Desmosomes in acquired disease

Architecture and dynamics of a desmosome-endoplasmic reticulum complex

The endoplasmic reticulum (ER) forms a dynamic network that contacts other cellular membranes to regulate stress responses, calcium signalling and lipid transfer. Here, using high-resolution volume electron microscopy, we find that the ER forms a previously unknown association with keratin intermediate filaments and desmosomal cell-cell junctions. Peripheral ER assembles into mirror image-like arrangements at desmosomes and exhibits nanometre proximity to keratin filaments and the desmosome cytoplasmic plaque. ER tubules exhibit stable associations with desmosomes, and perturbation of desmosomes or keratin filaments alters ER organization, mobility and expression of ER stress transcripts. These findings indicate that desmosomes and the keratin cytoskeleton regulate the distribution, function and dynamics of the ER network. Overall, this study reveals a previously unknown subcellular architecture defined by the structural integration of ER tubules with an epithelial intercellular junction.

A novel circadian cycle-related gene signature for prognosis prediction of patients with breast cancer

The extensive and intricate relationships between circadian rhythm and cancer have been reported in numerous studies. However, in breast cancer (BC), the potential role of circadian clock-related genes (CCRGs) in prognosis prediction has not been fully clarified. The transcriptome data and clinical information were downloaded from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus databases. A CCRGs-based risk signature was established by differential expression analysis, univariate, Lasso and multivariate Cox regression analyses. we conducted a gene set enrichment analysis (GSEA) between groups. A nomogram integrating independent clinical factors and risk score was generated and evaluated by calibration curves and decision curve analysis (DCA). Differentially expression analysis revealed 80 differentially expressed CCRGs, and 27 of them were significantly associated with the overall survival (OS) of BC. BC can be classified into 4 molecular subtypes with significant differences in prognosis based on the 27 CCRGs. Three prognostic CCRGs, including desmocollin 1 (DSC1), LEF1, and protocadherin 9 (PCDH9), were identified to be independent risk factors of BC prognosis and were used to construct a risk score model. BC patients were divided into high- and low-risk groups, and there were significant differences in prognosis between the 2 groups both in the training and validation cohorts. It was found that patients in different groups of race, status, or T stage had significant levels of risk score. Furthermore, patients of different risk levels exhibit varying degrees of sensitivity to vinorelbine, lapatinib, metformin, and vinblastine. GSEA showed that in the high-risk group, immune response-related activities were dramatically repressed whereas cilium-related processes were significantly stimulated. Cox regression analysis demonstrated that age, N stage, radiotherapy and the risk score were independent prognostic risk factors of BC, and a nomogram was established based on these variables. The nomogram exerted a favorable concordance index (0.798) as well as calibration performance, which strongly supports the clinical application of the nomogram. Our study indicated the disruption of the expression of CCRGs in BC and built a favorable prognostic risk model based on 3 independent prognostic CCRGs. These genes may be applied as candidate molecular targets for the diagnosis and therapy of BC.

Mechanisms Causing Acantholysis in Pemphigus-Lessons from Human Skin

Pemphigus vulgaris (PV) is an autoimmune bullous skin disease caused primarily by autoantibodies (PV-IgG) against the desmosomal adhesion proteins desmoglein (Dsg)1 and Dsg3. PV patient lesions are characterized by flaccid blisters and ultrastructurally by defined hallmarks including a reduction in desmosome number and size, formation of split desmosomes, as well as uncoupling of keratin filaments from desmosomes. The pathophysiology underlying the disease is known to involve several intracellular signaling pathways downstream of PV-IgG binding. Here, we summarize our studies in which we used transmission electron microscopy to characterize the roles of signaling pathways in the pathogenic effects of PV-IgG on desmosome ultrastructure in a human ex vivo skin model. Blister scores revealed inhibition of p38MAPK, ERK and PLC/Ca2+ to be protective in human epidermis. In contrast, inhibition of Src and PKC, which were shown to be protective in cell cultures and murine models, was not effective for human skin explants. The ultrastructural analysis revealed that for preventing skin blistering at least desmosome number (as modulated by ERK) or keratin filament insertion (as modulated by PLC/Ca2+) need to be ameliorated. Other pathways such as p38MAPK regulate desmosome number, size, and keratin insertion indicating that they control desmosome assembly and disassembly on different levels. Taken together, studies in human skin delineate target mechanisms for the treatment of pemphigus patients. In addition, ultrastructural analysis supports defining the specific role of a given signaling molecule in desmosome turnover at ultrastructural level.

