Characterization of the regulatory regions in the human desmoglein genes encoding the pemphigus foliaceous and pemphigus vulgaris antigens

Loss-of-function variants in KLF4 underlie autosomal dominant palmoplantar keratoderma

PURPOSE

Palmoplantar keratodermas (PPKs) form a group of disorders characterized by thickening of palm and sole skin. Over the past 2 decades, many types of inherited PPKs have been found to result from abnormal expression, processing, or function of adhesion proteins.

METHODS

We used exome and direct sequencing to detect causative pathogenic variants. Functional analysis of these variants was conducted using reverse transcription quantitative polymerase chain reaction, immunofluorescence confocal microscopy, immunoblotting, a promoter reporter assay, and chromatin immunoprecipitation.

RESULTS

We identified 2 heterozygous variants (c.1226A>G and c.633_634dupGT) in KLF4 in 3 individuals from 2 different unrelated families affected by a dominant form of PPK. Immunofluorescence staining for a number of functional markers revealed reduced epidermal DSG1 expression in patients harboring heterozygous KLF4 variants. Accordingly, human keratinocytes either transfected with constructs expressing these variants or downregulated for KLF4 displayed reduced DSG1 expression, which in turn has previously been found to be associated with PPK. A chromatin immunoprecipitation assay confirmed direct binding of KLF4 to the DSG1 promoter region. The ability of mutant KLF4 to transactivate the DSG1 promoter was significantly decreased when compared with wild-type KLF4.

CONCLUSION

Loss-of-function variants in KLF4 cause a novel form of dominant PPK and show its importance in the regulation of epidermal differentiation.

Desmosomes as Signaling Hubs in the Regulation of Cell Behavior

Desmosomes are intercellular junctions, which preserve tissue integrity during homeostatic and stress conditions. These functions rely on their unique structural properties, which enable them to respond to context-dependent signals and transmit them to change cell behavior. Desmosome composition and size vary depending on tissue specific expression and differentiation state. Their constituent proteins are highly regulated by posttranslational modifications that control their function in the desmosome itself and in addition regulate a multitude of desmosome-independent functions. This review will summarize our current knowledge how signaling pathways that control epithelial shape, polarity and function regulate desmosomes and how desmosomal proteins transduce these signals to modulate cell behavior.

150th Anniversary Series: Desmosomes and the Hallmarks of Cancer

Desmosomes represent adhesive, spot-like intercellular junctions that in association with intermediate filaments mechanically link neighboring cells and stabilize tissue architecture. In addition to this structural function, desmosomes also act as signaling platforms involved in the regulation of cell proliferation, differentiation, migration, morphogenesis, and apoptosis. Thus, deregulation of desmosomal proteins has to be considered to contribute to tumorigenesis. Proteolytic fragmentation and downregulation of desmosomal cadherins and plaque proteins by transcriptional or epigenetic mechanisms were observed in different cancer entities suggesting a tumor-suppressive role. However, discrepant data in the literature indicate that context-dependent differences based on alternative intracellular, signal transduction lead to altered outcome. Here, modulation of Wnt/β-catenin signaling by plakoglobin or desmoplakin and of epidermal growth factor receptor signaling appears to be of special relevance. This review summarizes current evidence on how desmosomal proteins participate in carcinogenesis, and depicts the molecular mechanisms involved.

Desmosomes: regulators of cellular signaling and adhesion in epidermal health and disease

Desmosomes are intercellular junctions that mediate cell-cell adhesion and anchor the intermediate filament network to the plasma membrane, providing mechanical resilience to tissues such as the epidermis and heart. In addition to their critical roles in adhesion, desmosomal proteins are emerging as mediators of cell signaling important for proper cell and tissue functions. In this review we highlight what is known about desmosomal proteins regulating adhesion and signaling in healthy skin-in morphogenesis, differentiation and homeostasis, wound healing, and protection against environmental damage. We also discuss how human diseases that target desmosome molecules directly or interfere indirectly with these mechanical and signaling functions to contribute to pathogenesis.

