to recessive forms of JEB. We confirmed the expected co-segregation of the genotypes in the Australian Shepherd family. The mutant allele was homozygous in two genotyped cases and heterozygous in three non-affected close relatives. It was not found in 242 other controls from the Australian Shepherd breed, nor in more than 600 other controls. These data suggest that LAMB3:c.1174T>C represents the causative variant. To the best of our knowledge, this study represents the first report of a LAMB3-related JEB in domestic animals.

Laminin 332 in cancer: When the extracellular matrix turns signals from cell anchorage to cell movement

Laminin 332 is crucial in the biology of epithelia. This large extracellular matrix protein consists of the heterotrimeric assembly of three subunits - α3, β3, and γ2 - and its multifunctionality relies on a number of extracellular proteolytic processing events. Laminin 332 is central to normal epithelium homeostasis by sustaining cell adhesion, polarity, proliferation, and differentiation. It also supports a major function in epithelial tissue formation, repair, and regeneration by buttressing cell migration and survival and basement membrane assembly. Interest in this protein increased after the discovery that its expression is perturbed in tumor cells, cancer-associated fibroblasts, and the tumor microenvironment. This review summarizes current knowledge regarding the established involvement of the laminin 332 γ2 chain in tumor invasiveness and discusses the role of its α3 and β3 subunits.

Structural and biophysical characterization of the type VII collagen vWFA2 subdomain leads to identification of two binding sites

Type VII collagen is an extracellular matrix protein, which is important for skin stability; however, detailed information at the molecular level is scarce. The second vWFA (von Willebrand factor type A) domain of type VII collagen mediates important interactions, and immunization of mice induces skin blistering in certain strains. To understand vWFA2 function and the pathophysiological mechanisms leading to skin blistering, we structurally characterized this domain by X-ray crystallography and NMR spectroscopy. Cell adhesion assays identified two new interactions: one with β1 integrin via its RGD motif and one with laminin-332. The latter interaction was confirmed by surface plasmon resonance with a K_D of about 1 mm. These data show that vWFA2 has additional functions in the extracellular matrix besides interacting with type I collagen.

Gene Therapy for Epidermolysis Bullosa

Epidermolysis bullosa is a family of diseases characterized by blistering and fragility of the skin in response to mechanical trauma. Advances in our understanding of epidermolysis bullosa pathophysiology have provided the necessary foundation for the first clinical trials of gene therapy for junctional and dystrophic epidermolysis bullosa. These therapies show that gene therapy is both safe and effective, with the potential to correct the molecular and clinical phenotype of patients with epidermolysis bullosa. Improvements in gene delivery and in preventing immune reactions will be among the challenges that lie ahead during further therapeutic development.

Epidermolysis bullosa: Molecular pathology of connective tissue components in the cutaneous basement membrane zone

Epidermolysis bullosa (EB), a group of heritable skin fragility disorders, is characterized by blistering, erosions and chronic ulcers in the skin and mucous membranes. In some forms, the blistering phenotype is associated with extensive mutilating scarring and development of aggressive squamous cell carcinomas. The skin findings can be associated with extracutaneous manifestations in the ocular as well as gastrointestinal and vesico-urinary tracts. The phenotypic heterogeneity reflects the presence of mutations in as many as 20 different genes expressed in the cutaneous basement membrane zone, and the types and combinations of the mutations and their consequences at the mRNA and protein levels contribute to the spectrum of severity encountered in different subtypes of EB. This overview highlights the molecular genetics of EB based on mutations in the genes encoding type VII and XVII collagens as well as laminin-332. The mutations identified in these protein components of the extracellular matrix attest to their critical importance in providing stability to the cutaneous basement membrane zone, with implications for heritable and acquired diseases.

Granzyme B is elevated in autoimmune blistering diseases and cleaves key anchoring proteins of the dermal-epidermal junction

In healthy skin, epidermis and dermis are anchored together at the dermal-epidermal junction (DEJ), a specialized basement membrane pivotal for skin integrity and function. However, increased inflammation in the DEJ is associated with the disruption and separation of this junction and sub-epidermal blistering. Granzyme B (GzmB) is a serine protease secreted by immune cells. Dysregulated inflammation may lead to increased GzmB accumulation and proteolysis in the extracellular milieu. Although elevated GzmB is observed at the level of the DEJ in inflammatory and blistering skin conditions, the present study is the first to explore GzmB in the context of DEJ degradation in autoimmune sub-epidermal blistering. In the present study, GzmB induced separation of the DEJ in healthy human skin. Subsequently, α6/β4 integrin, collagen VII, and collagen XVII were identified as extracellular substrates for GzmB through western blot, and specific cleavage sites were identified by mass spectrometry. In human bullous pemphigoid, dermatitis herpetiformis, and epidermolysis bullosa acquisita, GzmB was elevated at the DEJ when compared to healthy samples, while α6/β4 integrin, collagen VII, and collagen XVII were reduced or absent in the area of blistering. In summary, our results suggest that regardless of the initial causation of sub-epidermal blistering, GzmB activity is a common final pathway that could be amenable to a single targeted treatment approach.