Collective mechanical responses of cadherin-based adhesive junctions as predicted by simulations

Cadherin-based adherens junctions and desmosomes help stabilize cell-cell contacts with additional function in mechano-signaling, while clustered protocadherin junctions are responsible for directing neuronal circuits assembly. Structural models for adherens junctions formed by epithelial cadherin (CDH1) proteins indicate that their long, curved ectodomains arrange to form a periodic, two-dimensional lattice stabilized by tip-to-tip trans interactions (across junction) and lateral cis contacts. Less is known about the exact architecture of desmosomes, but desmoglein (DSG) and desmocollin (DSC) cadherin proteins are also thought to form ordered junctions. In contrast, clustered protocadherin (PCDH)-based cell-cell contacts in neuronal tissues are thought to be responsible for self-recognition and avoidance, and structural models for clustered PCDH junctions show a linear arrangement in which their long and straight ectodomains form antiparallel overlapped trans complexes. Here, we report all-atom molecular dynamics simulations testing the mechanics of minimalistic adhesive junctions formed by CDH1, DSG2 coupled to DSC1, and PCDHγB4, with systems encompassing up to 3.7 million atoms. Simulations generally predict a favored shearing pathway for the adherens junction model and a two-phased elastic response to tensile forces for the adhesive adherens junction and the desmosome models. Complexes within these junctions first unbend at low tensile force and then become stiff to unbind without unfolding. However, cis interactions in both the CDH1 and DSG2-DSC1 systems dictate varied mechanical responses of individual dimers within the junctions. Conversely, the clustered protocadherin PCDHγB4 junction lacks a distinct two-phased elastic response. Instead, applied tensile force strains trans interactions directly, as there is little unbending of monomers within the junction. Transient intermediates, influenced by new cis interactions, are observed after the main rupture event. We suggest that these collective, complex mechanical responses mediated by cis contacts facilitate distinct functions in robust cell-cell adhesion for classical cadherins and in self-avoidance signaling for clustered PCDHs.

Differential Pathomechanisms of Desmoglein 1 Transmembrane Domain Mutations in Skin Disease

Dominant and recessive mutations in the desmosomal cadherin, desmoglein (DSG) 1, cause the skin diseases palmoplantar keratoderma (PPK) and severe dermatitis, multiple allergies, and metabolic wasting (SAM) syndrome, respectively. In this study, we compare two dominant missense mutations in the DSG1 transmembrane domain (TMD), G557R and G562R, causing PPK (DSG1_PPK-TMD) and SAM syndrome (DSG1_SAM-TMD), respectively, to determine the differing pathomechanisms of these mutants. Expressing the DSG1_TMD mutants in a DSG-null background, we use cellular and biochemical assays to reveal the differences in the mechanistic behavior of each mutant. Super-resolution microscopy and functional assays showed a failure by both mutants to assemble desmosomes due to reduced membrane trafficking and lipid raft targeting. DSG1_SAM-TMD maintained normal expression levels and turnover relative to wildtype DSG1, but DSG1_PPK-TMD lacked stability, leading to increased turnover through lysosomal and proteasomal pathways and reduced expression levels. These results differentiate the underlying pathomechanisms of these disorders, suggesting that DSG1_SAM-TMD acts dominant negatively, whereas DSG1_PPK-TMD is a loss-of-function mutation causing the milder PPK disease phenotype. These mutants portray the importance of the DSG TMD in desmosome function and suggest that a greater understanding of the desmosomal cadherin TMDs will further our understanding of the role that desmosomes play in epidermal pathophysiology.

Desmosomal Cadherins in Health and Disease

Desmosomal cadherins are a recent evolutionary innovation that make up the adhesive core of highly specialized intercellular junctions called desmosomes. Desmosomal cadherins, which are grouped into desmogleins and desmocollins, are related to the classical cadherins, but their cytoplasmic domains are tailored for anchoring intermediate filaments instead of actin to sites of cell-cell adhesion. The resulting junctions are critical for resisting mechanical stress in tissues such as the skin and heart. Desmosomal cadherins also act as signaling hubs that promote differentiation and facilitate morphogenesis, creating more complex and effective tissue barriers in vertebrate tissues. Interference with desmosomal cadherin adhesive and supra-adhesive functions leads to a variety of autoimmune, hereditary, toxin-mediated, and malignant diseases. We review our current understanding of how desmosomal cadherins contribute to human health and disease, highlight gaps in our knowledge about their regulation and function, and introduce promising new directions toward combatting desmosome-related diseases.

Desmosomes undergo dynamic architectural changes during assembly and maturation

Desmosomes are macromolecular cell-cell junctions critical for maintaining adhesion and resisting mechanical stress in epithelial tissue. Desmosome assembly and the relationship between maturity and molecular architecture are not well understood. To address this, we employed a calcium switch assay to synchronize assembly followed by quantification of desmosome nanoscale organization using direct Stochastic Optical Reconstruction Microscopy (dSTORM). We found that the organization of the desmoplakin rod/C-terminal junction changed over the course of maturation, as indicated by a decrease in the plaque-to-plaque distance, while the plaque length increased. In contrast, the desmoplakin N-terminal domain and plakoglobin organization (plaque-to-plaque distance) were constant throughout maturation. This structural rearrangement of desmoplakin was concurrent with desmosome maturation measured by E-cadherin exclusion and increased adhesive strength. Using two-color dSTORM, we showed that while the number of individual E-cadherin containing junctions went down with the increasing time in high Ca²⁺, they maintained a wider desmoplakin rod/C-terminal plaque-to-plaque distance. This indicates that the maturation state of individual desmosomes can be identified by their architectural organization. We confirmed these architectural changes in another model of desmosome assembly, cell migration. Desmosomes in migrating cells, closest to the scratch where they are assembling, were shorter, E-cadherin enriched, and had wider desmoplakin rod/C-terminal plaque-to-plaque distances compared to desmosomes away from the wound edge. Key results were demonstrated in three cell lines representing simple, transitional, and stratified epithelia. Together, these data suggest that there is a set of architectural programs for desmosome maturation, and we hypothesize that desmoplakin architecture may be a contributing mechanism to regulating adhesive strength.

