Cloning of type XVII collagen. Complementary and genomic DNA sequences of mouse 180-kilodalton bullous pemphigoid antigen (BPAG2) predict an interrupted collagenous domain, a transmembrane segment, and unusual features in the 5‘-end of the gene and the 3‘-untranslated region of the mRNA

Low pH condition impairs BP-IgG binding to the basement membrane zone

Bullous pemphigoid (BP), an autoimmune subepidermal blistering disease, shows tense blisters associated with urticarial erythema. Tissue-bound Immunoglobulin G (IgG) at the basement membrane zone (BMZ) detected by direct immunofluorescence (DIF) is strong evidence for a diagnosis of BP. The sensitivity of DIF is higher in complement component 3 (C3) than in IgG, but the reason for this different sensitivity is not fully understood. In this study, we performed several ex vivo studies to investigate the possible mechanism of IgG negativity and C3 positivity at the BMZ by DIF in some BP cases. First, sera from BP patients showing IgG negativity by DIF were found to clearly react to the BMZ in their own DIF skin samples. Next, indirect immunofluorescence (IIF) was performed using sera diluted with different pH phosphate-buffered saline (PBS), pH 7.4, 6.0, and 3.0. Patients' sera diluted with pH 7.4 PBS showed linear staining at the BMZ, but sera diluted with pH 6.0 PBS and pH 3.0 PBS showed lower fluorescence intensities. Finally, sections of skin from BP patients were pre-incubated with different pH PBS (pH 3.0, 6.0, and 7.4), followed by staining with anti-human IgG and C3. The fluorescence intensities were notably lower for IgG and C3 that had been pre-incubated with pH 3.0 PBS and pH 6.0 PBS than for IgG and C3 that had been pre-incubated with pH 7.4 PBS. These results suggest that a low pH condition hinders the binding of autoantibodies to the BMZ, that is, the drop in tissue pH induced by inflammation inhibits autoantibodies from depositing at the BMZ. Furthermore, the drop in tissue pH causes tissue-bound autoantibodies to detach from the BMZ. Complement fragments are activated not only on IgG but also on the cell surface of cells close to IgG during complement activation. IgG may detach from the BMZ under low pH condition induced by inflammation, but some complement fragments remain at the BMZ. These phenomena may help to explain why C3 is more sensitive than IgG when DIF is used to diagnose BP.

Type XVII collagen: Relevance of distinct epitopes, complement-independent effects, and association with neurological disorders in pemphigoid disorders

Pemphigoid diseases (PD) are autoimmune skin blistering diseases characterized by autoantibodies directed against proteins of the cutaneous basement membrane zone (BMZ). One of the major antigens is type XVII collagen (BP180), a transmembrane glycoprotein, which is targeted in four PDs: bullous pemphigoid, mucous membrane pemphigoid, linear IgA dermatosis, and pemphigoid gestationis. To date, different epitopes on BP180 have been described to be recognized by PD disease patients’ autoantibodies. Different BP180 epitopes were associated with distinct clinical phenotypes while the underlying mechanisms are not yet fully understood. So far, the main effects of anti-BP180 reactivity are mediated by Fcγ-receptors on immune cells. More precisely, the autoantibody–antigen interaction leads to activation of complement at the BMZ and infiltration of immune cells into the upper dermis and, by the release of specific enzymes and reactive oxygen species, to the degradation of BP180 and other BMZ components, finally manifesting as blisters and erosions. On the other hand, inflammatory responses independent of Fcγ-receptors have also been reported, including the release of proinflammatory cytokines and internalization and depletion of BP180. Autoantibodies against BP180 can also be found in patients with neurological diseases. The assumption that the clinical expression of PD depends on epitope specificity in addition to target antigens, autoantibody isotypes, and antibody glycosylation is supported by the observation that epitopes of PD patients differ from those of PD patients. The aim of the present review is to describe the fine specificities of anti-BP180 autoantibodies in different PDs and highlight the associated clinical differences. Furthermore, the direct effects after binding of the autoantibodies to their target are summarized.

Genetic Disorders of the Extracellular Matrix: From Cell and Gene Therapy to Future Applications in Regenerative Medicine

Metazoans have evolved to produce various types of extracellular matrix (ECM) that provide structural support, cell adhesion, cell-cell communication, and regulated exposure to external cues. Epithelial cells produce and adhere to a specialized sheet-like ECM, the basement membrane, that is critical for cellular homeostasis and tissue integrity. Mesenchymal cells, such as chondrocytes in cartilaginous tissues and keratocytes in the corneal stroma, produce a pericellular matrix that presents optimal levels of growth factors, cytokines, chemokines, and nutrients to the cell and regulates mechanosensory signals through specific cytoskeletal and cell surface receptor interactions. Here, we discuss laminins, collagen types IV and VII, and perlecan, which are major components of these two types of ECM. We examine genetic defects in these components that cause basement membrane pathologies such as epidermolysis bullosa, Alport syndrome, rare pericellular matrix-related chondrodysplasias, and corneal keratoconus and discuss recent advances in cell and gene therapies being developed for some of these disorders. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

BP180/Collagen XVII: A Molecular View

BP180 is a type II collagenous transmembrane protein and is best known as the major autoantigen in the blistering skin disease bullous pemphigoid (BP). The BP180 trimer is a central component in type I hemidesmosomes (HD), which cause the adhesion between epidermal keratinocytes and the basal lamina, but BP180 is also expressed in several non-HD locations, where its functions are poorly characterized. The immunological roles of intact and proteolytically processed BP180, relevant in BP, have been subject to intensive research, but novel functions in cell proliferation, differentiation, and aging have also recently been described. To better understand the multiple physiological functions of BP180, the focus should return to the protein itself. Here, we comprehensively review the properties of the BP180 molecule, present new data on the biochemical features of its intracellular domain, and discuss their significance with regard to BP180 folding and protein-protein interactions.

Complement-independent blistering mechanisms in bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease that clinically demonstrates tense blisters with widespread erythema, histologically demonstrates subepidermal blistering and immunologically demonstrates the presence of circulating autoantibodies against hemidesmosomal molecules. Complement activation has long been regarded as necessary for the generation of the BP. However, certain evidence has recently come to support non-complemental blistering mechanisms. The story of BP blistering mechanisms is a complicated one. This review mainly focuses on a specific blistering mechanism that highlights the role of complements in BP blistering.