Lack of K140 immunoreactivity in junctional epidermolysis bullosa skin and keratinocytes associates with misfolded laminin epidermal growth factor-like motif 2 of the β3 short arm

Recessive mutations in the LAMA3, LAMB3 and LAMC2 genes that encode laminin-332 (LM332) (α3a, β3 and γ2 chains, respectively) cause different junctional epidermolysis bullosa (JEB) subtypes. Biallelic truncating mutations in any of these three genes usually lead to lack of protein expression resulting in the severe generalized JEB subtype, while missense or splice-site mutations in at least one allele lead to reduced expression typical of JEB generalized intermediate (JEB-gen intermed) or localized. Here, we molecularly characterized an adult patient with JEB showing negative skin staining for the anti-β3 chain monoclonal antibody K140. This antibody recognizes an as yet unidentified epitope within the laminin β3 short arm. The patient harbours a homozygous splice-site mutation resulting in highly aberrant transcripts with partial skipping of the LAMB3 exon that encodes the laminin epidermal growth factor-like motif 2 of the β3 short arm (β3-LE2). At the protein level, mutation consequences predict a misfolded β3-LE2 motif and, indeed, we found that LM332 is correctly assembled but retained in the endoplasmic reticulum (ER) where it colocalizes with the lumenal ER chaperone protein BiP, leading to dramatically reduced secretion. Lack of K140 reactivity to mutant LM332 was confirmed by immunoprecipitation and Western blot analyses. Our findings not only identify the β3-LE2 subdomain as the region recognized by K140, but also show that misfolding of LM332 structural motifs and subsequent protein retention in the ER is a common pathomechanism in JEB-gen intermed. In addition to its usefulness in antigen mapping diagnosis of JEB subtypes, this knowledge is relevant to the design of therapeutic strategies aimed at releasing ER-retained LM332 in JEB.

Humoral Epitope Spreading in Autoimmune Bullous Diseases

Autoimmune blistering diseases are characterized by autoantibodies against structural adhesion proteins of the skin and mucous membranes. Extensive characterization of their autoantibody targets has improved understanding of pathogenesis and laid the basis for the study of antigens/epitopes diversification, a process termed epitope spreading (ES). In this review, we have reported and discussed ES phenomena in autoimmune bullous diseases and underlined their functional role in disease pathogenesis. A functional ES has been proposed: (1) in bullous pemphigoid patients and correlates with the initial phase of the disease, (2) in pemphigus vulgaris patients with mucosal involvement during the clinical transition to a mucocutaneous form, (3) in endemic pemphigus foliaceus, underlining its role in disease pathogenesis, and (4) in numerous cases of disease transition associated with an intermolecular diversification of immune response. All these findings could give useful information to better understand autoimmune disease pathogenesis and to design antigen/epitope specific therapeutic approaches.

Structural proteins of the dermal-epidermal junction targeted by autoantibodies in pemphigoid diseases

The dermal-epidermal junction consists of a network of several interacting structural proteins that strengthen adhesion and mediate signalling events. This structural network consists of hemidesmosomal-anchoring filament complexes connecting the basal keratinocytes to the basement membrane. The anchoring filaments in turn interact with the anchoring fibrils to attach the basement membrane to the underlying dermis. Several of these structural proteins are recognized by autoantibodies in pemphigoid diseases, a heterogeneous group of clinically and immunopathologically diverse entities. Targeted proteins include the two intracellular plakins, plectin isoform 1a and BP230 (also called bullous pemphigoid antigen (BPAG) 1 isoform e (BPAG1e)). Plectin 1a and BP230 are connected to the intermediate filaments and to the cell surface receptor α6β4 integrin, which in turn is connected to laminin 332, a component of the anchoring filaments. Further essential adhesion proteins are BP180, a transmembrane protein, laminin γ1 and type VII collagen. Latter protein is the major constituent of the anchoring fibrils. Mutations in the corresponding genes of these adhesion molecules lead to inherited epidermolysis bullosa emphasizing the importance of these proteins for the integrity of the dermal-epidermal junction. This review will provide an overview on the structure and function of the proteins situated in the dermal-epidermal junction targeted by autoantibodies.

CONGENITAL EPIDERMOLYSIS BULLOSA: PECULIARITIES OF EPIDERMIS REGENERATION AND METHODS OF TREATMENT

Congenital epidermolysis bullosa is a group of hereditary skin diseases caused by mutations in the genes of structural proteins of the dermoepidermal junction of the skin, characterized by formation of blisters and erosions at the smallest mechanical trauma. In patients with severe subtypes of borderline and dystrophic epidermolysis bullosa there are long-term erosive and ulcerative defects with disruption of the healing process. Factors that impede healing include: malnutrition, anemia, pain, inactivity, local factors (presence of infection, prolonged inflammation, extensive nature of the lesion, absence of skin appendages in the affected area, deficiency or lack of formation of type VII collagen). Elimination of healing impeding factors is the main challenge in treatment of severe subtypes of bullous epidermolysis. Modern promising treatment techniques are at the stage of development and have not yet been introduced into clinical practice, and, as of today, skin care and optimal topical treatment with modern non-adhesive dressings remain the most widespread treatment methods that facilitate accelerated healing.

