Different effects of dominant negative mutants of desmocollin and desmoglein on the cell-cell adhesion of keratinocytes

Desmosomes contain two types of cadherin: desmocollin (Dsc) and desmoglein (Dsg). In this study, we examined the different roles that Dsc and Dsg play in the formation of desmosomes, by using dominant-negative mutants. We con structed recombinant adenoviruses (Ad) containing truncated mutants of E-ca dherin, desmocollin 3a, and desmoglein 3 lacking a large part of their extr acellular domains (Ecad Delta EC, Dsc3s Delta EC, Dsg3 Delta EC), using the Cre-loxP Ad system to circumvent the problem of the toxicity of the mutant s to virus-producing cells. When Dsc3a Delta EC Ad-infected HaCaT cells wer e cultured with high levels of calcium, E-cadherin and beta-catenin, which are marker molecules for the adherens junction, disappeared from the cell-c ell contact sites, and cell-cell adhesion was disrupted. This also occurred in the cells infected with Ecad Delta EC Ad. With Dsg3 Delta EC Ad infecti on, keratin insertion at the cell-cell contact sites was inhibited and desm oplakin, a marker of desmosomes, was stained in perinuclear dots while the adherens junctions remained intact. Dsc3a Delta EC Ad inhibited the inducti on of adherens junctions and the subsequent formation of desmosomes with th e calcium shift, while Dsg3 Delta EC Ad only inhibited the formation of des mosomes. To further determine whether Dsc3s Delta EC directly affected adhe rens junctions, mouse fibroblast L cells transfected,vith E-cadherin (LEC5) were infected with these mutant Ads. Both Ds3a Delta EC and Ecad Delta EC inhibited the cell-cell adhesion of LEGS cells, as determined by the cell a ggregation assay, while Dsg3 Delta EC did not. These results indicate that the dominant negative effects of Dsg3 Delta EC were restricted to desmosome s, while those of Dsc3a Delta EC were observed in both desmosomes and adher ens junctions. Furthermore, the cytoplasmic domain of Dsc3a Delta EC coprec ipitated both plakoglobin and beta-catenin in HaCaT cells. In addition, bet a-catenin was found to bind the endogenous Dsc in HaCaT cells. These findin gs lead us to speculate that Dsc interacts with components of the adherens junctions through beta-catenin, and plays a role in nucleating desmosomes a fter the adherens junctions have been established.