May play a role in the formation and regulation of the tight junction (TJ) paracellular permeability barrier. Interacts with ZO-1. Interacts with TJP1 and TJP3. Localized at tight junctions of both epithelial and endothelial cells. Highly expressed in lung and liver. Expressed at a lower level in brain. 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. The second extracellular domain may also be implicated in the permeability barrier function of the tight junction. Phosphorylated. Belongs to the ELL/occludin family.