Amlexanox Enhances Premature Termination Codon Read-Through in COL7A1 and Expression of Full Length Type VII Collagen: Potential Therapy for Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare monogenic blistering disorder caused by the lack of functional type VII collagen, leading to skin fragility and subsequent trauma-induced separation of the epidermis from the underlying dermis. A total of 46% of patients with RDEB harbor at least one premature termination codon (PTC) mutation in COL7A1, and previous studies have shown that aminoglycosides are able to overcome RDEB PTC mutations by inducing "read-through" and incorporation of an amino acid at the PTC site. However, aminoglycoside toxicity will likely prevent widespread clinical application. Here the FDA-approved drug amlexanox was tested for its ability to read-through PTC mutations in cells derived from patients with RDEB. Eight of 12 different PTC alleles responded to treatment and produced full length protein, in some cases more than 50% relative to normal controls. Read-through type VII collagen was readily detectable in cell culture media and also localized to the dermal-epidermal junction in organotypic skin culture. Amlexanox increased COL7A1 transcript and the phosphorylation of UPF-1, an RNA helicase associated with nonsense-mediated mRNA decay, suggesting that amlexanox inhibits nonsense-mediated mRNA decay in cells from patients with RDEB that respond to read-through treatment. This preclinical study demonstrates the potential of repurposing amlexanox for the treatment of patients with RDEB harboring PTC mutation in COL7A1.

Unique mouse monoclonal antibodies reactive with maturation-related epitopes on type VII collagen

In this study, we generated a new set of monoclonal antibodies (mAbs) to bovine and human type VII collagen (COL7) by immunizing mice with bovine cornea-derived basement membrane zone (BMZ) fraction. The four mAbs, tentatively named as COL7-like mAbs, showed speckled subepidermal staining in addition to linear BMZ staining of normal human skin and bovine cornea, a characteristic immunofluorescence feature of COL7, but showed no reactivity with COL7 by in vitro biochemical analyses. Taking advantage of the phenomenon that COL7-like mAbs did not react with mouse BMZ, we compared immunofluorescence reactivity between wild-type and COL7-rescued humanized mice and found that COL7-like mAbs reacted with BMZ of COL7-rescued humanized mice. In ELISAs, COL7-like mAbs reacted with intact triple-helical mammalian recombinant protein (RP) of COL7 but not with bacterial RP. Furthermore, COL7-like mAbs did not react with COL7 within either cultured DJM-1 cells or basal cells of skin of a bullous dermolysis of the newborn patient. These results confirmed that COL7-like mAbs reacted with human and bovine COL7. The epitopes for COL7-like mAbs were considered to be present only on mature COL7 after secretion from keratinocytes and deposition to BMZ and to be easily destroyed during immunoblotting procedure. Additional studies indicated association of the speckled subepidermal staining with both type IV collagen and elastin. These unique anti-COL7 mAbs should be useful in studies of both normal and diseased conditions, particularly dystrophic epidermolysis bullosa, which produces only immature COL7.

Clinical features and diagnosis of epidermolysis bullosa acquisita

INTRODUCTION

Epidermolysis bullosa acquisita (EBA) is a rare autoimmune blistering disease of skin and mucous membranes. EBA is caused by autoantibodies against type VII collagen, which is a major component of anchoring fibrils, attaching epidermis to dermis. Binding of autoantibodies to type VII collagen leads to skin fragility and, finally, blister formation. The clinical picture of EBA is polymorphic, with several distinct phenotypes being described. Despite recent progress in understanding the pathophysiology of EBA, its diagnosis is still challenging. Areas covered: This review provides an update on the clinical manifestations and diagnostic methods of EBA. We searched PubMed using the terms 'epidermolysis bullosa acquisita' covering articles in English between 1 January 2005 and 31 May 2016. Relevant older publications were retrieved form cited literature. Expert commentary: While the clinical picture is highly variable, diagnosis relies on direct immunofluorescence (IF) microscopy of a perilesional skin biopsy. Linear deposits of IgG, IgA and/or C3 along the dermal-epidermal junction with an u-serrated pattern are diagnostic for EBA alike the detection of serum autoantibodies against type VII collagen. Several test systems for the serological diagnosis of EBA have recently become widely available. In some patients, sophisticated diagnostic approaches only available in specialized centers are required.

Autoimmunity against laminins

Laminins are ubiquitous constituents of the basement membranes with major architectural and functional role as supported by the fact that absence or mutations of laminins lead to either lethal or severely impairing phenotypes. Besides genetic defects, laminins are involved in a wide range of human diseases including cancer, infections, and inflammatory diseases, as well as autoimmune disorders. A growing body of evidence implicates several laminin chains as autoantigens in blistering skin diseases, collagenoses, vasculitis, or post-infectious autoimmunity. The current paper reviews the existing knowledge on autoimmunity against laminins referring to both experimental and clinical data, and on therapeutic implications of anti-laminin antibodies. Further investigation of relevant laminin epitopes in pathogenic autoimmunity would facilitate the development of appropriate diagnostic tools for thorough characterization of patients' antibody specificities and should decisively contribute to designing more specific therapeutic interventions.

