Plays a role in tight junctions and adherens junctions. Homodimer (PubMed:17897942). Interacts with TJP1/ZO1 (PubMed:17897942). Interacts with occludin, SAFB and UBN1. Interaction with SAFB occurs in the nucleus. Interacts with SCRIB. Interacts with USP53 (via the C-terminal region) (By similarity). Interacts with claudins, including CLDN1, CLDN2, CLDN3, CLDN5 and CLDN7 (PubMed:12704386). Also nuclear under environmental stress conditions and in migratory endothelial cells and subconfluent epithelial cell cultures. This protein is found in epithelial cell junctions. Isoform A1 is abundant in the heart and brain. Detected in brain and skeletal muscle. It is present almost exclusively in normal tissues. Isoform C1 is expressed at high level in the kidney, pancreas, heart and placenta. Not detected in brain and skeletal muscle. Found in normal as well as in most neoplastic tissues. The disease may be caused by variants affecting distinct genetic loci, including the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Produced by alternative promoter usage. Produced by alternative splicing of isoform A1. Produced by alternative splicing of isoform A1. Produced by alternative promoter usage. Produced by alternative splicing of isoform C1. Belongs to the MAGUK family.