Dsg2 Upregulation as a Rescue Mechanism in Pemphigus.

In pemphigus vulgaris (PV), autoantibodies directed against the desmosomal cadherin desmoglein (Dsg) 3 cause loss of intercellular adhesion. It is known that Dsg3 interactions are directly inhibited by autoantibody binding and that Dsg2 is upregulated in epidermis of PV patients. Here, we investigated whether heterophilic Dsg2-Dsg3 interactions occur and would modulate PV pathogenesis. Dsg2 was upregulated in PV patients' biopsies and in a human ex vivo pemphigus skin model. Immunoprecipitation and cell-free atomic force microscopy (AFM) experiments demonstrated heterophilic Dsg2-Dsg3 interactions. Similarly, in Dsg3-deficient keratinocytes with severely disturbed intercellular adhesion Dsg2 was upregulated in the desmosome containing fraction. AFM revealed that Dsg2-Dsg3 heterophilic interactions showed binding frequency, strength, Ca2+-dependency and catch-bond behavior comparable to homophilic Dsg3-Dsg3 or homophilic Dsg2-Dsg2 interactions. However, heterophilic Dsg2-Dsg3 interactions had a longer lifetime compared to homophilic Dsg2-Dsg2 interactions and PV autoantibody-induced direct inhibition was significantly less pronounced for heterophilic Dsg2-Dsg3 interactions compared to homophilic Dsg3 interactions. In contrast, a monoclonal anti-Dsg2 inhibitory antibody reduced heterophilic Dsg2-Dsg3 and homophilic Dsg2-Dsg2 binding to the same degree and further impaired intercellular adhesion in Dsg3-deficient keratinocytes. Taken together, the data demonstrate that Dsg2 undergoes heterophilic interactions with Dsg3, which may attenuate autoantibody-induced loss of keratinocyte adhesion in pemphigus.

The desmosomal cadherin desmoglein-3 acts as a keratinocyte anti-stress protein via suppression of p53.

Desmoglein-3 (Dsg3), the Pemphigus Vulgaris (PV) antigen (PVA), plays an essential role in keratinocyte cell-cell adhesion and regulates various signaling pathways involved in the progression and metastasis of cancer where it is upregulated. We show here that expression of Dsg3 impacts on the expression and function of p53, a key transcription factor governing the responses to cellular stress. Dsg3 depletion increased p53 expression and activity, an effect enhanced by treating cells with UVB, mechanical stress and genotoxic drugs, whilst increased Dsg3 expression resulted in the opposite effects. Such a pathway in the negative regulation of p53 by Dsg3 was Dsg3 specific since neither E-cadherin nor desmoplakin knockdown caused similar effects. Analysis of Dsg3-/- mouse skin also indicated an increase of p53/p21WAF1/CIP1 and cleaved caspase-3 relative to Dsg3+/- controls. Finally, we evaluated whether this pathway was operational in the autoimmune disease PV in which Dsg3 serves as a major antigen involved in blistering pathogenesis. We uncovered increased p53 with diffuse cytoplasmic and/or nuclear staining in the oral mucosa of patients, including cells surrounding blisters and the pre-lesional regions. This finding was verified by in vitro studies where treatment of keratinocytes with PV sera, as well as a characterized pathogenic antibody specifically targeting Dsg3, evoked pronounced p53 expression and activity accompanied by disruption of cell-cell adhesion. Collectively, our findings suggest a novel role for Dsg3 as an anti-stress protein, via suppression of p53 function, and this pathway is disrupted in PV.

Desmoglein 3-Dependent Signaling Regulates Keratinocyte Migration and Wound Healing.