Analysis of the functional consequences of targeted exon deletion in COL7A1 reveals prospects for dystrophic epidermolysis bullosa therapy

Genetically evoked deficiency of collagen VII causes dystrophic epidermolysis bullosa (DEB)-a debilitating disease characterized by chronic skin fragility and progressive fibrosis. Removal of exons carrying frame-disrupting mutations can reinstate protein expression in genetic diseases. The therapeutic potential of this approach is critically dependent on gene, protein, and disease intrinsic factors. Naturally occurring exon skipping in COL7A1, translating collagen VII, suggests that skipping of exons containing disease-causing mutations may be feasible for the treatment of DEB. However, despite a primarily in-frame arrangement of exons in the COL7A1 gene, no general conclusion of the aptitude of exon skipping for DEB can be drawn, since regulation of collagen VII functionality is complex involving folding, intra- and intermolecular interactions. To directly address this, we deleted two conceptually important exons located at both ends of COL7A1, exon 13, containing recurrent mutations, and exon 105, predicted to impact folding. The resulting recombinantly expressed proteins showed conserved functionality in biochemical and in vitro assays. Injected into DEB mice, the proteins promoted skin stability. By demonstrating functionality of internally deleted collagen VII variants, our study provides support of targeted exon deletion or skipping as a potential therapy to treat a large number of individuals with DEB.

Chemical shift assignments of the fibronectin III like domains 7-8 of type VII collagen

Type VII collagen (Col7) is important for skin stability. This is underlined by the severe skin blistering phenotype in the Col7 related diseases dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita (EBA). Col7 has a large N-terminal non-collagenous domain (NC1) that is followed by the triple helical collagenous domain. The NC1 domain has subdomains with homology to adhesion molecules and mediates important interactions within the extracellular matrix. An 185 amino acid long part of the NC1-subdomain termed fibronectin III like domains 7 and 8 (FNIII7-8) was investigated. Antibodies against this region are pathogenic in a mouse model of EBA and one reported missense mutations of Col7 lies within these domains. The nearly complete NMR resonance assignment of recombinant FNIII7-8 of Col7 is reported.

A novel laminin β gene BmLanB1-w regulates wing-specific cell adhesion in silkworm, Bombyx mori

Laminins are important basement membrane (BM) components with crucial roles in development. The numbers of laminin isoforms in various organisms are determined by the composition of the different α, β, and γ chains, and their coding genes, which are variable across spieces. In insects, only two α, one β, and one γ chains have been identified thus far. Here, we isolated a novel laminin β gene, BmLanB1-w, by positional cloning of the mutant (crayfish, cf) with blistered wings in silkworm. Gene structure analysis showed that a 2 bp deletion of the BmLanB1-w gene in the cf mutant caused a frame-shift in the open reading frame (ORF) and generated a premature stop codon. Knockdown of the BmLanB1-w gene produced individuals exhibiting blistered wings, indicating that this laminin gene was required for cell adhesion during wing development. We also identified laminin homologs in different species and showed that two copies of β laminin likely originated in Lepidoptera during evolution. Furthermore, phylogenetic and gene expression analyses of silkworm laminin genes revealed that the BmLanB1-w gene is newly evolved, and is required for wing-specific cell adhesion. This is the first report showing the tissue specific distribution and functional differentiation of β laminin in insects.

Intravenously Administered Recombinant Human Type VII Collagen Derived from Chinese Hamster Ovary Cells Reverses the Disease Phenotype in Recessive Dystrophic Epidermolysis Bullosa Mice

Recessive dystrophic epidermolysis bullosa (RDEB) is an inherited disorder characterized by skin fragility, blistering, and multiple skin wounds with no currently approved or consistently effective treatment. It is due to mutations in the gene encoding type VII collagen (C7). Using recombinant human C7 (rhC7) purified from human dermal fibroblasts (FB-rhC7), we showed previously that intravenously injected rhC7 distributed to engrafted RDEB skin, incorporated into its dermal-epidermal junction (DEJ), and reversed the RDEB disease phenotype. Human dermal fibroblasts, however, are not used for commercial production of therapeutic proteins. Therefore, we generated rhC7 from Chinese hamster ovary (CHO) cells. The CHO-derived recombinant type VII collagen (CHO-rhC7), similar to FB-rhC7, was secreted as a correctly folded, disulfide-bonded, helical trimer resistant to protease degradation. CHO-rhC7 bound to fibronectin and promoted human keratinocyte migration in vitro. A single dose of CHO-rhC7, administered intravenously into new-born C7-null RDEB mice, incorporated into the DEJ of multiple skin sites, tongue and esophagus, restored anchoring fibrils, improved dermal-epidermal adherence, and increased the animals' life span. Furthermore, no circulating or tissue-bound anti-C7 antibodies were observed in the mice. These data demonstrate the efficacy of CHO-rhC7 in a preclinical murine model of RDEB.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

The hinge region of type VII collagen is intrinsically disordered

Type VII collagen (Col7) is important for skin integrity. As a major component of the anchoring fibrils, Col7 is essential for linking different skin layers together. The central collagenous domain of Col7 contains several interruptions of the collagen triple helix. The longest interruption is 39 amino acids long and referred to as the hinge region. The hinge region is highly conserved between species. This region was predicted to adopt a coiled coil structure and to serve as the trimerization domain of Col7. To gain insight into the potential function of the hinge region we investigated a heterologous expressed peptide by CD and NMR spectroscopy. CD spectroscopy implies that the hinge region is intrinsically disordered. Resonance assignment was performed and allowed secondary structure analysis based on the chemical shift values. Seven amino acids in the N-terminal moiety show residual α-helical conformation. Subsequent investigation of temperature dependency of amide chemical shifts indicated participation in hydrogen bonding of amino acid residues in the C-terminal moiety of the hinge region. Therefore, the hinge region does not form a coiled coil structure under the employed experimental conditions. The intrinsic disorder of the hinge region might be desired for flexibility to serve as a "hinge" or the hinge region is an important interaction site as typically observed for intrinsically disordered proteins.

