Selective Up-regulation of Claudin-1 and Claudin-2 in Colorectal Cancer

Background: To understand the molecular and morphological alterations in the tight junction in colorectal cancer (CRC) tissues, the expression of eight tight junction proteins in normal and cancer colorectal tissues were compared. Patients and Methods: Adenocarcinoma tissues and paired normal mucosa were resected from surgical specimens of CRC patients. The expression of occludin, ZO-1, ZO-2, and claudin-1 ~ 5 was analyzed at the mRNA level by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and at the protein level by immunohistochemistry. Results: The expression of claudin-1 and claudin-2 in cancer tissues was up-regulated 40- and 49.2-fold, respectively, at the mRNA level, as compared with that in normal tissues. The up-regulation of these two claudins was also observed at the protein level and it appeared to depend on the depth of tumor invasion. Conclusion: Claudin-1 and claudin-2 were found to be overexpressed in CRC tissues. They may be useful as tumor markers and targets for the treatment of colorectal cancer.