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Desmosomes mediate cell-cell adhesion and are prevalent in tissues under mechanical stress. However, their detailed structural characterization is not available. Here, we characterized the molecular architecture of the desmosomal outer dense plaque (ODP) using Bayesian integrative structural modeling via the Integrative Modeling Platform. Starting principally from the structural interpretation of a cryo-electron tomography (cryo-ET) map of the ODP, we integrated information from x-ray crystallography, an immuno-electron microscopy study, biochemical assays, in silico predictions of transmembrane and disordered regions, homology modeling, and stereochemistry information. The integrative structure was validated by information from imaging, tomography, and biochemical studies that were not used in modeling. The ODP resembles a densely packed cylinder with a plakophilin (PKP) layer and a plakoglobin (PG) layer; the desmosomal cadherins and PKP span these two layers. Our integrative approach allowed us to localize disordered regions, such as the N-terminus of PKP and the C-terminus of PG. We refined previous protein-protein interactions between desmosomal proteins and provided possible structural hypotheses for defective cell-cell adhesion in several diseases by mapping disease-related mutations on the structure. Finally, we point to features of the structure that could confer resilience to mechanical stress. Our model provides a basis for generating experimentally verifiable hypotheses on the structure and function of desmosomal proteins in normal and disease states., (© 2024 The Author(s). Protein Science published by Wiley Periodicals LLC on behalf of The Protein Society.)

Acquired resistance to endocrine treatments remains a major clinical challenge. In this study, we found that desmoglein-2 (DSG2) plays a major role in acquired endocrine resistance and cellular plasticity in ER + breast cancer (BC). By analysing the well-established fulvestrant-resistant ER + BC model using single-cell RNA-seq, we revealed that ER inhibition leads to a specific increase in DSG2 in cancer cell populations, which in turn enhances desmosome formation in vitro and in vivo and cell phenotypic plasticity that promotes resistance to treatment. DSG2 depletion reduced tumorigenesis and metastasis in fulvestrant-resistant xenograft models and promoted fulvestrant efficiency. Mechanistically, DSG2 forms a desmosome complex with JUP and Vimentin and triggers Wnt/PCP signalling. We showed that elevated DSG2 levels, along with reduced ER levels and an activated Wnt/PCP pathway, predicted poor survival, suggesting that a DSG2 high signature could be exploited for therapeutic interventions. Our analysis highlighted the critical role of DSG2-mediated desmosomal junctions following antiestrogen treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Previous data provided evidence for a critical role of desmosomes to stabilize intestinal epithelial barrier (IEB) function. These studies suggest that desmosomes not only contribute to intercellular adhesion but also play a role as signaling hubs. The contribution of desmosomal plaque proteins plakophilins (PKP) in the intestinal epithelium remains unexplored. The intestinal expression of PKP2 and PKP3 was verified in human gut specimens, human intestinal organoids as well as in Caco2 cells whereas PKP1 was not detected. Knock-down of PKP2 using siRNA in Caco2 cells resulted in loss of intercellular adhesion and attenuated epithelial barrier. This was paralleled by changes of the whole desmosomal complex, including loss of desmoglein2, desmocollin2, plakoglobin and desmoplakin. In addition, tight junction proteins claudin1 and claudin4 were reduced following the loss of PKP2. Interestingly, siRNA-induced loss of PKP3 did not change intercellular adhesion and barrier function in Caco2 cells, while siRNA-induced loss of both PKP2 and PKP3 augmented the changes observed for reduced PKP2 alone. Moreover, loss of PKP2 and PKP2/3, but not PKP3, resulted in reduced activity levels of protein kinase C (PKC). Restoration of PKC activity using Phorbol 12-myristate 13-acetate (PMA) rescued loss of intestinal barrier function and attenuated the reduced expression patterns of claudin1 and claudin4. Immunostaining, proximity ligation assays and co-immunoprecipitation revealed a direct interaction between PKP2 and PKC. In summary, our in vitro data suggest that PKP2 plays a critical role for intestinal barrier function by providing a signaling hub for PKC-mediated expression of tight junction proteins claudin1 and claudin4.

Loss-of-function mutations in PKP2, which encodes plakophilin-2, cause arrhythmogenic cardiomyopathy (AC). Restoration of deficient molecules can serve as upstream therapy, thereby requiring a human model that recapitulates disease pathology and provides distinct readouts in phenotypic analysis for proof of concept for gene replacement therapy. Here, we generated isogenic induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) with precisely adjusted expression of plakophilin-2 from a patient with AC carrying a heterozygous frameshift PKP2 mutation. After monolayer differentiation, plakophilin-2 deficiency led to reduced contractility, disrupted intercalated disc structures, and impaired desmosome assembly in iPSC-CMs. Allele-specific fluorescent labeling of endogenous DSG2 encoding desmoglein-2 in the generated isogenic lines enabled real-time desmosome-imaging under an adjusted dose of plakophilin-2. Adeno-associated virus-mediated gene replacement of PKP2 recovered contractility and restored desmosome assembly, which was sequentially captured by desmosome-imaging in plakophilin-2-deficient iPSC-CMs. Our isogenic set of iPSC-CMs recapitulates AC pathology and provides a rapid and convenient cellular platform for therapeutic development., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Desmosomes, strong cell-cell junctions of epithelia and cardiac muscle, link intermediate filaments to cell membranes and mechanically integrate cells across tissues, dissipating mechanical stress. They comprise five major protein classes - desmocollins and desmogleins (the desmosomal cadherins), plakoglobin, plakophilins and desmoplakin - whose individual contribution to the structure and turnover of desmosomes is poorly understood. Using live-cell imaging together with fluorescence recovery after photobleaching (FRAP) and fluorescence loss and localisation after photobleaching (FLAP), we show that desmosomes consist of two contrasting protein moieties or modules: a very stable moiety of desmosomal cadherins, desmoplakin and plakoglobin, and a highly mobile plakophilin (Pkp2a). As desmosomes mature from Ca2+ dependence to Ca2+-independent hyper-adhesion, their stability increases, but Pkp2a remains highly mobile. We show that desmosome downregulation during growth-factor-induced cell scattering proceeds by internalisation of whole desmosomes, which still retain a stable moiety and highly mobile Pkp2a. This molecular mobility of Pkp2a suggests a transient and probably regulatory role for Pkp2a in desmosomes. This article has an associated First Person interview with the first author of the paper., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Arrhythmogenic cardiomyopathy (ACM) is a familial disease, with approximately 60% of patients displaying a pathogenic variant. The majority of genes linked to ACM code for components of the desmosome: plakophilin-2 (PKP2), desmoglein-2 (DSG2) and desmocollin-2 (DSC2), plakoglobin (JUP) and desmoplakin (DSP). Genetic variants involving the desmosomes are known to cause dysfunction of cell-to-cell adhesions and intercellular gap junctions. In turn, this may result in failure to mechanically hold together the cardiomyocytes, fibrofatty myocardial replacement, cardiac conduction delay and ventricular arrhythmias. It is becoming clearer that pathogenic variants in desmosomal genes such as PKP2 are not only responsible for a mechanical dysfunction of the intercalated disc (ID), but are also the cause of various pro-arrhythmic mechanisms. In this review, we discuss in detail the different molecular interactions associated with desmosomal pathogenic variants, and their contribution to various ACM phenotypes., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Desmosomes (DSMs), together with adherens junctions (AJs) and tight junctions (TJs), constitute the apical cell junctional complex (AJC). While the importance of the apical and basolateral polarity machinery in the organization of AJs and TJs is well established, how DSMs are positioned within the AJC is not understood. Here we use highly polarized DLD1 cells as a model to address how DSMs integrate into the AJC. We found that knockout (KO) of the desmosomal ARM protein Pkp3, but not other major DSM proteins, uncouples DSMs from the AJC without blocking DSM assembly. DLD1 cells also exhibit a prominent extraDSM pool of Pkp3, concentrated in tricellular (tC) contacts. Probing distinct apicobasal polarity pathways revealed that neither the DSM's association with AJC nor the extraDSM pool of Pkp3 are abolished in cells with defects in Scrib module proteins responsible for basolateral membrane development. However, a loss of the apical polarity protein, Par3, completely eliminates the extraDSM pool of Pkp3 and disrupts AJC localization of desmosomes, dispersing these junctions along the entire length of cell-cell contacts. Our data are consistent with a model whereby Par3 facilitates DSM assembly within the AJC, controlling the availability of an assembly competent pool of Pkp3 stored in tC contacts.

