Characterization of insulin-like growth factor I binding sites in human bladder cancer cell lines

The role of insulin-like growth factor I (IGF-I) in the growth and development of bladder cancer cells was investigated using cultured human cell lines representing differentiated (RT-4, 5637) or undifferentiated (T-24, J-82, TCC-SUP) transitional cell carcinoma (TCC). In the presence of 2% serum, IGF-I significantly stimulated the growth of all cell lines. The proliferation of T-24, 5637, and RT-4 cells was more sensitive to IGF-I than that of J-82 and TCC-SUP cells. [125I]IGF-I binding to 5637 and J-82 cells was significantly higher than that to T-24 and TCC-SUP cells (P < 0.001). RT-4 cells possessed the lowest binding capacity among the cell lines tested. Scatchard analysis of [125I]IGF-I binding to four of the five cell lines indicated a single binding site for IGF-I, with apparent dissociation constants (Kd) of 1.27, 1.18, 1.34, and 1.39 nmol/l for TCC-SUP, J-82, 5637, and T-24, respectively. Therefore, the difference observed in [125I]IGF-I binding among the bladder cancer cell lines was attributed to the difference of IGF-I binding sites and not to a change in receptor binding affinity. Cross-linking studies supported the suggestion that [125I]IGF-I was bound to a receptor on these cells. The results indicate that cultured human bladder cancer cells contain functional IGF-I receptors. A differentiated cell line, RT-4, possesses significantly fewer IGF-I receptors than other cell lines. This suggests that the overexpression of IGF-I receptor may reflect the malignant potential of bladder cancer cells.