Brown N M, Wang J, Cotroneo M S, Zhao Y X, Lamartiniere C A
Department of Pharmacology and Toxicology, and the Comprehensive Cancer Center, University of Alabama at Birmingham, 35294, USA.
Mol Cell Endocrinol. 1998 Sep 25;144(1-2):149-65. doi: 10.1016/s0303-7207(98)00106-3.
We have previously demonstrated that exposure to genistein early in life protects against chemically-induced mammary cancer in rats. To gain insight into the mechanism of action, we have investigated the expression of the EGF-signaling pathway in the mammary glands of 21 and 50 day old rats treated on days 16, 18, and 20 postpartum with 500 microg genistein/g body weight (B.W.) or an equivalent volume of the vehicle, dimethylsulfoxide (DMSO). This prepubertal genistein treatment up-regulated TGF-alpha and the EGF-receptor (EGFR), but not EGF, in mammary terminal ductal structures at day 21 postpartum. TGF-alpha, EGF and EGFR mRNA levels were similar in 21 day old control- and genistein-treated animals. At day 50 postpartum, mammary glands of genistein treated rats had more lobules and fewer terminal end buds (TEBs) and terminal ducts (TDs), i.e. they were more differentiated. TGF-alpha mRNA levels were down-regulated in TEB of proestrous and estrous females; EGF mRNA levels were down-regulated in TDs of proestrous, but not in estrous females; and EGFR mRNA levels were not altered in 50 day old proestrous or estrous female rats. EGFR immunostaining intensity was decreased in TEBs, but not in the total gland. EGF was increased in TEBs and TDs. TGF-alpha, EGF and EGFR were also observed in the stroma and fat pad, but genistein treatment did not alter the expression of these proteins in those locations. TGF-alpha, but not EGF and EGFR, immunostaining was observed in cell nuclei (not modulated by genistein), suggesting that this growth factor may act directly on nuclear events such as transcription and DNA replication. For comparative purposes, prepubertal diethylstilbestrol treatment was investigated and found to decrease EGFR immunostaining intensity and total IHC staining in all terminal ductal structures. We conclude that prepubertal genistein treatment directly stimulates TGF-alpha and EGFR to enhance mammary gland differentiation. This programs the differentiated cells for a down-regulated EGF-signaling pathway in TEBs and TDs of adult mammary glands. Reduced EGFR expression at time of carcinogen exposure may account for genistein programming against mammary cancer.
我们之前已经证明，生命早期接触染料木黄酮可预防大鼠化学诱导的乳腺癌。为深入了解其作用机制，我们研究了产后第16、18和20天用500微克染料木黄酮/克体重（B.W.）或等量溶剂二甲基亚砜（DMSO）处理的21日龄和50日龄大鼠乳腺中表皮生长因子（EGF）信号通路的表达。这种青春期前的染料木黄酮处理在产后第21天上调了乳腺终末导管结构中的转化生长因子-α（TGF-α）和表皮生长因子受体（EGFR），但未上调EGF。在21日龄的对照和染料木黄酮处理动物中，TGF-α、EGF和EGFR的mRNA水平相似。产后第50天，染料木黄酮处理的大鼠乳腺有更多小叶，终末芽（TEB）和终末导管（TD）更少，即它们分化程度更高。动情前期和动情期雌性大鼠TEB中的TGF-α mRNA水平下调；动情前期雌性大鼠TD中的EGF mRNA水平下调，但动情期雌性大鼠未下调；50日龄动情前期或动情期雌性大鼠的EGFR mRNA水平未改变。EGFR免疫染色强度在TEB中降低，但在整个腺体中未降低。TEB和TD中的EGF增加。在基质和脂肪垫中也观察到TGF-α、EGF和EGFR，但染料木黄酮处理未改变这些部位这些蛋白的表达。在细胞核中观察到TGF-α免疫染色（不受染料木黄酮调节），而EGF和EGFR未观察到，这表明这种生长因子可能直接作用于转录和DNA复制等核事件。为作比较，研究了青春期前己烯雌酚处理，发现其降低了所有终末导管结构中的EGFR免疫染色强度和总免疫组化染色。我们得出结论，青春期前染料木黄酮处理直接刺激TGF-α和EGFR以增强乳腺分化。这使分化细胞在成年乳腺的TEB和TD中具有下调的EGF信号通路。致癌物暴露时EGFR表达降低可能解释了染料木黄酮对乳腺癌的预防作用。
