Altered expression and localization of the tight junction protein ZO-1 in primary and metastatic pancreatic cancer

Introduction: ZO-1 is a tight junction membrane protein that plays a critical role in cell-cell interaction, proliferation, and differentiation. Aim: To localize and evaluate the expression of ZO-1 in the normal human pancreas, in pancreatic ductal adenocarcinoma (PDAC), and in chronic pancreatitis (CP). Methodology and Results: Northern and Western blot analysis revealed ZO-1 expression in all six tested pancreatic cancer cell lines. Expression of ZO-1 mRNA was increased sixfold in PDAC samples in comparison with normal samples (p = 0.04). Confocal microscopy revealed the presence of ZO-1 in the apical and apicolateral areas of ductular cells in the normal pancreas. Similarly, in CP, ZO-1 was localized at apical and apicolateral areas of small proliferating ductular cells and large metaplastic ducts. In PDAC, however, ZO-1 expression was observed irrespective of whether the cancer cells formed duct-like structures or exhibited a diffuse infiltrating pattern. Metastatic pancreatic cancer cells within lymph nodes displayed variable staining patterns, ranging from apical and apicolateral to a diffuse membranous staining. Conclusion: These observations suggest that ZO-1 is overexpressed in PDAC and raise the possibility that this overexpression may confer a metastatic advantage to pancreatic cancer cells.