This gene encodes a member of the claudin family. Claudins are integral membrane proteins and components of tight junction strands. Tight junction strands serve as a physical barrier to prevent solutes and water from passing freely through the paracellular space between epithelial or endothelial cell sheets, and also play critical roles in maintaining cell polarity and signal transductions. This protein increases permeability for sodium ions in anion-selective epithelial cell sheets. The gene deficiency leads to megaintestine and decreases in intestinal epithelial paracellular ion permeability. This gene is a direct target for hepatocyte-nuclear-factor-4alpha, a mediator of ion epithelial transport, and is down-modulated in inflammatory bowel disease.