Human bladder carcinoma cells with an unusual pattern of in vitro growth: Transition from nonproliferative spheroids to active monolayer growth upon interaction with tumor-derived fibroblasts

A new transitional cell carcinoma cell line, BCCA-1, derived fr om a primar y urinary bladder carcinoma, was characterized with respect to the growth p atterns of in vitro culture, xenotransplantability in SCID mice and immunop henotypic profile. The most unusual finding was a strong tendency of formin g many aggregates (multicell spheroids) in the first few days of flask cult ures, followed by the attachment of spheroids to monolayer fibroblasts, whi ch came along from stroma of the same tumor: Unlike those reported tumor sp heroids whose peripheral layers contained proliferative cells, BCCA-1 spher oids rarely contained mitotic cells. The three-dimensional architecture of BCCA-1 spheroids drastically changed by the attachment of spheroids to fibr oblasts, from which epithelial tumor cells spread; this was accompanied by pseudopodia formation and highly aggressive growth of tumor cells. As the f ibroblasts degenerated due to overgrowth, tumor cells started to aggregate by retracting their pseudopods and forming many semi-attached spheroids, wh ich eventually detached from the sheet of degenerated fibroblasts. BCCA-1 p roduced solid tumors as xenografts in SCID mice by subcutaneous injection w ith as low as 5 x 10(6) cells, suggesting malignant nature of these cells. Immunostaining revealed the expression of MHC-class I, S100 protein, cytoke ratin CK7 and CK20, beta-HCG, CEA, epithelial membrane antigen, Le(y) and f olate-binding protein by this tumor. While the biological significance of s pheroid formation of this kind by BCCA-1 cells remains unclear it may repre sent a protection mechanism, by which TCC cells could sustain their viabili ty under unfavorable culture conditions, but proliferate when the condition s became improved such as the presence of fibroblasts. Our results point to the importance of tumor-associated stromal fibroblasts in TCC tumor progre ssion. Further mechanistic studies to elucidate the mechanism involved in t he stromal cell contact mediated-activation of TCC cells in this model syst em are warranted.