Background: Genomic screening holds great promise for presymptomatic identification of hidden disease, and prevention of dramatic events, including sudden cardiac death associated with arrhythmogenic cardiomyopathy (ACM). Herein, we present findings from clinical follow-up of carriers of ACM-associated pathogenic/likely pathogenic desmosome variants ascertained through genomic screening., Methods: Of 64 548 eligible participants in Geisinger MyCode Genomic Screening and Counseling program (2015-present), 92 individuals (0.14%) identified with pathogenic/likely pathogenic desmosome variants by clinical laboratory testing were referred for evaluation. We reviewed preresult medical history, patient-reported family history, and diagnostic testing results to assess both arrhythmogenic right ventricular cardiomyopathy and left-dominant ACM., Results: One carrier had a prior diagnosis of dilated cardiomyopathy with arrhythmia; no other related diagnoses or diagnostic family history criteria were reported. Fifty-nine carriers (64%) had diagnostic testing in follow-up. Excluding the variant, 21/59 carriers satisfied at least one arrhythmogenic right ventricular cardiomyopathy task force criterion, 11 (52%) of whom harbored DSP variants, but only 5 exhibited multiple criteria. Six (10%) carriers demonstrated evidence of left-dominant ACM, including high rates of atypical late gadolinium enhancement by magnetic resonance imaging and nonsustained ventricular tachycardia. Two individuals received new cardiomyopathy diagnoses and received defibrillators for primary prevention., Conclusions: Genomic screening for pathogenic/likely pathogenic variants in desmosome genes can uncover both left- and right-dominant ACM. Findings of overt cardiomyopathy were limited but were most common in DSP -variant carriers and notably absent in PKP2 -variant carriers. Consideration of the pathogenic/likely pathogenic variant as a major criterion for diagnosis is inappropriate in the setting of genomic screening.

Desmosome remodeling is crucial for epidermal regeneration, differentiation and wound healing. It is mediated by adapting the composition, and by post-translational modifications, of constituent proteins. We have previously demonstrated in mouse suprabasal keratinocytes that plakophilin (PKP) 1 mediates strong adhesion, which is negatively regulated by insulin-like growth factor 1 (IGF1) signaling. The importance of PKP3 for epidermal adhesion is incompletely understood. Here, we identify a major role of epidermal growth factor (EGF), but not IGF1, signaling in PKP3 recruitment to the plasma membrane to facilitate desmosome assembly. We find that ribosomal S6 kinases (RSKs) associate with and phosphorylate PKP3, which promotes PKP3 association with desmosomes downstream of the EGF receptor. Knockdown of RSKs as well as mutation of an RSK phosphorylation site in PKP3 interfered with desmosome formation, maturation and adhesion. Our findings implicate a coordinate action of distinct growth factors in the control of adhesive properties of desmosomes through modulation of PKPs in a context-dependent manner., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Background: Plakophilin-2 (PKP2) is classically defined as a desmosomal protein. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy. A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events consequent to PKP2 deficiency. Here, we sought to capture early molecular/cellular events that can act as nascent arrhythmic/cardiomyopathic substrates., Methods: We used multiple imaging, biochemical and high-resolution mass spectrometry methods to study functional/structural properties of cells/tissues derived from cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mice (PKP2cKO) 14 days post-tamoxifen injection, a time point preceding overt electrical or structural phenotypes. Myocytes from right or left ventricular free wall were studied separately., Results: Most properties of PKP2cKO left ventricular myocytes were not different from control; in contrast, PKP2cKO right ventricular (RV) myocytes showed increased amplitude and duration of Ca 2+ transients, increased Ca 2+ in the cytoplasm and sarcoplasmic reticulum, increased frequency of spontaneous Ca 2+ release events (sparks) even at comparable sarcoplasmic reticulum load, and dynamic Ca 2+ accumulation in mitochondria. We also observed early- and delayed-after transients in RV myocytes and heightened susceptibility to arrhythmias in Langendorff-perfused hearts. In addition, ryanodine receptor 2 in PKP2cKO-RV cells presented enhanced Ca 2+ sensitivity and preferential phosphorylation in a domain known to modulate Ca 2+ gating. RNAseq at 14 days post-tamoxifen showed no relevant difference in transcript abundance between RV and left ventricle, neither in control nor in PKP2cKO cells. Instead, we found an RV-predominant increase in membrane permeability that can permit Ca 2+ entry into the cell. Connexin 43 ablation mitigated the membrane permeability increase, accumulation of cytoplasmic Ca 2+ , increased frequency of sparks and early stages of RV dysfunction. Connexin 43 hemichannel block with GAP19 normalized [Ca 2+ ] i homeostasis. Similarly, protein kinase C inhibition normalized spark frequency at comparable sarcoplasmic reticulum load levels., Conclusions: Loss of PKP2 creates an RV-predominant arrhythmogenic substrate (Ca 2+ dysregulation) that precedes the cardiomyopathy; this is, at least in part, mediated by a Connexin 43-dependent membrane conduit and repressed by protein kinase C inhibitors. Given that asymmetric Ca 2+ dysregulation precedes the cardiomyopathic stage, we speculate that abnormal Ca 2+ handling in RV myocytes can be a trigger for gross structural changes observed at a later stage.

