The Head Domain of Plakophilin-1 Binds to Desmoplakin and Enhances Its Recruitment to Desmosomes

Abstract

The contribution of desmosomes to epidermal integrity is evident in the inherited blistering disorder associated with the absence of a functional gene for plakophilin-1. To define the function of plakophilin-1 in desmosome assembly, interactions among the desmosomal cadherins, desmoplakin, and the armadillo family members plakoglobin and plakophilin-1 were examined. In transient expression assays, plakophilin-1 formed complexes with a desmoplakin amino-terminal domain and enhanced its recruitment to cell-cell borders; this recruitment was not dependent on the equimolar expression of desmosomal cadherins. In contrast to desmoplakin-plakoglobin interactions, the interaction between desmoplakin and plakophilin-1 was not mediated by the armadillo repeat domain of plakophilin-1 but by the non-armadillo head domain, as assessed by yeast two-hybrid and recruitment assays. We propose a model whereby plakoglobin serves as a linker between the cadherins and desmoplakin, whereas plakophilin-1 enhances lateral interactions between desmoplakin molecules. This model suggests that epidermal lesions in patients lacking plakophilin-1 are a consequence of the loss of integrity resulting from a decrease in binding sites for desmoplakin and intermediate filaments at desmosomes.Desmosomes are intercellular adhesive junctions that act as anchorage points for intermediate filament networks. The desmosomal cadherins, desmogleins and desmocollins, bind directly to the cytoplasmic protein plakoglobin (1-3), a member of the armadillo gene family that includes the adherens junction protein ␤-catenin (4). The desmosomal cadherin-plakoglobin complex is coupled to the intermediate filament network by desmoplakin (5, 6), which binds to both plakoglobin and intermediate filaments (7-10).The disruption of desmosomes by gene ablation in experimental model systems (6,(11)(12)(13) or by autoimmune antibodies in human patients (14) severely compromises tissue integrity and function. Recently, the first human genetic disorders involving mutations in desmosomal genes have been reported. Haploinsufficiency of desmoplakin results in the disruption of intermediate filament interactions with desmosomes in palmoplantar epidermis (15). In addition, mutation of both alleles of plakophilin-1 (PKP-1) 1 and consequent loss of the protein causes epidermal fragility, perturbed desmoplakin localization, and detachment of intermediate filaments from the plasma membrane of keratinocytes (16). PKP-1 was originally identified as Band 6, a 75-kDa keratin-associated protein component of desmosomes in stratified tissues (17). PKP-1 is also part of the armadillo gene family (18 -22). In overlay assays, PKP-1 was recently found to bind to a number of desmosomal components, including desmoplakin and intermediate filament polypeptides (10). However, the mechanism by which PKP-1 contributes to desmosome assembly and attachment to intermediate filaments remains unknown.We report here that the non-armadillo head domain of PKP-1 binds directly to the amino-terminal domain of des...

Desmosomes and Intermediate Filaments: Their Consequences for Tissue Mechanics

“…This prevented Pemphigus vulgaris (PV)-IgG-mediated desmosome disruption (Tucker et al 2014), indicative of a very stable adhesive state. Moreover, PKP1 enhances desmosome size and number by laterally interacting with DSP in agreement with a postulated role of plaque proteins in mediating cadherin spacing (Kowalczyk et al 1999;Hatzfeld et al 2000;Bornslaeger et al 2001;Hatzfeld 2007). Thus, the desmosomal cadherins, as well as the plaque protein PKP1, cooperate to provide strong adhesion and stability under mechanical strain.…”

iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death

“…PKP2 is known to interact with the N-terminal amino acids 1-584 of desmoplakin (27); thus, the ability of iASPP to compete with PKP2 to interact with DSP-1(1-394) was tested. As expected, PKP2 interacted with DSP-1(1-394), and this interaction was not affected by the presence of iASPP (Fig.…”

Intercellular Connections in the Heart: The Intercalated Disc

“…In addition to ankyrin-G, plakophilin-2 interacts with PKC, which is necessary for phosphorylation and recruitment of desmoplakin to newly forming desmosomes in the developing heart and during repair of myocardial injury (reviewed in Garrod and Chidgey, 2008). Thus, through its multiple interactions, plakophilin-2 may serve as a scaffold to contribute to adhesion and signalling at the ID by facilitating the lateral interaction between desmosomes and adherens junctions (Kowalczyk et al, 1999). The critical roles of both plakoglobin and plakophilin-2 in desmosomal assembly and maintenance is evidenced by the severe phenotypes that relevant transgenic mice models exhibit and the different forms of heart disease associated with mutations in their respective genes (please see Tables 1 and 2).…”

“…2D; Franke et al, 1982). Through its coiled-coil region, desmoplakin has been suggested to form homodimers (Kowalczyk et al, 1994), while its NH 2 -terminal region binds to plakoglobins and plakophilins, targeting them to desmosomes (Bornslaeger et al, 1996;Bornslaeger et al, 2001;Holthofer et al, 2007;Kowalczyk et al, 1999). Its COOHterminal tail is composed of three plakin-repeat domains and a Gly-Ser-Arg rich motif; both shown to mediate binding to desmin (Choi et al, 2002;Getsios et al, 2004).…”

“…They possess five extracellular domains or cadherin repeats of ~110 amino acids and are separated by Ca 2+ binding motifs, which are necessary for dimerization (Fig 2B;Pokutta and Weis, 2007). A single-pass transmembrane domain and an intracellular anchoring segment follow the extracellular domains (Green and Simpson, 2007;Kowalczyk et al, 1999). Within their intracellular regions, desmogleins and desmocollins possess a cadherin-like sequence capable of binding catenins, or in the case of desmosomal cadherins, plakoglobin (Mathur et al, 1994).…”