Plakoglobin domains that define its association with the desmosomal cadherins and the classical cadherins: identification of unique and shared domains.

Two cell-cell junctions, the adherens junction and the desmosome, are prominent in epithelial cells. These junctions are composed of transmembrane cadherins which interact with cytoplasmic proteins that serve to link the cadherin to the cytoskeleton. One component of both adherens junctions and desmosomes is plakoglobin. In the adherens junction plakoglobin interacts with both the classical cadherin and with alpha-catenin. Alpha-catenin in turn interacts with microfilaments. The role plakoglobin plays in the desmosome is not well understood. Plakoglobin interacts with the desmosomal cadherins, but how and if this mediates interactions with the intermediate filament cytoskeleton is not known. Here we compare the domains of plakoglobin that allow it to associate with the desmosomal cadherins with those involved in interactions with the classical cadherins. We show that three sites on plakoglobin are involved in associations with the desmosomal cadherins. A domain near the N terminus is unique to the desmosomal cadherins and overlaps with the site that interacts with alpha-catenin, suggesting that there may be competition between alpha-catenin and the desmosomal cadherins for interactions with plakoglobin. In addition, a central domain is shared with regions used by plakoglobin to associate with the classical cadherins. Finally, a domain near the C terminus is shown to strongly modulate the interactions with the desmosomal cadherins. This latter domain also contributes to the association of plakoglobin with the classical cadherins.