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is associated with pathogenic/likely pathogenic (P/LP) variants in genes encoding the cardiac desmosomal proteins. Origin of these variants, including de novo mutation rate and extent of founder versus recurrent variants has implications for variant adjudication and clinical care, yet this has never been systematically investigated., Methods: We identified arrhythmogenic right ventricular cardiomyopathy probands who met 2010 Task Force Criteria and had undergone genotyping that included sequencing of the desmosomal genes (PKP2, DSP, DSG2, DSC2, and JUP) from 3 arrhythmogenic right ventricular cardiomyopathy registries in America and Europe. We classified the desmosomal variants, defined the contribution of unique versus nonunique (ie, not family-specific) P/LP variants, and identified the frequency and characteristics of de novo variants. Next, we haplotyped nonunique variants to determine how often they likely represent a single mutation event in a common ancestor (implied by shared haplotypes) versus multiple mutation events at the same genetic location., Results: Of 501 arrhythmogenic right ventricular cardiomyopathy probands, 322 (64.3%) carried 327 desmosomal P/LP variants. Most variants (n=247, 75.6%, in 245 patients) were identified in more than one proband and, therefore, considered nonunique. For 212/327 variants (64.8%) genetic cascade screening was performed extensively enough to identify the parental origin of the P/LP variant. Only 3 variants were de novo, 2 of which were whole gene deletions. For 24 nonunique P/LP PKP2 variants, haplotyping was conducted in 183 available families. For all 24 variants, multiple seemingly unrelated families sharing identical haplotypes were identified, suggesting that these variants originate from common founders., Conclusions: Most desmosomal P/LP variants are inherited, nonunique, and originate from ancient founders. Two of 3 de novo variants were large deletions. These observations inform genetic testing, cascade screening, and variant adjudication.

Desmosomes are essential for strong intercellular adhesion and are abundant in tissues exposed to mechanical strain. At the same time, desmosomes need to be dynamic to allow for remodeling of epithelia during differentiation or wound healing. Phosphorylation of desmosomal plaque proteins appears to be essential for desmosome dynamics. However, the mechanisms of how context-dependent post-translational modifications regulate desmosome formation, dynamics or stability are incompletely understood. Here, we show that growth factor signaling regulates the phosphorylation-dependent association of plakophilins 1 and 3 (PKP1 and PKP3) with 14-3-3 protein isoforms, and uncover unique and partially antagonistic functions of members of the 14-3-3 family in the regulation of desmosomes. 14-3-3γ associated primarily with cytoplasmic PKP1 phosphorylated at S155 and destabilized intercellular cohesion of keratinocytes by reducing its incorporation into desmosomes. In contrast, 14-3-3σ (also known as stratifin, encoded by SFN ) interacted preferentially with S285-phosphorylated PKP3 to promote its accumulation at tricellular contact sites, leading to stable desmosomes. Taken together, our study identifies a new layer of regulation of intercellular adhesion by 14-3-3 proteins., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

Background: Arrhythmogenic cardiomyopathy (AC) is an inherited heart muscle disease associated with point mutations in genes encoding for cardiac desmosome proteins. Conventional mutation screening is positive in ≈50% of probands. Copy number variations (CNVs) have recently been linked to AC pointing to the need to determine the prevalence of CNVs in desmosomal genes and to evaluate disease penetrance by cosegregation analysis in family members., Methods and Results: A total of 160 AC genotype-negative probands for 5 AC desmosomal genes by conventional mutation screening underwent multiplex ligation-dependent probe amplification. Nine heterozygous CNVs were identified in 11 (6.9%) of the 160 probands. Five carried a deletion of the entire plakophilin-2 ( PKP2 ) gene, 2 a deletion of only PKP2 exon 4, 1 a deletion of the PKP2 exons 6 to 11, 1 a PKP2 duplication of 5' untranslated region till exon 1, 1 the desmocollin-2 ( DSC2 ) duplication of exons 7 to 9, and 1 a large deletion of chromosome 18 comprising both DSC2 and desmoglein-2 genes. All probands were affected by moderate-severe forms of the disease, whereas 10 (32%) of the 31 family members carrying one of these deletions fulfilled the diagnostic criteria., Conclusions: Genomic rearrangements were detected in ≈7% of AC probands negative for pathogenic point mutations in desmosomal genes, highlighting the potential of CNVs analysis to substantially increase the diagnostic yield of genetic testing. Genotype-phenotype correlation demonstrated the presence of the disease in about one third of family members carrying the CNV, underlying the role of other factors in the development and progression of the disease., (© 2017 American Heart Association, Inc.)

Desmosomes mediate strong intercellular adhesion through desmosomal cadherins that interact with intracellular linker proteins including plakophilins (PKPs) 1-3 to anchor the intermediate filaments. PKPs show overlapping but distinct expression patterns in the epidermis. So far, the contribution of individual PKPs in differentially regulating desmosome function is incompletely understood. To resolve the role of PKP1 we ablated the PKP1 gene. Here, we report that PKP1(-/-) mice were born at the expected mendelian ratio with reduced birth weight, but they otherwise appeared normal immediately after birth. However, their condition rapidly declined, and the mice died within 24 hours, developing fragile skin with lesions in the absence of obvious mechanical trauma. This was accompanied by sparse and small desmosomes. Newborn PKP1(-/-) mice showed disturbed tight junctions with an impaired inside-out barrier, whereas the outside-in barrier was unaffected. Keratinocytes isolated from these mice showed strongly reduced intercellular cohesion, delayed tight junction formation, and reduced transepithelial resistance and reduced proliferation rates. Our study shows a nonredundant and essential role of PKP1 in desmosome and tight junction function and supports a role of PKP1 in growth control, a function that is crucial in wound healing and epidermal carcinogenesis., (Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Endurance exercise is associated with adverse outcomes in patients with arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). Exercise recommendations for family members remain undetermined., Objective: The purposes of this study were to determine if (1) endurance exercise (Bethesda class C) and exercise intensity (metabolic equivalent hours per year [MET-Hr/year]) increase the likelihood of fulfilling 2010 Task Force Criteria and ventricular arrhythmias/implantable cardioverter-defibrillator shock (ventricular tachycardia/ventricular fibrillation [VT/VF]), and (2) exercise restriction to the American Heart Association (AHA)-recommended minimum for healthy adults is associated with favorable outcomes of at-risk family members., Methods: Twenty-eight family members of 10 probands inheriting a PKP2 mutation were interviewed about exercise from age 10. Exercise threshold to maintain overall health was based on the 2007 AHA guidelines of a minimum 390 to 650 MET-Hr/year., Results: After adjustment for age, sex, and family membership, both participation in endurance athletics (odds ratio [OR] 7.4, P = .03) and higher-intensity exercise (OR = 4.2, P = .004) were associated with diagnosis (n = 13). Endurance athletes were also significantly more likely to develop VT/VF (n = 6, P = .02). Family members who restricted exercise at or below the upper bound of the AHA goal (≤650 MET-Hr/year) were significantly less likely to be diagnosed (OR = 0.07, P = .002) and had no VT/VF. At diagnosis and first VT/VF, family members had accumulated 2.8-fold (P = .002) and 3.5-fold (P = .03), respectively, greater MET-Hr exercise than the AHA-recommended minimum. Those who developed VT/VF had performed particularly high-intensity exercise in adolescence compared to unaffected family members (age 10-14: P = .04; age 14-19: P = .02)., Conclusion: The results of this study suggest restricting unaffected desmosomal mutation carriers from endurance and high-intensity athletics but potentially not from AHA-recommended minimum levels of exercise for healthy adults., (Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

The role of the juxtamembrane region of the desmocollin-2 cytoplasmic domain in desmosome formation was investigated by using gene knockout and reconstitution experiments. When a deletion construct of the desmocollin-2 juxtamembrane region was expressed in HaCaT cells, the mutant protein became localized linearly at the cell-cell boundary, suggesting the involvement of this region in desmosomal plaque formation. Then, desmocollin-2 and desmoglein-2 genes of epithelial DLD-1 cells were ablated by using the CRISPR/Cas9 system. The resultant knockout cells did not form desmosomes, but re-expression of desmocollin-2 in the cells formed desmosomal plaques in the absence of desmoglein-2 and the transfectants showed significant cell adhesion activity. Intriguingly, expression of desmocollin-2 lacking its juxtamembrane region did not form the plaques. The results of an immunoprecipitation and GST-fusion protein pull-down assay suggested the binding of plakophilin-2 and -3 to the region. Ablation of plakophilin-2 and -3 genes resulted in disruption of the plaque-like accumulation and linear localization of desmocollin-2 at intercellular contact sites. These results suggest that the juxtamembrane region of desmocollin-2 and plakophilins are involved in the desmosomal plaque formation, possibly through the interaction between this region and plakophilins., (© The Authors 2015. Published by Oxford University Press on behalf of the Japanese Biochemical Society. All rights reserved.)

