Acts as an important adapter that promotes epithelial cell polarity and tight junction formation via its interaction with DLG1. Involved in the assembly of protein complexes at sites of cell-cell contact. Heterodimer; able to heterodimerize via its C-terminal L27 domain with LIN7A, LIN7B and LIN7C. Forms a tripartite complex composed of DLG1, MPP7 and LIN7 (LIN7A or LIN7C). Interacts with DLG1 via its N-terminal L27 domain. Interacts with PALS1 and PATJ. In epidermal cells, detected primarily at the lateral cell membrane. Down-regulated in patients suffering of passive Heymann nephritis (at protein level). The phospho-regulated basic and hydrophobic (PRBH) motif is sufficient and important for interaction with phospholipids permitting cortical localization (PubMed:26481050). Phosphorylation of the PRBH motif by aPKC inhibits the association of the protein with the cortical membrane (PubMed:26481050). Phosphorylated by aPKC which promotes dissociation from the cell cortex. Belongs to the MAGUK family.