POSTTRANSLATIONAL REGULATION OF PLAKOGLOBIN EXPRESSION - INFLUENCE OFTHE DESMOSOMAL CADHERINS ON PLAKOGLOBIN METABOLIC STABILITY

Desmosomes are adhesive intercellular junctions that act as cell surfa ce attachment sites for intermediate filaments. The desmosomal glycopr oteins, desmogleins and desmocollins, are members of the cadherin fami ly of adhesion molecules. In addition, desmoglein has been shown to co immunoprecipitate with the junctional protein plakoglobin. To characte rize further the interaction between plakoglobin and the desmosomal ca dherins, stable mouse fibroblast (L-cells) cell lines were generated t hat express plakoglobin, desmoglein and plakoglobin, or desmocollin an d plakoglobin. L-cell lines transfected with a plasmid encoding human plakoglobin expressed plakoglobin mRNA but very little plakoglobin pro tein. However plakoglobin protein was expressed at high levels in L-ce lls coexpressing either desmoglein or desmocollin. In addition, both d esmocollin and desmoglein were found to coimmunoprecipitate with plako globin. The transient expression of desmoglein in L-cell Lines express ing plakoglobin mRNA resulted in the formation of a complex between pl akoglobin and desmoglein and in the accumulation of plakoglobin protei n. Furthermore, the rate of plakoglobin protein degradation was decrea sed by 15-20-fold in cell Lines expressing either desmoglein or desmoc ollin. These results demonstrate that the desmosomal cadherins posttra nslationally regulate plakoglobin expression by decreasing the rate of plakoglobin degradation.