The molecules in the corneal basement membrane zone affected by mustard exposure suggest potential therapies

Mustard exposures result in epithelial-stromal separations in the cornea and epidermal-dermal separations in the skin. Large blisters often manifest in skin, while the cornea develops microblisters, and, when enough form, the epithelium sloughs. If the exposure is severe, healing can be imperfect and can result in long-term adverse consequences. For the cornea, this could manifest as recurrent corneal erosions. Since the corneal epithelial-stromal separations are in the region identified by electron microscopy as the lamina lucida, the same region affected by the blistering disease junctional epidermolysis bullosa (JEB), we postulated that the molecules that are defective in JEB would be the same ones cleaved by mustard compounds. These molecules are α6β4 integrin and collagen XVII, which can be cleaved by matrix metalloproteinase-9 (MMP-9) and ADAM17, respectively. Therefore, our laboratory has tested MMP-9 and ADAM17 inhibitors as potential therapies to attenuate corneal mustard injury. Our results demonstrated that inhibiting MMP-9 and ADAM17 resulted in less epithelial-stromal separation in the corneas at 24 h postexposure, as compared with using only medium as a therapy.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Context-Dependent Regulation of Collagen XVII Ectodomain Shedding in Skin

Pemphigoid is a common autoimmune blistering disorder in which autoantibodies target transmembrane collagen XVII (COL17), a component of hemidesmosomes in basal keratinocytes. The ectodomain of COL17 can be cleaved from the cell surface within the juxtamembranous extracellular NC16A domain, and, interestingly, certain autoantibodies of pemphigoid patients preferentially react with the shed ectodomain. These findings suggest that COL17 ectodomain shedding generates neoepitopes on the shed form; however, the regulatory mechanism of the shedding in in vivo skin and the pathogenicity of the neoepitope-targeting antibodies still are uncertain. To address these issues, we produced rabbit antibodies specifically reacting with N-terminal cleavage sites of the shed COL17 ectodomain. The antibodies showed that certain amounts of the human COL17 ectodomain are cleaved physiologically at Gln(525) in in vivo skin. In contrast, migrating human keratinocytes cleave COL17 at Leu(524) but not at Gln(525). The passive transfer of antibodies reacting with an N-terminal cleavage site of the mouse COL17 ectodomain into neonatal wild-type mice failed to induce blister formation, even though the antibodies bound to the dermal-epidermal junctions, indicating that cleavage site-specific antibodies have reduced or absent pathogenicity for blister formation. This study shows the ectodomain shedding of COL17 to be a physiological event in in vivo human skin that probably generates nonpathologic epitopes on the cleavage sites.

Deletion of the major bullous pemphigoid epitope region of collagen XVII induces blistering, autoimmunization, and itching in mice

Bullous pemphigoid (BP) is the most common autoimmune subepidermal blistering skin disease with a characteristic of pruritus and blistering. BP patients carry inflammation-triggering autoantibodies against the collagen XVII (ColXVII, also known as BP180) juxtamembraneous extracellular noncollagenous 16A (NC16A) domain involved in ectodomain shedding. Deletion of the corresponding NC14A region in a genetically modified mouse model (ΔNC14A) decreased the amount of ColXVII in skin, but it did not prevent ectodomain shedding. Newborn ΔNC14A mice had no macroscopic phenotypic changes. However, subepidermal microblisters, rudimentary hemidesmosomes, and loose basement membrane zone were observed by microscopy. ΔNC14A mice grow normally, but at around 3 months of age they start to scratch themselves and develop crusted erosions. Furthermore, perilesional eosinophilic infiltrations in the skin, eosinophilia, and elevated serum IgE levels are detected. Despite the removal of the major BP epitope region, ΔNC14A mice developed IgG and IgA autoantibodies with subepidermal reactivity, indicating autoimmunization against a dermo-epidermal junction component. Moreover, IgG autoantibodies recognized a 180-kDa keratinocyte protein, which was sensitive to collagenase digestion. We show here that ΔNC14A mice provide a highly reproducible BP-related mouse model with spontaneous breakage of self-tolerance and development of autoantibodies.

Molecular architecture and function of the hemidesmosome

Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane. The mechanical stability of hemidesmosomes relies on multiple interactions of a few protein components that form a membrane-embedded tightly-ordered complex. The core of this complex is provided by integrin α6β4 and P1a, an isoform of the cytoskeletal linker protein plectin that is specifically associated with hemidesmosomes. Integrin α6β4 binds to the extracellular matrix protein laminin-332, whereas P1a forms a bridge to the cytoplasmic keratin intermediate filament network. Other important components are BPAG1e, the epithelial isoform of bullous pemphigoid antigen 1, BPAG2, a collagen-type transmembrane protein and CD151. Inherited or acquired diseases in which essential components of the hemidesmosome are missing or structurally altered result in tissue fragility and blistering. Modulation of hemidesmosome function is of crucial importance for a variety of biological processes, such as terminal differentiation of basal keratinocytes and keratinocyte migration during wound healing and carcinoma invasion. Here, we review the molecular characteristics of the proteins that make up the hemidesmosome core structure and summarize the current knowledge about how their assembly and turnover are regulated by transcriptional and post-translational mechanisms.

Bullous pemphigoid: role of complement and mechanisms for blister formation within the lamina lucida

Bullous pemphigoid (BP), an autoimmune subepidermal blistering skin disease, demonstrates tense blisters with or without widespread erythema, blistering along the lamina lucida, immunoglobulin G and/or complement deposits at the basement membrane zone, and the presence of circulating autoantibodies against hemidesmosomal molecules. These autoantibodies usually react against 180-kDa and/or 230-kDa proteins, designated as BP180 and BP230, respectively. The precise blistering mechanisms after autoantibodies bind to antigens are not fully understood. Immune complexes are thought to initially activate the complement cascade, which may induce activation of proteases and/or cytokines and cause dermal-epidermal separation. However, why does separation run specifically within the lamina lucida in a space as narrow as 500 nm wide? This review mainly focuses on the possible mechanisms of BP-specific blistering and how separation occurs along the lamina lucida, based on existing evidence.

Epidermolysis bullosa - a group of skin diseases with different causes but commonalities in gene expression

Epidermolysis bullosa (EB) is a group of hereditary skin disorders. Although each subtype is caused by mutations in genes encoding differentially located components of the skin, the resulting phenotype is similar. In this study, we investigated similarities in the gene expression profiles of each subtype on mRNA level. Type XVI collagen (COL16A1), G0/G1 switch 2 (G0S2), fibronectin (FN1), ribosomal protein S27A (RPS27A) and low density lipoprotein receptor (LDLR) were shown to exhibit corresponding changes in gene expression in all three EB subtypes. While COL16A1, G0S2 and FN1 are up-regulated, LDLR and RPS27A mRNA levels are decreased. These data indicate that EB cells seem to take measures increasing their mechanical stability. Apoptosis is likely to be exacerbated, and migratory potential appears to be elevated. Protein degradation is hampered, and the release of fatty acids and glycerol is restricted, probably to save energy. These commonalities might benefit existing EB treatment strategies or could help to reveal new starting points for the treatment of EB in the future.

