{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Claudin-4 proteins form tight junctions between adjacent epithelial cells and contribute to the formation of these specialized cell-cell adhesion structures that seal the paracellular space between epithelial cells. Tight junctions regulate the permeability of epithelial barriers, such as the epithelial lining of the gastrointestinal tract, kidney tubules, and blood-brain barrier, by controlling the passage of ions, solutes, and water between cells. Dysregulation of claudin-4 expression may compromise epithelial barrier function and contribute to the pathogenesis of various diseases, including inflammatory bowel disease, intestinal permeability disorders, and progression and metastasis in certain types of cancer. Increased expression of claudin-4 has been observed in breast cancer, ovarian cancer, pancreatic cancer, prostate cancer, and lung cancer, where it is associated with tumor aggressiveness, invasiveness, and poor clinical outcomes. Targeted therapies are being developed to selectively deliver therapeutic payloads to claudin-4-positive tumor cells while sparing normal tissues."}]}]}