Claudin-7 is one of the transmembrane proteins that seal tight junctions and is critical for maintaining cell-to-cell adhesion in epithelial cell sheets. Claudin-7 is localized in the intercellular junctions of the epithelial cells of the proximal tubules of the nephrons in mammalian kidney. It is reportedly down-regulated in head and neck squamous cell carcinomas and loss of claudin-7 expression has been linked to histological grade in ductal carcinoma and invasive ductal carcinoma. Claudin-7 has been shown to regulate the expression of prostate-specific antigen (PSA) and it is also expressed in normal human and mouse epithelia.