BPAG1-e restricts keratinocyte migration through control of adhesion stability

Seven naturally variant loci serve as genetic modifiers of Lamc2jeb induced non-Herlitz junctional Epidermolysis Bullosa in mice

Epidermolysis Bullosa (EB) is a group of rare genetic disorders that compromise the structural integrity of the skin such that blisters and subsequent erosions occur after minor trauma. While primary genetic risk of all subforms of EB adhere to Mendelian patterns of inheritance, their clinical presentations and severities can vary greatly, implying genetic modifiers. The Lamc2jeb mouse model of non-Herlitz junctional EB (JEB-nH) demonstrated that genetic modifiers can contribute substantially to the phenotypic variability of JEB and likely other forms of EB. The innocuous changes in an 'EB related gene', Col17a1, have shown it to be a dominant modifier of Lamc2jeb. This work identifies six additional Quantitative Trait Loci (QTL) that modify disease in Lamc2jeb/jeb mice. Three QTL include other known 'EB related genes', with the strongest modifier effect mapping to a region including the epidermal hemi-desmosomal structural gene dystonin (Dst-e/Bpag1-e). Three other QTL map to intervals devoid of known EB-associated genes. Of these, one contains the nuclear receptor coactivator Ppargc1a as its primary candidate and the others contain related genes Pparg and Igf1, suggesting modifier pathways. These results, demonstrating the potent disease modifying effects of normally innocuous genetic variants, greatly expand the landscape of genetic modifiers of EB and therapeutic approaches that may be applied.

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

Pathogenic DST sequence variants result in either epidermolysis bullosa simplex (EBS) or hereditary sensory and autonomic neuropathy type 6 (HSAN-VI)

DST encodes bullous pemphigoid antigen-1 (BPAG1), a protein with eight tissue-specific isoforms expressed in the skin, muscle, brain, and nerves. Accordingly, mutations in this gene are associated with epidermolysis bullosa simplex (EBS) and hereditary sensory and autonomic neuropathy type 6 (HSAN-VI). The genotypic spectrum is attested to by 19 distinct mutations but genotype-phenotype correlation for both disorders is not well established. In this study, we performed next-generation sequencing (NGS) on two families with different phenotypic presentations, one fetus (P1) with musculoskeletal and neurological malformations established by prenatal ultrasound and family history, and a 15-year-old female (P2) with skin blistering. P1 had a novel homozygous nonsense mutation, DST: NM_001144769, c.3805C>T, p.R1269* within a region of homozygosity (ROH). This mutation resides within the plakin domain of BPAG1 and ablates all isoforms of this protein, leading to novel extracutaneous phenotypes consistent with HSAN-VI in P1. P2 had a recurrent homozygous mutation DST: NM_001723.7, c.3370C>T, p.Gln1124* that presented with giant, trauma-induced skin blisters without extracutaneous involvement. This mutation is located within the coiled-coil domain present on the skin isoform of DST, BPGA1-e, associated with EBS. In summary, we report two families with pathogenic DST variants and expand the spectrum of DST genotype and phenotypes.

The Drosophila spectraplakin Short stop regulates focal adhesion dynamics by crosslinking microtubules and actin

The spectraplakin family of proteins includes ACF7/MACF1 and BPAG1/dystonin in mammals, VAB-10 in Caenorhabditis elegans, Magellan in zebrafish, and Short stop (Shot), the sole Drosophila member. Spectraplakins are giant cytoskeletal proteins that cross-link actin, microtubules, and intermediate filaments, coordinating the activity of the entire cytoskeleton. We examined the role of Shot during cell migration using two systems: the in vitro migration of Drosophila tissue culture cells and in vivo through border cell migration. RNA interference (RNAi) depletion of Shot increases the rate of random cell migration in Drosophila tissue culture cells as well as the rate of wound closure during scratch-wound assays. This increase in cell migration prompted us to analyze focal adhesion dynamics. We found that the rates of focal adhesion assembly and disassembly were faster in Shot-depleted cells, leading to faster adhesion turnover that could underlie the increased migration speeds. This regulation of focal adhesion dynamics may be dependent on Shot being in an open confirmation. Using Drosophila border cells as an in vivo model for cell migration, we found that RNAi depletion led to precocious border cell migration. Collectively, these results suggest that spectraplakins not only function to cross-link the cytoskeleton but may regulate cell–matrix adhesion.