The desmosome as a model for lipid raft driven membrane domain organization

Desmosomes are cadherin-based adhesion structures that mechanically couple the intermediate filament cytoskeleton of adjacent cells to confer mechanical stress resistance to tissues. We have recently described desmosomes as mesoscale lipid raft membrane domains that depend on raft dynamics for assembly, function, and disassembly. Lipid raft microdomains are regions of the plasma membrane enriched in sphingolipids and cholesterol. These domains participate in membrane domain heterogeneity, signaling and membrane trafficking. Cellular structures known to be dependent on raft dynamics include the post-synaptic density in neurons, the immunological synapse, and intercellular junctions, including desmosomes. In this review, we discuss the current state of the desmosome field and put forward new hypotheses for the role of lipid rafts in desmosome adhesion, signaling and epidermal homeostasis. Furthermore, we propose that differential lipid raft affinity of intercellular junction proteins is a central driving force in the organization of the epithelial apical junctional complex.

Scaling up single-cell mechanics to multicellular tissues - the role of the intermediate filament-desmosome network

Cells and tissues sense, respond to and translate mechanical forces into biochemical signals through mechanotransduction, which governs individual cell responses that drive gene expression, metabolic pathways and cell motility, and determines how cells work together in tissues. Mechanotransduction often depends on cytoskeletal networks and their attachment sites that physically couple cells to each other and to the extracellular matrix. One way that cells associate with each other is through Ca2+-dependent adhesion molecules called cadherins, which mediate cell-cell interactions through adherens junctions, thereby anchoring and organizing the cortical actin cytoskeleton. This actin-based network confers dynamic properties to cell sheets and developing organisms. However, these contractile networks do not work alone but in concert with other cytoarchitectural elements, including a diverse network of intermediate filaments. This Review takes a close look at the intermediate filament network and its associated intercellular junctions, desmosomes. We provide evidence that this system not only ensures tissue integrity, but also cooperates with other networks to create more complex tissues with emerging properties in sensing and responding to increasingly stressful environments. We will also draw attention to how defects in intermediate filament and desmosome networks result in both chronic and acquired diseases.

Role of PKC and ERK Signaling in Epidermal Blistering and Desmosome Regulation in Pemphigus

Desmosomes reinforce cohesion of epithelial cells at the interface between adjacent cells. They include the cadherin-type adhesion molecules desmoglein 1 (Dsg1) and Dsg3. Pemphigus vulgaris (PV) is an autoimmune disease in which circulating autoantibodies (PV-IgG) targeting Dsg1 and 3 cause characteristic epidermal blister formation. It has been shown that PV-IgG binding induced activation of kinases such as ERK and PKC, and inhibition of these signaling pathways prevented loss of cell cohesion in cell cultures. However, the role of Erk and PKC in blister formation and regulation of desmosome ultrastructure in human skin are unknown. Accordingly, we assessed the role of PKC and ERK signaling pathways in blister formation and regulation of desmosome ultrastructure in human epidermis. Here we performed electron microscopy analyses using human skin explants injected with PV-IgG together with inhibitors for PKC or ERK signaling. Inhibition of PKC was not effective to prevent suprabasal blister formation or ultrastructural alterations of desmosomes. In contrast, inhibition of ERK signaling significantly ameliorated blister formation and decrease in the number of desmosomes whereas shortening and splitting of desmosomes and keratin filament insertion were not different from samples treated with PV-IgG alone. However, apical desmosomes between basal and suprabasal cells remained unaltered when ERK signaling was inhibited. Therefore, our results show that inhibition of ERK but not PKC signaling appears to be effective to ameliorate blistering and alterations of desmosome ultrastructure triggered by PV-IgG in human skin.

Role of Dsg1- and Dsg3-Mediated Signaling in Pemphigus Autoantibody-Induced Loss of Keratinocyte Cohesion

Pemphigus is an autoimmune dermatosis in which mucocutaneous blisters are induced primarily by autoantibodies against Desmoglein (Dsg) 1 and 3. Pemphigus vulgaris (PV) usually is associated with autoantibodies against Dsg3 whereas pemphigus foliaceus (PF) patients present autoantibodies against Dsg1. Several signaling pathways were proposed to cause loss of keratinocyte adhesion. However, relevance of different signaling pathways and role of Dsg1 and 3 to trigger signaling are not fully understood. Here, we show that Ca²⁺ chelation reduced PV-IgG- and PF-IgG-mediated loss of HaCaT keratinocyte cohesion whereas EGFR inhibition did not inhibit effects of PF-IgG. PV-IgG activated EGFR in a Src-dependent manner whereas both PV-IgG and PF-IgG caused Ca²⁺ influx independent of EGFR. ERK activation was Src-dependent in response to PV-IgG but not PF-IgG. To delineate the roles of Dsg isoforms to trigger signaling pathways, Dsg3- and Dsg2-deficient HaCaT keratinocyte cell lines were generated using CRISPR/Cas9. Dsg3- but not Dsg2-deficient cells were protected against PV-IgG-induced loss of cell adhesion. Ca²⁺ influx and ERK activation in response to PF-IgG were preserved in both cell lines.