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a cardiomyopathy that primarily involves the right ventricle. Mutations in desmosomal genes have been associated with ARVC. But its prevalence and spectrum are much less defined in the Chinese population, especially Han Chinese, a majority ethnic group in China; also the genotype-phenotype correlation regarding left ventricular involvement is still poorly understood. The aim of this study was to elucidate the genotype in Han Chinese patients with ARVC and the phenotype regarding cardiac left ventricle involvement in mutation carriers of ARVC. 48 Han Chinese patients were recruited into the present study based on the Original International Task Force Criteria of ARVC. Clinical data were reassessed according to the modified criteria published in 2010. A total of 36 subjects were diagnosed with ARVC; 12 patients were diagnosed with suspected ARVC. Five desmosomal genes (PKP2, DSG2, DSP, DSC2 and JUP) were sequenced directly from genomic DNA. Among the 36 patients, 21 mutations, 12 of which novel, were discovered in 19 individuals (19 of 36, 53%). The distribution of the mutations was 25% in PKP2, 14% in DSP, 11% in DSG2, 6% in JUP, and 3% in DSC2. Multiple mutations were identified in 2 subjects (2 of 36, 6%); both had digenic heterozygosity. Eight mutations, of which six were novel, were located in highly conserved regions. Seven mutations introduced a stop codon prematurely, which would result in premature termination of the protein synthesis. Two-dimensional echocardiography showed that LDVd and LDVs parameters were significantly larger in nonsense mutation carriers than in carriers of other mutations. In this comprehensive desmosome genetic analysis, 21 mutations were identified in five desmosomal genes in a group of 48 local Han Chinese subjects with ARVC, 12 of which were novel. PKP2 mutations were the most common variants. Left ventricular involvement could be a sign that the patient is a carrier of a nonsense cardiac desmosomal gene mutation., (Copyright © 2015 Elsevier Masson SAS. All rights reserved.)

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare cardiac disease characterized by myocardial fibrofatty replacement, which can lead to sudden death. Previous studies have described a reduction of plakoglobin (PKG) protein at the level of intercalated disks as the hallmark of ARVC. The main objective of this study was to investigate the involvement of desmosome mutations in the histological phenotype of ARVC. We performed a genetic analysis of ARVC cases, and histological characterization of ARVC heart tissue samples. We genetically analyzed 48 ARVC cases distributed into two groups: 42 human tissue heart samples with conclusive diagnoses of ARVC after post-mortem examination; and six DNA samples from peripheral blood of living patients who were clinically diagnosed. Sequenom MassARRAY analysis revealed three ARVC-associated variants in three patients in 42 tissue samples (7.14 %). Three individuals carried one single pathogenic mutation, p.R811S _PKP2, p.S824L_DSC2, and p.T526M_PKP2 in postmortem samples. In the living patients group, Sequenom MassARRAY revealed no mutation, however, later Sanger sequencing analysis identified three ARVC mutations in 2/6 patients not included in the Sequenom design. In post-mortem tissue samples we performed immunohistochemical labeling for desmosomal proteins and Connexin 43. This study revealed that PKP2 carriers present either absent or clearly reduced PKG immunolabeling, while the DSC2 carrier showed PKG immunolabeling similar to control samples. Immunolabeling for Cx43 did not show any differences compared to controls. The present Sequenom MassARRAY design is a useful tool for post-mortem genetic diagnosis of ARVC. Plakoglobin reduction occurs at intercalated disks, while other desmosome proteins and Cx43 remain unaltered.

Plakophilins 1 and 3 (PKP1/3) are members of the arm repeat family of catenin proteins and serve as structural components of desmosomes, which are important for cell-cell-adhesion. In addition, PKP1/3 occur as soluble proteins outside desmosomes, yet their role in the cytoplasm is not known. We found that cytoplasmic PKP1/3 coprecipitated with the RNA-binding proteins FXR1, G3BP, PABPC1, and UPF1, and these PKP1/3 complexes also comprised desmoplakin and PKP2 mRNAs. Moreover, we showed that the interaction of PKP1/3 with G3BP, PABPC1, and UPF1 but not with FXR1 was RNase sensitive. To address the cytoplasmic function of PKP1/3, we performed gain-and-loss-of-function studies. Both PKP1 and PKP3 knockdown cell lines showed reduced protein and mRNA levels for desmoplakin and PKP2. Whereas global rates of translation were unaffected, desmoplakin and PKP2 mRNA were destabilized. Furthermore, binding of PKP1/3 to FXR1 was RNA independent, and both PKP3 and FXR1 stabilized PKP2 mRNA. Our results demonstrate that cytoplasmic PKP1/3 are components of mRNA ribonucleoprotein particles and act as posttranscriptional regulators of gene expression., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

The pathways driving desmosome and adherens junction assembly are temporally and spatially coordinated, but how they are functionally coupled is poorly understood. Here we show that the Armadillo protein plakophilin 3 (Pkp3) mediates both desmosome assembly and E-cadherin maturation through Rap1 GTPase, thus functioning in a manner distinct from the closely related plakophilin 2 (Pkp2). Whereas Pkp2 and Pkp3 share the ability to mediate the initial phase of desmoplakin (DP) accumulation at sites of cell-cell contact, they play distinct roles in later steps: Pkp3 is required for assembly of a cytoplasmic population of DP-enriched junction precursors, whereas Pkp2 is required for transfer of the precursors to the membrane. Moreover, Pkp3 forms a complex with Rap1 GTPase, promoting its activation and facilitating desmosome assembly. We show further that Pkp3 deficiency causes disruption of an E-cadherin/Rap1 complex required for adherens junction sealing. These findings reveal Pkp3 as a coordinator of desmosome and adherens junction assembly and maturation through its functional association with Rap1., (© 2014 Todorovic´ et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).)

Mutations in proteins of the desmosome are associated with arrhythmogenic cardiomyopathy (AC; also referred to as "ARVC" or "ARVD"). Life-threatening ventricular arrhythmias often occur in the concealed phase of the disease before the onset of structural changes. Among the various potential mechanisms for arrhythmogenesis in AC, in this article, we concentrate on the relation between desmosomes and sodium channel function. We review evidence indicating that (1) loss of desmosomal integrity (including mutations or loss of expression of plakophilin-2; PKP2) leads to reduced sodium current (INa), (2) the PKP2-INa relation could be partly consequent to the fact that PKP2 facilitates proper trafficking of proteins to the intercalated disc, and (3) PKP2 mutations can be present in patients diagnosed with Brugada syndrome (BrS), thus supporting the previously proposed notion that AC and BrS are not two completely separate entities, but "bookends" in a continuum of variable sodium current deficiency and structural disease., (Copyright © 2014 Elsevier Inc. All rights reserved.)