Desmosomal adhesion in vivo

Desmosomes are intercellular junctions that provide strong adhesion or hyper-adhesion in tissues. Here, we discuss the molecular and structural basis of this with particular reference to the desmosomal cadherins (DCs), their isoforms and evolution. We also assess the role of DCs as regulators of epithelial differentiation. New data on the role of desmosomes in development and human disease, especially wound healing and pemphigus, are briefly discussed, and the importance of regulation of the adhesiveness of desmosomes in tissue dynamics is considered.

Perturbed desmosomal cadherin expression in grainy head-like 1-null mice

In Drosophila, the grainy head (grh) gene plays a range of key developmental roles through the regulation of members of the cadherin gene family. We now report that mice lacking the grh homologue grainy head-like 1 (Grhl1) exhibit hair and skin phenotypes consistent with a reduction in expression of the genes encoding the desmosomal cadherin, desmoglein 1 (Dsg1). Grhl1-null mice show an initial delay in coat growth, and older mice exhibit hair loss as a result of poor anchoring of the hair shaft in the follicle. The mice also develop palmoplantar keratoderma, analogous to humans with DSG1 mutations. Sequence analysis, DNA binding, and chromatin immunoprecipitation experiments demonstrate that the human and mouse Dsg1 promoters are direct targets of GRHL1. Ultrastructural analysis reveals reduced numbers of abnormal desmosomes in the interfollicular epidermis. These findings establish GRHL1 as an important regulator of the Dsg1 genes in the context of hair anchorage and epidermal differentiation, and suggest that cadherin family genes are key targets of the grainy head-like genes across 700 million years of evolution.

Structure and function of desmosomes

Desmosomes are prominent adhesion sites that are tightly associated with the cytoplasmic intermediate filament cytoskeleton providing mechanical stability in epithelia and also in several nonepithelial tissues such as cardiac muscle and meninges. They are unique in terms of ultrastructural appearance and molecular composition with cell type-specific variations. The dynamic assembly properties of desmosomes are important prerequisites for the acquisition and maintenance of tissue homeostasis. Disturbance of this equilibrium therefore not only compromises mechanical resilience but also affects many other tissue functions as becomes evident in various experimental scenarios and multiple diseases.

Eyelid skin involvement in pemphigus foliaceus

PURPOSE

To report the involvement of eyelid skin in a patient with pemphigus foliaceus.

METHODS

Retrospective, interventional case report of a patient with pemphigus foliaceus involving both eyelids. The diagnosis of pemphigus foliaceus was based on histopathology and confirmed by direct immunofluorescence and immunoblot. Failure to respond to conventional immunosuppressive therapy, including high-dose corticosteroids, methotrexate, azathioprine, dapsone, and mycophenolate mofetil, necessitated the use of intravenous immunoglobulin (IVIg) therapy.

RESULTS

After successful treatment with IVIg, no change in visual acuity or other sequelae secondary to ocular pemphigus foliaceus were observed. Normal ocular architecture was maintained. Clinical remission was observed after successful therapy.

CONCLUSIONS

Pemphigus foliaceus involves the skin of the eyelid and does not involve the conjunctiva. The patient did not respond to conventional immunosuppressive therapy. The use of IVIg as mono-therapy resulted in long-term clinical remission.

Activation of Notch1 in the hair follicle leads to cell-fate switch and Mohawk alopecia

The Notch signaling pathway has been shown to control cell-fate decisions during mouse development. To study the role of Notch1 in epidermal differentiation and the development of the various cell types within the mouse hair follicle, we generated transgenic mice that express a constitutive activated form of Notch1 under the control of the involucrin promoter. Transgenic animals express the transgene in the suprabasal epidermal keratinocytes and inner root sheath of the hair follicle, and develop both skin and hair abnormalities. Notch1 overexpression leads to an increase of the differentiated cell compartment in the epidermis, delays inner root sheath differentiation, and leads to hair shaft abnormalities and alopecia associated with the anagen phase of the hair cycle.