Antibodies to pathogenic epitopes on type XVII collagen cause skin fragility in a complement-dependent and -independent manner

In bullous pemphigoid (BP), the most prevalent autoimmune blistering disease, type XVII collagen (COL17) is targeted by circulating autoantibodies. BP is thought to be an autoantibody-mediated complement-fixing blistering disease, and a juxtamembranous noncollagenous 16A (NC16A) domain spanning Glu(490) to Arg(566) was proved to be the main pathogenic region on COL17, although precise pathogenic epitopes within NC16A have not been elucidated. In this study, we showed that injection of rabbit IgG Abs targeting Asp(522) to Gln(545) induced skin fragility associated with in vivo deposition of IgG and complement in neonatal COL17-humanized mice. Notably, immunoadsorption of rabbit anti-NC16A IgG Ab with this epitope (Asp(522) to Gln(545)) or the anti-NC16A IgG administered together with the peptides of this epitope as a decoy ameliorated skin fragility in the injected neonatal COL17-humanized mice compared with the anti-NC16A IgG alone even though all of the mice showed both IgG and complement deposition. These results led us to investigate an additional, complement-independent mechanism of skin fragility in the mice injected with anti-COL17 Abs. The rabbit anti-NC16A IgG depleted the expression of COL17 in cultured normal human keratinocytes, whereas immunoadsorption of the same IgG with this epitope significantly suppressed the depletion effect. Moreover, passive transfer of F(ab')(2) fragments of the human BP or rabbit IgG Abs against COL17 demonstrated skin fragility in neonatal COL17-humanized mice. In summary, this study reveals the importance of Abs directed against distinct epitopes on COL17, which induce skin fragility in complement-dependent as well as complement-independent ways.

Neutrophil elastase cleaves the murine hemidesmosomal protein BP180/type XVII collagen and generates degradation products that modulate experimental bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies against the hemidesmosomal proteins BP180 and BP230. In the IgG passive transfer model of BP, blister formation is triggered by anti-BP180 IgG and depends on complement activation, mast cell degranulation, and neutrophil recruitment. Mice lacking neutrophil elastase (NE) do not develop experimental BP. Here, we demonstrated that NE degrades recombinant mouse BP180 within the immunodominant extracellular domain at amino acid positions 506 and 561, generating peptide p561 and peptide p506. Peptide p561 is chemotactic for neutrophils both in vitro and in vivo. Local injection of NE into B6 mice recruits neutrophils to the skin, and neutrophil infiltration is completely blocked by co-injection with the NE inhibitor α1-proteinase inhibitor. More importantly, NE directly cleaves BP180 in mouse and human skin, as well as the native human BP180 trimer molecule. These results demonstrate that (i) NE directly damages the extracellular matrix and (ii) NE degradation of mouse BP180 generates neutrophil chemotactic peptides that amplify disease severity at the early stage of the disease.

Dual targets for mouse mast cell protease-4 in mediating tissue damage in experimental bullous pemphigoid

Mouse mast cell protease-4 (mMCP-4) has been linked to autoimmune and inflammatory diseases, although the exact mechanisms underlying its role in these pathological conditions remain unclear. Here, we have found that mMCP-4 is critical in a mouse model of the autoimmune skin blistering disease bullous pemphigoid (BP). Mice lacking mMCP-4 were resistant to experimental BP. Complement activation, mast cell (MC) degranulation, and the early phase of neutrophil (PMN) recruitment occurred comparably in mMCP-4(-/-) and WT mice. However, without mMCP-4, activation of matrix metalloproteinase (MMP)-9 was impaired in cultured mMCP-4(-/-) MCs and in the skin of pathogenic IgG-injected mMCP-4(-/-) mice. MMP-9 activation was not fully restored by local reconstitution with WT or mMCP-4(-/-) PMNs. Local reconstitution with mMCP-4(+/+) MCs, but not with mMCP-4(-/-) MCs, restored blistering, MMP-9 activation, and PMN recruitment in mMCP-4(-/-) mice. mMCP-4 also degraded the hemidesmosomal transmembrane protein BP180 both in the skin and in vitro. These results demonstrate that mMCP-4 plays two different roles in the pathogenesis of experimental BP, by both activating MMP-9 and by cleaving BP180, leading to injury of the hemidesmosomes and extracellular matrix of the basement membrane zone.

Dynamic interactions of epidermal collagen XVII with the extracellular matrix: laminin 332 as a major binding partner

Transmembrane collagen XVII, a major component of the hemidesmosomes, is crucial for stable adhesion of the epidermis and dermis in the skin, and its dysfunction results in blistering diseases. The ectodomain of collagen XVII (Ecto-ColXVII) is constitutively shed from the cell surface, but its binding partner(s) in the extracellular matrix (ECM) and the physiologic roles of the ligand interactions remain elusive. Herein, we used a new cleavage site-specific antibody to address the dynamics of collagen XVII shedding and the interactions of Ecto-ColXVII with the ECM. Ecto-ColXVII was present in the migration tracks of primary human keratinocytes and co-localized with laminin 332. The presence of this laminin, but also of collagen IV and Matrigel, in the ECM enhanced shedding and incorporation of Ecto-ColXVII into the matrix. Laminin 332 is a major, but not exclusive, interaction partner in vivo because Ecto-ColXVII deposited in the ECM of laminin 332-deficient keratinocytes was drastically reduced, but Ecto-ColXVII was present in laminin 332-negative human skin. Expression of collagen XVII deletion mutants in HEK 293 cells identified the C-terminal ectodomain stretch Ser(978)-Pro(1497) as necessary for ECM binding. Taken together, migrating keratinocytes shed the Ecto-ColXVII, and this dynamically binds via its C-terminal domain to distinct partners in the ECM.

The C5a receptor on mast cells is critical for the autoimmune skin-blistering disease bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune skin-blistering disease characterized by the presence of autoantibodies against the hemidesmosomal proteins BP230 and BP180. In the IgG passive transfer mouse model of BP, subepidermal blistering is triggered by anti-BP180 antibodies and depends on the complement system, mast cell (MC) degranulation, and neutrophil infiltration. In this study, we have identified the signaling events that connect the activation of the complement system and MC degranulation. We found that mice deficient in MCs or the C5a receptor (C5aR) injected with pathogenic anti-BP180 IgG failed to develop subepidermal blisters and exhibited a drastic reduction in p38 MAPK phosphorylation compared with WT mice. Local reconstitution with MCs from WT but not C5aR-deficient mice restored high levels of p38 MAPK phosphorylation and subepidermal blistering in MC-deficient mice. Local injection of recombinant C5a induced phosphorylation of p38 MAPK in WT but not MC-deficient mice. Cultured mouse MCs treated with recombinant C5a exhibited a significant increase in p38 MAPK phosphorylation and MC degranulation. Taken together, these data demonstrate that C5a interacts with C5aR on MCs and that this C5a-C5aR interaction triggers activation of the p38 MAPK pathway, subsequent MC degranulation, and ultimately BP blistering.

