Characterization of E-cadherin-containing junctions involving skin- derived dendritic cells

Adherens junctions are sites of contact between epithelial cells in which adhesion is mediated by homophilic interactions of classical cadherins that are linked to the cytoskeleton via catenins. E-cadherin constitutes the major adhesion molecule in adherens junctions of keratinocytes (KC) and mediates the binding of Langerhans cells to KC in vitro. To characterize structures responsible for E-cadherin-mediated binding of Langerhans cells, we utilized Langerhans cells-like fetal skin-derived dendritic cells (FSDDC) capable of E-cadherin-mediated adhesion. Confocal microscopy of FSDDC aggregates demonstrated colocalization of E-cadherin and catenins to areas of cell-cell contact. Immunoprecipitation confirmed a physical association of E- cadherin with intracellular catenins (α-, β-, γ-catenin/plakoglobin and p120(CAS)). Transmission electron microscopy of FSDDC aggregates revealed structures with features of adherens junctions in areas of cell-cell contact, and post-embedding immunoelectron microscopy localized β-catenin to these regions. To characterize junctions that accounted for the adhesion of Langerhans cells-like dendritic cells and KC, disaggregated FSDDC were cocultured with primary murine KC. Transmission electron microscopy analysis of cocultures demonstrated FSDDC-KC contacts that were analogous to those seen in FSDDC aggregates. Confocal microscopy demonstrated focal accumulations of E-cadherin and colocalization of β-catenin in areas of contact between KC and immature (Langerhans cell-like) dendritic cells, but not in areas of contact between KC and mature (lymph node dendritic cell- like) dendritic cells. E-cadherin in Langerhans cells appears to be localized in structures that resemble adherens junctions formed by nonpolarized epithelial cells. Loss of ability to form or maintain these structures after the induction of Langerhans cells activation/maturation likely results in the attenuation of Langerhans cells-KC adhesion that preceeds Langerhans cells emigration from the epidermis.