Desmoglein genes are up-regulated in the pk mutant mouse

Plucked (pk) is an autosomal recessive mouse mutation with a hair phenotype that arose spontaneously in the DBA/2J strain. Histological studies indicate that adult pk mutant mice lose truncal hair because of the scarring of follicles due to an apparent obstruction of the outward movement of the hair shaft within the follicular canal. We mapped the pk mutant phenotype to a 1.1cM region of chromosome 18 (between 6.6 and 7.7 cM from the centromere) using 370 backcross progeny. Within this region, among others, are genes for desmosome cadherins. Desmosome cadherins are interesting candidates because of their critical roles for cell-cell adhesion in epidermal function. Northern Blot analysis of wild-type and pk mutant mice indicates that expression of both desmoglein 1 (Dsg1) and desmoglein 3 (Dsg3) is up-regulated in the skin of mutant pk mice.

Regulation of desmocollin gene expression in the epidermis: CCAAT/enhancer-binding proteins modulate early and late events in keratinocyte differentiation

Desmocollins (Dscs) are desmosomal cadherins that exhibit differentiation-specific patterns of expression in the epidermis. Dsc3 expression is strongest in basal cell layers, whereas Dsc1 is largely confined to upper, terminally differentiating strata. To understand better the processes by which Dsc expression is regulated in the epidermis, we have isolated Dsc3 and Dsc1 5'-flanking DNAs and analysed their activity in primary keratinocytes. In the present study, we found that transcription factors of the CCAAT/enhancer-binding protein family play a role in the regulation of expression of both Dscs and, in so doing, implicate this class of transcription factors in both early and late events in keratinocyte differentiation. We show that Dscs are differentially regulated by C/EBP (CCAAT/enhancer-binding protein) family members, with Dsc3 expression being activated by C/EBPbeta but not C/EBPalpha, and the reverse being the case for Dsc1. Expression of both Dscs is activated by another family member, C/EBPdelta. These results show for the first time how desmosomal cadherin gene expression is regulated and provide a mechanism for the control of other differentiation-specific genes in the epidermis.

Genetic evidence for a novel human desmosomal cadherin, desmoglein 4

Desmosomes are essential adhesion structures in most epithelia that link the intermediate filament network of one cell to its neighbor, thereby forming a strong bond. The molecular components of desmosomes belong to the cadherin superfamily, the plakin family, and the armadillo repeat protein family. The desmosomal cadherins are calcium-dependent transmembrane adhesion molecules and comprise the desmogleins and desmocollins. To date, three human desmoglein isoforms have been characterized, namely desmogleins 1, 2, and 3 that are expressed in a tissue- and differentiation-specific manner. Here we have identified and characterized, at the genetic level, a novel human desmoglein cDNA sharing homology with desmogleins 1, 2, 3 and we name this desmoglein 4. The human desmoglein 4 cDNA (3.6 kb) contains an open reading frame of 3120 bp that encodes a precursor protein of 1040 amino acids. The predicted mature protein comprises 991 amino acids with a molecular weight of 107822 Da at pI 4.38. Human desmoglein 4 shares 41% identity with human desmoglein 1, 37% with human desmoglein 2, and 50% with human desmoglein 3. Analysis of the exon/intron organization of the human desmoglein 4 gene (DSG4) demonstrates that it is composed of 16 exons spanning approximately 37 kb of 18q12 and is situated between DSG1 and DSG3. We have demonstrated using RT-PCR on multiple tissue cDNA samples that desmoglein 4 has very specific tissue expression in salivary gland, testis, prostate, and skin.

Tufted hair folliculitis associated with pemphigus vulgaris

Tufted hair folliculitis (THF) is a rare disease which is characterized by the emergence of multiple hairs from widely dilated follicular orifices surrounded by an inflammatory infiltrate resulting in scarring alopecia. The pathogenesis is not yet fully understood. Although colonization with Staphylococcus aureus could not always be detected and systemic treatment with antibiotics alone is not sufficient, this microorganism is considered to play an important role. Around 30 patients with THF have been reported since the first publication. We present a patient with pemphigus vulgaris who developed THF. To our knowledge, this is the fourth case with an association of these two entities. Amongst other causing mechanisms, the autoimmune reaction may play an important role for the development of THF.

