May play a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier. Interacts with ZO-1. Interacts with TJP1/ZO1. Interacts with VAPA. Interacts with CLDN1, CLDN6, CLDN9, CLDN11, CLDN12 and CLDN17. Interacts with PLSCR1. Interacts with LSR, ILDR1 and ILDR2. Localized at tight junctions of both epithelial and endothelial cells. The C-terminal is cytoplasmic and is important for interaction with ZO-1. Necessary for the tight junction localization. Involved in the regulation of the permeability barrier function of the tight junction (By similarity). Dephosphorylated by PTPRJ (By similarity). Less-phosphorylated forms are found in basolateral membrane, cytosol and tight junction. More-heavily phosphorylated forms are concentrated exclusively in tight junction. Belongs to the ELL/occludin family.