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 (By similarity). 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 (By similarity). In epidermal cells, detected primarily at the lateral cell membrane. The phospho-regulated basic and hydrophobic (PRBH) motif is sufficient and important for interaction with phospholipids permitting cortical localization (By similarity). Phosphorylation of the PRBH motif by aPKC inhibits the association of the protein with the cortical membrane (By similarity). Phosphorylated by aPKC which promotes dissociation from the cell cortex. Belongs to the MAGUK family. Contaminating sequence. Potential poly-A sequence.