Plakophilin-2 accelerates cell proliferation and migration through activating EGFR signaling in lung adenocarcinoma

BACKGROUND

Plakophilin 2 (PKP2), encodes a plakophilin protein that belongs to the member of desmosomal proteins. It has been reported that high expression of PKP2 is associated with several types of cancer in humans. However, the role of PKP2 in lung cancer remains obscure.

METHODS

PKP2 expression was investigated in non-small cell lung cancer (NSCLC) tissues and non-tumor tissues by performing immunohistochemistry on a tissue microarray and using The Cancer Genome Atlas (TCGA) database. Kaplan-Meier survival analysis and multivariate Cox-regression analysis were performed to identify the clinical significance of PKP2. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), colony formation, Transwell and xenograft tumor growth/ metastasis assays were conducted to evaluate the biological function of PKP2 in vitro and in vivo. Gene set enrichment analysis (GSEA), WB and immunoprecipitation (IP) assay were utilized to explore the potential downstream signaling pathway and molecule mechanism of PKP2 in lung adenocarcinoma (LUAD).

RESULTS

Analysis of PKP2 expression and clinicopathological parameters reveals a significant correlation of PKP2 expression with gender (n = 1020, P < 0.001) and histological type (n = 1020, P < 0.001). Subsequently, our results demonstrated that high PKP2 expression is not associated with poor survival in different gender of lung cancer patients, and is an unfavorable and independent prognostic biomarker for LUAD patients, but not for LUSC patients. Gene set enrichment analysis (GSEA) revealed that PKP2 expression is positively associated with EGFR signaling in LUAD. Further, in vitro and in vivo assays revealed that PKP2 promotes cell proliferation, migration and invasion through activating EGFR signaling pathway in LUAD cells.

CONCLUSION

Our study provides the basis for further investigation of the function and molecular mechanism by which upregulation of PKP2 promotes the development and progression of LUAD. PKP2 may serve as a potential target for anticancer therapies.

The desmosome is a mesoscale lipid raft-like membrane domain

Desmogleins (Dsgs) are cadherin family adhesion molecules essential for epidermal integrity. Previous studies have shown that desmogleins associate with lipid rafts, but the significance of this association was not clear. Here, we report that the desmoglein transmembrane domain (TMD) is the primary determinant of raft association. Further, we identify a novel mutation in the DSG1 TMD (G562R) that causes severe dermatitis, multiple allergies, and metabolic wasting syndrome. Molecular modeling predicts that this G-to-R mutation shortens the DSG1 TMD, and experiments directly demonstrate that this mutation compromises both lipid raft association and desmosome incorporation. Finally, cryo-electron tomography indicates that the lipid bilayer within the desmosome is ∼10% thicker than adjacent regions of the plasma membrane. These findings suggest that differences in bilayer thickness influence the organization of adhesion molecules within the epithelial plasma membrane, with cadherin TMDs recruited to the desmosome via the establishment of a specialized mesoscale lipid raft-like membrane domain.

RPGRIP1L is required for stabilizing epidermal keratinocyte adhesion through regulating desmoglein endocytosis

Cilia-related proteins are believed to be involved in a broad range of cellular processes. Retinitis pigmentosa GTPase regulator interacting protein 1-like (RPGRIP1L) is a ciliary protein required for ciliogenesis in many cell types, including epidermal keratinocytes. Here we report that RPGRIP1L is also involved in the maintenance of desmosomal junctions between keratinocytes. Genetically disrupting the Rpgrip1l gene in mice caused intraepidermal blistering, primarily between basal and suprabasal keratinocytes. This blistering phenotype was associated with aberrant expression patterns of desmosomal proteins, impaired desmosome ultrastructure, and compromised cell-cell adhesion in vivo and in vitro. We found that disrupting the RPGRIP1L gene in HaCaT cells, which do not form primary cilia, resulted in mislocalization of desmosomal proteins to the cytoplasm, suggesting a cilia-independent function of RPGRIP1L. Mechanistically, we found that RPGRIP1L regulates the endocytosis of desmogleins such that RPGRIP1L-knockdown not only induced spontaneous desmoglein endocytosis, as determined by AK23 labeling and biotinylation assays, but also exacerbated EGTA- or pemphigus vulgaris IgG-induced desmoglein endocytosis. Accordingly, inhibiting endocytosis with dynasore or sucrose rescued these desmosomal phenotypes. Biotinylation assays on cell surface proteins not only reinforced the role of RPGRIP1L in desmoglein endocytosis, but also suggested that RPGRIP1L may be more broadly involved in endocytosis. Thus, data obtained from this study advanced our understanding of the biological functions of RPGRIP1L by identifying its role in the cellular endocytic pathway.

Disassembling a cancer puzzle: Cell junctions and plasma membrane as targets for anticancer therapy

Despite an enhanced permeability and retention effect typical of many solid tumors, drug penetration is not always sufficient. Possible strategies for the drug delivery improvement are a modification of the tumor cell-to-cell junctions and usage of cell membrane permeabilization proteins. In this review we discuss epithelial cell junctions as targets for a combined anticancer therapy and propose new possible sources of such agents. We suggest considering viral and bacterial pathogens disrupting epithelial layers as plentiful sources of new therapeutic agents for increasing tumor permeability for other effector agents. We also observe the application of pore forming proteins and peptides of different origin for cytoplasmic delivery of anti-cancer agents and consider the main obstacles of their use in vivo.

