Receptor binding and growth-promoting activity of insulin-like growth factors in human breast cancer cells (T-47D) in culture

Insulin-like growth factors (IGFs) and insulin are known to be mitogenic to a variety of cell types, although a growth-regulatory role of IGFs on human breast cancer cells has not yet been fully investigated. In the present study, we examined the receptor binding and the effect on growth of IGFs and insulin in a human breast cancer cell line (T-47D). Specific binding of 125I-basic somatomedin (BSM/IGF-I), 125I-multiplication-stimulating activity (MSA III-2/IGF-II), and 125I-insulin has been demonstrated in monolayer T-47D cells grown on plastic substratum. When the binding of 125I-BSM and 125I-MSA III-2 was studied, unlabeled BSM and unlabeled MSA were the most effective competitors for the respective binding sites. Unlabeled insulin at high concentration also inhibited the binding of 125I-BSM and 125I-MSA III-2. For 125I-insulin binding, however, unlabeled MSA III-2 and MSA II were more effective than unlabeled insulin in displacing 125I-insulin from its binding sites. These observations suggest that the binding sites for IGF-I and IGF-II are distinct in T-47D cells and that insulin cross-reacts weakly with IGF-I and IGF-II binding sites. BSM (IGF-I) and MSA (IGF-II) (1 microgram/ml) produced a 1.5-fold increase in cell proliferation of T-47D cells grown on plastic substratum. The mitogenic effect of IGFs on T-47D was more apparent when cells were grown on collagen gel. At 500 ng/ml, MSA III-2, BSM, and insulin stimulated cell growth 4-, 2.5-, and 1.5-fold, respectively. Our results suggest that the IGFs may be involved in the growth regulation of human breast cancer cells.