Expression of claudin-7 in benign kidney and kidney tumors.

Claudins, a family of tight junction-related transmembrane proteins, have been implicated in the pathogenesis of various human neoplasms. Expression of claudin-7 was increased in chromophobe renal cell carcinoma in a recent oligonucleotide microarray study. We studied the expression of claudin-7 in benign and neoplastic kidneys by immunohistochemical staining. Distal nephron (distal convoluted tubule and thick ascending limb of Henle's loop) epithelium showed strong membranous staining in 100% (174/174) of the cases. Chromophobe renal cell carcinoma was positive for claudin-7 expression in 100% (36/36) of cases, while papillary renal cell carcinoma, oncocytoma and clear cell renal cell carcinoma were positive in 90% (71/80), 45% (21/47) and 7% (7/98) of the cases, respectively. Differential expression of Claudin-7 in different types of renal cell neoplasms can be useful in their differential diagnosis, particularly when used in a panel of markers. In addition, results from this study support previous reports of distal nephron origin for chromophobe renal cell carcinoma and oncocytoma. The data also suggest that, as far as claudin-7 expression is concerned, papillary renal cell carcinoma may be more closely related to the distal nephron, rather than the proximal nephron.