The Desmosomal Cadherin Desmoglein-2 Experiences Mechanical Tension as Demonstrated by a FRET-Based Tension Biosensor Expressed in Living Cells

Cell-cell junctions are critical structures in a number of tissues for mechanically coupling cells together, cell-to-cell signaling, and establishing a barrier. In many tissues, desmosomes are an important component of cell-cell junctions. Loss or impairment of desmosomes presents with clinical phenotypes in the heart and skin as cardiac arrhythmias and skin blistering, respectively. Because heart and skin are tissues that are subject to large mechanical stresses, we hypothesized that desmosomes, similar to adherens junctions, would also experience significant tensile loading. To directly measure mechanical forces across desmosomes, we developed and validated a desmoglein-2 (DSG-2) force sensor, using the existing TSmod F&ouml;rster resonance energy transfer (FRET) force biosensor. When expressed in human cardiomyocytes, the force sensor reported high tensile loading of DSG-2 during contraction. Additionally, when expressed in Madin-Darby canine kidney (MDCK) epithelial or epidermal (A431) monolayers, the sensor also reported tensile loading. Finally, we observed higher DSG-2 forces in 3D MDCK acini when compared to 2D monolayers. Taken together, our results show that desmosomes experience low levels of mechanical tension in resting cells, with significantly higher forces during active loading.

Keratin Retraction and Desmoglein3 Internalization Independently Contribute to Autoantibody-Induced Cell Dissociation in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a potentially lethal autoimmune disease characterized by blister formation of the skin and mucous membranes and is caused by autoantibodies against desmoglein (Dsg) 1 and Dsg3. Dsg1 and Dsg3 are linked to keratin filaments in desmosomes, adhering junctions abundant in tissues exposed to high levels of mechanical stress. The binding of the autoantibodies leads to internalization of Dsg3 and a collapse of the keratin cytoskeleton-yet, the relevance and interdependence of these changes for loss of cell-cell adhesion and blistering is poorly understood. In live-cell imaging studies, loss of the keratin network at the cell periphery was detectable starting after 60 min of incubation with immunoglobulin G fractions of PV patients (PV-IgG). These rapid changes correlated with loss of cell-cell adhesion detected by dispase-based dissociation assays and were followed by a condensation of keratin filaments into thick bundles after several hours. Dsg3 internalization started at 90 min of PV-IgG treatment, thus following the early keratin changes. By inhibiting casein kinase 1 (CK-1), we provoked keratin alterations resembling the effects of PV-IgG. Although CK-1-induced loss of peripheral keratin network correlated with loss of cell cohesion and Dsg3 clustering in the membrane, it was not sufficient to trigger the internalization of Dsg3. However, additional incubation with PV-IgG was effective to promote Dsg3 loss at the membrane, indicating that Dsg3 internalization is independent from keratin alterations. Vice versa, inhibiting Dsg3 internalization did not prevent PV-IgG-induced keratin retraction and only partially rescued cell cohesion. Together, keratin changes appear very early after autoantibody binding and temporally overlap with loss of cell cohesion. These early alterations appear to be distinct from Dsg3 internalization, suggesting a crucial role for initial loss of cell cohesion in PV.

Mechanisms Causing Loss of Keratinocyte Cohesion in Pemphigus

The autoimmune blistering skin disease pemphigus is caused by IgG autoantibodies against desmosomal cadherins, but the precise mechanisms are in part a matter of controversial discussions. This review focuses on the currently existing models of the disease and highlights the relevance of desmoglein-specific versus nondesmoglein autoantibodies, the contribution of nonautoantibody factors, and the mechanisms leading to cell dissociation and blister formation in response to autoantibody binding. As the review brings together the majority of laboratories currently working on pemphigus pathogenesis, it aims to serve as a solid basis for further investigations for the entire field.

Different signaling patterns contribute to loss of keratinocyte cohesion dependent on autoantibody profile in pemphigus

Pemphigus is an autoimmune blistering skin disease caused primarily by autoantibodies against desmoglein (Dsg)1 and 3. Here, we characterized the mechanisms engaged by pemphigus IgG from patients with different clinical phenotypes and autoantibody profiles. All pemphigus vulgaris (PV) and pemphigus foliaceus (PF) IgG and AK23, a monoclonal mouse antibody against Dsg3, caused loss of cell cohesion, cytokeratin retraction and p38MAPK activation. Strong alterations in Dsg3 distribution were caused by mucosal (aDsg3 antibodies), mucocutaneous (aDsg1 + aDsg3) as well as atypical (aDsg3) PV-IgG. All PV-IgG fractions and AK23 compromised Dsg3 but not Dsg1 binding and enhanced Src activity. In contrast, rapid Ca²⁺ influx and Erk activation were induced by mucocutaneous PV-IgG and pemphigus foliaceus (PF) IgG (aDsg1) whereas cAMP was increased by mucosal and mucocutaneous PV-IgG only. Selective inhibition of p38MAPK, Src or PKC blocked loss of keratinocyte cohesion in response to all autoantibody fractions whereas Erk inhibition was protective against mucocutaneous PV-IgG and PF-IgG only. These results demonstrate that signaling patterns parallel the clinical phenotype as some mechanisms involved in loss of cell cohesion are caused by antibodies targeting Dsg3 whereas others correlate with autoantibodies against Dsg1. The concept of key desmosome regulators may explain observations from several experimental models of pemphigus.

