Desmoglein 2 regulates cardiogenesis by restricting hematopoiesis in the developing murine heart.

Cardiac morphogenesis relies on intricate intercellular signaling. Altered signaling impacts cardiac function and is detrimental to embryonic survival. Here we report an unexpected regulatory role of the desmosomal cell adhesion molecule desmoglein 2 (Dsg2) on murine heart development. A large percentage of Dsg2-mutant embryos develop pericardial hemorrhage. Lethal myocardial rupture is occasionally observed, which is not associated with loss of cardiomyocyte contact but with expansion of abnormal, non-myocyte cell clusters within the myocardial wall. Two types of abnormal cell clusters can be distinguished: Type A clusters involve endocard-associated, round-shaped CD31+ cells, which proliferate and invade the myocardium. They acquire Runx1- and CD44-positivity indicating a shift towards a hematopoietic phenotype. Type B clusters expand subepicardially and next to type A clusters. They consist primarily of Ter119+ erythroid cells with interspersed Runx1+/CD44+ cells suggesting that they originate from type A cell clusters. The observed pericardial hemorrhage is caused by migration of erythrocytes from type B clusters through the epicardium and rupture of the altered cardiac wall. Finally, evidence is presented that structural defects of Dsg2-depleted cardiomyocytes are primary to the observed pathogenesis. We propose that cardiomyocyte-driven paracrine signaling, which likely involves Notch1, directs subsequent trans-differentiation of endo- and epicardial cells. Together, our observations uncover a hitherto unknown regulatory role of Dsg2 in cardiogenesis.

Further discussion on the association between desmoglein 2 and tumor size of non-small cell lung cancer.

We have read the article by Cai et al. and find there is a discrepancy between their data and conclusion. Their statement, "Specifically, DSG2 expression was associated with tumor size", is not supported by their own clinicopathological data and analysis. After reviewing some similar articles, we also found no available evidence showed a statistically significant association between them. Therefore, we would like to suggest Cai et al. to rectify the results they published.

Human adenovirus binding to host cell receptors: a structural view.

Human Adenoviruses (HAdVs) are a family of clinically and therapeutically relevant viruses. A precise understanding of their host cell attachment and entry mechanisms can be applied in inhibitor design and the construction of targeted gene delivery vectors. In this article, structural data on adenovirus attachment and entry are reviewed. HAdVs engage two types of receptors: first, an attachment receptor that is bound by the fibre knob protein protruding from the icosahedral capsid, and next, an integrin entry receptor bound by the pentameric penton base at the capsid vertices. Adenoviruses use remarkably diverse attachment receptors, five of which have been studied structurally in the context of HAdV binding: Coxsackie and Adenovirus Receptor, CD46, the glycans GD1a and polysialic acid, and desmoglein-2. Together with the integrin entry receptors, they display both symmetrical and asymmetrical modes of binding to the virus as demonstrated by the structural analyses reviewed here. The diversity of HAdV receptors contributes to the broad tropism of these viruses, and structural studies are thus an important source of information on HAdV-host cell interactions. The imbalance in structural data between the more and less extensively studied receptors remains to be addressed by future research.

Desmoglein 2 promotes vasculogenic mimicry in melanoma and is associated with poor clinical outcome.

Tumors can develop a blood supply not only by promoting angiogenesis but also by forming vessel-like structures directly from tumor cells, known as vasculogenic mimicry (VM). Understanding mechanisms that regulate VM is important, as these might be exploitable to inhibit tumor progression. Here, we reveal the adhesion molecule desmoglein 2 (DSG2) as a novel mediator of VM in melanoma. Analysis of patient-derived melanoma cell lines and tumor tissues, and interrogation of The Cancer Genome Atlas (TCGA) data, revealed that DSG2 is frequently overexpressed in primary and metastatic melanomas compared to normal melanocytes. Notably, this overexpression was associated with poor clinical outcome. DSG2+ melanoma cells self-organized into tube-like structures on Matrigel, indicative of VM activity, which was inhibited by DSG2 knockdown or treatment with a DSG2-blocking peptide. Mechanistic studies revealed that DSG2 regulates adhesion and cell-cell interactions during tube formation, but does not control melanoma cell viability, proliferation or motility. Finally, analysis of patient tumors revealed a correlation between DSG2 expression, VM network density and expression of VM-associated genes. These studies identify DSG2 as a key regulator of VM activity in human melanoma and suggest this molecule might be therapeutically targeted to reduce tumor blood supply and metastatic spread.