This review summarizes data in support of the notion that the cardiac intercalated disc is the host of a protein interacting network, called "the connexome", where molecules classically defined as belonging to one particular structure (e.g., desmosomes, gap junctions, sodium channel complex) actually interact with others, and together, control excitability, electrical coupling and intercellular adhesion in the heart. The concept of the connexome is then translated into the understanding of the mechanisms leading to two inherited arrhythmia diseases: arrhythmogenic cardiomyopathy, and Brugada syndrome. The cross-over points in these two diseases are addressed to then suggest that, though separate identifiable clinical entities, they represent "bookends" of a spectrum of manifestations that vary depending on the effect that a particular mutation has on the connexome as a whole., (Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

The regulation of adhesion and growth is important for epithelial function and dysfunction. β-catenin (armadillo in Drosophila) is the prototype of a multifunctional molecule that regulates cell adhesion via adherens junctions and cell signaling via LEF/TCF transcription factors. Desmosomal armadillo proteins comprise plakoglobin and the plakophilins 1, 2, and 3. These proteins are essential for building up the desmosome and linking the desmosomal cadherins to keratin filaments. High expression of plakophilins in desmosomes correlates with strong intercellular cohesion and is essential for tissue integrity under mechanical stress. However, like β-catenin, these proteins have diverse non-desmosomal functions, for example, in regulating actin organization, protein synthesis, and growth control. In line with these functions, their de-regulated expression with up- as well as down-regulation has been connected to cancer and metastasis. Now, recent evidence sheds light on the post-translational regulation and provides an explanation for how de-regulation of plakophilins can contribute to cancer.

Desmosomes anchor intermediate filaments at sites of cell contact established by the interaction of cadherins extending from opposing cells. The incorporation of cadherins, catenin adaptors, and cytoskeletal elements resembles the closely related adherens junction. However, the recruitment of intermediate filaments distinguishes desmosomes and imparts a unique function. By linking the load-bearing intermediate filaments of neighboring cells, desmosomes create mechanically contiguous cell sheets and, in so doing, confer structural integrity to the tissues they populate. This trait and a well-established role in human disease have long captured the attention of cell biologists, as evidenced by a publication record dating back to the mid-1860s. Likewise, emerging data implicating the desmosome in signaling events pertinent to organismal development, carcinogenesis, and genetic disorders will secure a prominent role for desmosomes in future biological and biomedical investigations.

Background: Mutations in genes encoding for desmosomal proteins are the most common cause of arrhythmogenic right ventricular cardiomyopathy (ARVC). We assessed the value of genotype for prediction of lifetime major arrhythmic events and sudden cardiac death (SCD) in desmosomal gene-related ARVC., Methods and Results: The overall study population included 134 desmosomal gene mutation carriers (68 men; median age 36 years [22-52]) from 44 consecutive ARVC families undergoing comprehensive genetic screening. The probability of experiencing a first major arrhythmic event or SCD during a lifetime was determined by using date of birth as start point for the time-to-event analysis, and was stratified by sex, desmosomal genes, mutation types, and genotype complexity (single versus multiple mutations). One hundred thirteen patients (84%) carried a single desmosomal gene mutation in desmoplakin (n=44; 39%), plakophilin-2 (n=38; 34%), desmoglein-2 (n=30; 26%), and desmocollin-2 (n=1; 1%), whereas 21 patients (16%) had a complex genotype with compound heterozygosity in 7 and digenic heterozygosity in 14. Over a median observation period of 39 (22-52) years, 22 patients (16%) from 20 different families had arrhythmic events, such as SCD (n=1), aborted SCD because of ventricular fibrillation (n=6), sustained ventricular tachycardia (n=14), and appropriate defibrillator intervention (n=1). Multiple desmosomal gene mutations and male sex were independent predictors of lifetime arrhythmic events with a hazard ratio of 3.71 (95% confidence interval, 1.54-8.92; P=0.003) and 2.76 (95% confidence interval, 1.19-6.41; P=0.02), respectively., Conclusions: Compound/digenic heterozygosity was identified in 16% of ARVC-causing desmosomal gene mutation carriers and was a powerful risk factor for lifetime major arrhythmic events and SCD. These results support the use of comprehensive genetic screening of desmosomal genes for arrhythmic risk stratification in ARVC.

Objectives: The aim of this study was to identify the incremental value and optimal role of cardiac magnetic resonance (CMR) imaging in arrhythmic risk stratification of arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C)-associated desmosomal mutation carriers without histories of sustained ventricular arrhythmia., Background: Risk stratification of ARVD/C mutation carriers is challenging., Methods: Sixty-nine patients (mean age 27.0 ± 15.3 years, 42% men) harboring ARVD/C-associated pathogenic mutations (83% plakophilin 2) without prior sustained ventricular arrhythmias were included. Electrocardiographic and 24-h Holter monitoring findings closest to presentation were analyzed for electrical abnormalities per revised task force criteria. CMR studies were done to identify abnormal cardiac structure and function according to the revised task force criteria., Results: Overall, 42 patients (61%) presented with electrical abnormalities on the basis of electrocardiography and Holter monitoring, of whom 20 (48%) had abnormal results on CMR. Only 1 of 27 patients (4%) without electrical abnormalities at initial evaluation had abnormal CMR results. Over a mean follow-up period of 5.8 ± 4.4 years, 11 patients (16%) experienced sustained ventricular arrhythmias, exclusively in patients with both electrical abnormalities (electrocardiography and/or Holter monitoring) and abnormal CMR results., Conclusions: These results suggest that electrical abnormalities on electrocardiography and Holter monitoring precede detectable structural abnormalities in ARVD/C mutation carriers. Therefore, evaluation of cardiac structure and function using CMR is probably not necessary in the absence of baseline electrical abnormalities. Among ARVD/C mutation carriers, the presence of both electrical and CMR abnormalities identifies patients at high risk for events and thus patients who might benefit from prophylactic implantable cardioverter-defibrillator placement., (Copyright © 2013 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Desmosomes are dynamic junctions between cells that maintain the structural integrity of skin and heart tissues by withstanding shear forces. Mutations in component genes cause life-threatening conditions including arrhythmogenic right ventricular cardiomyopathy, and desmosomal proteins are targeted by pathogenic autoantibodies in skin blistering diseases such as pemphigus. Here, we review a set of newly discovered pathogenic alterations and discuss the structural repercussions of debilitating mutations on desmosomal proteins. The architectures of native desmosomal assemblies have been visualized by cryo-electron microscopy and cryo-electron tomography, and the network of protein domain interactions is becoming apparent. Plakophilin and desmoplakin mutations have been discovered to alter binding interfaces, structures, and stabilities of folded domains that have been resolved by X-ray crystallography and NMR spectroscopy. The flexibility within desmoplakin has been revealed by small-angle X-ray scattering and fluorescence assays, explaining how mechanical stresses are accommodated. These studies have shown that the structural and functional consequences of desmosomal mutations can now begin to be understood at multiple levels of spatial and temporal resolution. This review discusses the recent structural insights and raises the possibility of using modeling for mechanism-based diagnosis of how deleterious mutations alter the integrity of solid tissues., (© 2013. Published by Elsevier Ltd. All rights reserved.)