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

Adherens junctions (AJs) and desmosomes connect the actin and keratin filament networks of adjacent cells into a mechanical unit. Whereas AJs function in mechanosensing and in transducing mechanical forces between the plasma membrane and the actomyosin cytoskeleton, desmosomes and intermediate filaments (IFs) provide mechanical stability required to maintain tissue architecture and integrity when the tissues are exposed to mechanical stress. Desmosomes are essential for stable intercellular cohesion, whereas keratins determine cell mechanics but are not involved in generating tension. Here, we summarize the current knowledge of the role of IFs and desmosomes in tissue mechanics and discuss whether the desmosome-keratin scaffold might be actively involved in mechanosensing and in the conversion of chemical signals into mechanical strength.

[Effects of embryonic lead exposure on food intake and bowel movement in offspring rats and possible mechanisms]

OBJECTIVE

To study the effects of embryonic lead exposure on food intake and bowel movement in offspring rats and possible mechanisms.

METHODS

Sprague-Dawley rats were given 0.1% (low-dose lead exposure group) or 0.2% (high-dose lead exposure group) lead acetate freely during pregnancy to establish an animal model of embryonic lead exposure. A blank control group was also established. The male offspring rats were enrolled in the study, and 10 male offspring rats from each group were selected to observe the changes in food intake, bowel movement, gastric emptying, intestine propulsion, and pathological inflammatory response in the gastric mucosa. Eight offspring rats were selected from each group, and electron microscopy and immunohistochemistry were used to observe the changes in the ultrastructure of jejunal microvilli and cell junction and the expression of cholecystokinin-8 (CCK-8) and motilin (MTL) in the feeding center, in order to reveal the possible mechanisms for abnormal gastrointestinal motility in offspring rats induced by embryonic lead exposure.

RESULTS

Compared with the control group, the low- and high-dose lead exposure groups had a significant reduction in daily food intake, a significant increase in water content of feces, a significant reduction in fecal pellet weight, and a significant increase in small intestine propulsion (P<0.05). The high-dose lead exposure group had a significant reduction in gastric emptying ability compared with the control group (P<0.05). Compared with the control group, the lead exposure groups had significantly greater pathological inflammatory changes in the gastric mucosa (P<0.05), significant reductions in the number and length of the jejunal microvilli and the number of epithelial desmosome junctions (P<0.05), a significant increase in the macula densa gap (P<0.05), and significant increases in the expression of MTL and CCK-8 in the feeding center (P<0.05), in a dose-dependent manner.

CONCLUSIONS

The degree of gastrointestinal structural injury and expression levels of MTL and CCK-8 in the feeding center are lead dose-dependent, which may be important mechanisms for changes in food intake, bowel movement, and digestive functions in offspring rats induced by embryonic lead exposure.

Adrenergic Signaling Strengthens Cardiac Myocyte Cohesion

RATIONALE

The sympathetic nervous system is a major mediator of heart function. Intercalated discs composed of desmosomes, adherens junctions, and gap junctions provide the structural backbone for coordinated contraction of cardiac myocytes.

OBJECTIVE

Gap junctions dynamically remodel to adapt to sympathetic signaling. However, it is unknown whether such rapid adaption also occurs for the adhesive function provided by desmosomes and adherens junctions.

METHODS AND RESULTS

Atomic force microscopy revealed that β-adrenergic signaling enhances both the number of desmoglein 2-specific interactions along cell junctions and the mean desmoglein 2-mediated binding forces, whereas N-cadherin-mediated interactions were not affected. This was accompanied by increased cell cohesion in cardiac myocyte cultures and murine heart slices. Enhanced desmoglein 2-positive contacts and increased junction length as revealed by immunofluorescence and electron microscopy reflected cAMP-induced reorganization of intercellular contacts. The mechanism underlying cAMP-mediated strengthening of desmoglein 2 binding was dependent on expression of the intercalated disc plaque protein plakoglobin (Pg) and direct phosphorylation at S665 by protein kinase A: Pg deficiency as well as overexpression of the phospho-deficient Pg-mutant S665A abrogated both cAMP-mediated junctional remodeling and increase of cohesion. Moreover, Pg knockout hearts failed to functionally adapt to adrenergic stimulation.

CONCLUSIONS

Taken together, we provide first evidence for positive adhesiotropy as a new cardiac function of sympathetic signaling. Positive adhesiotropy is dependent on Pg phosphorylation at S665 by protein kinase A. This mechanism may be of high medical relevance because loss of junctional Pg is a hallmark of arrhythmogenic cardiomyopathy.

Sequencing thousands of single-cell genomes with combinatorial indexing

Single-cell genome sequencing has proven valuable for the detection of somatic variation, particularly in the context of tumor evolution. Current technologies suffer from high library construction costs, which restrict the number of cells that can be assessed and thus impose limitations on the ability to measure heterogeneity within a tissue. Here, we present single-cell combinatorial indexed sequencing (SCI-seq) as a means of simultaneously generating thousands of low-pass single-cell libraries for detection of somatic copy-number variants. We constructed libraries for 16,698 single cells from a combination of cultured cell lines, primate frontal cortex tissue and two human adenocarcinomas, and obtained a detailed assessment of subclonal variation within a pancreatic tumor.

