DIRECT CA2-DEPENDENT HETEROPHILIC INTERACTION BETWEEN DESMOSOMAL CADHERINS, DESMOGLEIN AND DESMOCOLLIN, CONTRIBUTES TO CELL-CELL ADHESION()

Human fibrosarcoma cells, HT-1080, feature extensive adherens junction s, lack mature desmosomes, and express a single known desmosomal prote in, Desmoglein 2 (Dsg2). Transfection of these cells with bovine Desmo collin 1a (Dsc1a) caused dramatic changes in the subcellular distribut ion of endogenous Dsg2. Both cadherins clustered in the areas of the a dherens junctions, whereas only a minor portion of Dsg2 was seen in th ese areas in the parental cells. Deletion mapping showed that intact e xtracellular cadherin-like repeats of Dsc1a (Arg(1)-Thr(170)) are requ ired for the translocation of Dsg2. Deletion of the intracellular C-do main that mediates the interaction of Dsc1a with plakoglobin, or the C SI region that is involved in the binding to desmoplakin, had no effec t. Coimmunoprecipitation experiments of cell lysates stably expressing Dsc1a with anti-Dsc or -Dsg antibodies demonstrate that the desmosoma l cadherins, Dsg2 and Dsc1a, are involved in a direct Ca2+-dependent i nteraction. This conclusion was further supported by the results of so lid phase binding experiments. These showed that the Dsc1a fragment co ntaining cadherin-like repeats 1 and 2 binds directly to the extracell ular portion of Dsg in a Ca2+-dependent manner. The contribution of th e Dsg/Dsc interaction to cell-cell adhesion was tested by coculturing HT-1080 cells expressing Dsc1a with HT-1080 cells lacking Dsc but expr essing myc-tagged plakoglobin (MPg). In the latter cells, MPg and the endogenous Dsg form stable complexes. The observed specific coimmunopr ecipitation of MPg by anti-Dsc antibodies in coculture indicates that an intercellular interaction between Dsc1 and Dsg is involved in cell- cell adhesion.