Hyperactivation of MAPK induces loss of ERα expression in breast cancer cells
Hyperactivation of MAPK induces loss of ERα expression in breast cancer cells
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DOI：
10.1210/me.15.8.1344
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发表时间：
2001-08-01
影响因子：
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通讯作者：
El-Ashry, D
中科院分区：
文献类型：
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作者：
Oh, AS;Lorant, LA;El-Ashry, D
ER α阴性乳腺肿瘤倾向于过度表达生长因子受体，如表皮生长因子受体或c-erbB-2。Raf-1是这些受体信号转导途径中的关键中间体。高水平的组成型Raf激酶（Δ raf）活性赋予ER α阳性MCF-7乳腺癌细胞在缺乏雌激素的情况下生长的能力。维持在雌激素耗尽培养基中的Delta raf转染子对17 β-雌二醇或纯抗雌激素ICI 182，780的反应大大减弱。Western印迹、配体结合和免疫组织化学分析揭示ER α蛋白表达的损失，并且核糖核酸酶保护分析表明这与ER α信息的损失相关。在用雌激素反应元件-报告基因构建体和Δ raf或组成型活性MAPK激酶（Δ MEK）检查稳定转染子或瞬时共转染测定中雌激素诱导基因的基础表达时，未观察到ER α的配体非依赖性活化。Delta raf的瞬时表达和双标记免疫染色显示ER α在瞬时表达Delta raf的细胞中丢失。通过用MEK抑制剂PD 098059或U 0126处理消除Raf信号传导导致ER a的再表达。用过表达表皮生长因子受体或c-erbB-2的MCF-7细胞进行的类似研究证实，MAPK的过度活化导致ER α的下调，这通过MEK抑制或用显性负性ERK 1和ERK 2构建体转染是可逆的。这些数据表明，在表皮生长因子受体或c-erbB-2过表达的乳腺癌细胞中MAPK的过度活化直接导致ER α阴性表型的产生，更重要的是，该过程可以通过抑制这些途径来消除，从而恢复ER α表达。
ER alpha -negative breast tumors tend to overexpress growth factor receptors such as epidermal growth factor receptor or c-erbB-2. Raf-1 is a key intermediate in the signal transduction pathways of these receptors. High levels of constitutive Raf kinase (Delta raf) activity imparts ER alpha- positive MCF-7 breast cancer cells with the ability to grow in the absence of estrogen. Delta raf transfectants maintained in estrogen-depleted media showed greatly diminished responses to 17 beta -estradiol or the pure antiestrogen ICI 182,780. Western blotting, ligand binding, and immunohistochemistry assays revealed a loss of ER alpha protein expression, and ribonuclease protection assays indicated that this correlated with loss of ER alpha message. In examining the basal expression of estrogen-induced genes in the stable transfectants or in transient cotransfection assays with an estrogen-response element-reporter construct and Delta raf or constitutively active MAPK kinase (Delta MEK), no ligand- independent activation of ER alpha was observed. Transient expression of Delta raf and double-label immunostaining showed ER alpha was lost in those cells that transiently expressed Delta raf. Abrogation of Raf signaling via treatment with the MEK inhibitors PD 098059 or U0126 resulted in reexpression of ERa. Similar studies performed with MCF-7 cells overexpressing epidermal growth factor receptor or c-erbB-2 confirmed that hyperactivation of MAPK resulted in down-regulation of ER alpha that was reversible by MEK inhibition or transfection with dominant negative ERK1 and ERK2 constructs. These data suggest that the hyperactivation of MAPK in epidermal growth factor receptor- or c-erbB-2-overexpressing breast cancer cells is directly responsible for generation of an ER alpha -negative phenotype and, more importantly, that this process may be abrogated by inhibiting these pathways, thus restoring ER alpha expression.