Ample evidence confirms that certain
cancer cells have the capacity to produce multiple
peptides as
growth factors and that expression of their receptor may act in tumour cell paracrine and/or autocrine loop mechanisms, either by extracellular release of the
growth factor or by the tumour itself. To study the possibility of an autocrine growth mechanism in bladder
carcinoma, we investigated the ability of various bladder
carcinoma cell lines to proliferate in serum-free medium. A rat bladder
carcinoma cell line, BC47, demonstrated exponential and density-dependent growth in serum-free medium. Furthermore,
conditioned medium from BC47 cells induced growth-stimulating activity for BC47 cells themselves. Purification and further characterization of this activity was performed by chromatographic methods, SDS-PAGE and N-terminal
amino acid analysis. Finally, we have identified that a
transferrin-like 70-kDa
protein is found to be the main growth-promoting factor in this
conditioned medium. In addition, specific
antibodies against
transferrin and the
transferrin-receptor inhibit the in vitro growth of this cell line. Our data suggest that this
transferrin-like factor possibly acts as an autocrine
growth factor for
cancer cells.