May play a role as scaffolding protein at cell-cell junctions. May regulate acid-induced ASIC3 currents by modulating its expression at the cell surface (By similarity). Interacts through its WW 2 domain with SYNPO and through its PDZ 5 domain with ACTN4 (PubMed:12042308). Interacts with cytoplasmic domain of ADGRB1 (PubMed:9647739). Interacts via its WW domains with DRPLA (PubMed:9647693). Interacts with ESAM, LRP2 and CXADR (By similarity). May interact with CTNNB1 (By similarity). Interacts through its PDZ 1 domain with NET1 (By similarity). Interacts with ASIC3 and AMOT (PubMed:15317815, PubMed:16043488). Interacts with FCHSD2 (PubMed:14627983). Interacts with IGSF5/JAM4 and through its PDZ 2 and 3 domains with NPHS1 forming a tripartite complex (By similarity) (PubMed:12773569). Interacts with DDN (PubMed:16751601). Isoform 3 (via PDZ domain) interacts with RAPGEF2 (PubMed:11168587). Interacts with DLL1 (By similarity). Interacts with KCNJ10 and possibly with KCNJ10/KCNJ16 heterodimer; this interaction may facilitate KCNJ10/KCNJ16 potassium channel expression at the basolateral membrane in kidney tubular cells. Interacts with PRRG4 (via cytoplasmic domain) (PubMed:23873930). Localizes to epithelial cells tight junctions. Additional isoforms seem to exist. Widely expressed with the exception of skeletal muscle. Isoform 1, isoform 2 and isoform 6 are highly expressed in colon, kidney, lung, liver, and pancreas. Isoform 5 is predominantly expressed in brain and heart. Isoform 3 and isoform 4 are highly expressed in pancreas and brain.