Characterization of mammary-derived growth factor 1 receptors and response in human mammary epithelial cell lines

Mammary-derived growth factor 1 (MDGF1, with a molecular mass of 62 kDa and pi of 4.8) has been purified from human milk (Bano, M., Salomon, D. S., and Kidwell, W. R. (1985) J. Biol. Chem. 260, 5745-5752). N-terminal sequence of 18 amino acids showed no homology to any known growth promoting peptides. The present study was carried out to evaluate the biological effects of and binding sites for MDGF1 on normal human and breast cancer cell lines. At a concentration of 10-25 ng/ml the factor stimulated the growth of estrogen receptor-positive MCF-7 human breast cancer cells by 50% and also stimulated the synthesis of collagen IV by 40%. It did not have any effect on ZR75-1, T47-D, and MDA-MB 231 cells. The factor showed a biphasic effect on the estrogen receptor-negative MDA-MB 468 cells at concentrations above 5 ng/ml. The growth of normal human mammary epithelial cells (184 strain) was enhanced by 35%, whereas immortalized non-tumorigenic 184A1N4 human mammary epithelial cells were stimulated by about 60-70%. However, transformation of these cells by SV40-T, v-Ha-ras, or v-mos desensitized them to MDGFl. Iodinated MDGF1 binds to moderate affinity sites on the responsive MCF-7, MDA-MB 468, and 184A1N4 cell lines (K_D = 6 × 10^-9 M). Cross-linking of ¹²⁵I-MDGF1 to binding sites revealed the presence of a major band of molecular mass of approximately 180-200 kDa in MCF-7 and MDA-MB 468 cell lines. Labeling of this band was inhibited by excess unlabeled MDGF1. These data suggest that human mammary epithelial cell lines possess receptors for MDGF1.