May play a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier. 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. Highly expressed in the testis, kidney, lung, liver and brain. Not detected in skeletal muscle, spleen and heart. Found diffusely on the lateral membranes of Sertoli cells in the early prepubertal period. With development, became gradually concentrated at the most basal regions of Sertoli 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). May be phosphorylated by PKC during translocation to cell-cell contacts. Mice have a complex phenotype including abnormalities of salivary gland, gastric epithelium, bone, testis and intracranial calcification. Belongs to the ELL/occludin family.