THE AMINO-TERMINAL DOMAIN OF DESMOPLAKIN BINDS TO PLAKOGLOBIN AND CLUSTERS DESMOSOMAL CADHERIN-PLAKOGLOBIN COMPLEXES

The desmosome is a highly organized plasma membrane domain that couple s intermediate filaments to the plasma membrane at regions of cell-cel l adhesion. Desmosomes contain two classes of cadherins, desmogleins, and desmocollins, that bind to the cytoplasmic protein plakoglobin. De smoplakin is a desmosomal component that plays a critical role in link ing intermediate filament networks to the desmosomal plaque, and the a mino-terminal domain of desmoplakin targets desmoplakin to the desmoso me. However, the desmosomal protein(s) that bind the amino-terminal do main of desmoplakin have not been identified. To determine if the desm osomal cadherins and plakoglobin interact with the amino-terminal doma in of desmoplakin, these proteins were co-expressed in L-cell fibrobla sts, cells that do not normally express desmosomal components. When ex pressed in L-cells, the desmosomal cadherins and plakoglobin exhibited a diffuse distribution. However, in the presence of an amino-terminal desmoplakin polypeptide (DP-NTP), the desmosomal cadherins and plakog lobin were observed in punctate clusters that also contained DP-NTP. I n addition, plakoglobin and DP-NTP were recruited to cell-cell interfa ces in L-cells co-expressing a chimeric cadherin with the E-cadherin e xtracellular domain and the desmoglein-1 cytoplasmic domain, and these cells formed structures that were ultrastructurally similar to the ou ter plaque of the desmosome. In transient expression experiments in CO S cells, the recruitment of DP-NTP to cell borders by the chimera requ ired co-expression of plakoglobin. Plakoglobin and DP-NTP co-immunopre cipitated when extracted from L-cells, and yeast two hybrid analysis i ndicated that DP-NTP binds directly to plakoglobin but not Dsg1. These results identify a role for desmoplakin in organizing the desmosomal cadherin-plakoglobin complex and provide new insights into the hierarc hy of protein interactions that occur in the desmosomal plaque.