Direct binding of cell polarity protein PAR-3 to cell-cell adhesion molecule nectin at neuroepithelial cells of developing mouse.

PAR-3 is a cell polarity protein that localizes at tight junctions (TJs) by direct binding to an immunoglobulin (Ig)-like cell-cell adhesion molecule JAM-1 in mammalian epithelial cells. Another Ig-like cell-cell adhesion molecule nectin plays a role in the localization of JAM-1 at TJs in epithelial cells. Nectin furthermore plays a role in the organization of adherens junctions (AJs) and TJs. Nectin comprises a family of four members, nectin-1, -2, -3, and -4. Nectins are associated with the actin cytoskeleton through afadin, of which the PDZ domain binds to nectins through their C-terminal four amino acids. We show here that PAR-3 binds to nectin-1 and -3 in neuroepithelial cells of the embryonic telencephalon, which are equipped with AJs, but not with typical TJs. Nectin-1, -2, -3, and afadin, but not JAM-1, were concentrated at AJs in neuroepithelial cells of the embryonic telencephalon at E13.5 and PAR-3 co-localized with nectins. PAR-3 was co-immunoprecipitated with nectin-1 and -3, but not with nectin-2 or JAM-1, from the mouse whole brain at E13.5. Recombinant PAR-3 stoichiometrically bound to recombinant nectin-1 and -3. The first one of the three PDZ domains of PAR-3 bound to the C-terminal four amino acids of nectin-1 and -3. The affinities of PAR-3 and afadin for nectin-1 and -3 were similar. Cadherin-deficient L cells expressing nectin-1 and -3 formed nectin-1- and -3-based cell-cell junctions, respectively, where PAR-3 as well as afadin was recruited. These results indicate that nectin-1 and -3 are involved in the localization of PAR-3 at AJs in the neuroepithelial cells of the embryonic telencephalon.