Lateral Clustering of Cadherin-4 without Homophilic Interaction: Possible Involvement in the Concentration Process at Cell–Cell Adhesion Sites as Well as in the Cell Adhesion Activity

Abstract

It is thought that the concentration of classic cadherins at cell–cell adhesion sites is essential for generating strong cell–cell adhesion activity, but the mechanism is not well understood. To clarify the structural basis of the concentration process and the cell adhesion activity, we constructed various mutants of cadherin-4 and examined the adhesion properties of the transfectants. A deletion mutant lacking the entire cytoplasmic domain had weak, but significant Ca2+-dependent cell adhesion activity. Interestingly, the deletion mutant showed intrinsic cluster formation in the absence of cell–cell adhesion, possible lateral cluster formation. The cytoplasmic domain-deleted cadherin-4 containing the mutation of Trp-2 to Ala, which is known to inhibit the strand dimer formation required for the cell–cell adhesion, retained the possible activity of lateral cluster formation, supporting this notion. These results suggest that the extracellular domain has intrinsic activity of lateral cluster formation. Indeed, deletion of a cadherin repeat in the extracellular domain significantly reduced or abolished the lateral cluster formation as well as the concentration of cadherin-4 at cell–cell contact sites and cell adhesion activity. When transfectants of the cytoplasmic domain-deleted cadherin-4 made cell–cell contact and formed intimate cell–cell adhesion, the lateral clusters of cadherin-4 initially gathered at cell–cell contact sites, and a smooth linear concentration was gradually formed along the cell–cell adhesion interface. The results suggest that the lateral cluster formation is involved in the concentration process of cadherin-4 at cell–cell adhesion sites, hence in the strong cell adhesion activity of cadherin-4 as well.