Ectodomain shedding generates Neoepitopes on collagen XVII, the major autoantigen for bullous pemphigoid

As a type II transmembrane protein in basal keratinocytes, collagen XVII provides stable adhesion between epidermis and dermis in the skin. Its ectodomain can be shed from the cell surface, and autoantibodies in certain blistering diseases preferentially recognize the shed form. Major epitopes of collagen XVII are clustered within the juxtamembranous noncollagenous 16th A domain, and ectodomain shedding occurs within this region, suggesting that cleavage generates neoepitopes. However, the candidate cleavage sites have been controversial, and the mechanism of neoepitope generation is unclear. In this study, we investigated cleavage sites in the noncollagenous 16th A domain to understand the generation of neoepitopes and their pathological role. Polyclonal Abs recognizing the stretch Leu(524)-Gly(532) preferentially reacted with the shed ectodomain, but not with the full-length form, indicating that a neoepitope was localized at this site. The neoepitope-specific Ab fixed complement and induced granulocyte-dependent dermal-epidermal separation in cryosections of normal human skin. The physiological cleavage sites were identified using mass spectrometry. N termini were found at Asp(514), Leu(524), Glu(525), and Gly(526), among which Asp(514) and Glu(525) were blocked by acetylation and pyroglutaminate. In silico prediction of B cell epitopes indicated that the antigenicity of the Leu(524)-Gly(532) region increased substantially after shedding, regardless of the cleavage sites. Correspondingly, neoepitopes were found in the skin and blister fluids of patients with bullous pemphigoid, and bullous pemphigoid sera reacted with the peptide Leu(524)-Gly(532). Taken together, these data demonstrate that physiological shedding of collagen XVII generates neoepitopes, which may serve as a target of blister-inducing autoantibodies.

Cross-reactivity of autoantibodies from patients with epidermolysis bullosa acquisita with murine collagen VII

The pathomechanism of antibody-mediated tissue damage in autoimmune diseases can be best studied in experimental models by passively transferring specific autoantibodies into animals. The reproduction of the disease in animals depends on several factors, including the cross-reactivity of patient autoantibodies with the animal tissue. Here, we show that autoantibodies from patients with epidermolysis bullosa acquisita (EBA), a subepidermal autoimmune blistering disease, recognize multiple epitopes on murine collagen VII. Indirect immunofluorescence microscopy revealed that EBA patients' IgG cross-reacts with mouse skin. Overlapping, recombinant fragments of murine collagen VII were used to characterize the reactivity of EBA sera and to map the epitopes on the murine antigen by ELISA and immunoblotting. The patients' autoantibody binding to murine collagen VII triggered pathogenic events as demonstrated by a complement fixing and an ex vivo granulocyte-dependent dermal-epidermal separation assay. These findings should greatly facilitate the development of improved disease models and novel therapeutic strategies.

Shedding of collagen XVII/BP180 in skin depends on both ADAM10 and ADAM9

Collagen XVII is a transmembrane collagen and the major autoantigen of the autoimmune skin blistering disease bullous pemphigoid. Collagen XVII is proteolytically released from the membrane, and the pathogenic epitope harbors the cleavage site for its ectodomain shedding, suggesting that proteolysis has an important role in regulating the function of collagen XVII in skin homeostasis. Previous studies identified ADAMs 9, 10, and 17 as candidate collagen XVII sheddases and suggested that ADAM17 is a major sheddase. Here we show that ADAM17 only indirectly affects collagen XVII shedding and that ADAMs 9 and 10 are the most prominent collagen XVII sheddases in primary keratinocytes because (a) collagen XVII shedding was not stimulated by phorbol esters, known activators of ADAM17, (b) constitutive and calcium influx-stimulated shedding was sensitive to the ADAM10-selective inhibitor GI254023X and was strongly reduced in Adam10(-/-) cells, (c) there was a 55% decrease in constitutive collagen XVII ectodomain shedding from Adam9(-/-) keratinocytes, and (d) H(2)O(2) enhanced ADAM9 expression and stimulated collagen XVII shedding in skin and keratinocytes of wild type mice but not of Adam9(-/-) mice. We conclude that ADAM9 and ADAM10 can both contribute to collagen XVII shedding in skin with an enhanced relative contribution of ADAM9 in the presence of reactive oxygen species. These results provide critical new insights into the identity and regulation of the major sheddases for collagen XVII in keratinocytes and skin and have implications for the treatment of blistering diseases of the skin.

The role of T cells in cutaneous autoimmune disease

T cells assume a fundamental function in immunosurveillance and maintenance of the cutaneous immune barrier, yet derangement of their requisite role effects a range of cutaneous autoimmune diseases with significant associated morbidity. While blistering skin diseases, such as pemphigus vulgaris (PV), pemphigus foliaceus (PF) and bullous pemphigoid (BP) are mediated by antibodies directed against autoantigens found in the skin, recent evidence has shown that T cell activation is crucial for the initiation and coordination of this humoral response. Non-blistering skin diseases, such as alopecia areata (AA), vitiligo (VL) and psoriasis (PS) are increasingly believed to be directly mediated by the activities of autoreactive T cells. Here, we examine T lymphocyte control of antibody-mediated and cell-mediated processes involved in the pathoimmunology of the above mentioned skin diseases.

Overview of extracellular matrix

The extracellular matrix provides an environment for cells. It is produced, assembled and modified by cells and in turn, it modifies the functions and behavior of the cells it encounters. The molecules that make up the matrix are diverse in both structure and function. This well-illustrated unit provides an introduction to the structure and function of the major components of matrix and serves as a background for the other units in the chapter which include protocols for isolation and analysis of individual components.

The pathophysiology of bullous pemphigoid

Bullous pemphigoid (BP) is a blistering skin disease characterized by an autoimmune response to 2 hemidesmosomal proteins within the dermal-epidermal junction, designated BP180 and BP230. While BP230 localizes intracellularly and associates with the hemidesmosomal plaque, BP180 is a transmembrane glycoprotein with an extracellular domain. Most BP patients have autoantibodies binding to an immunodominant region of BP180, the noncollagenous 16A domain (NC16A), which is located extracellularly close to the transmembrane domain of the protein. Autoreactive T and B cell responses to BP180 have been found in patients with BP. Passive transfer of antibodies to the murine BP180 ectodomain triggers a blistering skin disease in mice that closely mimics human BP. Lesion formation in this animal model depends upon complement activation, mast cell degranulation and accumulation of neutrophils and eosinophils. Patients' autoantibodies to BP180 induce dermal-epidermal separation in cryosections of human skin when co-incubated with leukocytes. The loss of cell-matrix adhesion is mediated by proteinases released by granulocytes. The increased knowledge of the pathophysiology of BP should facilitate the development of novel therapeutic strategies for this disease.

14-3-3 sigma isoform interacts with the cytoplasmic domain of the transmembrane BP180 in keratinocytes

The protein bullous pemphigoid antigen-2 (BPAG2/BP180/collagen type XVII) plays a key role in attachment of basal keratinocytes to epidermal basement membrane. The binding of BP180 with either integrin alpha6, integrin beta4, or bullous pemphigoid antigen-1 (BPAG1/BP230) is critical for this attachment in skin. The protein 14-3-3 sigma, also known as stratifin and a marker for epithelial cells, is a member of a highly conserved small acidic 14-3-3 protein family naturally found in all eukaryotic cells. Here, we have used a 14-3-3sigma GST pull-down screening assay and showed that sigma (sigma) isoform of the 14-3-3 protein family interacts with the cytoplasmic N-terminal domain of BP180. Analysis of a series of truncated or deleted 14-3-3sigma revealed that only intact 14-3-3sigma molecule, but not any of its fragments can interact with BP180. This finding suggests that conformation and possible dimerization of 14-3-3 sigma is essential for this interaction. Further, a BP180 co-immunoprecipitation (IP) and its reverse IP assays were conducted and the results confirmed that 14-3-3 sigma interacts with cytoplasmic domain, but not ecto-domain of the BP180. In conclusion, the finding of this study provides evidence that 14-3-3sigma isoform interacts with BP180 which is a major component of hemidesmosome involved in the attachment of epidermis to the basement membrane in skin. However, the significance of this interaction in hemidesmosome formation and/or attachment needs to be explored.

