Acts as a scaffolding protein at cell-cell junctions, thereby regulating various cellular and signaling processes. Cooperates with PTEN to modulate the kinase activity of AKT1. Its interaction with PTPRB and tyrosine phosphorylated proteins suggests that it may link receptor tyrosine phosphatase with its substrates at the plasma membrane. In polarized epithelial cells, involved in efficient trafficking of TGFA to the cell surface. Regulates the ability of LPAR2 to activate ERK and RhoA pathways. Regulates the JNK signaling cascade via its interaction with FZD4 and VANGL2. Interacts with ADRB1, ADGRB1, LPAR2/EDG4, GRIN2B, PTEN, and PTPRB. Interacts with unidentified tyrosine phosphorylated proteins (By similarity). Interacts with FZD4, FZD7, TGFA and VANGL2. Interacts with DLL1 (PubMed:15509766). Interacts with PRRG4 (via cytoplasmic domain) (By similarity). Concentrates in specific sites at the plasma membrane and in the nucleus. In epithelial cells, it localizes at tight junctions (By similarity). Widely expressed. Colocalizes with TGFA in neurons in the cortex and dentate gyrus, as well as in ependymal cells and some astrocytes (at protein level). Present in lens epithelium. Belongs to the MAGUK family. The sequence differs from that shown because it seems to be derived from a pre-mRNA.