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1.  A novel desmocollin-2 mutation reveals insights into the molecular link between desmosomes and gap junctions 
Heart Rhythm  2011;8(5):711-718.
Background
Cellular adhesion mediated by cardiac desmosomes is a prerequisite for proper electric propagation mediated by gap junctions in the myocardium. However, the molecular principles underlying this interdependence are not fully understood.
Objective
The purpose of this study was to determine potential causes of right ventricular conduction abnormalities in a patient with borderline diagnosis of arrhythmogenic right ventricular cardiomyopathy.
Methods
To assess molecular changes, the patient's myocardial tissue was analyzed for altered desmosomal and gap junction (connexin43) protein levels and localization. In vitro functional studies were performed to characterize the consequences of the desmosomal mutations.
Results
Loss of plakoglobin signal was evident at the cell junctions despite expression of the protein at control levels. Although the distribution of connexin43 was not altered, total protein levels were reduced and changes in phosphorylation were observed. The truncation mutant in desmocollin-2a is deficient in binding plakoglobin. Moreover, the ability of desmocollin-2a to directly interact with connexin43 was abolished by the mutation. No pathogenic potential of the desmoglein-2 missense change was identified.
Conclusion
The observed abnormalities in gap junction protein expression and phosphorylation, which precede an overt cardiac phenotype, likely are responsible for slow myocardial conduction in this patient. At the molecular level, altered binding properties of the desmocollin-2a mutant may contribute to the changes in connexin43. In particular, the newly identified interaction between the desmocollin-2a isoform and connexin43 provides novel insights into the molecular link between desmosomes and gap junctions.
doi:10.1016/j.hrthm.2011.01.010
PMCID: PMC3085091  PMID: 21220045
Cardiomyopathy; Conduction; Connexin43; Desmocollin-2; Desmoglein-2; Desmosome; Functional studies; Gap junction; Mutation; Plakoglobin; ARVC, arrhythmogenic right ventricular cardiomyopathy; Cx43, connexin43; DAPI, 4′,6-diamidino-2-phenylindole; DSC2, desmocollin-2; DSG2, desmoglein-2; DSP, desmoplakin; GFP, green fluorescent protein; GST, glutathione-S-transferase; ICS, intracellular cadherin segment; PG, plakoglobin; PKP2, plakophilin-2; RV, right ventricle; YFP, yellow fluorescent protein
2.  Mechanistic insights into arrhythmogenic right ventricular cardiomyopathy caused by desmocollin-2 mutations 
Cardiovascular Research  2010;90(1):77-87.
Aims
Recent immunohistochemical studies observed the loss of plakoglobin (PG) from the intercalated disc (ID) as a hallmark of arrhythmogenic right ventricular cardiomyopathy (ARVC), suggesting a final common pathway for this disease. However, the underlying molecular processes are poorly understood.
Methods and results
We have identified novel mutations in the desmosomal cadherin desmocollin 2 (DSC2 R203C, L229X, T275M, and G371fsX378). The two missense mutations (DSC2 R203C and T275M) have been functionally characterized, together with a previously reported frameshift variant (DSC2 A897fsX900), to examine their pathogenic potential towards PG's functions at the ID. The three mutant proteins were transiently expressed in various cellular systems and assayed for expression, processing, localization, and binding to other desmosomal components in comparison to wild-type DSC2a protein. The two missense mutations showed defects in proteolytic cleavage, a process which is required for the functional activation of mature cadherins. In both cases, this is thought to cause a reduction of functional DSC2 at the desmosomes in cardiac cells. In contrast, the frameshift variant was incorporated into cardiac desmosomes; however, it showed reduced binding to PG.
Conclusion
Despite different modes of action, for all three variants, the reduced ability to provide a ligand for PG at the desmosomes was observed. This is in agreement with the reduced intensity of PG at these structures observed in ARVC patients.
doi:10.1093/cvr/cvq353
PMCID: PMC3058729  PMID: 21062920
Arrhythmogenic right ventricular cardiomyopathy; Desmocollin-2; Desmosome; Functional studies; Mutation
3.  Novel missense mutations in exon 15 of desmoglein-2: Role of the intracellular cadherin segment in arrhythmogenic right ventricular cardiomyopathy? 
Heart Rhythm  2010;7(10):1446-1453.
Background
The diagnosis of arrhythmogenic right ventricular cardiomyopathy can be challenging. Disease-causing mutations in desmosomal genes have been identified. A novel diagnostic feature, loss of immunoreactivity for plakoglobin from the intercalated disks, recently was proposed.
Objective
The purpose of this study was to identify two novel mutations in the intracellular cadherin segment of desmoglein-2 (G812S and C813R in exon 15). Co-segregation of the G812S mutation with disease expression was established in a large Caucasian family. Endomyocardial biopsies of two individuals showed reduced plakoglobin signal at the intercalated disk.
Methods
To understand the pathologic changes occurring in the diseased myocardium, functional studies on three mutations in exon 15 of desmoglein-2 (G812C, G812S, C813R) were performed.
Results
Localization studies failed to detect any differences in targeting or stability of the mutant proteins, suggesting that they act via a dominant negative mechanism. Binding assays were performed to probe for altered binding affinities toward other desmosomal proteins, such as plakoglobin and plakophilin-2. Although no differences were observed for the mutated proteins in comparison to wild-type desmoglein-2, binding to plakophilin-2 depended on the expression system (i.e., bacterial vs mammalian protein expression). In addition, abnormal migration of the C813R mutant protein was observed in gel electrophoresis.
Conclusion
Loss of plakoglobin immunoreactivity from the intercalated disks appears to be the endpoint of complex pathologic changes, and our functional data suggest that yet unknown posttranslational modifications of desmoglein-2 might be involved.
doi:10.1016/j.hrthm.2010.08.007
PMCID: PMC2994644  PMID: 20708101
Arrhythmogenic right ventricular cardiomyopathy; Desmoglein-2; Desmosome; Genetics; Missense mutation; Plakophilin-2; ARVC, arrhythmogenic right ventricular cardiomyopathy; Cx43, connexin43; DSC2, desmocollin-2; DSG2, desmoglein-2; DSP, desmoplakin; GFP, green fluorescent protein; GST, glutathione-S-transferase; ICS, intracellular cadherin segment; PG, plakoglobin; PKP2, plakophilin-2; RV, right ventricle

Results 1-3 (3)