Age related gene DST represents an independent prognostic factor for MYCN non-amplified neuroblastoma

Background

MYCN amplification and age are two critical prognostic factors of pediatric neuroblastoma. Previously, we had revealed the prognosis of MYCN target genes. However, the prognostic effects of age related genes in neuroblastoma are unclear.

Methods

The prognostic significance of age and MYCN amplification was determined through multivariate cox regression and Kaplan-Meier survival analysis. Genes differentially expressed in MYCN non-amplified younger neuroblastoma patients were identified using Therapeutically Applicable Research to Generate Effective Treatments (TARGET) and Gene Expression Omnibus (GEO) datasets. The prognostic effects of age related genes ALCAM, CACNA2D3, DST, EPB41L4A and KIF1B in pediatric neuroblastoma patients were determined by Kaplan-Meier survival.

Results

In a pediatric pan-cancer analysis, age was associated with the overall survival of pediatric B-lineage acute lymphoblastic leukemia, neuroblastoma and wilms tumor in TARGET dataset. Moreover, the prognostic effects of age in neuroblastoma were validated using two independent neuroblastoma cohorts. Furthermore, age and MYCN amplification were independent prognostic factors in pediatric neuroblastoma. Compared with MYCN non-amplified older neuroblastoma patients, MYCN non-amplified younger neuroblastoma patients had better clinical outcomes. ALCAM, CACNA2D3, DST, EPB41L4A and KIF1B were highly expressed in MYCN non-amplified younger neuroblastoma patients. And the higher expression levels of ALCAM, CACNA2D3, DST, EPB41L4A or KIF1B were associated with better prognosis of MYCN non-amplified neuroblastoma patients. DST was an independent prognostic factor in MYCN non-amplified neuroblastoma patients and MYCN non-amplified neuroblastoma younger patients with higher DST expression levels had the best clinical overall survival.

Conclusions

Age related gene DST was an independent prognostic factor in MYCN non-amplified neuroblastoma. MYCN non-amplified younger neuroblastoma patients with higher DST expression levels had the best clinical overall survival.

Epidermolysis bullosa simplex due to bi-allelic DST mutations: Case series and review of the literature

BACKGROUND

Epidermolysis bullosa simplex (EBS) is a heterogeneous group of inherited disorders characterized by skin fragility due to intraepidermal separation. Most cases result from heterozygous mutations in KRT5 or KRT14; however, a minority of affected individuals carry mutations in non-keratin genes including DST encoding an epithelial isoform of dystonin. DST-associated EBS is transmitted as an autosomal recessive trait. Here, we report a series of EBS patients carrying bi-allelic DST mutations and review previously reported cases aiming to delineate phenotype-genotype correlations.

METHODS

Whole-exome and direct sequencing were used for variant analysis. Review of previously reported cases was performed.

RESULTS

Mutation analysis revealed DST mutations in five patients belonging to three families. Two variants have not been previously reported: c.7097dupA (p.Tyr2366X) and c.7429delC (p.Leu2477Serfs*13). We identified an additional six cases in the literature, bringing the total number of individuals affected with EBS due to DST variants to 11. Patients displayed distinctive phenotypes regardless of the causative variant.

CONCLUSIONS

The current study expands the clinical and genetic spectrum of DST-associated EBS subtype.

