Regulation of insulin-like growth factor binding protein secretion by a murine mammary epithelial cell line

The regulation of insulin-like growth factor binding protein (IGFBP) secretion by mammogenic and lactogenic hormones was investigated in a mouse mammary epithelial cell line (COMMA-D/MME). Cells were grown to confluency on plastic culture plates in serum-containing medium. The confluent cells were exposed to the hormonal treatments in serum-free medium for 6 days. Conditioned medium was collected on Days 5 and 6 and analyzed for IGFBPs by 125I-labeled insulin-like growth factor (IGF)-II ligand blotting and quantified by densitometry. IGFBP data were expressed as absorbance units x millimeters (AUxmm) that were corrected for DNA per well. In basal serum-free media, the COMMA-D/MME cells secreted predominantly IGFBP-3, but also some IGFBP-2. The mammogenic growth factors, IGF-I (13.3 nM) and epidermal growth factor (EGF; 1.7 nM), both stimulated DNA synthesis (P < 0.05); however, their effects on IGFBP-3 secretion differed. IGF-I stimulated IGFBP-3 secretion whereas EGF was inhibitory. In addition, EGF inhibited IGFBP-2 secretion and IGF-I tended to increase it. No interaction was observed between IGF-I and EGF for any of the parameters measured. Three lactogenic hormones (insulin, 154 nM; prolactin, 4.3 nM; and cortisol, 1.4 microM) in all combinations were tested to determine their effects on IGFBP secretion. Insulin stimulated IGFBP-3 secretion and DNA synthesis, but had no effect on IGFBP-2 secretion. Cortisol inhibited IGFBP-3 secretion and DNA synthesis, but increased IGFBP-2 secretion. Prolactin had no effect on any of the parameters examined. In summary, the COMMA-D/MME cells secrete IGFBP-2 and IGFBP-3 in serum-free media. Although the secretion of IGFBP-2 and IGFBP-3 in serum-free media. Although the secretion of IGFBP-2 and IGFBP-3 was regulated by several of the hormones and growth factors tested, no clear distinction was observed between the mammogenic and lactogenic treatments.