A possible role of catenin dyslocalization in pemphigus vulgaris pathogenesis

BACKGROUND

Pemphigus vulgaris (PV) is an autoimmune blistering disease of the skin and mucosa due to the presence of autoantibodies against the components of desmosomes. To date, less is known about the expression levels of beta- and gamma-catenins in blistering diseases. The objective of this study was to evaluate the role of beta- and gamma-catenins in the pathogenesis of acantholysis in pemphigus vulgaris.

METHODS

beta- and gamma-catenin expression was evaluated by immunohistochemistry in 30 cases of PV at various stages of the disease and, as controls, in 18 specimens of the skin/oral mucosa of healthy patients.

RESULTS

Healthy skin and normal oral mucosa showed a strong beta- and gamma-catenin expression in basal and spinous layers with a prevalent cellular membrane distribution; the intensity of staining progressively decreased toward the superficial layers of epithelium. In PV patients, cytoplasmic expression of gamma-catenin was detected in 28/30 cases, and in 19/30 cases of PV for beta-catenin. Moreover, a progressive displacement of the signal toward the nucleus was found in 14/30 cases for beta-catenin, with dyslocalization toward the nucleus, particularly in areas with intense acantholysis, and in 22/30 cases of PV for gamma-catenin.

CONCLUSIONS

Abnormal distribution of gamma-catenin, consequent to PV IgG, may be considered a direct consequence of Dg3 dissociation from catenin. gamma-catenin likely plays a direct role in PV pathogenesis through its dyslocalization toward the nucleus or indirectly through the beta-catenin dyslocalization toward the nucleus, which is thought to induce transcription of selected target genes, such as uPAR.

Spectrum of dominant mutations in the desmosomal cadherin desmoglein 1, causing the skin disease striate palmoplantar keratoderma

The adhesive proteins of the desmosome type of cell junction consist of two types of cadherin found exclusively in that structure, the desmogleins and desmocollins, coded by two closely linked loci on human chromosome 18q12.1. Recently we have identified a mutation in the DSG1 gene coding for desmoglein 1 as the cause of the autosomal dominant skin disease striate palmoplantar keratoderma (SPPK) in which affected individuals have marked hyperkeratotic bands on the palms and soles. In the present study we present the complete exon-intron structure of the DSG1 gene, which occupies approximately 43 kb, and intron primers sufficient to amplify all the exons. Using these we have analysed the mutational changes in this gene in five further cases of SPPK. All were heterozygotic mutations in the extracellular domain leading to a truncated protein, due either to an addition or deletion of a single base, or a base change resulting in a stop codon. Three mutations were in exon 9 and one in exon 11, both of which code for part of the third and fourth extracellular domains, and one was in exon 2 coding for part of the prosequence of this processed protein. This latter mutation thus results in the mutant allele synthesising only 25 amino acid residues of the prosequence of the protein so that this is effectively a null mutation implying that dominance in the case of this mutation was caused by haploinsufficiency. The most severe consequences of SPPK mutations are in regions of the body where pressure and abrasion are greatest and where desmosome function is most necessary. SPPK therefore provides a very sensitive measure of desmosomal function.

The regulatory region of the human desmocollin 3 promoter forms a DNA four-way junction

Adhesion between desmosomal junctions is mediated by structural proteins of the cadherin family, viz. three desmocollins (DSC) and three desmogleins (DSG). Promoter and primer extension analysis of human DSC3 showed a TATA-less sequence initiating transcription via a cluster of sites upstream of the coding region. Deletion analysis of 1 kb of the promoter showed that expression is regulated between --303 and --203 bp upstream of the start-site of translation. Tertiary structure analysis of this cis-active region (cis 1) revealed a potential DNA 4-way junction which is notably G/C-rich in sequence. PAGE analysis of this region identified four differently migrating forms of the DNA. Structure-specific cleavage of the DNA with bacteriophage T7 endonuclease I showed the slowest migrating form to be either an extended/cruciform or stacked-X 4-way junction. DNA-binding, gel retardation assays of the cis 1 region showed distinct DNA-protein complexes and by competition experiments and using purified junction DNA we show that one of these complexes bound with both sequence and structure specificity to the 4-way junction DNA.

