The role of E-cadherin in the differentiation of gallbladder cancer cells
We previously developed a model in which rabbit gall bladder epithelial cells in collagen gels proliferated and formed multicellular spherical cysts after 2 to 4 days. In the present study, we examined in depth the dynamic processes of loss and reestablishment of cell polarity of rabbit gallbladder epithelial cells isolated and cultured in collagen gel. Six hours after being place in culture, the isolated epithelial cells had lost the morphologic features and phenotypic markers inherent in the in vivo gallbladder mucosa, and autophagic vacuoles appeared transiently, reflecting epithelial cell injury, or remodelling, or both. After 12 hours, mucin dots appeared in clumps of epithelial cells and gradually became larger, and the epithelial cell clumps were transformed into multicellular cysts after 1 to 2 days. The luminal surfaces of the mucin dots (intracytoplasmic inclusions or small lumens sealed by several epithelial cells) and multicellular cysts were covered by microvilli and presented profiles of mucus glycoprotein and carbohydrate residues shared with the in vivo gallbladder mucosa. The presence of cellular adhesion structures and the distribution of cellular organelles toward the luminal surface implied the reestablishment of epithelial cell polarity. The addition of cytochalasin B induced many mucin-positive cytoplasmic inclusions covered by microvilli in the epithelial cells of the multicellular cysts, while the addition of transforming growth factor beta 1 promoted maturation of the multicellular cysts. This short term culture is useful for the analysis of the polarity of biliary epithelial cells and for examining disorders in this polarity.