| Summary: | The ovarian steroid 17β-estradiol (E₂) is critically involved in the growth control of both normal and malignant mammary epithelial cells (MEC) in vivo. However, it has not yet been determined if E₂ directly stimulates the growth of MEC, or if it stimulates growth via production of locally acting autocrine and paracrine growth factors. Epidermal growth factor (EGF) and transforming growth factor-α (TGF-α) are both peptide growth factors which interact with the EGF receptor (EGFR) to stimulate the growth of MEC in vivo and in vitro. E₂-stimulated growth in human breast cancer cell lines has been shown to be accompanied by increased production of EGF, TGF-α and EGFR. In this thesis the effects of E₂, EGF and TGF-α, alone and in combination, on the growth of human MEC (HMEC) in primary culture were examined. HMEC from reduction mammoplasties, fibroadenomas and carcinomas were cultured on collagen-coated dishes in serum-free medium (DME:F12 (1:1), 5 mg/ml BSA, 10 ng/ml choleratoxin, 0.5 μg/ml cortisol, 10 μg/ml insulin) in the presence and absence of E₂, EGF and TGF-α. Tritiated-thymidine (³H-TdR) incorporation into DNA was used as a measure of cell growth.E₂, at concentrations of 1-1000 nM, did not stimulate growth of any of the cultures examined in the serum-free medium described above. However, E₂ stimulated growth of 1 culture in medium with a reduced insulin concentration (0.1 μg/ml). E₂ inhibited the growth of HMEC in some cultures from all mammary tissue types examined. E₂ effects on HMEC growth were studied in cells grown on fibroblast feeder layers. E₂ still failed to stimulate growth of the cells, but the growth-inhibitory effects of E₂ differed in cells grown on collagen and fibroblasts. EGF,at concentrations of 1-100 ng/ml, consistently stimulated the growth of HMEC from all mammary tissue types examined. The EGF stimulation of growth was reduced by a monoclonal antibody (MAb 528) against the EGF receptor. TGF-α was equally or more effective in stimulating HMEC growth, although its dose response range was different than that of EGF. E₂ plus EGF synergized in the stimulation of HMEC growth in 33% of the samples examined. These studies suggest that E₂ alone under the conditions used cannot directly stimulate the growth of HMEC in primary culture. However, E₂ can exert effects on HMEC growth via modulation of the cells' response to EGF. === Medicine, Faculty of === Graduate
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