Crosstalk between Desmoglein 2 and Patched 1 accelerates chemical-induced skin tumorigenesis.

Aberrant activation of Hedgehog (Hh) signaling is causative of BCCs and has been associated with a fraction of SCCs. Desmoglein 2 (Dsg2) is an adhesion protein that is upregulated in many cancers and overexpression of Dsg2 in the epidermis renders mice more susceptible to squamous-derived neoplasia. Here we examined a potential crosstalk between Dsg2 and Hh signaling in skin tumorigenesis. Our findings show that Dsg2 modulates Gli1 expression, in vitro and in vivo. Ectopic expression of Dsg2 on Ptc1(+/lacZ) background enhanced epidermal proliferation and interfollicular activation of the Hh pathway. Furthermore, in response to DMBA/TPA, the Dsg2/Ptc1+/lacZ mice developed squamous lessons earlier than the WT, Ptc1(+/lacZ), and Inv-Dsg2 littermates. Additionally, DMBA/TPA induced BCC formation in all mice harboring the Ptc1(+/lacZ) gene and the presence of Dsg2 in Dsg2/Ptc1(+/lacZ) mice doubled the BCC tumor burden. Reporter analysis revealed activation of the Hh pathway in the BCC tumors. However, in the SCCs we observed Hh activity only in the underlying dermis of the tumors. Furthermore, Dsg2/Ptc1(+/lacZ) mice demonstrated enhanced MEK/Erk1/2 activation within the tumors and expression of Shh in the dermis. In summary, our results demonstrate that Dsg2 modulates Hh signaling, and this synergy may accelerate skin tumor development by different mechanisms.

Desmoglein as a target in skin disease and beyond.

Much of the original research on desmosomes and their biochemical components was through analysis of skin and mucous membranes. The identification of desmogleins 1 and 3, desmosomal adhesion glycoproteins, as targets in pemphigus, a fatal autoimmune blistering disease of the skin and mucous membranes, provided the first link between desmosomes, desmogleins, and human diseases. The clinical and histological similarities of staphylococcal scalded skin syndrome or bullous impetigo and pemphigus foliaceus led us to identify desmoglein 1 as the proteolytic target of staphylococcal exfoliative toxins. Genetic analysis of striate palmoplantar keratoderma and hypotrichosis identified their responsible genes as desmogleins 1 and 4, respectively. More recently, these fundamental findings in cutaneous biology were extended beyond the skin. Desmoglein 2, which is expressed earliest among the four isoforms of desmoglein in development and found in all desmosome-bearing epithelial cells, was found to be mutated in arrythmogenic right ventricular cardiomyopathy and has also been identified as a receptor for a subset of adenoviruses that cause respiratory and urinary tract infections. The story of desmoglein research illuminates how dermatological research, originally focused on one skin disease, pemphigus, has contributed to understanding the biology and pathophysiology of many seemingly unrelated tissues and diseases.

Epithelial junction opener JO-1 improves monoclonal antibody therapy of cancer.

The efficacy of monoclonal antibodies (mAb) used to treat solid tumors is limited by intercellular junctions which tightly link epithelial tumor cells to each another. In this study, we define a small, recombinant adenovirus serotype 3-derived protein, termed junction opener 1 (JO-1), which binds to the epithelial junction protein desmoglein 2 (DSG2). In mouse xenograft models employing Her2/neu- and EGFR-positive human cancer cell lines, JO-1 mediated cleavage of DSG2 dimers and activated intracellular signaling pathways which reduced E-cadherin expression in tight junctions. Notably, JO-1-triggered changes allowed for increased intratumoral penetration of the anti-Her2/neu mAb trastuzumab (Herceptin) and improved access to its target receptor, Her2/neu, which is partly trapped in tight junctions. This effect translated directly into increased therapeutic efficacy of trastuzumab in mouse xenograft models using breast, gastric, and ovarian cancer cells that were Her2/neu-positive. Furthermore, combining JO-1 with the EGFR-targeting mAb cetuximab (Erbitux) greatly improved therapeutic outcomes in a metastatic model of EGFR-positive lung cancer. A combination of JO-1 with an approach that triggered transient degradation of tumor stroma proteins elicited eradication of tumors. Taken together, our findings offer preclinical proof of concept to employ JO-1 in combination with mAb therapy.