Enzyme-linked immunosorbent assay using multimers of the 16th non-collagenous domain of the BP180 antigen for sensitive and specific detection of pemphigoid autoantibodies

Bullous pemphigoid (BP) and pemphigoid gestationis (PG) are acquired autoimmune subepidermal blistering diseases characterized by autoantibodies against the hemidesmosomal proteins BP180/type XVII collagen and BP230. In the vast majority of BP and PG patients, these autoantibodies bind to epitopes clustered within the 16th non-collagenous domain of BP180. An ELISA system for the detection of these autoantibodies was developed and evaluated using 16th non-collagenous domain (NC16A) tetramers instead of monomers. In contrast to antigens fused to large proteins used in the past for the detection of autoantibodies against type XVII collagen, tetrameric antigen fragments bearing a small hexahistidine tag allow for high expression levels without the need to cleave off the fusion partner. Using tetrameric BP180 NC16A, positive reactions were found in 106 (89.8%) of 118 randomly selected BP sera and in all of 20 (100%) randomly selected PG sera, whereas only 2.2% of a large cohort of control subjects were positive in this assay, including patients with rheumatoid arthritis (two of 107), progressive systemic sclerosis (two of 50), systemic lupus erythematosus (one of 72), and healthy blood donors (10 of 494). Thus, the sensitivity and specificity of the new anti-tetrameric NC16A ELISA were 89.9% and 97.8% respectively. Levels of circulating autoantibodies against BP180 paralleled disease activity in the pemphigoid patients. In conclusion, the use of tetrameric NC16A in ELISA results in a sensitive and specific tool for diagnosis and monitoring of BP and PG.

Cell instructive polymers

Polymeric materials used in tissue engineering were initially used solely as delivery vehicles for transplanting cells. However, these materials are currently designed to actively regulate the resultant tissue structure and function. This control is achieved through spatial and temporal regulation of various cues (e.g., adhesion ligands, growth factors) provided to interacting cells from the material. These polymeric materials that control cell function and tissue formation are termed cell instructive polymers, and recent trends in their design are outlined in this chapter.

Role of different pathways of the complement cascade in experimental bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies directed against the hemidesmosomal proteins BP180 and BP230 and inflammation. Passive transfer of antibodies to the murine BP180 (mBP180) induces a skin disease that closely resembles human BP. In the present study, we defined the roles of the different complement activation pathways in this model system. Mice deficient in the alternative pathway component factor B (Fb) and injected with pathogenic anti-mBP180 IgG developed delayed and less intense subepidermal blisters. Mice deficient in the classical pathway component complement component 4 (C4) and WT mice pretreated with neutralizing antibody against the first component of the classical pathway, C1q, were resistant to experimental BP. These mice exhibited a significantly reduced level of mast cell degranulation and polymorphonuclear neutrophil (PMN) infiltration in the skin. Intradermal administration of compound 48/80, a mast cell degranulating agent, restored BP disease in C4(-/-) mice. Furthermore, C4(-/-) mice became susceptible to experimental BP after local injection of PMN chemoattractant IL-8 or local reconstitution with PMNs. These findings provide the first direct evidence to our knowledge that complement activation via the classical and alternative pathways is crucial in subepidermal blister formation in experimental BP.

Role of FcRs in animal model of autoimmune bullous pemphigoid

Bullous pemphigoid (BP) is a bullous dermatosis associated with autoantibodies directed against the hemidesmosomal Ags BP180 and BP230. Lesional skin is characterized by detachment of the epidermis from the dermis with an intense inflammatory cell infiltrate in the upper dermis. In experimental BP, subepidermal blistering is triggered by rabbit anti-murine BP180 (mBP180) IgG and depends upon complement activation, mast cell degranulation, and neutrophil infiltration. In this study, we determined the role of Fc gammaRs on neutrophils in experimental BP. Mice deficient in Fc gammaRIII (Fc gammaRIII-/-) and those deficient in both Fc gammaRI and Fc gammaRIII (Fc gammaRI&III-/-) but not in Fc gammaRII (Fc gammaRII-/-) were resistant to BP. Pathogenic IgG activated wild-type neutrophils, but not Fc gammaRIII-deficient neutrophils, to secrete proteolytic enzymes. The function of anti-mBP180 IgG depended entirely on its Fc domain; F(ab')2 of IgG had no pathogenic activities. In wild-type mice injected with pathogenic IgG, an Fc gammaR blocker abolished the BP phenotype and inhibited activation of wild-type neutrophils stimulated by pathogenic IgG. Results from this study establish that Fc gammaRIII plays a critical role in the activation of infiltrating neutrophils and the subsequent blistering in experimental BP.

Interferon-gamma down-regulates expression of the 230-kDa bullous pemphigoid antigen gene (BPAG1) in epidermal keratinocytes via novel chimeric sequences of ISRE and GAS

The 230-kDa bullous pemphigoid antigen (BPAG1) is an integral component of hemidesmosomes. We have previously reported that interferon-gamma (IFNgamma) inhibits the transcription of the BPAG1 gene (1). Here we investigated the target sequences of IFNgamma-signal transduction pathway in the BPAG1 promoter in epidermal keratinocytes. Transient transfections with 5'-deletion constructs of BPAG1 promoter-luciferase reporter gene plasmids in cultured normal human epidermal keratinocytes (NHEK) allowed us to narrow the DNA region containing IFNgamma inhibitory element (IGIE) to between -1 and -89, upstream from the transcription initiation site (+1). Homology search in this region identified a chimeric sequence, consisting of IFN-stimulated responsive element (ISRE) with a partial 7-bp sequence of IFNgamma activation site (GAS), as identified in the guanylate-binding protein (GBP) gene, inserted at its center. Functional analysis of IGIE, inserted in front of the heterologous thymidine kinase promoter, indicated that IGIE acts as a down-regulatory element of the promoter through IFNgamma-dependent signal pathway. Transient transfection studies with BPAG1 promoter-reporter gene constructs containing mutated IGIE (with TT to GG transversions in the region of 5'ISRE, GAS, and 3'ISRE) demonstrated that disruption of the ISRE sequences, but not GAS, markedly suppressed the BPAG1 basal promoter activity and resulted in attenuated IFNgamma response in keratinocytes. Our findings provide novel insight into the mechanism of IFNgamma regulation in keratinocyte differentiation and proliferation.