Desmosomes are prominent cell-cell adhesive junctions in stratified squamous epithelia and disruption of desmosomal adhesion has been shown to have dramatic effects on the function and integrity of these tissues. During normal physiologic processes, such as tissue development and wound healing, intercellular adhesion must be modified locally to allow coordinated cell movements. The mechanisms that control junction integrity and adhesive strength under these conditions are poorly understood. We utilized a proteomics approach to identify plakophilin-3 associated proteins and identified the 14-3-3 family member stratifin. Stratifin interacts specifically with plakophilin-3 and not with other plakophilin isoforms and mutation analysis demonstrated the binding site includes serine 285 in the amino terminal head domain of plakophilin-3. Stratifin interacts with a cytoplasmic pool of plakophilin-3 and is not associated with the desmosome in cultured cells. FRAP analysis revealed that decreased stratifin expression leads to an increase in the exchange rate of cytoplasmic plakophilin-3/GFP with the pool of plakophilin-3/GFP in the desmosome resulting in decreased desmosomal adhesion and increased cell migration. We propose a model by which stratifin plays a role in regulating plakophilin-3 incorporation into the desmosomal plaque by forming a plakophilin-3 stratifin complex in the cytosol and thereby affecting desmosome dynamics in squamous epithelial cells.

Desmosomes in keratinocytes are the most important intercellular adhering junctions that provide structural strength for the epidermis. These junctions are connected directly with desmosomal cadherin proteins. Desmosomal cadherins are divided into four desmogleins (Dsgs), Dsg1-4, and three desmocollins (Dscs), Dsc1-3, all of which are involved in desmosomal adhesion by homo- and/or heterophilic binding between Dsgs and Dscs in a Ca(2+)-dependent manner. Cadherins are present on the cell surface and anchor keratin intermediate filaments (KIFs) to their inner cytoplasmic surface to generate an intracellular KIF-skeletal scaffold through several associate proteins, including plakoglobin, plakophillin, and desmoplakins. As such, the desmosomal contacts between adjacent cells generate an intercellular KIF scaffold throughout the whole epidermal sheet. However, despite these critical roles in maintaining epidermal adhesion and integrity, desmosomes are not static structures. Rather, they are dynamic units that undergo regular remodeling, i.e., assembly and disassembly, to allow for cell migration within the epidermis in response to outside-in signaling during epidermal differentiation. Recently, two cell-cell adhesion states controlled by desmosomes have been recognized, including "stable hyperadhesion (Ca(2+)-independent)" and "dynamic weak-adhesion (Ca(2+)-dependent)" conditions. These conditions are mutually reversible through cell signaling events involving protein kinase C (PKC) and epidermal growth factor receptor. Pemphigus vulgaris (PV) is an autoimmune bullous disease caused by anti-Dsg3 antibodies. Binding of these antibodies to Dsg3 causes endocytosis of Dsg3 from the cell surface and results in the specific depletion of Dsg3 from desmosomes, an event linked to acantholysis in the epidermis. This binding of anti-Dsg3 antibody to Dsg3 in epidermal keratinocytes activates PKC, to generate the "weak-adhesion (Ca(2+)-dependent)" state of desmosomes. The weak-adhesion desmosomes appear to be the susceptible desmosomal state and a prerequisite for Dsg3 depletion from desmosomes, pivotal and specific events leading to PV blistering. These observations allow us to propose a concept for pemphigus blistering disorders as a "desmosome-remodeling impairment disease" involving a mechanism of Dsg3 nonassembly and depletion from desmosomes through PV immunoglobulin G-activated intracellular signaling events., (Copyright © 2012. Published by Elsevier B.V.)

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an uncommon heart disease characterised by arrhythmias, right ventricular scarring, and fibrofatty change. Although mutations in the desmosome have been frequently observed in patients clinically diagnosed with ARVC, recent data have put a direct causal relationship in question. Many patients with ARVC and mutations have not had histological confirmation, and many family members with mutations are not affected. Desmosomal mutations have been found in other cardiac diseases, and the specificity of histopathological features is even in question. We aim to review the purported link between ARVC and the desmosome by a critical analysis of reported data.

The association of estrogen receptor alpha (ERα) expression with differentiated breast tumors presenting a lower metastasis risk could be explained by the estrogen modulation of cell adhesion, motility and invasiveness. Since desmosomes play a crucial role in cell-cell adhesion and may interfere in tumor progression, we studied their regulation by estrogens in human breast cancer and normal mammary cells. Estrogens increased the formation of desmosomes in normal and malignant cells. Furthermore, four desmosomal proteins (desmocollin, γ-catenin, plakophilin and desmoplakin) appeared significantly up-regulated by estrogens in three ERα-expressing cancer cell lines and this effect was reversed by a pure antiestrogen. Finally, silencing of ERα or desmoplakin expression by specific siRNA revealed that estrogen-modulated desmosomal proteins are essential for the estrogenic control of intercellular adhesion. This estrogen modulation of desmosome formation could contribute to the lower invasiveness of ERα-positive tumors and to the integrity of epithelial layers in estrogen target tissues., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

Desmosomes are intercellular junctions that contribute to cell-cell adhesion, signalling, development and differentiation in various tissues, including the skin. Composed of a network of transmembranous and intracellular plaque proteins, pathogenic autosomal dominant or recessive mutations have been reported in 10 different desmosomal genes, resulting in a spectrum of phenotypes variably affecting skin, hair and heart. This review summarizes the molecular pathology and phenotypes that predominantly affect the skin/hair. Recent desmosomal genodermatoses described include lethal congenital epidermolysis bullosa (plakoglobin), cardiomyopathy with alopecia and palmoplantar keratoderma (plakoglobin), hypotrichosis with scalp vesicles (desmocollin 3), and generalized peeling skin disease (corneodesmosin). Understanding the range of clinical phenotypes in combination with knowledge of the inherent desmosome gene mutation(s) is helpful in managing and counselling patients, as well as providing insight into the biological function of specific components of desmosomes in skin and other tissues., (© 2011 The Authors. BJD © 2011 British Association of Dermatologists.)

A single report has associated mutations in TMEM43 (LUMA) with a distinctive form of arrhythmogenic right ventricular cardiomyopathy (ARVC). We aimed at performing mutational analysis of the gene and characterizing the associated immunohistochemical features. Sixty-five unrelated patients (55 fulfilling Task Force criteria and 10 borderline cases) were screened for mutations in TMEM43. Immunohistochemistry with anti-TMEM43, anti-plakoglobin, anti-plakophilin-2, anti-connexin-43, and anti-emerin antibodies was performed on myocardium from TMEM43-positive patients (n = 3) and healthy controls (n = 3). The genetic screening identified heterozygous variants in two families: one reported mutation (c.1073C> T; in two related patients) and one novel variant (c.705+ 7G> A; in one patient) of unknown significance. All three patients fulfilled Task Force criteria and did not carry mutations in any other ARVC-related gene. Immunostaining with TMEM43 antibody showed intense staining of the sarcolemma. The signal level was reduced in all the three TMEM43-positive patients. Immunostaining with plakoglobin-specific antibody also showed reduced signal levels in the three carriers. All patients displayed a similar immunoreactive signal for plakophilin-2, connexin-43, and emerin. In conclusion, two TMEM43 sequence variants were identified in this Danish ARVC cohort. Evaluation of the expression of TMEM43 showed a unique cardiac localization. The immunoreactive signal for the desmosomal protein plakoglobin was reduced in mutation carriers. The TMEM43 gene underlies a distinctive form of ARVC which may share a final common pathway with desmosome-associated ARVC., (2011 John Wiley & Sons A/S.)