Pathophysiology of the Desmo-Adhesome

Advances in our understanding of desmosomal diseases have provided a clear demonstration of the key role played by desmosomes in tissue and organ physiology, highlighting the importance of their dynamic and finely regulated structure. In this context, non-desmosomal regulatory molecules have acquired increasing relevance in the study of this organelle resulting in extending the desmosomal interactome, named the "desmo-adhesome." Spatiotemporal changes in the expression and regulation of the desmo-adhesome underlie a number of genetic, infectious, autoimmune, and malignant conditions. The aim of the present article was to examine the structural and functional relationship of the desmosome, by providing a comprehensive, yet focused overview of the constituents targeted in human disease. The inclusion of the novel regulatory network in the desmo-adhesome pathophysiology opens new avenues to a deeper understanding of desmosomal diseases, potentially unveiling pathogenic mechanisms waiting to be explored. J. Cell. Physiol. 232: 496-505, 2017. © 2016 Wiley Periodicals, Inc.

Cadherin tales: Regulation of cadherin function by endocytic membrane trafficking

Cadherins are the primary adhesion molecules in adherens junctions and desmosomes and play essential roles in embryonic development. Although significant progress has been made in understanding cadherin structure and function, we lack a clear vision of how cells confer plasticity upon adhesive junctions to allow for cellular rearrangements during development, wound healing and metastasis. Endocytic membrane trafficking has emerged as a fundamental mechanism by which cells confer a dynamic state to adhesive junctions. Recent studies indicate that the juxtamembrane domain of classical cadherins contains multiple endocytic motifs, or "switches," that can be used by cellular membrane trafficking machinery to regulate adhesion. The cadherin-binding protein p120-catenin (p120) appears to be the master regulator of access to these switches, thereby controlling cadherin endocytosis and turnover. This review focuses on p120 and other cadherin-binding proteins, ubiquitin ligases, and growth factors as key modulators of cadherin membrane trafficking.

Palmitoylation of Desmoglein 2 Is a Regulator of Assembly Dynamics and Protein Turnover

Desmosomes are prominent adhesive junctions present between many epithelial cells as well as cardiomyocytes. The mechanisms controlling desmosome assembly and remodeling in epithelial and cardiac tissue are poorly understood. We recently identified protein palmitoylation as a mechanism regulating desmosome dynamics. In this study, we have focused on the palmitoylation of the desmosomal cadherin desmoglein-2 (Dsg2) and characterized the role that palmitoylation of Dsg2 plays in its localization and stability in cultured cells. We identified two cysteine residues in the juxtamembrane (intracellular anchor) domain of Dsg2 that, when mutated, eliminate its palmitoylation. These cysteine residues are conserved in all four desmoglein family members. Although mutant Dsg2 localizes to endogenous desmosomes, there is a significant delay in its incorporation into junctions, and the mutant is also present in a cytoplasmic pool. Triton X-100 solubility assays demonstrate that mutant Dsg2 is more soluble than wild-type protein. Interestingly, trafficking of the mutant Dsg2 to the cell surface was delayed, and a pool of the non-palmitoylated Dsg2 co-localized with lysosomal markers. Taken together, these data suggest that palmitoylation of Dsg2 regulates protein transport to the plasma membrane. Modulation of the palmitoylation status of desmosomal cadherins can affect desmosome dynamics.

Lower DSC1 expression is related to the poor differentiation and prognosis of head and neck squamous cell carcinoma (HNSCC)

PURPOSE

Although desmocollins have an important position in cancer-related research, there are little reports about the relations between cancers and desmocollin 1 (DSC1). The present study was designed to investigate the correlations between DSC1 and head and neck squamous cell carcinoma (HNSCC).

METHODS

First we analyzed the GEO database; then, HNSCC and pericarcinous tissues were collected to verify the results. DSC1 expression was detected by western blot and real-time PCR. The co-expression genes of DSC1 were extracted from Cancer Cell Line Encyclopedia database (CCLE database), and their correlation was analyzed in The Cancer Genome Atlas HNSCC database (TCGA HNSCC database). Next the gene ontology analysis (GO) was carried out. Moreover, we suppressed DSC1 in FaDu cell to investigate the internal mechanism.

RESULTS

GEO database showed that DSC1 was higher in HNSCC and patients with higher DSC1 had unfavorable prognosis. The results of the samples showed that DSC1 was significantly higher in HNSCC than in normal tissue, which was consistent with the results of GEO database. The co-expression genes of DSC1 were extracted from CCLE database and verified in TCGA HNSCC database. It revealed that DSC1 was related to cell signal transduction. In FaDu/siDSC1 cells, the proliferation and migration were decreased compared to FaDu cells, and the expression levels of β-catenin, c-myc and cyclin D1 down-regulated significantly.

CONCLUSIONS

The increased expression of DSC1 can promote the occurrence of HNSCC and is associated with tumor. The increased expression of DSC1 also indicates a poor prognosis of the patients with HNSCC.

