Dataset Information

Interactions of plakoglobin and beta-catenin with desmosomal cadherins: basis of selective exclusion of alpha- and beta-catenin from desmosomes.

ABSTRACT: Plakoglobin and beta-catenin are homologous armadillo repeat proteins found in adherens junctions, where they interact with the cytoplasmic domain of classical cadherins and with alpha-catenin. Plakoglobin, but normally not beta-catenin, is also a structural constituent of desmosomes, where it binds to the cytoplasmic domains of the desmosomal cadherins, desmogleins and desmocollins. Here, we report structural, biophysical, and biochemical studies aimed at understanding the molecular basis of selective exclusion of beta-catenin and alpha-catenin from desmosomes. The crystal structure of the plakoglobin armadillo domain bound to phosphorylated E-cadherin shows virtually identical interactions to those observed between beta-catenin and E-cadherin. Trypsin sensitivity experiments indicate that the plakoglobin arm domain by itself is more flexible than that of beta-catenin. Binding of plakoglobin and beta-catenin to the intracellular regions of E-cadherin, desmoglein1, and desmocollin1 was measured by isothermal titration calorimetry. Plakoglobin and beta-catenin bind strongly and with similar thermodynamic parameters to E-cadherin. In contrast, beta-catenin binds to desmoglein-1 more weakly than does plakoglobin. beta-Catenin and plakoglobin bind with similar weak affinities to desmocollin-1. Full affinity binding of desmoglein-1 requires sequences C-terminal to the region homologous to the catenin-binding domain of classical cadherins. Although pulldown assays suggest that the presence of N- and C-terminal beta-catenin "tails" that flank the armadillo repeat region reduces the affinity for desmosomal cadherins, calorimetric measurements show no significant effects of the tails on binding to the cadherins. Using purified proteins, we show that desmosomal cadherins and alpha-catenin compete directly for binding to plakoglobin, consistent with the absence of alpha-catenin in desmosomes.

SUBMITTER: Choi HJ

PROVIDER: S-EPMC2797248 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Interactions of plakoglobin and beta-catenin with desmosomal cadherins: basis of selective exclusion of alpha- and beta-catenin from desmosomes.

Choi Hee-Jung HJ Gross Julia C JC Pokutta Sabine S Weis William I WI

The Journal of biological chemistry 20090916 46

Plakoglobin and beta-catenin are homologous armadillo repeat proteins found in adherens junctions, where they interact with the cytoplasmic domain of classical cadherins and with alpha-catenin. Plakoglobin, but normally not beta-catenin, is also a structural constituent of desmosomes, where it binds to the cytoplasmic domains of the desmosomal cadherins, desmogleins and desmocollins. Here, we report structural, biophysical, and biochemical studies aimed at understanding the molecular basis of se ...[more]

PMID: 19759396

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Project description:Coxsackievirus B3 (CVB3) is the primary etiologic agent of viral myocarditis, a major heart disease that occurs predominantly in children and young adolescents. In the heart, intercalated disks (ICD) are important structural formations that connect adjacent cardiomyocytes to maintain cardiac architecture and mediate signal communication. Deficiency in ICD components, such as desmosome proteins, leads to heart dysfunction. ?-catenin, a component protein of desmosomes, normally binds directly to desmocollin-2 and desmoglein-2. In this study, we found that CVB3 infection downregulated ?-catenin at the protein level but not the mRNA level in mouse HL-1 cardiomyocytes. We further found that this reduction of ?-catenin protein is a result of ubiquitin proteasome-mediated degradation, since the addition of proteasome inhibitor MG132 inhibited ?-catenin downregulation. In addition, we found that desmocollin-2 and desmoglein-2 were cleaved by both viral protease 3C and virus-activated cellular caspase, respectively. These cleavages led to the release of bound ?-catenin from the desmosome into the cytosol, resulting in rapid degradation of ?-catenin. Since ?-catenin shares high sequence homology with ?-catenin in binding the TCF/LEF transcription factor, we further studied the effect of ?-catenin degradation on Wnt/?-catenin signaling. Luciferase assay showed that ?-catenin expression inhibited Wnt/?-catenin signaling. This finding was substantiated by qPCR to show that overexpression of ?-catenin downregulated transcription of Wnt signal target genes, c-myc and MMP9, while silencing ?-catenin upregulated these target genes. Finally, we demonstrated that ?-catenin expression inhibited CVB3 replication. In search for the underlying mechanism, we found that silencing ?-catenin caused down-regulation of interferon-? and its stimulated antiviral genes MDA5, MAVS, and ISG15. Taken together, our results indicate, for the first time, that CVB3 infection causes cardiomyocyte death through, at least in part, direct damage to the desmosome structure and reduction of ?-catenin protein, which in return promotes Wnt/?-catenin signaling and downregulates interferon-? stimulated immune responses.

Project description:Desmosomes are large, macromolecular protein assemblies that mechanically couple the intermediate filament cytoskeleton to sites of cadherin-mediated cell adhesion, thereby providing structural integrity to tissues that routinely experience large forces. Proper desmosomal adhesion is necessary for the normal development and maintenance of vertebrate tissues, such as epithelia and cardiac muscle, while dysfunction can lead to severe disease of the heart and skin. Therefore, it is important to understand the relationship between desmosomal adhesion and the architecture of the molecules that form the adhesive interface, the desmosomal cadherins (DCs). However, desmosomes are embedded in two plasma membranes and are linked to the cytoskeletal networks of two cells, imposing extreme difficulty on traditional structural studies of DC architecture, which have yielded conflicting results. Consequently, the relationship between DC architecture and adhesive function remains unclear. To overcome these challenges, we utilized excitation-resolved fluorescence polarization microscopy to quantify the orientational order of the extracellular and intracellular domains of three DC isoforms: desmoglein 2, desmocollin 2, and desmoglein 3. We found that DC ectodomains were significantly more ordered than their cytoplasmic counterparts, indicating a drastic difference in DC architecture between opposing sides of the plasma membrane. This difference was conserved among all DCs tested, suggesting that it may be an important feature of desmosomal architecture. Moreover, our findings suggest that the organization of DC ectodomains is predominantly the result of extracellular adhesive interactions. We employed azimuthal orientation mapping to show that DC ectodomains are arranged with rotational symmetry about the membrane normal. Finally, we performed a series of mathematical simulations to test the feasibility of a recently proposed antiparallel arrangement of DC ectodomains, finding that it is supported by our experimental data. Importantly, the strategies employed here have the potential to elucidate molecular mechanisms for diseases that result from defective desmosome architecture.

Dataset Information

Interactions of plakoglobin and beta-catenin with desmosomal cadherins: basis of selective exclusion of alpha- and beta-catenin from desmosomes.

Publications

Interactions of plakoglobin and beta-catenin with desmosomal cadherins: basis of selective exclusion of alpha- and beta-catenin from desmosomes.

Similar Datasets

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