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 from a primary urinary bladder carcinoma, was characterized with respect to the growth patterns of in vitro culture, xenotransplantability in SCID mice and immunophenotypic profile. The most unusual finding was a strong tendency of forming many aggregates (multicell spheroids) in the first few days of flask cultures, followed by the attachment of spheroids to monolayer fibroblasts, which came along from stroma of the same tumor. Unlike those reported tumor spheroids whose peripheral layers contained proliferative cells, BCCA-1 spheroids rarely contained mitotic cells. The three-dimensional architecture of BCCA-1 spheroids drastically changed by the attachment of spheroids to fibroblasts, from which epithelial tumor cells spread; this was accompanied by pseudopodia formation and highly aggressive growth of tumor cells. As the fibroblasts degenerated due to overgrowth, tumor cells started to aggregate by retracting their pseudopods and forming many semi-attached spheroids, which eventually detached from the sheet of degenerated fibroblasts. BCCA-1 produced solid tumors as xenografts in SCID mice by subcutaneous injection with as low as 5 x 10⁶ cells, suggesting malignant nature of these cells. Immunostaining revealed the expression of MHC-class I, S100 protein, cytokeratin CK7 and CK20, β-HCG, CEA, epithelial membrane antigen, Le(Y) and folate-binding protein by this tumor. While the biological significance of spheroid formation of this kind by BCCA-1 cells remains unclear, it may represent a protection mechanism, by which TCC cells could sustain their viability under unfavorable culture conditions, but proliferate when the conditions became improved, such as the presence of fibroblasts. Our results point to the importance of tumor-associated stromal fibroblasts in TCC tumor progression. Further mechanistic studies to elucidate the mechanism involved in the stromal cell contact mediated-activation of TCC cells in this model system are warranted.