Two major 5'-untranslated regions for type XVII collagen mRNA

BACKGROUND

Type XVII collagen is an important structural component of keratinocyte hemidesmosomes and its functional loss in genetic or autoimmune disease results in blistering of the skin. In neoplastic tissue aberrant expression is seen dependent on the stage of the tumor. While the sequence of the type XVII collagen encoding gene -COL17A1 - is now completely elucidated, the sequence of the 5'-untranslated region (UTR) of the mRNA is still unknown. Since UTRs can modulate translation efficiency, the determination of the UTR sequence is indispensable for understanding the regulation of translation of type XVII collagen mRNA.

OBJECTIVE

To resolve the sequence of the 5'UTR of type XVII collagen mRNA and to analyse the promoter region for transcription motifs.

METHODS

5' Rapid amplification of cDNA ends (RACE) followed by sequence analysis and ribonuclease protection assays (RPA) were performed.

RESULTS

RACE and sequence analysis revealed the presence of six different 5'UTRs for the type XVII collagen mRNA. The start points of these six transcripts differ but no alternative exons are used. The longest 5'UTR starts 220 nucleotides before the open reading frame, whereas the shortest UTR is only 89 nucleotides in length. RPA confirmed the RACE results and furthermore demonstrated that the 5'UTRs with lengths of 102 and 220 nucleotides are the two major transcripts. Transcription motif analysis of the 5' region of the COL17A gene demonstrated several binding sites for transcription factors including the Sp1 and activating protein-1 (AP-1) families.

CONCLUSION

Type XVII collagen mRNA is alternatively transcribed, which may result in complex regulation of type XVII collagen.

Multiple correcting COL17A1 mutations in patients with revertant mosaicism of epidermolysis bullosa

Revertant mosaicism by somatic reversion of inherited mutations has been described for a number of genetic diseases. Several mechanisms can underlie this reversion process, such as gene conversion, crossing-over, true back mutation, and second-site mutation. Here, we report the occurrence of multiple corrections in two unrelated probands with revertant mosaicism of non-Herlitz junctional epidermolysis bullosa, an autosomal recessive genodermatosis due to mutations in the COL17A1 gene. Immunofluorescence microscopy and laser dissection microscopy, followed by DNA and RNA analysis, were performed on skin biopsy specimens. In patient 1, a true back mutation, 3781T-->C, was identified in the specimen from the arm, and a second-site mutation, 4463-1G-->A, which compensated for the frameshift caused by the inherited 4424-5insC mutation, was identified in the 3' splice site of exon 55 in a specimen from the middle finger. Patient 2 showed--besides two distinct gene conversion events in specimens from the arm and hand sites, both of which corrected the 1706delA mutation--a second-site mutation (3782G-->C) in an ankle specimen, which prevented the premature ending of the protein by the 3781C-->T nonsense mutation (R1226X). Thus, both inherited mutations, paternal as well as maternal, reverted at least once by different reversion events in distinct cell clusters in the described patients. The occurrence of multiple correcting mutations within the same patient indicates that in vivo reversion is less unusual than was generally thought. Furthermore, in the male patient, mosaic patterns of type XVII collagen-positive keratinocytes were present in clinically unaffected and affected skin. This latter observation makes it likely that reversion may be overlooked and may happen more often than expected.

Differential roles for beta2 integrins in experimental autoimmune bullous pemphigoid

Bullous pemphigoid (BP) is an autoimmune disease associated with autoantibodies directed against the hemidesmosomal antigens anti-BP230 and anti-B180. Neonatal mice injected with rabbit anti-mouse BP180 (mBP10) IgG develop a BP-like disease. Complement, immune complexes, mast cells, and neutrophils play a key role in subepidermal blistering in this animal model. In this study we investigated the role of beta2 integrins in experimental BP. Wild-type (WT) mice pretreated with neutralizing antibody against CD11a (LFA-1), CD11b (Mac-1), CD11a plus CD11b, or CD18 alone failed to develop BP when injected with pathogenic anti-mBP180 IgG. This was associated with a significant reduction in neutrophil accumulation in neutralizing antibody-treated mice. Mac-1-deficient (Mac-1 knockout [KO]) mice were resistant to experimental BP despite normal complement deposition and mast cell and neutrophil degranulation. Neutrophil infiltration in Mac-1 KO mice was severely impaired at 24 hours. However, more neutrophils accumulated in the skin of Mac-1 KO mice compared with WT mice at early time points (2-4 hours), which was associated with an increase in their survival as determined by apoptosis markers. These data suggest that beta2 integrins play differential roles in experimental BP: LFA-1 is required for neutrophil recruitment, while Mac-1 mediates late neutrophil accumulation and apoptosis of infiltrating neutrophils.

Collagen XVII and BPAG1 expression in the retina: evidence for an anchoring complex in the central nervous system

The ectoderm gives rise not only to the skin but also to the entire CNS. This common embryonic lineage suggests that some molecular isoforms might serve analogous functions in both tissues. Indeed, not only are laminins important components of dermal adhesion mechanisms, but they also regulate some aspects of synaptic development in both the CNS and the PNS. In the skin, laminins are part of a hemidesmosome complex essential for basal keratinocyte adhesion that includes collagen XVII (BP180) and BPAG1 (dystonin/BP230). Here, we show that CNS neurons also express collagen XVII and BPAG1 and that these molecules are expressed in the adult and developing retina. In the retina, isoforms of collagen XVII and BPAG1 are colocalized with laminins at photoreceptor synapses and around photoreceptor outer segments; both molecules are expressed by rods, whereas cones express collagen XVII but not BPAG1. Moreover, biochemical data demonstrate that collagen XVII complexes with retinal laminins. We propose that collagen XVII and BPAG1 isoforms may help to anchor elements of the rod photoreceptor cytomatrix to the extracellular matrix.

Number 1Epithelial biology

The oral mucous membrane has features similar to skin but also differs in several ways. This paper reviews the aspects of epithelial biology necessary for an understanding of the vesiculoerosive disorders.

Single Amino Acid Substitutions in Procollagen VII Affect Early Stages of Assembly of Anchoring Fibrils

Procollagen VII is a homotrimer of 350-kDa pro-alpha1(VII) chains, each consisting of a central collagenous domain flanked by the noncollagenous N-terminal NC1 domain and the C-terminal NC2 domain. After secretion from cells, procollagen VII molecules form anti-parallel dimers with a C-terminal 60-nm overlap. Characteristic alignment of procollagen VII monomers forming a dimer depends on site-specific binding between the NC2 domain and the triple-helical region adjacent to Cys-2634 of the interacting procollagen VII molecules. Formation of the intermolecular disulfide bonds between Cys-2634 and either Cys-2802 or Cys-2804 is promoted by the cleavage of the NC2 domain by procollagen C-proteinase. By employing recombinant procollagen VII variants harboring G2575R, R2622Q, or G2623C substitutions previously disclosed in patients with dystrophic epidermolysis bullosa, we studied how these amino acid substitutions affect intermolecular interactions. Binding assays utilizing an optical biosensor demonstrated that the G2575R substitution increased affinity between mutant molecules. In contrast, homotypic binding between the R2622Q or G2623C molecules was not detected. In addition, kinetics of heterotypic binding of all analyzed mutants to wild type collagen VII were different from those for binding between wild type molecules. Moreover, solid-state binding assays demonstrated that R2622Q and G2623C substitutions prevent formation of stable assemblies of procollagen C-proteinase-processed mutants. These results indicate that single amino acid substitutions in procollagen VII alter its self-assembly and provide a basis for understanding the pathomechanisms leading from mutations in the COL7A1 gene to fragility of the dermal-epidermal junction seen in patients with dystrophic forms of epidermolysis bullosa.

