CLDN8 (claudin 8) 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 plays important roles in the paracellular cation barrier of the distal renal tubule, and in the paracellular barrier to prevent sodium back-leakage in distal colon. Differential expression of CLDN8 has been observed in colorectal carcinoma and renal cell tumors, and along with claudin-7, is an immunohistochemical marker for the differential diagnosis of chromophobe renal cell carcinoma and renal oncocytoma.