Slac2-b Coordinates Extracellular Vesicle Secretion to Regulate Keratinocyte Adhesion and Migration

Slac2-b, also known as exophilin-5, is a Rab27b effector protein with a role in exosome transport and is encoded by the EXPH5 gene. We previously described biallelic loss-of-function mutations in EXPH5 in an autosomal recessive form of epidermolysis bullosa simplex. However, how the loss of Slac2-b expression leads to skin fragility and erosions is unknown. In this study, we demonstrate that keratinocytes (KCs) isolated from two different individuals with mutations in EXPH5 have significant defects in cell‒matrix adhesion. EXPH5-mutant KCs also showed increased perinuclear accumulation and significantly reduced trafficking of CD63⁺ vesicles. These phenotypes were also seen in Slac2-b‒deficient KCs. This was coincident with a reduction in Rab27a protein expression in Slac2-b‒mutant KCs as well as reduced secretion of extracellular vesicles containing extracellular matrix proteins. Live imaging analysis revealed a strong correlation between CD63⁺ vesicle trafficking to the plasma membrane and focal adhesion dynamics. These findings support a role for Slac2-b in regulating local focal adhesion dynamics to support effective KC adhesion and provide insight into the underlying pathophysiology of inherited skin blistering.

Diverse dystonin gene mutations cause distinct patterns of Dst isoform deficiency and phenotypic heterogeneity in Dystonia musculorum mice

Loss-of-function mutations in dystonin (DST) can cause hereditary sensory and autonomic neuropathy type 6 (HSAN-VI) or epidermolysis bullosa simplex (EBS). Recently, DST-related diseases were recognized to be more complex than previously thought because a patient exhibited both neurological and skin manifestations, whereas others display only one or the other. A single DST locus produces at least three major DST isoforms: DST-a (neuronal isoform), DST-b (muscular isoform) and DST-e (epithelial isoform). Dystonia musculorum (dt) mice, which have mutations in Dst, were originally identified as spontaneous mutants displaying neurological phenotypes. To reveal the mechanisms underlying the phenotypic heterogeneity of DST-related diseases, we investigated two mutant strains with different mutations: a spontaneous Dst mutant (Dstdt-23Rbrc mice) and a gene-trap mutant (DstGt mice). The Dstdt-23Rbrc allele possesses a nonsense mutation in an exon shared by all Dst isoforms. The DstGt allele is predicted to inactivate Dst-a and Dst-b isoforms but not Dst-e There was a decrease in the levels of Dst-a mRNA in the neural tissue of both Dstdt-23Rbrc and DstGt homozygotes. Loss of sensory and autonomic nerve ends in the skin was observed in both Dstdt-23Rbrc and DstGt mice at postnatal stages. In contrast, Dst-e mRNA expression was reduced in the skin of Dstdt-23Rbrc mice but not in DstGt mice. Expression levels of Dst proteins in neural and cutaneous tissues correlated with Dst mRNAs. Because Dst-e encodes a structural protein in hemidesmosomes (HDs), we performed transmission electron microscopy. Lack of inner plaques and loss of keratin filament invasions underneath the HDs were observed in the basal keratinocytes of Dstdt-23Rbrc mice but not in those of DstGt mice; thus, the distinct phenotype of the skin of Dstdt-23Rbrc mice could be because of failure of Dst-e expression. These results indicate that distinct mutations within the Dst locus can cause different loss-of-function patterns among Dst isoforms, which accounts for the heterogeneous neural and skin phenotypes in dt mice and DST-related diseases.

Splicing and Chromatin Factors Jointly Regulate Epidermal Differentiation

Epidermal homeostasis requires balanced progenitor cell proliferation and loss of differentiated cells from the epidermal surface. During this process, cells undergo major changes in their transcriptional programs to accommodate new cellular functions. We found that transcriptional and post-transcriptional mechanisms underlying these changes jointly control genes involved in cell adhesion, a key process in epidermal maintenance. Using siRNA-based perturbation screens, we identified DNA and/or RNA binding regulators of epidermal differentiation. Computational modeling and experimental validation identified functional interactions between the matrin-type 2 zinc-finger protein ZMAT2 and the epigenetic modifiers ING5, SMARCA5, BRD1, UHRF1, BPTF, and SMARCC2. ZMAT2 is an interactor of the pre-spliceosome that is required to keep cells in an undifferentiated, proliferative state. RNA immunoprecipitation and transcriptome-wide RNA splicing analysis showed that ZMAT2 associates with and regulates transcripts involved in cell adhesion in conjunction with ING5. Thus, joint control by splicing regulation, histone, and DNA modification is important to maintain epidermal cells in an undifferentiated state.

