Fenton S E, Sheffield L G
Endocrinology-Reproductive Physiology Program, University of Wisconsin-Madison 53706.
Mol Biol Cell. 1993 Aug;4(8):773-80. doi: 10.1091/mbc.4.8.773.
We have previously shown that lactogenic hormones stimulate epidermal growth factor (EGF) mRNA accumulation in mouse mammary glands in vivo and in mouse mammary epithelial cells (NMuMG line). However, our in vitro studies indicate that the lactogenic hormone prolactin (PRL) completely inhibits EGF-stimulated DNA synthesis. PRL does not alter cholera toxin or insulin-like growth factor-1-stimulated cell growth, thus the inhibition appears to be specific for EGF. Our current studies are designed to evaluate the effects of PRL on EGF-stimulated signaling events in the NMuMG cell line. Cells treated with PRL for 30 min demonstrated a loss of high affinity EGF-binding ability. After long-term PRL treatment (18 h) there was a decrease in EGF receptor (R) number, as determined by [125I]EGF binding. PRL treatment (8 h) also decreased EGF-R mRNA levels. An EGF-stimulated increase in EGF-R mRNA observed 2-4 h after treatment was decreased when PRL was added to the cultures. Furthermore, levels of EGF-stimulated tyrosine phosphorylation of the EGF-R (170 kDa) and phospholipase C gamma (145 kDa) are dramatically decreased in cells treated with PRL. Also of great interest was a decrease in EGF-stimulated c-myc mRNA in PRL-treated cells. We conclude that PRL is acting to down-regulate the EGF-R, thus limiting EGF-stimulated cell signaling in mammary tissue.
我们之前已经表明，泌乳激素可在体内刺激小鼠乳腺以及小鼠乳腺上皮细胞（NMuMG系）中表皮生长因子（EGF）mRNA的积累。然而，我们的体外研究表明，泌乳激素催乳素（PRL）完全抑制EGF刺激的DNA合成。PRL不会改变霍乱毒素或胰岛素样生长因子-1刺激的细胞生长，因此这种抑制似乎对EGF具有特异性。我们当前的研究旨在评估PRL对NMuMG细胞系中EGF刺激的信号转导事件的影响。用PRL处理30分钟的细胞表现出高亲和力EGF结合能力的丧失。通过[125I]EGF结合测定，长期PRL处理（18小时）后EGF受体（R）数量减少。PRL处理（8小时）也降低了EGF-R mRNA水平。当向培养物中添加PRL时，处理后2-4小时观察到的EGF刺激的EGF-R mRNA增加减少。此外，在PRL处理的细胞中，EGF刺激的EGF-R（170 kDa）和磷脂酶Cγ（145 kDa）的酪氨酸磷酸化水平显著降低。同样引起极大兴趣的是，PRL处理的细胞中EGF刺激的c-myc mRNA减少。我们得出结论，PRL起到下调EGF-R的作用，从而限制乳腺组织中EGF刺激的细胞信号转导。
