Desmoplakin is a protein in humans that is encoded by the DSP gene. [5] [6] [7] Desmoplakin is a critical component of desmosome structures in cardiac muscle and epidermal cells, which function to maintain the structural integrity at adjacent cell contacts. In cardiac muscle, desmoplakin is localized to intercalated discs which mechanically couple cardiac cells to function in a coordinated syncytial structure. Mutations in desmoplakin have been shown to play a role in dilated cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy, where it may present with acute myocardial injury; [8] [9] striate palmoplantar keratoderma, Carvajal syndrome and paraneoplastic pemphigus.
Desmoplakin exists as two predominant isoforms; the first, known as "DPII", has molecular weight 260.0 kDa (2272 amino acids) and the second, known as "DPI", has molecular weight 332.0 kDa (2871 amino acids). [10] [11] These isoforms are identical except for the shorter rod domain in DPII. DPI is the predominant isoform expressed in cardiac muscle. [12] The DSP gene is located on chromosome 6p24.3, containing 24 exons and spanning approximately 45 kDa of genomic DNA. [13] Desmoplakin is a large desmosomal plaque protein that homodimerizes and adopts a dumbbell-shaped conformation. [13] The N-terminal globular head domain of desmoplakin is composed of a series of alpha helical bundles, and is required for both the localization to the desmosome and interaction with the N-terminal region of plakophilin 1 and plakoglobin as well as desmocollin and desmoglein. [14] This is further sub divided into a region called the "Plakin domain" made up of six spectrin repeat domains separated by SH3 domain. [15] A crystal structure of part of the plakin domain has been resolved, [16] while the entire plakin domain has been elucidated using small angle X-ray scattering which revealed a non-linear structure, an unexpected result considering spectrin repeats are observed in linear orientations. [17] The C-terminal region of desmoplakin is composed of three plakin repeat domains, termed A, B and C, which are essential for coalignment and binding of intermediate filaments. [14] [18] [19] Located at the most distal C-terminus of desmoplakin is a region rich in glycine–serine–arginine; it has been demonstrated that serine phosphorylation of this domain may modify desmoplakin-intermediate filament interactions. [20] In the mid-region of desmoplakin, a coiled-coil rod domain is responsible for homodimerization. [21]
Desmosomes are intercellular junctions that tightly link adjacent cells. Desmoplakin is an obligate component of functional desmosomes that anchors intermediate filaments to desmosomal plaques. In cardiomyocytes, desmoplakin forms desmosomal plaques with the intermediate filament desmin, whereas in endothelial cells cytokeratin type intermediate filaments are recruited, and vimentin in arachnoid and follicular dendritic cell types. [21] [22] Both types of intermediate filaments attach in a lateral fashion to desmoplakin to form the plaque. [23] In cardiac muscle, desmoplakin is localized to desmosomes in intercalated discs. Desmoplakin isoform DPI is highly expressed and is thought to play a role in both the assembly and stabilization of desmosomes; its role is critical, as desmoplakin knockout mice display embryonic lethality. [24] In mice overexpressing a C-terminal mutated desmoplakin protein, desmoplakin binding to desmin is disrupted in cardiac muscle and hearts display abnormal intercalated disc formation and structure. [25] Much has been learned regarding desmoplakin function from mutations in patients with arrhythmogenic right ventricular cardiomyopathy, where mutations in specific binding domains alter desmoplakin binding to plakoglobin or desmin and result in cell death and dysfunction. [26]
Mutations in this gene are the cause of several cardiomyopathies, including dilated cardiomyopathy [27] [28] and arrhythmogenic right ventricular cardiomyopathy. [25] [29] [30] [31] [32] [17] The presence of pathogenic mutations in this gene has been associated with episodes of acute myocardial injury, which may mimic episodes of myocarditis. [33] [34] Mutations in DSP have also been associated with striate palmoplantar keratoderma. [27] [31] [35] [36] [37] Carvajal syndrome results from an autosomal recessive mutation of a frameshift (7901delG) in DSP that results in a combination of above conditions, including dilated cardiomyopathy, keratoderma and woolly hair. [38] Patients with Carvajal syndrome often suffer from heart failure in teenage years. A case of compound heterozygosity for two DSP nonsense mutations resulting in lethal acantholytic epidermolysis bullosa has been reported. [39] [40] Autoantibodies to DSP are a hallmark of the autoimmune disease paraneoplastic pemphigus. [41] [42] Decreased desmoplakin expression has been found in patients with oropharyngeal cancer and breast cancer, which may alter cell-cell adhesion properties and propagate metastasis. [43] [44]
Desmoplakin has been shown to interact with:
Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate Branchiostoma.
