Expression of E-Cadherin and β-Catenin in Two Cholangiocarcinoma Cell Lines (OZ and HuCCT1) with Different Degree of Invasiveness of the Primary Tumor

Background: Cholangiocarcinoma (CC) is the most frequent malignant epithelial tumor of the biliary sys- tem. CC has received increasing interest due to its different etiologic factors, invasiveness, and the difficulty of diagno - sis at an early stage. The pathogenesis of CC has not been clearly defined, but cohesiveness of tumor cells seems to be a critical factor. Calcium-dependent adherence proteins or cadherins are a family of proteins essential for connecting the plasma membrane of adjacent cells. Linkage of cadherins with the cytoskeleton occurs through another class of proteins, called catenins. E-cadherin forms a mutually exclusive complex or unit with β-catenin. Loss of E-cadherin - β-catenin adhesion represents an important step in the progression of many epithelial malignancies. Cell lines arising from CC are not often investigated and may show a differential expression of cell adhesion molecules, particularly E-cadherin - β-catenin. We hypothesized that a moderately invasive cell line of CC may co-localize both molecules in cytoplasm and cytoplasmic membrane, indicating a greater "tightness" of the tumor cells, while a metastasizing cell line may show isolated cytoplasmic membrane localization, indicating tumor cells probably more keen to reach the blood stream and give metastases. Thus, our aim was to investigate the expression and localization of E-cadherin and β-catenin in two CC cell lines, including a rapidly metastasizing cell line and a moderately invasive cell line, cor- relating to a different degree of invasiveness of the primary tumor. Materials and Methods: OZ and HuCCT1 cells represent homogeneous, functional human biliary epithelial tumor cell lines that were originally isolated in Japan. Following cell line growth we extracted total proteins. Western blot analysis, immunofluorescence and confocal laser microscopy were used to identify the protein expression and their cyto-localization and co-localization. Results: Both CC cell lines expressed E-cadherin and β-catenin, but they showed remarkably different localization patterns. In HuCCT1, both E-cadherin and β-catenin were localized in the cytoplasm, while in OZ these proteins were localized in the cytoplasmic membrane only. This was attributed to a different degree of invasiveness of the primitive CC from which the cell lines were characterized, OZ being a metastasizing cell line, HuCCT1 being a moderately invasive cell line. Conclusion: To the best of our knowledge, this is the first time that E-cadherin and β-catenin have been studied in detail in these two cell lines. These data seem to be very promising in terms of adding insight into the cell biology of CC and initiating investigations that aim to identify cytoskeletal dynamics and ultimately provide guidelines for developing new therapeutic strategies.