Type VII collagen regulates expression of OATP1B3, promotes front-to-rear polarity and increases structural organisation in 3D spheroid cultures of RDEB tumour keratinocytes

Type VII collagen is the main component of anchoring fibrils, structures that are integral to basement membrane homeostasis in skin. Mutations in the gene encoding type VII collagen COL7A1 cause recessive dystrophic epidermolysis bullosa (RDEB) an inherited skin blistering condition complicated by frequent aggressive cutaneous squamous cell carcinoma (cSCC). OATP1B3, which is encoded by the gene SLCO1B3, is a member of the OATP (organic anion transporting polypeptide) superfamily responsible for transporting a wide range of endogenous and xenobiotic compounds. OATP1B3 expression is limited to the liver in healthy tissues, but is frequently detected in multiple cancer types and is reported to be associated with differing clinical outcome. The mechanism and functional significance of tumour-specific expression of OATP1B3 has yet to be determined. Here, we identify SLCO1B3 expression in tumour keratinocytes isolated from RDEB and UV-induced cSCC and demonstrate that SLCO1B3 expression and promoter activity are modulated by type VII collagen. We show that reduction of SLCO1B3 expression upon expression of full-length type VII collagen in RDEB cSCC coincides with acquisition of front-to-rear polarity and increased organisation of 3D spheroid cultures. In addition, we show that type VII collagen positively regulates the abundance of markers implicated in cellular polarity, namely ELMO2, PAR3, E-cadherin, B-catenin, ITGA6 and Ln332.

A combinatorial cell-laden gel microarray for inducing osteogenic differentiation of human mesenchymal stem cells

Development of three dimensional (3D) microenvironments that direct stem cell differentiation into functional cell types remains a major challenge in the field of regenerative medicine. Here, we describe a new platform to address this challenge by utilizing a robotic microarray spotter for testing stem cell fates inside various miniaturized cell-laden gels in a systematic manner. To demonstrate the feasibility of our platform, we evaluated the osteogenic differentiation of human mesenchymal stem cells (hMSCs) within combinatorial 3D niches. We were able to identify specific combinations, that enhanced the expression of osteogenic markers. Notably, these 'hit' combinations directed hMSCs to form mineralized tissue when conditions were translated to 3D macroscale hydrogels, indicating that the miniaturization of the experimental system did not alter stem cell fate. Overall, our findings confirmed that the 3D cell-laden gel microarray can be used for screening of different conditions in a rapid, cost-effective, and multiplexed manner for a broad range of tissue engineering applications.

The cysteine-rich region of type VII collagen is a cystine knot with a new topology

Collagens are a group of extracellular matrix proteins with essential functions for skin integrity. Anchoring fibrils are made of type VII collagen (Col7) and link different skin layers together: the basal lamina and the underlying connective tissue. Col7 has a central collagenous domain and two noncollagenous domains located at the N and C terminus (NC1 and NC2), respectively. A cysteine-rich region of hitherto unknown function is located at the transition of the NC1 domain to the collagenous domain. A synthetic model peptide of this region was investigated by CD and NMR spectroscopy. The peptide folds into a collagen triple helix, and the cysteine residues form disulfide bridges between the different strands. The eight cystine knot topologies that are characterized by exclusively intermolecular disulfide bridges have been analyzed by molecular modeling. Two cystine knots are energetically preferred; however, all eight disulfide bridge arrangements are essentially possible. This novel cystine knot is present in type IX collagen, too. The conserved motif of the cystine knot is CX3CP. The cystine knot is N-terminal to the collagen triple helix in both collagens and therefore probably impedes unfolding of the collagen triple helix from the N terminus.

Cutaneous manifestations of gastrointestinal disease: part II

The gastrointestinal (GI) and cutaneous organ systems are closely linked. In part I of this continuing medical education article, the intricacies of this relationship were explored as they pertained to hereditary polyposis disorders, hamartomatous disorders, and paraneoplastic disease. Part II focuses on the cutaneous system's links to inflammatory bowel disease and vascular disorders. An in-depth analysis of inflammatory bowel disease skin findings is provided to aid dermatologists in recognizing and facilitating early consultation and intervention by gastroenterologists. Cutaneous signs of inflammatory bowel disease include fissures and fistulae, erythema nodosum, pyoderma gangrenosum, pyostomatitis vegetans, oral aphthous ulcers, cutaneous polyarteritis nodosa, necrotizing vasculitis, and epidermolysis bullosa acquisita. Additional immune-mediated conditions, such as diverticulitis, bowel-associated dermatosis-arthritis syndrome, Henoch-Schönlein purpura, dermatitis herpetiformis, and Degos disease, in which the skin and GI system are mutually involved, will also be discussed. Genodermatoses common to both the GI tract and the skin include Hermansky-Pudlak syndrome, pseudoxanthoma elasticum, Ehlers-Danlos syndrome, hereditary hemorrhagic telangiectasia, and blue rubber bleb nevus syndrome. Kaposi sarcoma is a neoplastic disease with lesions involving both the skin and the gastrointestinal tract. Acrodermatitis enteropathica, a condition of zinc deficiency, likewise affects both the GI and dermatologic systems. These conditions are reviewed with updates on the genetic basis, diagnostic and screening modalities, and therapeutic options. Finally, GI complications associated with vascular disorders will also be discussed.

Epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic autoimmune subepidermal bullous disease with clinical features similar to the genetic form of dystrophic epidermolysis bullosa. EBA is characterized by the presence of autoantibodies against type VII collagen which is a major component of the anchoring fibrils at the dermal-epidermal junction. EBA can be divided into two main clinical types; mechanobullous and inflammatory EBA. Mechanobullous EBA, referred to as classic EBA, presents with skin fragility, blisters and dystrophic changes on trauma-prone areas. Inflammatory EBA resembles other autoimmune subepidermal bullous diseases. Compelling evidence from mouse models supports a pathogenic role of autoantibodies against type VII collagen in EBA. Treatment of EBA is often unsatisfactory. The most widely used systemic treatment is corticosteroids. Colchicine and dapsone have been reported to be good treatment modalities when combined with corticosteroids. Some intractable cases of EBA have successfully been treated with intravenous immunoglobulin or rituximab.

The laminin family

Laminins are large molecular weight glycoproteins constituted by the assembly of three disulfide-linked polypeptides, the α, β and γ chains. The human genome encodes 11 genetically distinct laminin chains. Structurally, laminin chains differ by the number, size and organization of a few constitutive domains, endowing the various members of the laminin family with common and unique important functions. In particular, laminins are indispensable building blocks for cellular networks physically bridging the intracellular and extracellular compartments and relaying signals critical for cellular behavior, and for extracellular polymers determining the architecture and the physiology of basement membranes.

The vWFA2 domain of type VII collagen is responsible for collagen binding

Type VII collagen (Col7) is the major component of anchoring fibrils and very important for skin integrity. This is emphasized by the Col7 related skin blistering diseases dystrophic epidermolysis bullosa and epidermolysis bullosa acquisita. Structural data that provides insights into the interaction network of Col7 and thus providing a basis for a better understanding of the pathogenesis of the diseases is missing. We proved that the von-Willebrand-factor A like domain 2 (vWFA2) of Col7 is responsible for type I collagen binding. The interaction has a K(D) value of 90 μM as determined by SPR and is enthalpy driven as derived from the van't Hoff equation. Furthermore, a hitherto unknown interaction of this domain with type IV collagen was identified. The interaction of vWFA2 with type I collagen is sensitive to the presence of magnesium ions, however, vWFA2 does not contain a magnesium binding site thus magnesium must bind to type I collagen. A lysine residue has been identified to be crucial for type I collagen binding. This allowed localization of the binding site. Mutational analysis suggests different interaction mechanisms in different species and that these interactions might be of covalent nature.

Type VII collagen deficiency causes defective tooth enamel formation due to poor differentiation of ameloblasts

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in the gene encoding type VII collagen (COL7), a major component of anchoring fibrils in the epidermal basement membrane zone. Patients with RDEB present a low oral hygiene index and prevalent tooth abnormalities with caries. We examined the tooth enamel structure of an RDEB patient by scanning electron microscopy. It showed irregular enamel prisms, indicating structural enamel defects. To elucidate the pathomechanisms of enamel defects due to COL7 deficiency, we investigated tooth formation in Col7a1(-/-) and COL7-rescued humanized mice that we have established. The enamel from Col7a1(-/-) mice had normal surface structure. The enamel calcification and chemical composition of Col7a1(-/-) mice were similar to those of the wild type. However, transverse sections of teeth from the Col7a1(-/-) mice showed irregular enamel prisms, which were also observed in the RDEB patient. Furthermore, the Col7a1(-/-) mice teeth had poorly differentiated ameloblasts, lacking normal enamel protein-secreting Tomes' processes, and showed reduced mRNA expression of amelogenin and other enamel-related molecules. These enamel abnormalities were corrected in the COL7-rescued humanized mice expressing a human COL7A1 transgene. These findings suggest that COL7 regulates ameloblast differentiation and is essential for the formation of Tomes' processes. Collectively, COL7 deficiency is thought to disrupt epithelial-mesenchymal interactions, leading to defective ameloblast differentiation and enamel malformation in RDEB patients.

Laminin 332 deposition is diminished in irradiated skin in an animal model of combined radiation and wound skin injury

Skin exposure to ionizing radiation affects the normal wound healing process and greatly impacts the prognosis of affected individuals. We investigated the effect of ionizing radiation on wound healing in a rat model of combined radiation and wound skin injury. Using a soft X-ray beam, a single dose of ionizing radiation (10-40 Gy) was delivered to the skin without significant exposure to internal organs. At 1 h postirradiation, two skin wounds were made on the back of each rat. Control and experimental animals were euthanized at 3, 7, 14, 21 and 30 days postirradiation. The wound areas were measured, and tissue samples were evaluated for laminin 332 and matrix metalloproteinase (MMP) 2 expression. Our results clearly demonstrate that radiation exposure significantly delayed wound healing in a dose-related manner. Evaluation of irradiated and wounded skin showed decreased deposition of laminin 332 protein in the epidermal basement membrane together with an elevated expression of all three laminin 332 genes within 3 days postirradiation. The elevated laminin 332 gene expression was paralleled by an elevated gene and protein expression of MMP2, suggesting that the reduced amount of laminin 332 in irradiated skin is due to an imbalance between laminin 332 secretion and its accelerated processing by elevated tissue metalloproteinases. Western blot analysis of cultured rat keratinocytes showed decreased laminin 332 deposition by irradiated cells, and incubation of irradiated keratinocytes with MMP inhibitor significantly increased the amount of deposited laminin 332. Furthermore, irradiated keratinocytes exhibited a longer time to close an artificial wound, and this delay was partially corrected by seeding keratinocytes on laminin 332-coated plates. These data strongly suggest that laminin 332 deposition is inhibited by ionizing radiation and, in combination with slower keratinocyte migration, can contribute to the delayed wound healing of irradiated skin.

