Insulin-like growth factor (IGF) binding to a murine mammary epithelial cell line

The goal of this study was to relate insulin-like growth factor (IGF) binding with IGF-stimulated growth in a murine mammary epithelial (COMMA-D/MME) cell line. Affinity crosslinking with [125I]IGF-I showed major bands at 224,000 and 148,000 Mr that were ablated by the inclusion of IGF-I or -II at 130 nM. Scatchard-transformed [125I]IGF-I binding data was best fit by a two-site model, with 24,000 sites possessing a Kd of 0.33 nM and 1,000 sites possessing a Kd of 8.09 nM per cell. Competition analysis showed ED50 values for IGF-I, -II, and insulin to be 0.90 +/- 0.03, 7.15 +/- 4.27, and 335 +/- 104 nM, respectively. Affinity crosslinking of [125I]IGF-II showed three major bands of 230,000, 148,000, and 61,000 to 58,000 Mr. Unlabeled IGF-II ablated all bands, while IGF-I and insulin ablated only the 148,000 Mr band. Competition analysis showed ED50 values for unlabeled IGF-I and -II to be 0.10 +/- 0.01 and 5.31 +/- 2.04 nM, respectively. In spite of the receptor affinity differences, no significant difference was noted in IGF-I and -II in capacity to stimulate cell growth. These data indicate that COMMA-D/MME cells express IGF receptors and that both IGFs are mitogenic.