Defining desmosomal plakophilin-3 interactions

Abstract

Plakophilin 3 (PKP3) is a recently described armadillo protein of the desmosomal plaque, which is synthesized in simple and stratified epithelia. We investigated the localization pattern of endogenous and exogenous PKP3 and fragments thereof. The desmosomal binding properties of PKP3 were determined using yeast two-hybrid, coimmunoprecipitation and colocalization experiments. To this end, novel mouse anti-PKP3 mAbs were generated. We found that PKP3 binds all three desmogleins, desmocollin (Dsc) 3a and -3b, and possibly also Dsc1a and -2a. As such, this is the first protein interaction ever observed with a Dsc-b isoform. Moreover, we determined that PKP3 interacts with plakoglobin, desmoplakin (DP) and the epithelial keratin 18. Evidence was found for the presence of at least two DP–PKP3 interaction sites. This finding might explain how lateral DP–PKP interactions are established in the upper layers of stratified epithelia, increasing the size of the desmosome and the number of anchoring points available for keratins. Together, these results show that PKP3, whose epithelial and epidermal desmosomal expression pattern and protein interaction repertoire are broader than those of PKP1 and -2, is a unique multiprotein binding element in the basic architecture of a vast majority of epithelial desmosomes.

Arrhythmogenic Right Ventricular Cardiomyopathy Plakophilin-2 Mutations Disrupt Desmosome Assembly and Stability

“…Plakophilins share a small region of conserved amino acid identity in the amino terminus termed the HR2 domain (Bonne et al 2003). The function of this domain is currently unclear ( Figure 5A); however, previous studies have suggested this domain in plakophilin-1 plays a role in mediating interactions with desmoplakin (Sobolik-Delmaire et al 2006).…”

“…Structurally, plakophilins are comprised of 9 armadillo repeats located in the carboxyl and amino termini that are largely unrelated to one another (Choi and Weis 2005). In addition, there is a relatively small amino acid sequence in the extreme amino terminus, termed the HR2 domain that is highly conserved among plakophilins and is not present in p120 (Bonne et al 2003). The functional significance of the HR2 domain is currently unknown.…”

The Desmosome

“…In support of this model, PKP1 is highly expressed in the suprabasal layers of the epidermis where desmosomes are larger and more numerous than in the lower layers of the tissue. In contrast, PKP3 overexpression does not result in larger desmosomes or an increase in desmosome number (Bonne et al 1999;Schmidt et al 1999;Bonne et al 2003). However, PKP3 interacts with the largest number of desmosomal proteins, including desmoplakin, plakoglobin, all three desmoglein proteins, Dsc 3a and 3b, and Dsc 1a and 2a (Hatzfeld 2007).…”

The p.A897KfsX4 frameshift variation in desmocollin-2 is not a causative mutation in arrhythmogenic right ventricular cardiomyopathy

“…25 Moreover, PKP1, for which strong in vitro association with the 'a' form of Dsc1 has been reported, 24 was also found to overlap with the 'b' form. 26 The possibility that Dscb isoforms contain a PKP-binding domain should be investigated further.…”