Fibronectin 1 mRNA expression correlates with advanced disease in renal cancer

Background

Fibronectin 1 (FN1) is a glycoprotein involved in cellular adhesion and migration processes. The aim of this study was to elucidate the role of FN1 in development of renal cell cancer (RCC) and to determine a prognostic relevance for optimal clinical management.

Methods

212 renal tissue samples (109 RCC, 86 corresponding tissues from adjacent normal renal tissue and 17 oncocytomas) were collected from patients undergoing surgery for renal tumors and subjected to total RNA extraction. Detection of FN1 mRNA expression was performed using quantitative real time PCR, three endogenous controls, renal proximal tubular epithelial cells (RPTEC) as biological control and the ΔΔCt method for calculation of relative quantities.

Results

Mean tissue specific FN1 mRNA expression was found to be increased approximately seven fold comparing RCC and corresponding kidney control tissues (p < 0.001; ANOVA). Furthermore, tissue specific mean FN1 expression was increased approx. 11 fold in clear cell compared to papillary RCC (p = 9×10^-5; Wilcoxon rank sum test). Patients with advanced disease had higher FN1 expression when compared to organ-confined disease (p < 0.001; Wilcoxon rank sum test). Applying subgroup analysis we found a significantly higher FN1 mRNA expression between organ-confined and advanced disease in the papillary and not in the clear cell RCC group (p = 0.02 vs. p = 0.2; Wilcoxon rank sum test). There was an increased expression in RCC compared to oncocytoma (p = 0.016; ANOVA).

Conclusions

To our knowledge, this is the first study to show that FN1 mRNA expression is higher in RCC compared to normal renal tissue. FN1 mRNA expression might serve as a marker for RCC aggressiveness, indicating early systemic progression particularly for patients with papillary RCC.

Laminin deposition in the extracellular matrix: a complex picture emerges

Laminins are structural components of basement membranes. In addition, they are key extracellular-matrix regulators of cell adhesion, migration, differentiation and proliferation. This Commentary focuses on a relatively understudied aspect of laminin biology: how is laminin deposited into the extracellular matrix? This topic has fascinated researchers for some time, particularly considering the diversity of patterns of laminin that can be visualized in the matrix of cultured cells. We discuss current ideas of how laminin matrices are assembled, the role of matrix receptors in this process and how laminin-associated proteins modulate matrix deposition. We speculate on the role of signaling pathways that are involved in laminin-matrix deposition and on how laminin patterns might play an important role in specifying cell behaviors, especially directed migration. We conclude with a description of new developments in the way that laminin deposition is being studied, including the use of tagged laminin subunits that should allow the visualization of laminin-matrix deposition and assembly by living cells.

Role of dermal-epidermal basement membrane zone in skin, cancer, and developmental disorders

The dermal-epidermal basement membrane zone is an important epithelial and stromal interface, consisting of an intricately organized collection of intracellular, transmembrane, and extracellular matrix proteins. The basement membrane zone has several main functions including acting as a permeability barrier, forming an adhesive interface between epithelial cells and the underlying matrix, and controlling cellular organization and differentiation. This article identifies key molecular players of the dermal-epidermal membrane zone, and highlights recent research studies that have identified structural and functional roles of these components in the context of various blistering, neoplastic, and developmental syndromes.

T and B cells target identical regions of the non-collagenous domain 1 of type VII collagen in epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a severe immunobullous disease and is caused by IgG against type VII collagen (Col VII) of anchoring fibrils. In this study, utilizing ELISA and immunoblot, 13/15 EBA sera but 0/20 bullous pemphigoid sera and 0/30 healthy control sera showed IgG reactivity with distinct recombinant subregions of the non-collagenous domain 1 (NC1) of Col VII. In two EBA patients, IgG titers against Col VII-NC1 were grossly correlated to clinical disease activity. Moreover, Col VII-reactive T cells were identified in a representative EBA patient which recognized identical subdomains of Col VII-NC1. These findings strongly suggest that (1) the Col VII-NC1 ELISA is a powerful tool for making the diagnosis of EBA, (2) Col VII-specific IgG grossly relates to disease activity and (3) IgG reactivity is associated with T cell recognition of identical subdomains of Col VII-NC1.

Fluorescent protein markers to tag collagenous proteins: the paradigm of procollagen VII

Fluorescent proteins are powerful markers allowing tracking expression, intracellular localization, and translocation of tagged proteins but their effects on the structure and assembly of complex extracellular matrix proteins has not been investigated. Here, we analyzed the utility of fluorescent proteins as markers for procollagen VII, a triple-helical protein critical for the integrity of dermal-epidermal junction. DNA constructs encoding a red fluorescent protein-tagged wild type mini-procollagen VII alpha chain and green fluorescent protein-tagged alpha chains harboring selected mutations were genetically engineered. These DNA constructs were co-expressed in HEK-293 cells and the assembly of heterogeneous triple-helical mini-procollagen VII molecules was analyzed. Immunoprecipitation and fluorescence resonance energy transfer assays demonstrated that the presence of different fluorescent protein markers at the C-termini of individual alpha chains neither altered formation of triple-helical molecules nor affected their secretion to the extracellular space. Our study provides a basis for employing fluorescent proteins as tags for complex structural proteins of extracellular matrix.

