IDENTIFICATION OF THE PLAKOGLOBIN-BINDING DOMAIN IN DESMOGLEIN AND ITS ROLE IN PLAQUE ASSEMBLY AND INTERMEDIATE FILAMENT ANCHORAGE

The carboxyterminal cytoplasmic portions (tails) of desmosomal cadheri ns of both the desmoglein (Dsg) and desmocollin type are integral comp onents of the desmosomal plaque and are involved in desmosome assembly and the anchorage of intermediate-sized filaments. When additional Ds g tails were introduced by cDNA transfection into cultured human epith elial cells, in the form of chimeras with the aminoterminal membrane i nsertion domain of rat connexin32 (Co32), the resulting stably transfe cted cells showed a dominant-negative defect specific for desmosomal j unctions: despite the continual presence of all desmosomal proteins, t he endogenous desmosomes disappeared and the formation of Co32-Dsg chi meric gap junctions was inhibited. Using cell transfection in combinat ion with immunoprecipitation techniques, we have examined a series of deletion mutants of the Dsg1 tail in Co32-Dsg chimeras. We show that u pon removal of the last 262 amino acids the truncated Dsg tail still e ffects the binding of plakoglobin but not of detectable amounts of any catenin and induces the dominant-negative phenotype. However, further truncation or excision of the next 41 amino acids, which correspond t o the highly conserved carboxyterminus of the C-domain in other cadher ins, abolishes plakoglobin binding and allows desmosomes to reform. Th erefore, we conclude that this short segment provides a plakoglobin-bi nding site and is important for plaque assembly and the specific ancho rage of either actin filaments in adherens junctions or Ifs in desmoso mes.