Adaptation of human bladder carcinoma cell lines to serum-free growth. Evidence for autocrine growth stimulation.

Tumor transformation is associated with a partial breakdown of the normal regulatory systems governing cell proliferation and differentiation. As a consequence, malignant cells are often less dependent on external growth factors and may be refractory to differentiation signals. Consistent with this view, we here show that 5 of 9 human bladder carcinoma cell lines (5637, HU549, SD, TCCSuP and T24) as well as a colon carcinoma line, HCT-8, and the melanoma line, HS294T, could be adapted to grow continuously in medium without serum or any other source of protein. The cells grown under these conditions displayed a longer generation time and were more dependent on a high initial cell concentration for survival and outgrowth. However, in most other respects, including cell morphology, growth pattern and antigenic phenotype, the cells were very similar to the original cultures. Conditioned medium from all the cell lines of bladder tumor origin as well as the HCT-8 colon carcinoma line was shown to contain autocrine growth stimulatory activity. Furthermore, criss-cross experiments showed that supernatants stimulated not only proliferation of the autologous cell line but also growth of the other cell lines, suggesting the production of a common autocrine factor/s in bladder tumor cells. Incubation of cells with radioiodinated supernatant allowed the identification of several candidate molecules for this factor activity. The study supports previous observations of autocrine stimulation as a mechanism for tumor cells to acquire autonomous growth capacity and indicates that this may be an important element in the oncogenesis of bladder tumors.