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

Abstract

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 constructed recombinant adenoviruses (Ad) containing truncated mutants of E-cadherin, desmocollin 3a, and desmoglein 3 lacking a large part of their extracellular domains (EcadΔEC, Dsc3aΔEC, Dsg3ΔEC), using the Cre-loxP Ad system to circumvent the problem of the toxicity of the mutants to virus-producing cells. When Dsc3aΔEC Ad-infected HaCaT cells were cultured with high levels of calcium, E-cadherin and β-catenin, which are marker molecules for the adherens junction, disappeared from the cell-cell contact sites, and cell-cell adhesion was disrupted. This also occurred in the cells infected with EcadΔEC Ad. With Dsg3ΔEC Ad infection, keratin insertion at the cell-cell contact sites was inhibited and desmoplakin, a marker of desmosomes, was stained in perinuclear dots while the adherens junctions remained intact. Dsc3aΔEC Ad inhibited the induction of adherens junctions and the subsequent formation of desmosomes with the calcium shift, while Dsg3ΔEC Ad only inhibited the formation of desmosomes. To further determine whether Dsc3aΔEC directly affected adherens junctions, mouse fibroblast L cells transfected with E-cadherin (LEC5) were infected with these mutant Ads. Both Dsc3aΔEC and EcadΔEC inhibited the cell-cell adhesion of LEC5 cells, as determined by the cell aggregation assay, while Dsg3ΔEC did not. These results indicate that the dominant negative effects of Dsg3ΔEC were restricted to desmosomes, while those of Dsc3aΔEC were observed in both desmosomes and adherens junctions. Furthermore, the cytoplasmic domain of Dsc3aΔEC coprecipitated both plakoglobin and β-catenin in HaCaT cells. In addition, β-catenin was found to bind the endogenous Dsc in HaCaT cells. These findings lead us to speculate that Dsc interacts with components of the adherens junctions through β-catenin, and plays a role in nucleating desmosomes after the adherens junctions have been established.