DEMONSTRATION OF RECEPTORS FOR INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 ON HS578T HUMAN BREAST-CANCER CELLS

Hs578T human breast cancer cells are from an estrogen receptor-negativ e breast cell line derived from a highly aggressive mammary tumor. Our previous insulin-like growth factor binding protein-3 (IGFBP-3) bindi ng studies (Oh, Y., Muller, H. L., Lamson, G., and Rosenfeld, R. G. (1 993) J. Biol. Chem. 268, 14964-14971) have demonstrated specific bindi ng of IGFBP-3 on the Hs578T cell surface and a significant inhibitory effect of IGFBP-3, itself, on monolayer growth. In this study, we have demonstrated cell surface association proteins that are specific for IGFBP-3 by showing: 1) detection of 20-, 26-, and 50-kDa proteins by a ffinity cross-linking with I-125-IGFBP-3E. coli and immunoprecipitatio n of cell monolayers and cell lysates with anti-IGFBP-3 antibodies; 2) dose-dependent competition of I-125-IGFBP-3E. coli by unlabeled IGFBP -3E. coli; 3) inhibition of IGFBP-3 binding to these cell surface prot eins by EDTA and by coincubation with native insulin-like growth facto r II (IGF-II), but not by coincubation with [Gln6,Ala7,Tyr18, Leu19,Le u27]IGF-II, an IGF-II analog with decreased affinity for IGFBP-3; and 4) partial purification of 20- and 26-kDa species by IGFBP-3-anti-IGFB P-3 antibody immunoaffinity membranes. Characteristics of these specif ic IGFBP-3 cell surface association proteins are identical to those ob served in our previous monolayer binding assay and monolayer growth as say experiments. The specificity of binding and the inhibitory effect of IGFBP-3 binding on Hs578T cell growth suggest that these cell surfa ce proteins are IGFFBP-3-specific receptors or receptor subunits media ting the direct inhibitory effect of IGFBP-3 on monolayer growth of Hs 578T cells.