A desmosome, also known as a macula adherens, is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes. Desmosomes are one of the stronger cell-to-cell adhesion types and are found in tissue that experience intense mechanical stress, such as cardiac muscle tissue, bladder tissue, gastrointestinal mucosa, and epithelia.
Arrhythmogenic cardiomyopathy (ACM), arrhythmogenic right ventricular dysplasia (ARVD), or arrhythmogenic right ventricular cardiomyopathy (ARVC), most commonly is an inherited heart disease.
Keratin 9 is a protein that in humans is encoded by the KRT9 gene.
Desmin is a protein that in humans is encoded by the DES gene. Desmin is a muscle-specific, type III intermediate filament that integrates the sarcolemma, Z disk, and nuclear membrane in sarcomeres and regulates sarcomere architecture.
Plectin is a giant protein found in nearly all mammalian cells which acts as a link between the three main components of the cytoskeleton: actin microfilaments, microtubules and intermediate filaments. In addition, plectin links the cytoskeleton to junctions found in the plasma membrane that structurally connect different cells. By holding these different networks together, plectin plays an important role in maintaining the mechanical integrity and viscoelastic properties of tissues.
Desmoglein-1 is a protein that in humans is encoded by the DSG1 gene. Desmoglein-1 is expressed everywhere in the skin epidermis, but mainly it is expressed in the superficial upper layers of the skin epidermis.
Desmoglein-2 is a protein that in humans is encoded by the DSG2 gene. Desmoglein-2 is highly expressed in epithelial cells and cardiomyocytes. Desmoglein-2 is localized to desmosome structures at regions of cell-cell contact and functions to structurally adhere adjacent cells together. In cardiac muscle, these regions are specialized regions known as intercalated discs. Mutations in desmoglein-2 have been associated with arrhythmogenic right ventricular cardiomyopathy and familial dilated cardiomyopathy.
Plakoglobin, also known as junction plakoglobin or gamma-catenin, is a protein that in humans is encoded by the JUP gene. Plakoglobin is a member of the catenin protein family and homologous to β-catenin. Plakoglobin is a cytoplasmic component of desmosomes and adherens junctions structures located within intercalated discs of cardiac muscle that function to anchor sarcomeres and join adjacent cells in cardiac muscle. Mutations in plakoglobin are associated with arrhythmogenic right ventricular dysplasia.
Desmocollin-2 is a protein that in humans is encoded by the DSC2 gene. Desmocollin-2 is a cadherin-type protein that functions to link adjacent cells together in specialized regions known as desmosomes. Desmocollin-2 is widely expressed, and is the only desmocollin isoform expressed in cardiac muscle, where it localizes to intercalated discs. Mutations in DSC2 have been causally linked to arrhythmogenic right ventricular cardiomyopathy.
Periplakin is a protein that in humans is encoded by the PPL gene.
Desmocollin-1 is a protein that in humans is encoded by the DSC1 gene.
Plakophilin-1 is a protein that in humans is encoded by the PKP1 gene.
Desmocollin-3 is a protein that in humans is encoded by the DSC3 gene.
Plakophilin-2 is a protein that in humans is encoded by the PKP2 gene. Plakophilin 2 is expressed in skin and cardiac muscle, where it functions to link cadherins to intermediate filaments in the cytoskeleton. In cardiac muscle, plakophilin-2 is found in desmosome structures located within intercalated discs. Mutations in PKP2 have been shown to be causal in arrhythmogenic right ventricular cardiomyopathy.
Envoplakin is a protein that in humans is encoded by the EVPL gene.
Plakophilin-3 is a protein that in humans is encoded by the PKP3 gene.
Desmocollins are a subfamily of desmosomal cadherins, the transmembrane constituents of desmosomes. They are co-expressed with desmogleins to link adjacent cells by extracellular adhesion. There are seven desmosomal cadherins in humans, three desmocollins and four desmogleins. Desmosomal cadherins allow desmosomes to contribute to the integrity of tissue structure in multicellular living organisms.
Naxos disease is a cutaneous condition characterized by a palmoplantar keratoderma. The prevalence of the syndrome is up to 1 in every 1000 people in the Greek islands.
Nikos Protonotarios was a Greek researcher and cardiologist who made fundamental contributions to the field of arrhythmogenic myocardial diseases.