Demonstration of insulin-like growth factor (IGF-I and -II) receptors and binding protein in human breast cancer cell lines

The insulin like growth factors (IGFs), potent mitogens for a variety of normal and transformed cells, have been reported to be secreted by several human breast cancer cell lines (BC). We have investigated the binding characteristics of IGF-I and -II in four human BC: MCF-7, T-47D, MDA 231 and Hs578T. Binding studies in microsomal membrane preparations detected high specific binding for both IGF in all four BC studied. Cross-linking with ¹²⁵I-IGF-I, followed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under reduced conditions, revealed the presence of an α subunit of apparent M_r = 130,000 in MCF-7, T-47D and MDA 213 cells. When ¹²⁵I-IGF-II was cross-linked, a major band of apparent M_r = 260,000 was seen in all BC. This band was inhibited by IGF-II, but not by insulin. Cross-linking of ¹²⁵I-IGF-I to conditioned media from BC demonstrated the presence of three binding proteins of apparent M_r = 45,000, 36,000 and 29,000 in all BC but T-47D, in which the 36,000 band was not seen. These data demonstrate that BC possess classical receptors for both IGF-I and -II and, furthermore, that BC produce specific binding proteins for these growth factors.