Characterization and hormonal regulation of radioimmunoassayable IGF-I (insulin-like growth factor I) like activity and IGF-binding proteins secreted by human breast cancer cells.
Insulin-like growth factor-I (IGF-I) is considered an important local mitogenic growth factor involved in autocrine/paracrine regulation of human breast cancer cell proliferation. We have characterized the IGF-I-like activity and studied its hormonal regulation by estradiol in the MCF-7 human breast cancer cell line. We found that the radioimmunoassayable IGF-I-like activity measured in conditioned medium (CM) is predominantly due to the presence of IGF-binding proteins (IGFBP). Acid chromatography demonstrated that most of the IGF-I-like activity eluted in the high molecular weight fractions and less than 10% co-eluted with authentic IGF-I (mol wt 7500). Binding protein activity measured by a 125I-IGF-I-ligand binding IGFBP-assay was present in these same high molecular weight fractions. SDS-polyacrylamide gel electrophoresis and 125I-IGF-I-ligand blot analysis of the CM showed the presence of two species of binding proteins of 29 kDa and 41 kDa molecular weight which demonstrated specific 125I-IGF-I binding activity. Estradiol did not stimulate IGFBP activity as assessed by the IGFBP-assay and as indirectly reflected by the IGF-I-like activity in the high molecular weight fractions. We conclude that the IGF-I-like activity in CM from human breast cancer cell cultures is predominantly due to the presence of IGFBP. Binding proteins of apparent molecular weight 29 kDa and 41 kDa are present in CM from MCF-7 cells. Assessment of their hormonal regulation showed that estradiol did not stimulate IGFBP. However, this needs to be assessed more stringently using better quantitative estimations for BP. The IGF-binding proteins may have an important role in the regulation of tumor cell growth by influencing the local concentrations and receptor mediated actions of IGF-I.
Department of Medicine, Milton S. Hershey Medical Center, Pennsylvania State University, College of Medicine, Hershey 17033.
S R
SR
Ahmed
A
A
Manni
G
G
Gray
J M
JM
Hammond
D001943:Breast Neoplasms / Q000378:metabolism*; D002352:Carrier Proteins / Q000032:analysis* / Q000276:immunology; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D008970:Molecular Weight; D011863:Radioimmunoassay; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D003470:Culture Media; D018969:Insulin-Like Growth Factor Binding Proteins; D004958:Estradiol; D007334:Insulin-Like Growth Factor I