The claudin family is composed of 23 integral membrane proteins, and their expression, which varies among tissue types, may determine both the strength and properties of the epithelial barrier. Alteration in claudin protein expression pattern is associated with several types of cancer . Claudin-2 is expressed primarily in the proximal tubule of the normal mammalian kidney, where it regulates transepithelial ion (e.g., Na+, Cl-) reabsorption . Increased expression of Claudin-2 has been reported in some cancer cell lines , including A549 lung adenocarcinoma cells, where its nuclear distribution was positively associated with enhanced proliferation .