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Bladder cancer is the fifth most common malignancy in the UK. Clinically, the most important process in determining prognosis is the development of invasion, initially of the lamina propria and then beyond as these transitional cell carcinomas (TCCs) progress from stage pT1 to stages T2+. Cadherins and catenins are the main mediators of cell–cell interactions in epithelial tissues, and loss of membranous E-cadherin immunoreactivity is strongly correlated with high grade, advanced stage and poor prognosis in bladder cancer and other malignancies. However, the role of P-cadherin is yet to be fully elucidated in bladder TCC. The objectives of this study were to establish how the expression of cadherins and catenins determines clinical andin vitrobehaviour in bladder TCC. Utilizing immunohistochemistry, immunofluorescence and western blotting, we demonstrated a significant reduction in the expression of E-cadherin and β-catenin as grade and stage of bladder TCC progress, accompanied by a significant increase in P-cadherin expression (allp< 0.05, Pearson's χ2 test). Increased P-cadherin expression was also associated with a significantly worse bladder cancer-specific survival (log rankp= 0.008), with Cox regression showing P-cadherin to be an independent prognostic factor. Utilizing a variety of tissue culture models in a range of functional studies, we demonstrated that P-cadherin mediates defective cell–cell adhesion and enhances anchorage-independent growth. The results provide evidence that increased P-cadherin expression promotes a more malignant and invasive phenotype of bladder cancer, and appears to have a novel role late in the disease. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.