BCG internalization in human bladder cancer cell lines, especially with regard to cell surface-expressed fibronectin

Purpose. Several lines of evidence suggest a functional role of urothelial (tumor) cells in the bacillus Calmette-Guerin (BCG) immunotherapy for super ficial bladder cancer. In this study the interaction between BCG organisms and a series of human transitional bladder cancer (TCC) cell lines was addr essed, focusing on the role of cell-associated fibronectin (FN) in BCC inte rnalization. Materials and Methods. FN expression, and BCG attachment and internalizatio n were evaluated in a series of human TCC cell lines. Effects of anti-FN an tibodies (alpha FN) on cell-associated BCC were studied in the human TCC ce ll line T24. Results. In contrast to the well differentiated cell lines, RT-4, SEC-2 and SBC-7, fibronectin expression was high in the poorly differentiated cell l ines, T24, TCC-SUP and J82. A correlation between FN expression and the cap acity to internalize BCC was observed. The possibility of causal relationsh ip between FN expression and BCG internalization was studied in detail with T24 cells. The results showed that pre-incubation of T24 cells with alpha FN did not prevent the internalization of BCC. Conclusions. Cell membrane-expressed fibronectin does not seem to be crucia lly involved in the internalization of BCG by TCC cells. A correlation betw een cellular fibronectin expression and the ability of TCC cells to interna lize BCC may be considered as a fortuitous coincidence.