Identification of Protein Kinase A as a Regulator of Desmosomal Assembly

Objectives: Desmosomes are prominent cell-cell adhesive junctions found in a variety of complex epithelial tissues, including the oral epithelium. Plakophilin-3 is a cytoplasmic component of the desmosome and plays an important role in assembly and clustering of the desmosome at the plasma membrane. Previous work suggests that phosphorylation of plakophilin-3 regulates 14-3-3 sigma binding and affects plakophilin-3 incorporation into the desmosomal structure. In this study we sought to identify the kinase that acts on plakophilin-3 to create a 14-3-3 binding site and regulate desmosome assembly.
Methods: We generated recombinant plakophilin-3 proteins to be used as in vitro kinase assay substrates. Wild type plakophilin-3 and plakophilin-3 harboring a serine to alanine mutation at amino acid 285 were tested. Additionally we examined the phosphorylation of plakophilin-3 at serine 285 in cells treated with protein kinase A activators and inhibitors.
Results: Protein kinase A phosphorylated plakophilin-3 at serine 285 in vitro and this phosphorylation was not observed when plakophilin-3 S285A was used as a substrate. Cells treated with pharmacologic activators of protein kinase A showed an increase in phosphorylation of plakophilin-3 at serine 285.
Conclusions: These studies suggest that plakophilin-3 is a physiologic target of protein kinase A signaling and protein kinase A is a potential novel regulator of desmosome dynamics in epithelial tissues