Structure and regulation of the envoplakin gene

Envoplakin, a member of the plakin family of proteins, is a component of desmosomes and the epidermal cornified envelope. To understand how envoplakin expression is regulated, we have analyzed the structure of the mouse envoplakin gene and characterized the promoters of both the human and mouse genes. The mouse gene consists of 22 exons and maps to chromosome 11E1, syntenic to the location of the human gene on 17q25. The exon-intron structure of the mouse envoplakin gene is common to all members of the plakin family: the N-terminal protein domain is encoded by 21 small exons, and the central rod domain and the C-terminal globular domain are coded by a single large exon. The C terminus shows the highest sequence conservation between mouse and human envoplakins and between envoplakin and the other family members. The N terminus is also conserved, with sequence homology extending to Drosophila Kakapo. A region between nucleotides -101 and 288 was necessary for promoter activity in transiently transfected primary keratinocytes. This region is highly conserved between the human and mouse genes and contains at least two different positively acting elements identified by site-directed mutagenesis and electrophoretic mobility shift assays. Mutation of a GC box binding Sp1 and Sp3 proteins or a combined E box and Krüppel-like element interacting with unidentified nuclear proteins virtually abolished promoter activity. 600 base pairs of the mouse upstream sequence was sufficient to drive expression of a beta-galactosidase reporter gene in the suprabasal layers of epidermis, esophagus, and forestomach of transgenic mice. Thus, we have identified a regulatory region in the envoplakin gene that can account for the expression pattern of the endogenous protein in stratified squamous epithelia.

Differential expression of cytokeratin after orthotopic implantation of newly established human tongue cancer cell lines of defined metastatic ability

Two human tongue squamous cell carcinoma cell lines, SQUU-A and SQUU-B, were established from the same patient. Cervical lymph node metastasis was detected in the mice orthotopically implanted with SQUU-B (86.7%, 13/15), but not in those with SQUU-A (0/13). Histologically, SQUU-B showed invasive growth and intravasation in the tongue, whereas SQUU-A simply demonstrated expansive growth without intravasation. By Western blot analysis, nonmetastatic clone SQUU-A expressed cytokeratin (CK)13/4, 14, 16/6, 18/8, and 19, whereas a high metastatic clone SQUU-B expressed CK18/8 and 19. The reverse transcription-polymerase chain reaction technique showed that CK13/4 mRNA was expressed in both cell lines, but CK14 and 16 mRNA was expressed only in SQUU-A. CK13 was immunohistochemically expressed in both SQUU-A and SQUU-B transplanted into the tongues of nude mice; CK14 and 16 were detected in SQUU-A of the tongues, but not in SQUU-B. As seen in SQUU-B cell line, SQUU-B of the cervical lymph node metastasis did not exhibit CK13, 14, or 16. These results suggest that the loss or down-regulation of CK13, 14, or 16 is related to the invasive and metastatic ability of cancer. The cytoskeletal system is thus considered to be closely related to the malignant phenotype.

Pemphigus foliaceus successfully treated with mycophenolate mofetil as a steroid-sparing agent

Pemphigus foliaceus is an autoimmune blistering disease of unknown origin with antibodies produced against desmoglein 1, an adhesive protein found in the desmosomal cell junction in the suprabasal layers of the epidermis. The disease is primarily treated with corticosteroids and corticosteroid-sparing immunosuppressive agents. We report a case of pemphigus foliaceus successfully treated with mycophenolate mofetil. It remains to be seen whether this agent has a significant effect on the course of the disease and remission induction.

