Plays a role in tight junctions and adherens junctions. Homodimer, and heterodimer with TJP1/ZO1 and UBN1. Interacts with SCRIB (By similarity). Interacts with occludin and SAFB. Interaction with SAFB occurs in the nucleus. Interacts with USP53 (via the C-terminal region) (By similarity). Also nuclear under environmental stress conditions and in migratory endothelial cells and subconfluent epithelial cell cultures. Phosphorylated. Belongs to the MAGUK family.