Molecular cloning of a cDNA encoding the porcine type XVII collagen noncollagenous 16 A domain and localization of the domain to the upper part of porcine skin basement membrane zone

Bullous pemphigoid is an autoimmune blistering human skin disease mediated by immunoglobulin (Ig)G autoantibodies targeting skin basement membrane component type XVII collagen, a transmembrane protein. Also designated BP180 and BPAG2, type XVII collagen is an extracellular matrix element essential for the connection between the epidermis and the underlying dermis. In addition to being a target antigen in the human disease bullous pemphigoid, type XVII collagen is also targeted by autoantibodies of canine, feline, equine and porcine patients suffering from a similar blistering skin disease. Previously, enzyme-linked immunosorbent assay and Western blot analyses have shown that autoantibodies from pigs affected with bullous pemphigoid recognize the human NC16A domain of type XVII collagen. To facilitate the development of porcine model of bullous pemphigoid, we isolated cDNA encoding the porcine type XVII collagen NC16A domain using a reverse transcription-polymerase chain reaction technique. The amino acids deduced from the NC16A cDNA showed 61% identity with the sequence of human NC16A. An antibody generated against a 20-amino acid peptide within the porcine NC16A localized the NC16A epitope to the upper part of porcine skin basement membrane zone. Our data provide further information of the porcine bullous pemphigoid target antigen and may help investigators for their further studies of this disease.

Hemidesmosomes: molecular organization and their importance for cell adhesion and disease

In the skin, basal epithelial cells constantly divide to renew the epidermis. The newly formed epithelial cells then differentiate in a process called keratinization, ultimately leading to the death of these cells and a pile-up of cell material containing vast amounts of keratins. The basal keratinocytes in skin are attached to their underlying basement membrane via specialized adhesion complexes termed hemidesmosomes (HDs). These complexes ascertain stable adhesion of the epidermis to the dermis, and mutations in components of these complexes often result in tissue fragility and blistering of the skin. In this review, we will describe the various hemidesmosomal proteins in detail as well as, briefly, the protein families to which they belong. Specifically, we will report the protein-protein interactions involved in the assembly of hemidesmosomes and their molecular organization. Some signaling pathways involving primarily the alpha6beta4 integrin will be discussed, since they appear to profoundly modulate the assembly and function of hemidesmosomes. Furthermore, the importance of these hemidesmosomal components for the maintenance of tissue homeostasis and their involvement in various clinical disorders will be emphasized. Finally, we will present a model for the assembly of HDs, based on our present knowledge.

Type XIII collagen and some other transmembrane collagens contain two separate coiled-coil motifs, which may function as independent oligomerization domains

Type XIII collagen is a homotrimeric transmembrane collagen composed of a short intracellular domain, a single membrane-spanning region, and an extracellular ectodomain with three collagenous domains (COL1-3) separated by short non-collagenous domains (NC1-4). Several collagenous transmembrane proteins have been found to harbor a conserved sequence next to their membrane-spanning regions, and in the case of type XIII collagen this sequence has been demonstrated to be important for chain association. We show here that this 21-residue sequence is necessary but not sufficient for NC1 association. Furthermore, the NC1 association region was predicted to form an alpha-helical coiled-coil structure, which may already begin at the membrane-spanning region, as is also predicted for the related collagen types XXIII and XXV. Interestingly, a second coiled-coil structure is predicted to be located in the NC3 domain of type XIII collagen and in the corresponding domains of types XXIII and XXV. It is found experimentally that the absence of the NC1 coiled-coil domain leads to a lack of disulfide-bonded trimers and misfolding of the membrane-proximal collagenous domain COL1, whereas the COL2 and COL3 domains are correctly folded. We suggest that the NC1 coiled-coil domain is important for association of the N-terminal part of the type XIII collagen alpha chains, whereas the NC3 coiled-coil domain is implicated in the association of the C-terminal part of the molecule. All in all, we propose that two widely separated coiled-coil domains of type XIII and related collagens function as independent oligomerization domains participating in the folding of distinct areas of the molecule.

Alterations of collagen XVII expression during transformation of oral epithelium to dysplasia and carcinoma

Collagen XVII (BP180) is a hemidesmosomal transmembrane component that has been hypothesized to participate in keratinocyte adhesion and motility. Using immunohistochemical (IHC) and in situ hybridization (ISH) methods, we showed downregulation of collagen XVII in basal cells in mild dysplasias and upregulation in suprabasal keratinocytes in moderate and severe dysplasias as well as in the central cells of grade II and III squamous cell carcinomas (SCCs). Overexpression of collagen XVII was found at the invasive front of the tumors. Collagen XVII and its cleaved ectodomain were characterized from culture extracts and precipitates of oral keratinocytes, tongue carcinoma cells, and tumor tissue extract. Malignant cell lines exhibited increased collagen XVII expression in immunoblotting analysis. In oral keratinocytes, collagen XVII gene expression was significantly induced by PMA but not by the inflammatory cytokines TGF-beta1, TNF-alpha, EGF, IL-1beta, and IL-6. These results indicate altered expression of collagen XVII at different stages of carcinogenesis and suggest a correlation between overexpression of collagen XVII and tumor progression. The reduced collagen XVII expression at the early step of carcinogenesis may reflect disturbed keratinocyte adhesion to the basement membrane.

Keratinocyte responsive element 3: analysis of a keratinocyte-specific regulatory sequence in the 230-kDa bullous pemphigoid antigen gene promoter

The 230-kDa bullous pemphigoid antigen gene is expressed primarily, if not exclusively, in basal keratinocytes of the epidermis. Keratinocyte responsive element 3, a cis-element at position -216 to -197 of the human 230-kDa bullous pemphigoid antigen gene promoter, confers tissue-specific expression to this gene (Tamai et al: J Biol Chem 270:7609-7614, 1995). In this study, we investigated the functional characteristics of keratinocyte responsive element 3 on the 230-kDa bullous pemphigoid antigen gene core promoter by transient transfections of cultured normal human keratinocytes and normal human fibroblasts, as well as of lung carcinoma (A549), osteosarcoma (OST), and gastric adenocarcinoma (GT3TKB) cell lines. A 230-kDa bullous pemphigoid antigen gene core promoter/luciferase reporter gene plasmid construct, pBPL, was modified to develop a series of constructs (pKBPL-p4KBPL), which have insertions of one, two, three, or four tandem repeats of keratinocyte responsive element 3, and these plasmids were used in transient transfections of the cultured cells. The promoter activities of pKBPL-p4KBPL constructs, relative to pBPL, in normal human keratinocytes were 7.6-, 15.5-, 4.6-, and 2.7-fold higher, respectively, whereas no upregulatory effect by keratinocyte responsive element 3 insertion was observed in other cell lines tested. prKBPL, a plasmid constructed with keratinocyte responsive element 3 in reverse orientation, showed essentially no activity in normal human keratinocytes. Insertion of a random 20 bp sequence between keratinocyte responsive element 3 and the 230-kDa bullous pemphigoid antigen gene core promoter resulted in about 40% reduction of luciferase activity in normal human keratinocytes. These data suggest that keratinocyte responsive element 3 functions as a position-, copy number-, and orientation-dependent cis-element contributing to tissue-specific regulation of the 230-kDa bullous pemphigoid antigen gene.