Desmoglein 2 mutant mice develop cardiac fibrosis and dilation.

Desmosomes are cell-cell adhesion sites and part of the intercalated discs, which couple adjacent cardiomyocytes. The connection is formed by the extracellular domains of desmosomal cadherins that are also linked to the cytoskeleton on the cytoplasmic side. To examine the contribution of the desmosomal cadherin desmoglein 2 to cardiomyocyte adhesion and cardiac function, mutant mice were prepared lacking a part of the extracellular adhesive domain of desmoglein 2. Most live born mutant mice presented normal overall cardiac morphology at 2 weeks. Some animals, however, displayed extensive fibrotic lesions. Later on, mutants developed ventricular dilation leading to cardiac insufficiency and eventually premature death. Upon histological examination, cardiomyocyte death by calcifying necrosis and replacement by fibrous tissue were observed. Fibrotic lesions were highly proliferative in 2-week-old mutants, whereas the fibrotic lesions of older mutants showed little proliferation indicating the completion of local muscle replacement by scar tissue. Disease progression correlated with increased mRNA expression of c-myc, ANF, BNF, CTGF and GDF15, which are markers for cardiac stress, remodeling and heart failure. Taken together, the desmoglein 2-mutant mice display features of dilative cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, an inherited human heart disease with pronounced fibrosis and ventricular arrhythmias that has been linked to mutations in desmosomal proteins including desmoglein 2.

Desmoglein 2 is a receptor for adenovirus serotypes 3, 7, 11 and 14.

We have identified desmoglein-2 (DSG-2) as the primary high-affinity receptor used by adenoviruses Ad3, Ad7, Ad11 and Ad14. These serotypes represent key human pathogens causing respiratory and urinary tract infections. In epithelial cells, adenovirus binding of DSG-2 triggers events reminiscent of epithelial-to-mesenchymal transition, leading to transient opening of intercellular junctions. This opening improves access to receptors, for example, CD46 and Her2/neu, that are trapped in intercellular junctions. In addition to complete virions, dodecahedral particles (PtDds), formed by excess amounts of viral capsid proteins, penton base and fiber during viral replication, can trigger DSG-2-mediated opening of intercellular junctions as shown by studies with recombinant Ad3 PtDds. Our findings shed light on adenovirus biology and pathogenesis and may have implications for cancer therapy.

Desmoglein 2-mediated adhesion is required for intestinal epithelial barrier integrity.

The integrity of intercellular junctions that form the "terminal bar" in intestinal epithelium is crucial for sealing the intestinal barrier. Whereas specific roles of tight and adherens junctions are well known, the contribution of desmosomal adhesion for maintaining the intestinal epithelial barrier has not been specifically addressed. For the present study, we generated a desmoglein 2 antibody directed against the extracellular domain (Dsg2 ED) to test whether impaired Dsg2-mediated adhesion affects intestinal epithelial barrier functions in vitro. This antibody was able to specifically block Dsg2 interaction in cell-free atomic-force microscopy experiments. For in vitro studies of the intestinal barrier we used Caco2 cells following differentiation into tight enterocyte-like epithelial monolayers. Application of Dsg2 ED to Caco2 monolayers resulted in increased cell dissociation compared with controls in a dispase-based enterocyte dissociation assay. Under similar conditions, Dsg2 antibody significantly decreased transepithelial electrical resistance and increased FITC-dextran flux, indicating that Dsg2 interaction is critically involved in the maintenance of epithelial intestinal barrier functions. As revealed by immunostaining, this was due to Dsg2 ED antibody-induced rupture of tight junctions because tight junction proteins claudins 1, 4, and 5, occludin, and tight junction-associated protein zonula occludens-1 were partially removed from cell borders by Dsg2 ED treatment. Similar results were obtained by application of a commercial monoclonal antibody directed against the ED of Dsg2. Antibody-induced effects were blocked by absorption experiments using Dsg2-Fc-coated beads. Our data indicate that Dsg2-mediated adhesion affects tight junction integrity and is required to maintain intestinal epithelial barrier properties.

Myocyte necrosis underlies progressive myocardial dystrophy in mouse dsg2-related arrhythmogenic right ventricular cardiomyopathy.