Background: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive myocardial disorder caused by mutations of desmosomal cell adhesion proteins. The prevalence of these variants in the general population is unknown., Objective: This study examined the spectrum and population prevalence of desmosomal mutations predisposing to ARVC in Finland., Methods: We screened 29 Finnish ARVC probands for mutations in the DSP, DSG2, and DSC2 genes. All Finnish-type ARVC-associated mutations, including those 3 previously identified in PKP2 in the same patient group, were analyzed in the population-based Health 2000 cohort of 6,334 individuals and tested for association with electrocardiographic variables., Results: We detected 2 novel mutations: DSG2 3059_3062delAGAG and DSP T1373A. DSG2 3059_3062delAGAG was present in a family with 5 mutation carriers. The endomyocardial samples of the DSG2 deletion carrier showed reduced immunoreactive signal for desmoglein-2, plakophilin-2, plakoglobin, and desmoplakin. DSP T1373A was found in 1 proband with typical right ventricular disease and exercise-related ventricular tachycardia. In the population sample, the collective prevalence of all 5 mutations identified in the 29 ARVC patients (PKP2 Q62K, Q59L, N613K, DSG2 3059_3062delAGAG, and DSP T1373A) was 31 of 6,334 individuals, or 0.5%. The apparent founder mutation PKP2 Q59L is present in 0.3% of Finns and was previously shown to have an approximately 20% disease penetrance., Conclusion: One of 200 Finns carries a desmosomal mutation that may predispose to ARVC and its clinical sequelae. ARVC-associated mutations may thus be more prevalent in the population than expected based on the published ARVC prevalence data., (Copyright © 2011 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

A decrease in the levels of the desmosomal plaque protein, plakophilin3 (PKP3), leads to a decrease in desmosome size and cell-cell adhesion. To test the hypothesis that PKP3 is required for desmosome formation, the recruitment of desmosomal components to the cell surface was studied in the PKP3 knockdown clones. The PKP3 knockdown clones showed decreased cell border staining for multiple desmosomal proteins, when compared to vector controls, and did not form desmosomes in a calcium switch assay. Further analysis demonstrated that PKP3, plakoglobin (PG) and E-cadherin are present at the cell border at low concentrations of calcium. Loss of either PG or E-cadherin led to a decrease in the levels of PKP3 and other desmosomal proteins at the cell border. The results reported here are consistent with the model that PG and E-cadherin recruit PKP3 to the cell border to initiate desmosome formation.

Plakophilin 2 (PKP2), an armadillo family member closely related to p120 catenin (p120ctn), is a constituent of the intercellular adhesive junction, the desmosome. We previously showed that PKP2 loss prevents the incorporation of desmosome precursors enriched in the plaque protein desmoplakin (DP) into newly forming desmosomes, in part by disrupting PKC-dependent regulation of DP assembly competence. On the basis of the observation that DP incorporation into junctions is cytochalasin D-sensitive, here we ask whether PKP2 may also contribute to actin-dependent regulation of desmosome assembly. We demonstrate that PKP2 knockdown impairs cortical actin remodeling after cadherin ligation, without affecting p120ctn expression or localization. Our data suggest that these defects result from the failure of activated RhoA to localize at intercellular interfaces after cell-cell contact and an elevation of cellular RhoA, stress fibers, and other indicators of contractile signaling in squamous cell lines and atrial cardiomyocytes. Consistent with these observations, RhoA activation accelerated DP redistribution to desmosomes during the first hour of junction assembly, whereas sustained RhoA activity compromised desmosome plaque maturation. Together with our previous findings, these data suggest that PKP2 may functionally link RhoA- and PKC-dependent pathways to drive actin reorganization and regulate DP-IF interactions required for normal desmosome assembly.

Background: Idiopathic dilated cardiomyopathy is a familial disorder in 25% to 50% of patients, but the genetic basis in the majority of cases remains unknown. Genes encoding desmosomal proteins, currently regarded as synonymous with another disorder, arrhythmogenic right ventricular cardiomyopathy, are known to cause left ventricular dysfunction, but their importance in unselected patients with unequivocal dilated cardiomyopathy is unknown. The objective of this study was to determine the prevalence of mutations in 5 desmosomal protein genes in patients with dilated cardiomyopathy., Methods and Results: We studied 100 unrelated patients with idiopathic dilated cardiomyopathy consecutively referred to a dedicated cardiomyopathy unit. Patients underwent clinical evaluation, ECG, echocardiography, exercise testing, 24-hour ambulatory ECG monitoring, and mutation screening of 5 genes implicated in arrhythmogenic right ventricular cardiomyopathy: plakoglobin, desmoplakin, plakophilin-2, desmoglein-2, and desmocollin-2. Of the 100 patients (mean age at evaluation, 46.8+/-13.8 years; range, 17.0 to 72.8 years; male sex, 63%), 5 were found to carry pathogenic desmosomal protein gene mutations. An additional 13 patients had sequence variants of uncertain pathogenic significance and were excluded from further comparative analysis. Patients harboring desmosomal gene mutations had a phenotype indistinguishable from the 82 noncarriers, with the exception of exercise-induced ventricular ectopy, which was more frequent in the desmosomal mutation carriers (P=0.033). None of the 5 carriers of desmosomal mutations fulfilled current diagnostic criteria for arrhythmogenic right ventricular cardiomyopathy, but 1 had fibrofatty change in the left ventricle at autopsy., Conclusions: Heart failure caused by a dilated, poorly contracting left ventricle and arrhythmogenic right ventricular cardiomyopathy have been considered distinct clinicopathologic entities. This study suggests that both clinical presentations can be caused by mutations in desmosomal protein genes.

Aims: Five desmosomal genes have been recently implicated in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) but the clinical impact of genetics remains poorly understood. We wanted to address the potential impact of genotyping., Methods and Results: Direct sequencing of the five genes (JUP, DSP, PKP2, DSG2, and DSC2) was performed in 135 unrelated patients with ARVD/C. We identified 41 different disease-causing mutations, including 28 novel ones, in 62 patients (46%). In addition, a genetic variant of unknown significance was identified in nine additional patients (7%). Distribution of genes was 31% (PKP2), 10% (DSG2), 4.5% (DSP), 1.5% (DSC2), and 0% (JUP). The presence of desmosomal mutations was not associated with familial context but was associated with young age, symptoms, electrical substrate, and extensive structural damage. When compared with other genes, DSG2 mutations were associated with more frequent left ventricular involvement (P = 0.006). Finally, complex genetic status with multiple mutations was identified in 4% of patients and was associated with more frequent sudden death (P = 0.047)., Conclusion: This study supports the use of genetic testing as a new diagnostic tool in ARVC/D and also suggests a prognostic impact, as the severity of the disease appears different according to the underlying gene or the presence of multiple mutations.

