The present experiments were designed to test the role of insulin-like growth factor-related peptides (IGF-RPs) in hormonally stimulated N-nitrosomethylurea (NMU)-induced mammary tumor colony formation in soft agar. To evaluate production of IGF-RP by NMU cells, we tested the abilities of a monoclonal antibody directed against insulin-like growth factor I (α sm 1.20B) and of a polyclonal antibody raised against the insulin-like growth factor I (Ab 134) to inhibit the colony-stimulating effects of conditioned media (CM) obtained from estradiol (E2) prolactin (PRL)-, and progesterone (Pg)-treated NMU-induced rat mammary tumors. Both Abs abolished the colony-stimulating action of genuine insulin-like growth factor I while having no effect when added alone or with control CM. The addition of either α sm 1.20B or Ab 134 (but not that of an irrelevant Ab) consistently blocked the colony-stimulating action of E2-CM, PRL-CM, and Pg-CM, suggesting that IGF-RPs are produced by NMU mammary tumor cells exposed to these hormones. Next, we directly tested the role of IGF-RPs as mediators of hormonally stimulated growth. We indeed observed that the addition of a sm 1.20B markedly inhibited the colony-stimulating actions of E2, PRL, and Pg added to NMU mammary tumor cells in soft agar in the absence of serum. We conclude that, in our experimental system, IGF-RPs not only are produced upon exposure to E2, PRL, and Pg, but also are important mediators of hormonally stimulated growth.
|Original language||English (US)|
|Number of pages||5|
|State||Published - Nov 12 1990|
All Science Journal Classification (ASJC) codes
- Cancer Research