Defining the role of laminin-332 in carcinoma

The deadly feature of cancer, metastasis, requires invasion of cells through basement membranes (BM), which normally act as barriers between tissue compartments. In the case of many epithelially-derived cancers (carcinomas), laminin-332 (Ln-332) is a key component of the BM barrier. This review provides a historical examination of Ln-332 from its discovery through identification of its functions in BM and possible role in carcinomas. Current understanding points to distinct roles for the three Ln-332 subunits (alpha3, beta3, gamma2) in cell adhesion, extracellular matrix stability, and cell signaling processes in cancer. Given the large number of studies linking Ln-332 gamma2 subunit with cancer prognosis, particular attention is given to the crucial role of this subunit in cancer invasion and to the unanswered questions in this area.

Upregulation of gamma-2 laminin-332 in the mouse ear vesicant wound model

Epithelial cell migration during wound healing is regulated in part by enzymatic processing of laminin-332 (formerly LN-5), a heterodimer formed from alpha, beta, and gamma polypeptide chains. Under static conditions, laminin-332 is secreted into the extracellular matrix as a proform and has two chains processed to smaller forms, allowing it to anchor epithelial cells to the basement membrane of the dermis. During incisional wounding, laminin gamma2 chains in particular are processed to smaller sizes and function to promote epithelial sheet migration over the wound bed. The present study examines whether this same function occurs following chemical injury. The mouse ear vesicant model (MEVM) was used to follow the pathology in the ear and test whether processed laminin-332 enhances epithelial cell migration. Skin biopsies of sulfur mustard (SM) exposed ears for several time points were analyzed by histology, immunohistochemistry, real-time PCR, and Western blot analysis. SM exposure greatly increased mRNA levels for laminin-gamma2 in comparison to the other two chains. Protein production of laminin-gamma2 was upregulated, and there was an increase in the processed forms. Protein production was in excess of the amount required to form heterotrimeric laminin-332 and was associated with the migrating epithelial sheet, suggesting a potential role in wound healing for monomeric laminin-gamma2.

Laminin-332 is a substrate for hepsin, a protease associated with prostate cancer progression

Hepsin, a cell surface protease, is widely reported to be overexpressed in more than 90% of human prostate tumors. Hepsin expression correlates with tumor progression, making it a significant marker and target for prostate cancer. Recently, it was reported that in a prostate cancer mouse model, hepsin up-regulation in tumor tissue promotes progression and metastasis. The underlying mechanisms, however, remain largely uncharacterized. Hepsin transgenic mice displayed reduced laminin-332 (Ln-332) expression in prostate tumors. This is an intriguing cue, since proteolytic processing of extracellular matrix macromolecules, such as Ln-332, is believed to be involved in cancer progression, and Ln-332 expression is lost during human prostate cancer progression. In this study, we provide the first direct evidence that hepsin cleaves Ln-332. Cleavage is specific, since it is both inhibited in a dose-dependent manner by a hepsin inhibitor (Kunitz domain-1) and does not occur when catalytically inactive hepsin is used. By Western blotting and mass spectrometry, we determined that hepsin cleaves the beta3 chain of Ln-332. N-terminal sequencing identified the cleavage site at beta3 Arg(245), in a sequence context (SQLR(245) LQGSCFC) conserved among species and in remarkable agreement with reported consensus target sequences for hepsin activity. In vitro cell migration assays showed that hepsin-cleaved Ln-332 enhanced motility of DU145 prostate cancer cells, which was inhibited by Kunitz domain-1. Further, hepsin-overexpressing LNCaP prostate cancer cells also exhibited increased migration on Ln-332. Direct cleavage of Ln-332 may be one mechanism by which hepsin promotes prostate tumor progression and metastasis, possibly by up-regulating prostate cancer cell motility.

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.

Laminin-332 and -511 in skin

The extracellular matrix (ECM) was long thought to be merely a structural tissue support and/or a filter. However, recent studies have suggested that ECM proteins regulate many intracellular and extracellular events, including cell growth, cell adhesion, cell division, cell movement, and apoptosis. They do so through activation of several families of cell surface receptor, including the integrins and syndecans. The focus of this review is on two laminin isoforms expressed in the skin. Laminins are an important molecular component of the basement membranes in a variety of tissue types. They have a cruciform shape, and are composed of three chains-alpha, beta, and gamma. Keratinocytes of the skin secrete numerous laminin isoforms, including laminin-511 and laminin-332. The latter are known to affect the behaviour of keratinocytes through binding to membrane-penetrating receptors (outside-in signal transduction). Conversely, the expression, secretion and assembly of laminin-rich matrices is regulated by cell surface receptors through inside-out signal transduction. We will review how integrins regulate laminin matrix assembly and the signals elicited by laminins that support either migration or stable adhesion of keratinocytes. We will also discuss recent data indicating that laminins plays key regulatory roles in the development of skin appendages and contribute to the pathogenesis of skin cancer.