Background: Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a progressive cardiomyopathy showing a wide clinical spectrum in terms of clinical expressions and prognoses., Objective: This study sought to estimate the occurrence of compound and double heterozygotes for mutations in desmosomal proteins encoding genes in a cohort of ARVC/D Italian index cases, and to assess the clinical phenotype of mutations carriers., Methods: Fourty-two consecutive ARVC/D index cases who fulfilled the International Task Force diagnostic criteria were screened for mutations in PKP2, DSP, DSG2, DSC2, and JUP genes by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing., Results: Three probands (7.1%) showing a family history of sudden death carried multiple mutations. Family screening identified an additional 7 multiple-mutation carriers. Among the 7 double heterozygotes for mutations in different genes, 2 were clinically unaffected, 2 were affected, and 3 showed some clinical signs of ARVC/D even if they did not fulfill the diagnostic criteria. Two compound heterozygotes for mutations in the same gene and 1 subject carrying 3 different mutations showed a severe form of the disease with heart failure onset at a young age. Moreover, multiple-mutation carriers showed a higher prevalence of left ventricular involvement (P = .025) than single-mutation carriers., Conclusion: Occurrence of compound and double heterozygotes in ARVC/D index cases is particularly relevant to mutation screening strategy and to genetic counseling. Even if multiple-mutation carriers show a wide variability in clinical expression, the extent of the disease is higher compared to that in single-mutation carriers.

Background: Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is an inherited disorder typically caused by mutations in components of the cardiac desmosome. The prevalence and significance of desmosome mutations among patients with ARVD/C in North America have not been described previously. We report comprehensive desmosome genetic analysis for 100 North Americans with clinically confirmed or suspected ARVD/C., Methods and Results: In 82 individuals with ARVD/C and 18 people with suspected ARVD/C, DNA sequence analysis was performed on PKP2, DSG2, DSP, DSC2, and JUP. In those with ARVD/C, 52% harbored a desmosome mutation. A majority of these mutations occurred in PKP2. Notably, 3 of the individuals studied have a mutation in more than 1 gene. Patients with a desmosome mutation were more likely to have experienced ventricular tachycardia (73% versus 44%), and they presented at a younger age (33 versus 41 years) compared with those without a desmosome mutation. Men with ARVD/C were more likely than women to carry a desmosome mutation (63% versus 38%). A mutation was identified in 5 of 18 patients (28%) with suspected ARVD. In this smaller subgroup, there were no significant phenotypic differences identified between individuals with a desmosome mutation compared with those without a mutation., Conclusions: Our study shows that in 52% of North Americans with ARVD/C a mutation in one of the cardiac desmosome genes can be identified. Compared with those without a desmosome gene mutation, individuals with a desmosome gene mutation had earlier-onset ARVD/C and were more likely to have ventricular tachycardia.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is characterized by life-threatening ventricular arrhythmias and fibrofatty replacement of the cardiac tissue. Desmosomes are prominent cell-cell junctions found in a variety of tissues that resist mechanical stress, including the heart, and recruit the intermediate filament cytoskeleton to sites of cell-cell contact. Mutations in several desmosomal components including plakophilin-2 have been identified in ARVC patients; however, the molecular interactions disrupted by plakophilin-2 mutations are currently unknown. To understand the pathological basis of ARVC, the authors analyzed desmosome assembly and stability in epithelial cell lines expressing mutants of plakophilin-2 found in ARVC patients. Mutant plakophilin-2 proteins were unable to disrupt established desmosomes when expressed in an E-cadherin-expressing epithelial cell model; however, they were unable to initiate de novo assembly of desmosomes in an N-cadherin-expressing epithelial cell model. These studies expand our understanding of desmosome assembly and dynamics.

Objective: To sequence the exonic and splice site regions of the 4 desmosomal genes associated with the human form of familial arrhythmogenic right ventricular cardiomyopathy (ARVC) in Boxers with ARVC and identify a causative mutation., Animals: 10 unrelated Boxers with ARVC and 2 unaffected Labrador Retrievers (control dogs)., Procedures: Exonic and splice site regions of the 4 genes encoding the desmosomal proteins plakophilin-2, plakoglobin, desmoplakin, and desmoglein-2 were sequenced. Sequences were compared for nucleotide sequence changes between affected dogs and the published sequences for clinically normal dogs and between affected dogs and the control dogs. Base-pair changes were considered to be causative for ARVC if they were detected in an affected dog but not in unaffected dogs, and if they involved a conserved amino acid and changed that amino acid to one of a different polarity, acid-base status, or structure., Results: A causative mutation for ARVC in Boxers was not identified, although single nucleotide polymorphisms were detected in some affected dogs within exon 3 of the plakophilin-2 gene; exon 3 of the plakoglobin gene; exons 3 and 7 of the desmoglein-2 gene; and exons 6, 14, 15, and 24 of the desmoplakin gene. None of these changed the amino acid of the respective protein., Conclusions and Clinical Relevance: Mutations within the desmosomal genes associated with the development of ARVC in humans do not appear to be causative for ARVC in Boxers. Genomewide scanning for genetic loci of interest in dogs should be pursued.

Plakophilins 1-3 are members of the p120(ctn) family of armadillo-related proteins. The plakophilins have been characterized as desmosomal proteins, whereas p120(ctn) and the closely related delta-catenin, ARVCF and p0071 associate with adherens junctions and play essential roles in stabilizing cadherin mediated adhesion. Recent evidence suggests that plakophilins are essential components of the desmosomal plaque where they interact with desmosomal cadherins as well as the cytoskeletal linker protein desmoplakin. Plakophilins stabilize desmosomal proteins at the plasma membrane and therefore may function in a manner similar to p120(ctn) in the adherens junctions. The three plakophilins reveal distinct expression patterns, and although partially redundant in their function, mediate distinct effects on desmosomal adhesion. Besides a structural role, a function in signaling has been postulated in analogy to other armadillo proteins such as beta-catenin. At least plakophilins 1 and 2 are also localized in the nucleus, and all three proteins occur in a cytoplasmic pool. This review aims to summarize the current knowledge of plakophilin function in the context of cell adhesion, signaling and their putative role in diseases.

Desmosomes are highly organized intercellular junctions that provide mechanical integrity to tissues by anchoring intermediate filaments to sites of strong adhesion. These cell-cell adhesion junctions are found in skin, heart, lymph nodes and meninges. Over the last 8 years, several naturally occurring human gene mutations in structural components of desmosomes have been reported. These comprise autosomal dominant or recessive mutations in plakophilin 1, plakophilin 2, desmoplakin, plakoglobin, desmoglein 1, desmoglein 4 and corneodesmosin. These discoveries have often highlighted novel or unusual phenotypes, including abnormal skin fragility and differentiation, and developmental anomalies of various ectodermal appendages, especially hair. Some desmosomal gene mutations may also result in cardiac disease, notably cardiomyopathy. This article describes the spectrum of clinical features that may be found in the inherited disorders of desmosomes and highlights the key functions of several of the desmosomal proteins in tissue adhesion and cell biology.