Mutations in the cardiac desmosomal protein desmoglein-2 (DSG2) are associated with arrhythmogenic right ventricular cardiomyopathy (ARVC). We studied the explanted heart of a proband carrying the DSG2-N266S mutation as well as transgenic mice (Tg-NS) with cardiac overexpression of the mouse equivalent of this mutation, N271S-dsg2, with the aim of investigating the pathophysiological mechanisms involved. Transgenic mice recapitulated the clinical features of ARVC, including sudden death at young age, spontaneous ventricular arrhythmias, cardiac dysfunction, and biventricular dilatation and aneurysms. Investigation of transgenic lines with different levels of transgene expression attested to a dose-dependent dominant-negative effect of the mutation. We demonstrate for the first time that myocyte necrosis is the key initiator of myocardial injury, triggering progressive myocardial damage, including an inflammatory response and massive calcification within the myocardium, followed by injury repair with fibrous tissue replacement, and myocardial atrophy. These observations were supported by findings in the explanted heart from the patient. Insight into mechanisms initiating myocardial damage in ARVC is a prerequisite to the future development of new therapies aimed at delaying onset or progression of the disease.

Suprabasal Dsg2 expression in transgenic mouse skin confers a hyperproliferative and apoptosis-resistant phenotype to keratinocytes.

Desmoglein 2 (Dsg2), a component of the desmosomal cell-cell adhesion structure, has been linked to invasion and metastasis in squamous cell carcinomas. However, it is unknown whether--and if so how--Dsg2 contributes to the malignant phenotype of keratinocytes. In this study, we addressed the consequences of Dsg2 overexpression under control of the involucrin promoter (Inv-Dsg2) in the epidermis of transgenic mice. These mice exhibited epidermal hyperkeratosis with slightly disrupted early and late differentiation markers, but intact epidermal barrier function. However, Inv-Dsg2 transgene expression was associated with extensive epidermal hyperplasia and increased keratinocyte proliferation in basal and suprabasal epidermal strata. Cultured Inv-Dsg2 keratinocytes showed enhanced cell survival in the anchorage-independent state that was critically dependent on EGF receptor activation and NF-kappaB activity. Consistent with the hyperproliferative and apoptosis-resistant phenotype of Inv-Dsg2 transgenic keratinocytes, we observed enhanced activation of multiple growth and survival pathways, including PI 3-kinase/AKT, MEK-MAPK, STAT3 and NF-kappaB, in the transgenic skin in situ. Finally, Inv-Dsg2 transgenic mice developed intraepidermal skin lesions resembling precancerous papillomas and were more susceptible to chemically induced carcinogenesis. In summary, overexpression of Dsg2 in epidermal keratinocytes deregulates multiple signaling pathways associated with increased growth rate, anchorage-independent cell survival, and the development of skin tumors in vivo.

The area composita of adhering junctions connecting heart muscle cells of vertebrates. I. Molecular definition in intercalated disks of cardiomyocytes by immunoelectron microscopy of desmosomal proteins.

Among sarcomeric muscles the cardiac muscle cells are unique by, inter alia, a systemic and extended cell-cell contact structure, the intercalated disk (ID), comprising frequent and closely spaced arrays of plaque-coated cell-cell adhering junctions (AJs). As some of these junctions may look somewhat like desmosomes and others like fasciae adhaerentes, the dogma has emerged in the literature that IDs contain - like epithelial cells - both kinds of AJs formed by - for the most - mutually exclusive molecular ensembles. This, however, is not the case. In comprehensive immunoelectron microscopic studies of mammalian (human, bovine, rat, mouse) and non-mammalian (chicken, amphibia, fishes) heart muscle tissues, we have localized major constituents of the desmosomal plaques of polar epithelia, desmoplakin, plakophilin-2 and plakoglobin, as well as the desmosomal cadherins, desmoglein Dsg2 and desmocollin Dsc2, in both kinds of ID AJs, independent of the specific morphological appearance. The desmosomal molecules are not restricted to the desmosome-like-looking junctions but can also be detected in junctions appearing similar to the zonula or fascia adhaerens structures. These AJs of cardiac ID are therefore subsumed under the collective term area composita. We discuss our results with respect to the importance of ID junction molecules for the formation, maintenance and function of the heart, particularly in relation to recent findings that deletions of - or mutations in - genes encoding such proteins can cause severe, sometimes lethal damages.