The desmosomal transmembrane adhesion molecules desmoglein 3 (Dsg3) and desmocollin 3 (Dsc3) are required for strong keratinocyte cohesion. Recently, we have shown that Dsg3 associates with p38 mitogen-activated protein kinase (p38MAPK) and suppresses its activity. Here, we further investigated the role of Dsg3-dependent control of p38MAPK function. Dsg3-deficient mice display recurrent spontaneously healing skin erosions. In lesional and perilesional biopsies, p38MAPK activation was detectable compared with control animals. This led us to speculate that Dsg3 regulates wound repair in a p38MAPK-dependent manner. Indeed, scratch-wounded keratinocyte monolayers exhibited p38MAPK activation and loss of Dsg3 in cells lining the wound edge. Human keratinocytes after silencing of Dsg3 as well as primary cells isolated from Dsg3 knockout animals exhibited accelerated migration, which was further corroborated in an ex vivo skin outgrowth assay. Importantly, migration was efficiently blocked by inhibition of p38MAPK, indicating that p38MAPK mediates the effects observed upon loss of Dsg3. In line with this, we show that levels of active p38MAPK associated with Dsc3 are increased in Dsg3-deficient cells. These data indicate that Dsg3 controls a switch from an adhesive to a migratory keratinocyte phenotype via p38MAPK inhibition. Thus, loss of Dsg3 adhesion may foster wound closure by allowing p38MAPK-dependent migration.

Inhibition of JNK in HaCaT cells induced tight junction formation with decreased expression of cytokeratin 5, cytokeratin 17 and desmoglein 3.

Epidermal keratinocytes proliferate in the basal layer, differentiate, migrate through the spinous layer, granular layer and cornified layer, and finally are peeled off from the surface of skin with layer-specific expression of differentiation markers, including cytokeratins and cell-cell junction proteins such as desmogleins. Basal cells express CK5, CK14 and Ki67. In contrast, the suprabasal cells in the spinous and granular layers express CK1 and CK10 without Ki67. Inhibition of c-Jun NH2-terminal protein kinase (JNK) in HaCaT cells, a human epidermal keratinocyte cell line, induced the formation of tight junctions, which occurs in the granular layer in vivo. These cells lost their expression of CK5 and CK17, exhibited decreased expression of desmoglein 3 and had no Ki67 labeling in the nucleus. These results suggest that inhibition of JNK causes HaCaT cells to differentiate from basal- and spinous-like cells to granular-like cells. The inhibition of JNK in HaCaT cells provides a useful in vitro model system to study the differentiation of epidermal keratinocytes.

DSG3 facilitates cancer cell growth and invasion through the DSG3-plakoglobin-TCF/LEF-Myc/cyclin D1/MMP signaling pathway.

Desmoglein 3 (DSG3) is a component of the desmosome, which confers strong cell-cell adhesion. Previously, an oncogenic function of DSG3 has been found in head neck cancer (HNC). Here, we investigated how this molecule contributes to the malignant phenotype. Because DSG3 is associated with plakoglobin, we examined whether these phenotypic alterations were mediated through the plakoglobin molecule. Immunoprecipitation and immunofluorescence staining revealed that DSG3 silencing disrupted its interaction with plakoglobin and induced plakoglobin translocation from the cytoplasm to the nucleus. Knockdown of DSG3 significantly increased the interaction of plakoglobin with the transcriptional factor TCF and suppressed the TCF/LEF transcriptional activity. These effects further conferred to reduced expression of the TCF/LEF downstream target genes, including c-myc, cyclin D1, and MMP-7. Functional analyses showed that DSG3 silencing reduced cell growth and arrested cells at G0/G1 phase. Besides, cell migration and invasion abilities were also decreased. These cellular results were confirmed using tumor xenografts in mice, as DSG3 silencing led to the suppressed tumor growth, plakoglobin translocation and reduced expression of TCF/LEF target genes in tumors. Therefore, our study shows that the desmosomal protein DSG3 additionally functions to regulate malignant phenotypes via nuclear signaling. In conclusion, we found that DSG3 functions as an oncogene and facilitates cancer growth and invasion in HNC cells through the DSG3-plakoglobin-TCF/LEF pathway.

Ectopic expression of epidermal antigens renders the lung a target organ in paraneoplastic pemphigus.

