Regulation of the Assembly and Adhesion Activity of E-Cadherin by Nectin and Afadin for the Formation of Adherens Junctions in MDCK Cells

The Ca-independent immunoglobulin-like molecule nectin first forms cell-cell adhesions and then assembles cadherin at nectin-based cell-cell adhesion sites, resulting in the formation of adherens junctions (AJs). Afadin is a nectinand actin filament-binding protein that connects nectin to the actin cytoskeleton. Here, we studied the roles and modes of action of nectin and afadin in the formation of AJs in cultured MDCK cells. The trans-interaction of nectin assembled E-cadherin, which was associated with p120, β-catenin, and α-catenin. However, the assembled E-cadherin showed weak cell-cell adhesion activity, presumably the non-trans-interacting form, at the nectin-based cell-cell adhesion sites in an afadin-independent manner. The assembly was mediated by the IQGAP1-dependent actin cytoskeleton, which was organized by Cdc42 and Rac small G proteins that were activated by the action of trans-interacting nectin through c-Src and Rap1 small G protein in an afadin-independent manner. However, Rap1 bound to afadin, and this Rap1-afadin complex then interacted with p120 associated with non-trans-interacting E-cadherin, thereby causing the trans-interaction of E-cadherin. Thus, nectin regulates the assembly and cell-cell adhesion activity of E-cadherin through afadin, nectin signaling, and p120 for the formation of AJs in MDCK cells.