Clustered cadherin genes: a sequence-ready contig for the desmosomal cadherin locus on human chromosome 18

We describe the assembly of a cosmid and PAC contig of approximately 700 kb on human chromosome 18q12 spanning the DSC and DSG genes coding for the desmocollins and desmogleins. These are members of the cadherin superfamily of calcium-dependent cell adhesion proteins present in the desmosome type of cell junction found especially in epithelial cells. They provide the strong cell-cell adhesion generated by this type of cell junction for which expression of both a desmocollin and a desmoglein is required. In the autoimmune skin diseases pemphigus foliaceous and pemphigus vulgaris (PV), where the autoantigens are, respectively, encoded by the DSG1 and DSG3 genes, severe areas of acantholysis (cell separation), potentially life-threatening in the case of PV, are evident. Dominant mutations in the DSG1 gene causing striate palmoplantar keratoderma result in hyperkeratosis of the skin on the parts of the body where pressure and abrasion are greatest, viz., on the palms and soles. These genes are also candidate tumor suppressor genes in squamous cell carcinomas and other epithelial cancers. We have screened two chromosome 18-specific cosmid libraries by hybridization with previously isolated YAC clones and DSC and DSG cDNAs, and a whole genome PAC library, both by hybridization with the YACs and by screening by PCR using cDNA sequences and YAC end sequence. The contigs were extended by further PCR screens using STSs generated by vectorette walking from the ends of the cosmids and PACs, together with sequence from PAC ends. Despite screening of two libraries, the cosmid contig still had four gaps. The PAC contig filled these gaps and in fact covered the whole locus. The positions of 45 STSs covering the whole of this region are presented. The desmocollin and desmoglein genes, which are about 30-35 kb in size, are quite well separated at approximately 20-30 kb apart and are arranged in two clusters, one DSC cluster and one DSG cluster, which are transcribed outward from the interlocus region. The order of the genes is correlated with the spatial order of gene expression in the developing mouse embryo, and this, and previous transgenic experiments, suggests that long-range genetic elements that coordinate expression of these genes may be present. The complete bacterial clone contig described in this paper is thus a resource not only for future sequencing but also for investigations into the control of expression of these clustered genes.

Localization of a new prostate-specific antigen-related serine protease gene, KLK4, is evidence for an expanded human kallikrein gene family cluster on chromosome 19q13.3-13.4

The human tissue kallikrein (KLK) family of serine proteases, which is important in post-translational processing events, currently consists of just three genes-tissue kallikrein (KLK1), KLK2, and prostate-specific antigen (PSA) (KLK3)-clustered at chromosome 19q13. 3-13.4. We identified an expressed sequence tag from an endometrial carcinoma cDNA library with 50% identity to the three known KLK genes. Primers designed to putative exon 2 and exon 3 regions from this novel kallikrein-related sequence were used to polymerase chain reaction-screen five cosmids spanning 130 kb around the KLK locus on chromosome 19. This new gene, which we have named KLK4, is 25 kb downstream of the KLK2 gene and follows a region that includes two other putative KLK-like gene fragments. KLK4 spans 5.2 kb, has an identical genomic structure-five exons and four introns-to the other KLK genes and is transcribed on the reverse strand, in the same direction as KLK1 but opposite to that of KLK2 and KLK3. It encodes a 254-amino acid prepro-serine protease that is most similar (78% identical) to pig enamel matrix serine protease but is also 37% identical to PSA. These data suggest that the human kallikrein gene family locus on chromosome 19 is larger than previously thought and also indicate a greater sequence divergence within this family compared with the highly conserved rodent kallikrein genes.

Desmosomes: intercellular adhesive junctions specialized for attachment of intermediate filaments

Cell-cell adhesion is thought to play important roles in development, in tissue morphogenesis, and in the regulation of cell migration and proliferation. Desmosomes are adhesive intercellular junctions that anchor the intermediate filament network to the plasma membrane. By functioning both as an adhesive complex and as a cell-surface attachment site for intermediate filaments, desmosomes integrate the intermediate filament cytoskeleton between cells and play an important role in maintaining tissue integrity. Recent observations indicate that tissue integrity is severely compromised in autoimmune and genetic diseases in which the function of desmosomal molecules is impaired. In addition, the structure and function of many of the desmosomal molecules have been determined, and a number of the molecular interactions between desmosomal proteins have now been elucidated. Finally, the molecular constituents of desmosomes and other adhesive complexes are now known to function not only in cell adhesion, but also in the transduction of intracellular signals that regulate cell behavior.