Desmosomes in disease: a guide for clinicians

The large number of diseases occurring when desmosome constituents are impaired provides striking evidence for the key role of desmosomes in maintaining tissue integrity. A detailed understanding of the molecular alterations causing desmosomal dysfunction has, in turn, underpinned the development of novel diagnostic tools. This has salient clinical implications for dentists and oral medicine practitioners because the majority of desmosomal diseases affect the oral cavity. In the present article, we review the autoimmune, infectious, genetic, and neoplastic diseases that target the desmosome, with particular emphasis on clinical manifestations, diagnostic pathways, and relevant laboratory investigations.

Molecular organization of the desmosome as revealed by direct stochastic optical reconstruction microscopy

Desmosomes are macromolecular junctions responsible for providing strong cell-cell adhesion. Because of their size and molecular complexity, the precise ultrastructural organization of desmosomes is challenging to study. Here, we used direct stochastic optical reconstruction microscopy (dSTORM) to resolve individual plaque pairs for inner and outer dense plaque proteins. Analysis methods based on desmosomal mirror symmetry were developed to measure plaque-to-plaque distances and create an integrated map. We quantified the organization of desmoglein 3, plakoglobin and desmoplakin (N-terminal, rod and C-terminal domains) in primary human keratinocytes. Longer desmosome lengths correlated with increasing plaque-to-plaque distance, suggesting that desmoplakin is arranged with its long axis at an angle within the plaque. We next examined whether plaque organization changed in different adhesive states. Plaque-to-plaque distance for the desmoplakin rod and C-terminal domains decreased in PKP-1-mediated hyperadhesive desmosomes, suggesting that protein reorganization correlates with function. Finally, in human epidermis we found a difference in plaque-to-plaque distance for the desmoplakin C-terminal domain, but not the desmoplakin rod domain or plakoglobin, between basal and suprabasal cells. Our data reveal the molecular organization of desmosomes in cultured keratinocytes and skin as defined by dSTORM.

Structural basis of adhesive binding by desmocollins and desmogleins

Desmosomes are intercellular adhesive junctions that impart strength to vertebrate tissues. Their dense, ordered intercellular attachments are formed by desmogleins (Dsgs) and desmocollins (Dscs), but the nature of trans-cellular interactions between these specialized cadherins is unclear. Here, using solution biophysics and coated-bead aggregation experiments, we demonstrate family-wise heterophilic specificity: All Dsgs form adhesive dimers with all Dscs, with affinities characteristic of each Dsg:Dsc pair. Crystal structures of ectodomains from Dsg2 and Dsg3 and from Dsc1 and Dsc2 show binding through a strand-swap mechanism similar to that of homophilic classical cadherins. However, conserved charged amino acids inhibit Dsg:Dsg and Dsc:Dsc interactions by same-charge repulsion and promote heterophilic Dsg:Dsc interactions through opposite-charge attraction. These findings show that Dsg:Dsc heterodimers represent the fundamental adhesive unit of desmosomes and provide a structural framework for understanding desmosome assembly.

Super-Resolution Microscopy Reveals Altered Desmosomal Protein Organization in Tissue from Patients with Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an autoimmune epidermal blistering disease in which autoantibodies (IgG) are directed against the desmosomal cadherin desmoglein 3 (Dsg3). In order to better understand how PV IgG alters desmosome morphology and function in vivo, PV patient biopsies were analyzed by structured illumination microscopy (SIM), a form of super-resolution fluorescence microscopy. In patient tissue, desmosomal proteins were aberrantly clustered and localized to PV IgG-containing endocytic linear arrays. Patient IgG also colocalized with markers for lipid rafts and endosomes. Additionally, steady-state levels of Dsg3 were decreased and desmosomes were reduced in size in patient tissue. Desmosomes at blister sites were occasionally split, with PV IgG decorating the extracellular faces of split desmosomes. Desmosome splitting was recapitulated in vitro by exposing cultured keratinocytes both to PV IgG and to mechanical stress, demonstrating that splitting at the blister interface in patient tissue is due to compromised desmosomal adhesive function. These findings indicate that Dsg3 clustering and endocytosis are associated with reduced desmosome size and adhesion defects in PV patient tissue. Further, this study reveals that super-resolution optical imaging is powerful approach for studying epidermal adhesion structures in normal and diseased skin.

Pathophysiology and prevention of sudden cardiac death

Sudden cardiac death (SCD) is known to occur in individuals with diverse diseases. Each disease state has a specific etiology and pathophysiology, and is diagnosed and treated differently. Etiologies for SCD include cardiac arrhythmias, coronary artery disease, congenital coronary artery anomalies, hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, dilated cardiomyopathy, and aortic valve stenosis. A potential unifying mechanism of SCD in these diseases involves a massive stimulation of the sympathetic nervous system’s stress response and the subsequent elevation of circulating catecholamines. The diagnosis of cardiac diseases that contribute to an increased risk for SCD is accomplished by a combination of different techniques including electrocardiography, echocardiography, magnetic resonance imaging, and invasive cardiac catheterization. Several therapies including anti-arrhythmic drugs, β-blockers, and antiplatelet agents may be used as medical treatment in patients for the prevention of SCD. Invasive therapies including percutaneous angioplasty, coronary artery bypass surgery, and implantable cardioverter-defibrillators are also used in the clinical management of SCD.