Expression of claudin-4 (CLDN4) mRNA in intraductal papillary mucinous neoplasms of the pancreas.

Claudin-4, encoding a protein for tight junction formation and function, is highly overexpressed in pancreatic ductal adenocarcinoma and is also associated with invasive adenocarcinomas arising in intraductal papillary mucinous neoplasms of the pancreas. However, the expression pattern of claudin-4 during neoplastic progression of intraductal papillary mucinous neoplasms remains unknown. Using quantitative real-time reverse transcription-PCR, we analyzed claudin-4 mRNA in a panel of 14 pancreatic cancer cell lines and in formalin-fixed paraffin-embedded tissues from 80 patients with intraductal papillary mucinous neoplasms of different histological grades and papillary subtypes. Increased expression of claudin-4 was confirmed in all the pancreatic cancer cell lines tested as compared with normal ductal epithelial cells and fibroblast cultures. The claudin-4 expression was significantly higher in high-grade intraductal papillary mucinous neoplasms (borderline neoplasm and carcinoma) than in low-grade intraductal papillary mucinous neoplasms (adenoma) (P<0.0001). In addition, claudin-4 mRNA levels were significantly higher in intestinal-type intraductal papillary mucinous neoplasms than in non-intestinal-type intraductal papillary mucinous neoplasms based on papillary subclassification (P<0.0001). Our findings suggest that claudin-4 expression is associated with neoplastic progression of intraductal papillary mucinous neoplasms and, especially, with a distinct pathway to intestinal differentiation.