Paraneoplastic pemphigus (PNP) is an autoimmune disease of the skin and mucous membranes that can involve fatal lung complications. IgG autoantibodies target the cell adhesion molecules desmoglein (Dsg)3 and plakins, but the nature and targets of infiltrating T cells are poorly characterized. Moreover, the lung involvement in this skin Ag-specific autoimmune condition represents a paradox. To mimic autoimmunity in PNP, we grafted wild-type skin onto Dsg3(-/-) mice, which resulted in graft rejection and generation of anti-Dsg3 IgG and Dsg3-specific T cells. Transfer of splenocytes from these mice into Rag2(-/-) mice induced a combination of suprabasilar acantholysis and interface dermatitis, a histology unique to PNP. Furthermore, the recipient mice showed prominent bronchial inflammation of CD4(+) and CD8(+) T cells with high mortality. Intriguingly, ectopic Dsg3 expression was observed in the lungs of PNP mice, mirroring the observation that squamous metaplasia is often found in the lungs of PNP patients. Dsg3 and other epidermal Ags were ectopically expressed in the lungs after pulmonary injuries by naphthalene, which was sufficient for recruitment of Dsg3-specific CD4(+) T cells. These findings demonstrate that squamous metaplasia after pulmonary epithelial injury may play a crucial role in redirecting the skin-specific autoimmune reaction to the lungs in PNP.

Desmosomal adhesion and pemphigus vulgaris: the first half of the story.

Pemphigus vulgaris (PV) is a paradigm of autoimmune disease affecting intercellular adhesion. The mechanisms that lead to cell-cell detachment (acantholysis) have crucial therapeutic implications and are currently undergoing major scrutiny. The first part of this review focuses on the classical view of the pathogenesis of PV, which is dominated by the cell adhesion molecules of the desmosome, namely desmogleins (Dsgs). Cloning of the DSG3 gene, generation DSG3 knock-out mice and isolation of monoclonal anti-Dsg3 IgG have aided to clarify the pathogenic mechanisms of PV, which are in part dependent on the fate of desmosomal molecules. These include perturbation of the desmosomal network at the transcriptional, translational, and interaction level, kinase activation, proteinase-mediated degradation, and hyper-adhesion. By the use of PV models, translational research has in turn helped shed light into the basic structure, function, and dynamics of assembly of desmosomal cadherins. The combined efforts of basic and applied research has resulted in tremendous advance into the understanding of epidermal adhesion and helped debunk old myths on the supposedly unique role of desmogleins in the mechanisms of cell-cell detachment in PV.

The extent of desmoglein 3 depletion in pemphigus vulgaris is dependent on Ca(2+)-induced differentiation: a role in suprabasal epidermal skin splitting?

Pemphigus vulgaris (PV) is an autoimmune disease of the skin and mucous membranes and is characterized by development of autoantibodies against the desmosomal cadherins desmoglein (Dsg) 3 and Dsg1 and formation of intraepidermal suprabasal blisters. Depletion of Dsg3 is a critical mechanism in PV pathogenesis. Because we did not detect reduced Dsg3 levels in keratinocytes cultured for longer periods under high-Ca(2+) conditions, we hypothesized that Dsg depletion depends on Ca(2+)-mediated keratinocyte differentiation. Our data indicate that depletion of Dsg3 occurs specifically in deep epidermal layers both in skin of patients with PV and in an organotypic raft model of human epidermis incubated using IgG fractions from patients with PV. In addition, Dsg3 depletion and loss of Dsg3 staining were prominent in cultured primary keratinocytes and in HaCaT cells incubated in high-Ca(2+) medium for 3 days, but were less pronounced in HaCaT cultures after 8 days. These effects were dependent on protein kinase C signaling because inhibition of protein kinase C blunted both Dsg3 depletion and loss of intercellular adhesion. Moreover, protein kinase C inhibition blocked suprabasal Dsg3 depletion in cultured human epidermis and blister formation in a neonatal mouse model. Considered together, our data indicate a contribution of Dsg depletion to PV pathogenesis dependent on Ca(2+)-induced differentiation. Furthermore, prominent depletion in basal epidermal layers may contribute to the suprabasal cleavage plane observed in PV.

Transgenic rescue of desmoglein 3 null mice with desmoglein 1 to develop a syngeneic mouse model for pemphigus vulgaris.