Tetraspanin CD151 and integrin α3β1 contribute to the stabilization of integrin α6β4-containing cell-matrix adhesions

Tetraspanin CD151 has been suggested to regulate cell adhesion through its association with laminin-binding integrins α3β1 and α6β4; however, its precise function in keratinocyte adhesion remains elusive. In this study, we investigated the role of CD151 in the formation and maintenance of laminin-associated adhesions. We show that CD151, through binding to integrin α3β1, plays a critical role in the stabilization of an adhesion structure with a distinct molecular composition of hemidesmosomes with tetraspanin features. These hybrid cell-matrix adhesions, which are formed early during cell adhesion and spreading and at later stages of cell spreading, are present in the central region of the cells. They contain the CD151-α3β1/α6β4 integrin complexes and the cytoskeletal linker protein plectin, but are not anchored to the keratin filaments. In contrast, hemidesmosomes, keratin filament-associated adhesions that contain integrin α6β4, plectin, BP180 (encoded by COL17A1) and BP230 (encoded by DST), do not require CD151 for their formation or maintenance. These findings provide new insights into the dynamic and complex regulation of adhesion structures in keratinocytes and the pathogenic mechanisms underlying skin blistering diseases caused by mutations in the gene for CD151.

The Tissue-Engineered Human Psoriatic Skin Substitute: A Valuable In Vitro Model to Identify Genes with Altered Expression in Lesional Psoriasis

Psoriasis is a chronic inflammatory skin disease for which no cure has emerged. Its complex etiology requires the development of an in vitro model representative of the pathology. In this study, we exploited gene profiling analyses on microarray in order to characterize and further optimize the production of a human psoriatic skin model representative of this in vivo skin disease. Various skin substitutes were produced by tissue-engineering using biopsies from normal, healthy donors, or from lesional or non-lesional skin samples from patients with psoriasis, and their gene expression profiles were examined by DNA microarray. We demonstrated that more than 3540 and 1088 genes (two-fold change) were deregulated between healthy/lesional and lesional/non-lesional psoriatic substitutes, respectively. Moreover, several genes related to lipid metabolism, such as PLA2G4E and PLA2G4C, were identified as repressed in the lesional substitutes. In conclusion, gene profiling analyses identified a list of deregulated candidate genes associated with various metabolic pathways that may contribute to the progression of psoriasis.

New susceptibility loci for cutaneous melanoma risk and progression revealed using a porcine model

Despite major advances, it is estimated that a large part of melanoma predisposing genes remains to be discovered. Animal models of spontaneous diseases are valuable tools and experimental crosses can be used to identify and fine-map new susceptibility loci associated with melanoma. We performed a Genome-Wide Association Study (GWAS) of melanoma occurrence and progression (clinical ulceration and presence of metastasis) in a porcine model of spontaneous melanoma, the MeLiM pig. Five loci on chromosomes 2, 5, 7, 8 and 16 showed genome-wide significant associations (p < 5 × 10^–6) with either one of these phenotypes. Suggestive associations (p < 5 × 10^–5) were also found at 16 additional loci. Moreover, comparison of the porcine results to those reported by human melanoma GWAS indicated shared association signals notably at CDKAL1 and TERT loci but also nearby CCND1, FTO, PLA2G6 and TMEM38B-RAD23B loci. Extensive search of the literature revealed a potential key role of genes at the identified porcine loci in tumor invasion (DST, PLEKHA5, CBY1, LIMK2 and ETV5) and immune response modulation (ETV5, HERC3 and DICER1) of the progression phenotypes. These biological processes are consistent with the clinico-pathological features of MeLiM tumors and can open new routes for future melanoma research in humans.

