Chen X, Danes C, Lowe M, Herliczek T W, Keyomarsi K
Division of Molecular Medicine, Wadsworth Center, Albany, NY, USA.
J Natl Cancer Inst. 2000 Sep 6;92(17):1403-13. doi: 10.1093/jnci/92.17.1403.
Estrogen stimulates the proliferation of cells in normal mammary glands and most estrogen receptor (ER)-positive mammary carcinomas by binding to the ER and promoting the transcription of ER-responsive genes. In cells with functional ERs, estrogen mediates the transition of cells from the G(1) to S phase of the cell cycle. Several cell cycle regulatory proteins have been implicated in the ER-signaling pathway involved in estrogen-mediated growth stimulation and antiestrogen-mediated growth arrest. We sought to determine whether p21, a cyclin-dependent kinase inhibitor, is a component of this pathway and, if so, whether it can mediate estrogen's action in ER-negative breast cancer cells.
We overexpressed p21 with a tetracycline-inducible system in ER-negative, p21-negative breast cancer cells. Activity of the ER-signaling pathway was monitored in transient transfection assays by using constructs in which the ER promoter or the estrogen-response element (ERE) controls Luciferase expression. The growth-modulating effects of estradiol and antiestrogens on p21-overexpressing clones were assessed. All P: values are from two-sided tests.
A strong positive association was found between the expression of p21 and ER in nine breast cancer cell lines and in tumor samples from 60 patients with breast cancer (P:<. 001). Overexpression of p21 in a p21-negative, ER-negative cell line induced both the ER and ERE promoters in an estrogen-responsive manner. Last, stable p21 clones that also lack the expression of wild-type ER were responsive to the growth-inhibitory effects of ICI 182,780, a potent antiestrogen, and the growth-stimulatory effects of 17beta-estradiol.
The ability of p21 to mediate the activation of the estrogen-signaling pathway in ER-negative tumor cells suggests that p21 plays a novel role in this pathway, a finding that also has important clinical implications.
雌激素通过与雌激素受体（ER）结合并促进ER反应性基因的转录，刺激正常乳腺组织及大多数ER阳性乳腺癌细胞的增殖。在具有功能性ER的细胞中，雌激素介导细胞从细胞周期的G1期过渡到S期。几种细胞周期调节蛋白参与了雌激素介导的生长刺激和抗雌激素介导的生长停滞的ER信号通路。我们试图确定细胞周期蛋白依赖性激酶抑制剂p21是否是该通路的组成部分，如果是，它是否能介导雌激素在ER阴性乳腺癌细胞中的作用。
我们用四环素诱导系统在ER阴性、p21阴性的乳腺癌细胞中过表达p21。通过使用ER启动子或雌激素反应元件（ERE）控制荧光素酶表达的构建体，在瞬时转染试验中监测ER信号通路的活性。评估雌二醇和抗雌激素对p21过表达克隆的生长调节作用。所有P值均来自双侧检验。
在9个乳腺癌细胞系和60例乳腺癌患者的肿瘤样本中，发现p21表达与ER之间存在强正相关（P<0.001）。在一个p21阴性、ER阴性的细胞系中过表达p21以雌激素反应性方式诱导ER和ERE启动子。最后，同样缺乏野生型ER表达的稳定p21克隆对强效抗雌激素ICI 182,780的生长抑制作用和17β-雌二醇的生长刺激作用有反应。
p21在ER阴性肿瘤细胞中介导雌激素信号通路激活的能力表明，p21在该通路中发挥了新的作用，这一发现也具有重要的临床意义。
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