BACKGROUND: An active disease mouse model of pemphigus vulgaris (PV) was developed using the adoptive transfer of splenocytes from Dsg3(-/-) mice with a mixed C57BL/6J (B6) and 129/Sv genetic background into B6-Rag2(-/-) mice. Further immunological investigation is needed to resolve the genetic mismatch between host and recipient mice. The B6-Dsg3(-/-) mice did not grow old enough to provide splenocytes, probably due to severe oral erosions, with resulting inhibition of food intake. OBJECTIVE: To rescue the B6-Dsg3(-/-) mice and to produce syngeneic PV model mice. METHODS: Transgenic expression of mouse Dsg1 was attempted to compensate for the genetic loss of Dsg3 using the keratin 5 promoter. We evaluated the compensatory ability of Dsg1 in vivo by comparing Dsg1(wt/wt), Dsg1(tg/wt), and Dsg1(tg/tg) mice. We generated a PV model via the adoptive transfer of B6-Dsg1(tg/tg)Dsg3(-/-) splenocytes to B6-Rag2(-/-) mice. RESULTS: Dsg1(tg/tg) and Dsg1(tg/wt) mice expressed ectopic Dsg1 on keratinocyte cell surfaces in the lower layers of the epidermis, oral epithelium, and telogen hair follicles. Ectopic Dsg1 blocked the pathogenic effects of AK23 anti-Dsg3 mAb, and improved the body weight loss, telogen hair loss, and survival rate dose-dependently. While the B6-Dsg1(wt/wt)Dsg3(-/-) mice died by week 2, over 80% of the B6-Dsg1(tg/tg)Dsg3(-/-) mice survived at week 6. Furthermore, the syngeneic PV model mice showed the characteristic phenotype, including stable anti-Dsg3 antibody production and suprabasilar acantholysis on histology. CONCLUSION: Transgenic expression of Dsg1 rescued the severe B6-Dsg3(-/-) phenotype and provided a syngeneic mouse model of PV, which may be a valuable tool for clarifying immunological mechanisms in autoimmunity and tolerance of Dsg3.

Confirmation of a disease model of pemphigus vulgaris: characterization and correlation between disease parameters in 90 mice.

Pemphigus vulgaris (PV) is a chronic autoimmune bullous disease associated with immunoglobulin G (IgG) autoantibodies against desmoglein 3 (Dsg3). Previously, a mouse model of PV was established by adoptive transfer of naive splenocytes from Dsg3(-/-) mice to Rag2(-/-) mice. The model is unique as Dsg3-specific naive lymphocytes from Dsg3(-/-) mice can be primed and activated by the endogenous Dsg3 in recipient mice, resulting in pathogenic anti-Dsg3 IgG without any active immunization. Here, we show that PV occurs after both intravenous (i.v.) and intraperitoneal (i.p.) transfer of naive splenocytes. We evaluated the robustness of the model by comparing engraftment as well as PV phenotype using several disease parameters. While engraftment of spleen cells was significantly better after i.p. transfer, anti-Dsg3 IgG antibody production, IgG deposition and disease score were comparable after both i.v. and i.p. cell transfer. Thus, transferred cells can be primed, activated and gain effector function. However, we detected heterogeneity in disease development, as only 46% of the mice developed hair loss, whereas 76% of the mice developed anti-Dsg3 IgG. We also tested cyclophosphamide in the model, as this drug is reported to be beneficial to PV patients. Cyclophosphamide significantly inhibited disease development in a preventive setting, and mice were free of symptoms 35 days after discontinuing the treatment. We have successfully confirmed the induction of PV after both i.v. and i.p. transfer. In addition, we have shown that this model can be used for evaluation of immunosuppressive drugs.

Subcellular localization of desmosomal components is different between desmoglein3 knockout mice and pemphigus vulgaris model mice.