Profiling plasma extracellular vesicle by pluronic block-copolymer based enrichment method unveils features associated with breast cancer aggression, metastasis and invasion

Extracellular vesicle (EV)-based liquid biopsies have been proposed to be a readily obtainable biological substrate recently for both profiling and diagnostics purposes. Development of a fast and reliable preparation protocol to enrich such small particles could accelerate the discovery of informative, disease-related biomarkers. Though multiple EV enrichment protocols are available, in terms of efficiency, reproducibility and simplicity, precipitation-based methods are most amenable to studies with large numbers of subjects. However, the selectivity of the precipitation becomes critical. Here, we present a simple plasma EV enrichment protocol based on pluronic block copolymer. The enriched plasma EV was able to be verified by multiple platforms. Our results showed that the particles enriched from plasma by the copolymer were EV size vesicles with membrane structure; proteomic profiling showed that EV-related proteins were significantly enriched, while high-abundant plasma proteins were significantly reduced in comparison to other precipitation-based enrichment methods. Next-generation sequencing confirmed the existence of various RNA species that have been observed in EVs from previous studies. Small RNA sequencing showed enriched species compared to the corresponding plasma. Moreover, plasma EVs enriched from 20 advanced breast cancer patients and 20 age-matched non-cancer controls were profiled by semi-quantitative mass spectrometry. Protein features were further screened by EV proteomic profiles generated from four breast cancer cell lines, and then selected in cross-validation models. A total of 60 protein features that highly contributed in model prediction were identified. Interestingly, a large portion of these features were associated with breast cancer aggression, metastasis as well as invasion, consistent with the advanced clinical stage of the patients. In summary, we have developed a plasma EV enrichment method with improved precipitation selectivity and it might be suitable for larger-scale discovery studies.

Mammalian Plakins, Giant Cytolinkers: Versatile Biological Functions and Roles in Cancer

Cancer is a highly lethal disease that is characterized by aberrant cell proliferation, migration, and adhesion, which are closely related to the dynamic changes of cytoskeletons and cytoskeletal-adhesion. These will further result in cell invasion and metastasis. Plakins are a family of giant cytolinkers that connect cytoskeletal elements with each other and to junctional complexes. With various isoforms composed of different domain structures, mammalian plakins are broadly expressed in numerous tissues. They play critical roles in many cellular processes, including cell proliferation, migration, adhesion, and signaling transduction. As these cellular processes are key steps in cancer development, mammalian plakins have in recent years attracted more and more attention for their potential roles in cancer. Current evidence shows the importance of mammalian plakins in various human cancers and demonstrates mammalian plakins as potential biomarkers for cancer. Here, we introduce the basic characteristics of mammalian plakins, review the recent advances in understanding their biological functions, and highlight their roles in human cancers, based on studies performed by us and others. This will provide researchers with a comprehensive understanding of mammalian plakins, new insights into the development of cancer, and novel targets for cancer diagnosis and therapy.

Hemidesmosomal linker proteins regulate cell motility, invasion and tumorigenicity in oral squamous cell carcinoma derived cells

BPAG1e and Plectin are hemidesmosomal linker proteins which anchor intermediate filament proteins to the cell surface through β4 integrin. Recent reports indicate that these proteins play a role in various cellular processes apart from their known anchoring function. However, the available literature is inconsistent. Further, the previous study from our laboratory suggested that Keratin8/18 pair promotes cell motility and tumor progression by deregulating β4 integrin signaling in oral squamous cell carcinoma (OSCC) derived cells. Based on these findings, we hypothesized that linker proteins may have a role in neoplastic progression of OSCC. Downregulation of hemidesmosomal linker proteins in OSCC derived cells resulted in reduced cell migration accompanied by alterations in actin organization. Further, decreased MMP9 activity led to reduced cell invasion in linker proteins knockdown cells. Moreover, loss of these proteins resulted in reduced tumorigenic potential. SWATH analysis demonstrated upregulation of N-Myc downstream regulated gene 1 (NDRG1) in linker proteins downregulated cells as compared to vector control cells. Further, the defects in phenotype upon linker proteins ablation were rescued upon loss of NDRG1 in linker proteins knockdown background. These data together indicate that hemidesmosomal linker proteins regulate cell motility, invasion and tumorigenicity possibly through NDRG1 in OSCC derived cells.

