The overall goal of this application is to examine the mechanisms controlling plakophilin-3 incorporation into the desmosomal plaque and in turn regulate epithelial cell migration. Desmosomes are prominent cadherin based cell-cell adhesive junctions found in epithelial tissues such as the skin and oral mucosa. These junctions associate with the keratin intermediate filament cytoskeleton and provide a means to link the cytoskeletal systems between adjacent cells in an epithelial tissue. Therefore, desmosomes provide epithelial tissues with a means to withstand mechanical stress. During normal physiologic processes epithelial cells must re-model their adhesive contacts to allow cells to migrate in a controlled manner. Re- epithelialization of cutaneous wounds by keratinocytes at the wound edge is an example where controlled keratinocyte migration is required. The mechanisms that coordinate the re-modeling of the desmosome are largely unknown. Plakophilins are desmosomal plaque proteins that assist in clustering the desmosomal cadherins as well as recruit keratin intermediate filaments to the desmosomal plaque. We have recently identified a novel plakophilin-3 binding partner (stratifin) that binds phosphorylated plakophilin-3 and in turn restricts plakophilin-3 localization to the desmosomal plaque. Reduced stratifin expression leads to increased exchange of plakophilin-3 with the desmosomal plaque, decreased desmosomal adhesion and increased cell migration. Our preliminary studies suggest that protein kinase A phosphorylates plakophilin-3 to create the stratifin binding motif and that plakophilin-3 interacts with a protein phosphatase 2A regulatory subunit to recruit this phosphatase to plakophilin-3 and potentially inhibit stratifin association. These preliminary studies led us to hypothesize plakophilin-3 incorporation into the desmosomal plaque and desmosomal adhesion are regulated by PKA and PP2A. We will test this hypothesis by delineating the effects of PKA and PP2A activity on stratifin association with plakophilin-3 and by examining the effect of altering desmosomal adhesion on cell migration. Additionally we will expand our studies into the broader regulation of additional plakophilin isoforms by other 14-3-3 proteins. At the completion of these studies we expect to better understand the mechanisms and signaling inputs controlling desmosome dynamics and cell migration.
The goal of this project is to delineate mechanisms affecting assembly and adhesive strength of desmosomal cell-cell adhesive junctions and to investigate how changes in cell-cell adhesion affect epithelial cell-cell migration. We will utilize cell cultue based assays and live cell microscopy to determine the mechanisms controlling desmosome dynamics in migrating epithelial cells.