BACKGROUND: The desmoglein 3 (Dsg3) knockout mouse and pemphigus vulgaris (PV) mouse model present a similar type of supra-basal acantholysis, even though the subcellular mechanism is considered to be completely different. OBJECTIVES: To detect changes in the desmosomal molecular composition in Dsg3-/- mice and PV model mice to highlight the precise mechanism for acantholysis at an ultrastructural level. METHODS: Using epithelia from Dsg3-/- mice, PV model mice, and their respective control mice, the desmosomal components were immunostained using a post-embedding immunogold labeling method, and their precise localization and the labeling density were statistically analyzed in the desmosomes before the occurrence of acantholysis. RESULTS: Positive findings were detected in desmoplakin and plakoglobin. In the Dsg3-/- mice, the localization of desmoplakin shifted 12.6nm toward the cytoplasm and the plakoglobin labeling density per desmosome decreased 31% in the desmosomes. In the PV model mice Desmoplakin shifted 22.7nm more distantly from the plasma membrane but the labeling density per desmosome showed no significant difference, including plakoglobin. Similar results were obtained when analyzing the desmosomes of spinous cells in the mid-epidermis. CONCLUSION: These results showed the functional blocking of Dsg3 by autoantibody binding and the genetic defect of Dsg3 to induce different changes in the cytoplasmic desmosomal plaque proteins. A decrease in the level of plakoglobin is therefore not involved in the acantholysis in the PV model mice. The desmoplakin shift from the desmosomal plaque, which is induced by autoantibody binding under in vivo conditions in the PV model mouse, could be an early molecular change before the occurrence of acantholysis.

A single helper T cell clone is sufficient to commit polyclonal naive B cells to produce pathogenic IgG in experimental pemphigus vulgaris.

The development of naive B cells into IgG-producing memory B cells requires cognate T cell-B cell interaction in Ag-specific immune responses. It is unknown whether a single T cell clone is sufficient or whether multiple clones are necessary to induce polyclonal IgG production in vivo. We addressed this issue using a mouse model of pemphigus vulgaris, a fatal autoimmune blistering skin disease caused by IgG autoantibodies against desmoglein (Dsg) 3. We previously isolated several Dsg3-reactive T cell clones from Dsg3(-/-) mice. Among these, two pathogenic T cell clones induced anti-Dsg3 IgG production and the development of a pemphigus phenotype when adoptively transferred with unprimed B cells from Dsg3(-/-) mice. IgG Abs harvested from recipient mice reacted with at least three parts of the extracellular domain of Dsg3, as determined using domain-swapped Dsg3/Dsg1 molecules. The anti-Dsg3 IgGs included at least two subclasses among IgG1, IgG2a, IgG2b, and IgG3 in each mouse. The anti-Dsg3 IgG induced by Dsg3-reactive T cell clones with primed B cells from Dsg3(-/-) mice also showed reactivity against different parts of the molecule, with a similar epitope distribution. Together, these results indicate that a single potent Dsg3-reactive T cell is sufficient to commit polyclonal naive B cells to produce pathogenic anti-Dsg3 IgG Abs and induce the PV phenotype. These findings provide an important framework for examining immunological mechanisms in Ab-mediated autoimmune diseases.

Significance of autoimmunity to non-desmoglein targets in pemphigus.

The pathogenesis of pemphigus vulgaris (PV) is a highly controversial, "hot" topic that has received considerable enrichment in recent years by both clinical and basic researchers. On the one hand, the classical view of desmogleins (Dsg) as main targets of this autoimmune disease is supported by the characterization of pathogenic anti-Dsg3 antibodies from both patients and animal models. On the other hand, fundamental doubt has been raised towards this monopathogenic view by several independent factors: (1) pemphigus lesions can be induced in Dsg3-knockout (KO) mice; (2) pemphigus sera contain multiple autoantibodies against different adhesion molecules and also cholinergic receptors; (3) experimental inhibition of PV IgG induced acantholysis can be obtained by interference with different signaling cascades regulating both calcium homeostasis and apoptosis; and (4) cholinergic agonists exhibit anti-acantholytic activity both in vitro and in vivo. The field is open for controlled clinical trials and further basic research to unfold the true story of the pemphigus enigma and provide the basis for a better treatment of pemphigus patients.