Spectraplakin family proteins - cytoskeletal crosslinkers with versatile roles

The different cytoskeletal networks in a cell are responsible for many fundamental cellular processes. Current studies have shown that spectraplakins, cytoskeletal crosslinkers that combine features of both the spectrin and plakin families of crosslinkers, have a critical role in integrating these different cytoskeletal networks. Spectraplakin genes give rise to a variety of isoforms that have distinct functions. Importantly, all spectraplakin isoforms are uniquely able to associate with all three elements of the cytoskeleton, namely, F-actin, microtubules and intermediate filaments. In this Review, we will highlight recent studies that have unraveled their function in a wide range of different processes, from regulating cell adhesion in skin keratinocytes to neuronal cell migration. Taken together, this work has revealed a diverse and indispensable role for orchestrating the function of different cytoskeletal elements in vivo.

Molecular and cytoskeletal regulations in epidermal development

At the surface of the body, the epidermis covers great depth in its developmental regulation. While many genes have been shown to be important for skin development through their associations with disease phenotypes in mice and human, it is in the past decade that the intricate interplay between various molecules become gradually revealed through sophisticated genetic models and imaging analyses. In particular, there is increasing evidence suggesting that cytoskeleton-associated proteins, including adhesion proteins and the crosslinker proteins may play critical roles in regulating epidermis development. We here provide a broad overview of the various molecules involved in epidermal development with special emphasis on the cytoskeletal components.

Recently Identified Forms of Epidermolysis Bullosa

Epidermolysis bullosa (EB) comprises a collection of clinically diverse inherited blistering diseases that affect the skin and, in some subtypes, mucous membranes and other organs. Currently classified into four main subtypes (EB simplex, junctional EB, dystrophic EB, and Kindler syndrome, mainly based on the level of skin cleavage), the spectrum of EB extends to more than 30 clinical subtypes with pathogenic mutations in at least 18 distinct genes. This review focuses on three recent additions to variants of EB: all are autosomal recessive, and result from mutations in either DST-e (coding for epidermal dystonin, also known as the 230 kDa bullous pemphigoid antigen, BP230), EXPH5 (coding for exophilin-5, also known as Slac2-b), or ITGA3 (coding for the integrin alpha-3 subunit). Each of these new forms of EB is reviewed with respect to the initial gene discovery, clinical features, the current mutation database, and skin pathology. Awareness of these recently described forms of EB is helpful in the clinical evaluation of patients with EB and in defining genotype-phenotype correlation for inherited blistering skin diseases.

An epigenetic memory of pregnancy in the mouse mammary gland

Pregnancy is the major modulator of mammary gland activity. It induces a tremendous expansion of the mammary epithelium and the generation of alveolar structures for milk production. Anecdotal evidence from multiparous humans indicates that the mammary gland may react less strongly to the first pregnancy than it does to subsequent pregnancies. Here, we verify that the mouse mammary gland responds more robustly to a second pregnancy, indicating that the gland retains a long-term memory of pregnancy. A comparison of genome-wide profiles of DNA methylation in isolated mammary cell types reveals substantial and long-lasting alterations. Since these alterations are maintained in the absence of the signal that induced them, we term them epigenetic. The majority of alterations in DNA methylation affect sites occupied by the Stat5a transcription factor and mark specific genes that are upregulated during pregnancy. We postulate that the epigenetic memory of a first pregnancy primes the activation of gene expression networks that promote mammary gland function in subsequent reproductive cycles. More broadly, our data indicate that physiological experience can broadly alter epigenetic states, functionally modifying the capacity of the affected cells to respond to later stimulatory events.