Cloning of hamster type XVII collagen cDNA, and pathogenesis of anti-type XVII collagen antibody and complement in hamster bullous pemphigoid

Bullous pemphigoid is an inflammatory subepidermal blistering skin disease associated with an IgG autoimmune response to the type XVII collagen. The immunopathologic features of bullous pemphigoid can be reproduced in mice by the passive transfer of anti-type XVII collagen antibodies. In this model, it is thought that blister formation depends upon complement activation, neutrophil recruitment, and some proteolytic enzymes. In this study, we cloned hamster type XVII collagen cDNA, which contains a 4296 bp coding region and which is predicted to be a transmembrane protein with an extracellular collagenous domain, residing in type II orientation. Antipeptide antibodies (anti-1191 IgG) were obtained against a segment of hamster type XVII collagen homologous with the human type XVII collagen autoantibody-reactive site. The antipeptide antibodies were passively transferred to neonatal Syrian hamsters. The injected hamsters developed a microscopic subepidermal blister as seen previously in the mice. In order to test whether antigen-antibody complexes and complement initiate the subepidermal blister formation, we carried out experiments in vitro on condition that inflammatory cells were completely eliminated. Complement activation in sera was inhibited either by heating (at 56 degrees C for 30 min) or by preincubating with cobra venom factor. When the hamster skin was incubated with fresh anti-1191 antisera, separation of dermal-epidermal junction was observed. The anti-1191 IgG failed to induce C3 deposition and dermal-epidermal junction separation, however, if the anti-1191 IgG was added alone or complement activation in sera was inhibited. Under these conditions, IgG but not C3 was deposited on the basement membrane. These results strongly suggest that antigen-antibody complexes and complement initiate dermal-epidermal junction separation.

Comprehensive analysis of gene expression profiles in keratinocytes from patients with generalized atrophic benign epidermolysis bullosa

Generalized atrophic benign epidermolysis bullosa [GABEB (OMIM no. 226650)] is an inherited subepidermal blistering disease typically caused by null mutations in COL17A1, the gene encoding type XVII collagen. Studies of GABEB keratinocytes homozygous for 4003delTC showed that this 2 bp deletion results in markedly reduced COL17A1 transcripts due to nonsense mediated-mRNA decay. To explore consequences of this null mutation in COL17A1 on the expression of other genes, RNA samples from reference GABEB and normal keratinocytes were profiled in comparative screens of microarrays of known cDNAs (n = 6180) and expressed sequence tags (ESTs) (n = 15 144). All comparative hybridization experiments were performed > or = twice; data were quantitated by densitometry and analyzed using peak quantification statistical comparative analysis (P-SCAN) software to identify differentially expressed genes. Representative genes found to be differentially expressed were verified using real-time reverse transcription-polymerase chain reaction (RT-PCR). These experiments determined that expression of nonsense-mediated mRNA decay trans-acting factor (NMD-F), the regulator of nonsense transcripts (i.e. the human homolog of the yeast Upf1 protein), was upregulated in GABEB keratinocytes. NMD-F was subsequently found to be upregulated in cultured keratinocytes from other GABEB patients homozygous for 4003delTC. These findings indicate that the gene responsible for nonsense-mediated mRNA decay is upregulated in keratinocytes known to eliminate mutant COL17A1 transcripts via this highly conserved mechanism.

Deletion of the cytoplasmatic domain of BP180/collagen XVII causes a phenotype with predominant features of epidermolysis bullosa simplex

BP180/collagen XVII is a hemidesmosomal transmembrane molecule serving as cell-surface receptor. Mutations in its gene cause junctional epidermolysis bullosa. Here, we report a patient with mutations in the gene for BP180/collagen XVII, COL17A1, but predominant phenotypic features of epidermolysis bullosa simplex. At birth, the proband presented with bullous lesions on the trunk, face, and hands. Ultrastructurally, hemidesmosomes were fairly normal, but the attachment of intermediate filaments with the hemidesmosomal plaques appeared to be impaired. Blister formation demonstrated both intraepidermal and junctional cleavage. Immunofluorescence staining with antibodies to keratins, several hemidesmosomal proteins, and the extracellular domain of BP180/collagen XVII showed normal staining patterns, whereas an antibody against the intracellular domain of BP180/collagen XVII yielded a negative immunofluorescence signal. Analysis of BP180/collagen XVII cDNA revealed a 1172 bp deletion corresponding to an in-frame deletion from Ile-18 to Asn-407 from the intracellular domain of the polypeptide. Mutation analysis of the COL17A1 gene disclosed a paternal nonsense mutation, R1226X, and a large maternal genomic deletion extending from intron 2 to intron 15, but no mutations in basal keratin genes. These findings underline the functional importance of the intracellular BP180/collagen XVII domain for the interaction of hemidesmosomes with keratin intermediate filaments and for the spatial stability of basal keratinocytes, and provide a functional explanation for the epidermolysis-bullosa- simplex-like phenotype. Further, the data demonstrate that defects in a given gene can cause unexpected phenotypes of epidermolysis bullosa categories, depending on the function of the affected protein domain.

Characterization of BALB/c mice B lymphocyte autoimmune responses to skin basement membrane component type XVII collagen, the target antigen of autoimmune skin disease bullous pemphigoid

Bullous pemphigoid is an autoimmune blistering skin disease characterized by IgG autoantibodies targeting the skin basement membrane component type XVII collagen (BPAg2). To gain understanding of the disease's induction phase, we subcutaneously immunized adult BALB/c mice with peptides of human and/or the murine-equivalent BPAg2 pathogenic NC16A domain. Female mice were injected with peptides (human, murine, or combined human and murine), or PBS control emulsified in CFA, on a four-week interval. At the fourth and subsequent immunizations, all peptide-immunized mice were given murine peptides. Two weeks after the sixth immunization, ELISA detected IgG circulating autoantibodies against self peptides in 92% (47/51) of mice immunized with murine peptides; whereas none of the preimmune sera or the sera from PBS control-immunized mice reacted to the self peptides. In four mice their autoantibodies labeled mouse skin basement membrane. Breaking B-cell tolerance to BPAg2 sets the first step in dissecting the disease's induction phase.