Claudins are a family of proteins that are structural and functional components of tight junctions and have crucial roles in the maintenance of cellular arrangement, adhesion and paracellular transport. Recent studies have shown that changes and/or loss of claudin expression plays an important role in tumorigenesis and tumor progression, and altered expression of claudins has been reported in various human carcinomas. Non-keratinizing nasopharyngeal carcinoma (NPC) is a common Epstein-Barr virus (EBV)-associated carcinoma with characteristic clinicopathological features. The aim of this study was to investigate claudin expression profiles in EBV-associated non-keratinizing NPC. We analyzed expressions of claudin-1, -2, -3, and -4 in 18 cases of EBV-associated non-keratinizing NPC by immunohistochemical methods. Claudin-1 was expressed in all 18 cases, but claudin-2 was not expressed in any of the 18 cases. Claudin-3 expression was variable, with 8 of the 18 cases (45%) showing no immunoreactivity for claudin-3. Claudin-4 displayed positive immunoreactivity in all cases, even in claudin-3-negative cases. Claudin-3 and -4 are receptors for cytotoxic Clostridium perfringens enterotoxin (CPE) and CPE has emerged as a potential therapeutic target for malignant tumors expressing claudin-3 and/or -4, because CPE specifically and rapidly lyses cells expressing these proteins. Clinically, treatment of distant metastases is a serious problem in EBV-associated non-keratinizing NPC, because frequently there is lymph node involvement and distant metastasis before detection of the primary tumor. Therefore, CPE therapy may be a potential therapeutic target for EBV-associated non-keratinizing NPC, since our results clearly showed claudin-3 and/or -4 expression in all cases studied.

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