Regulation of keratin network organization

Keratins form the major intermediate filament cytoskeleton of epithelia and are assembled from heterodimers of 28 type I and 26 type II keratins in cell- and differentiation-dependent patterns. By virtue of their primary sequence composition, interactions with cell adhesion complexes and components of major signaling cascades, keratins act as targets and effectors of mechanical force and chemical signals to determine cell mechanics, epithelial cohesion and modulate signaling in keratin isotype-specific manners. Therefore, cell-specific keratin expression and organization impact on cell growth, migration and invasion. Here, we review the recent literature, focusing on the question how keratin networks are regulated and how the interplay of keratins with adhesion complexes affects these processes and provides a framework to understand keratins contribution to blistering and inflammatory disorders and to tumor metastasis.

Founder mutation in dystonin-e underlying autosomal recessive epidermolysis bullosa simplex in Kuwait

Only two homozygous nonsense mutations in the epidermal isoform of the dystonin gene, DST-e, have been reported previously in autosomal recessive epidermolysis bullosa simplex (EBS); the affected pedigrees were Kuwaiti and Iranian. This subtype of EBS is therefore considered to be a rare clinicopathological entity. In this study, we identified four seemingly unrelated Kuwaiti families in which a total of seven individuals had predominantly acral trauma-induced blistering since infancy. All affected individuals were homozygous for the mutation p.Gln1124* in DST-e, the same mutation that was identified in the originally reported family from Kuwait. Haplotype analysis in the five pedigrees (including the previous case) revealed a shared block of ~60 kb of genomic DNA across the site of the mutation, consistent with a founder effect. Most heterozygotes had no clinical abnormalities although one subject had mild transient skin fragility during childhood, an observation noted in the previously reported Iranian pedigree, suggesting that the condition may also be semidominant in some pedigrees rather than purely autosomal recessive. Our study reveals propagation of a mutant ancestral allele in DST-e throughout Kuwait, indicating that this subtype of EBS may be more common in Kuwait, and perhaps other Middle Eastern countries, than is currently appreciated.

Remodeling of keratin-coupled cell adhesion complexes

Epithelial cells constitute the main barrier between the inside and outside of organs, acting as gatekeepers of their structure and integrity. Hemidesmosomes and desmosomes are respectively cell-matrix and cell-cell adhesions coupled to the intermediate filament cytoskeleton. These adhesions ensure mechanical integrity of the epithelial barrier. Although desmosomes and hemidesmosomes are essential in maintaining strong cell-cell and cell-matrix adhesions, there is an emerging view that they should be remodeled in order to maintain epithelial homeostasis. Here we review the adhesion properties of desmosomes and hemidesmosomes, as well as the mechanisms driving their remodeling. We also discuss recent data suggesting that keratin-coupled adhesion complexes can sense the biomechanical cellular environment and participate in the cellular response to such external cues.

Plakins, a versatile family of cytolinkers: roles in skin integrity and in human diseases

The plakin family consists of giant proteins involved in the cross-linking and organization of the cytoskeleton and adhesion complexes. They further modulate several fundamental biological processes, such as cell adhesion, migration, and polarization or signaling pathways. Inherited and acquired defects of plakins in humans and in animal models potentially lead to dramatic manifestations in the skin, striated muscles, and/or nervous system. These observations unequivocally demonstrate the key role of plakins in the maintenance of tissue integrity. Here we review the characteristics of the mammalian plakin members BPAG1 (bullous pemphigoid antigen 1), desmoplakin, plectin, envoplakin, epiplakin, MACF1 (microtubule-actin cross-linking factor 1), and periplakin, highlighting their role in skin homeostasis and diseases.