Recombinant insulin-like growth factor binding protein-1 inhibits IGF-I, serum, and estrogen-dependent growth of MCF-7 human breast cancer cells.
The insulin-like growth factors (IGFs) are potent mitogens for breast cancer cells and their activity is modulated by high affinity binding proteins (IGFBPs). We have recently shown that IGFBP-1 purified from human amniotic fluid neutralizes IGF-I-dependent growth of MCF-7 cells. In this study we examined the effects of recombinant IGFBP-1 (rBP-1) on IGF-I, estradiol (E2), and serum-induced monolayer and anchorage independent growth (AIG) of MCF-7 cells. Under serum-free conditions, rBP-1 had no effect on MCF-7 basal monolayer growth. However, 40 nM rBP-1 completely blocked the mitogenic action of both IGF-I and 5% charcoal stripped serum (CSS). This concentration of rBP-1 partially inhibited E2-induced growth, while 80 nM rBP-1 completely abolished E2 mitogenicity. The addition of either excess IGF-I or 5 nM [Arg3]IGF-I, a species that does not bind IGFBPs, neutralized rBP-1 inhibitory effects. In AIG assays, 80 nM rBP-1 reduced colony number by at least 70% and decreased colony size in all treatment groups compared to control. We examined rBP-1 effects on both IGF-I binding to MCF-7 membranes and activation of type I IGF receptor (IGFR1) and found that 80 nM rBP-1 reduced IGF-I receptor binding to levels of nonspecific binding and completely abolished ligand-dependent IGFR1 phosphorylation. However, neither treatment with 5% CSS nor exposure to E2 resulted in IGFR1 phosphorylation suggesting that different mechanism(s) are responsible for rBP-1 inhibitory action under this condition. Our data suggest rBP-1 may serve as an antagonist of human breast cancer growth by interfering with growth factor-mediated cell proliferation.
Figueroa
J A
JA
Department of Medicine, University of Texas Health Science Center, San Antonio 78284-7884.
Sharma
J
J
Jackson
J G
JG
McDermott
M J
MJ
Hilsenbeck
S G
SG
Yee
D
D
D000704:Analysis of Variance; D001798:Blood Proteins / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology*; D002352:Carrier Proteins / Q000494:pharmacology*; D002448:Cell Adhesion / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010766:Phosphorylation; D011233:Precipitin Tests; D011994:Recombinant Proteins / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D001798:Blood Proteins; D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D011994:Recombinant Proteins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I