Han Youqi, Yang Lin, Suarez-Saiz Fernando, San-Marina Serban, Cui Jie, Minden Mark D
Princess Margaret Hospital/Ontario Cancer Institute, University Health Network, Toronto, Ontario, Canada M5G 2M9.
Mol Cancer Res. 2008 Aug;6(8):1347-55. doi: 10.1158/1541-7786.MCR-07-2179.
The antiestrogen tamoxifen has been used in the treatment of hormone-responsive breast cancer for over a decade. The loss of estrogen receptor (ER) expression is the most common mechanism for de novo antiestrogen resistance. Wilms' tumor 1 suppressor gene (WT1) is a clinically useful marker that is associated with poor prognosis in breast cancer patients; its high level expression is frequently observed in cases of breast cancer that are estrogen and progesterone receptor negative. The lack of expression of these receptors is characteristic of tumor cells that are not responsive to hormonal manipulation. To determine whether there is a linkage between WT1 expression and antiestrogen resistance in breast cancer cells, we studied the effect of WT1 on tamoxifen responsiveness in ERalpha-positive MCF-7 cells. We found that overexpression of WT1 in MCF-7 markedly abrogated tamoxifen-induced cell apoptosis and 17beta-estradiol (E(2))-mediated cell proliferation. The expressions of ERalpha and its downstream target genes were significantly repressed following overexpression of WT1, whereas the down-regulation of WT1 by WT1 shRNA could enhance ERalpha expression and the sensitivity to tamoxifen treatment in ERalpha-negative MDA468 and HCC1954 cells that express high levels of WT1. Furthermore, we have confirmed that the WT1 protein can bind to endogenous WT1 consensus sites in the proximal promoter of ERalpha and thus inhibit the transcriptional activity of the ERalpha promoter in a WT1 site sequence-specific manner. Our study clearly implicates WT1 as a mediator of antiestrogen resistance in breast cancer through down-regulation of ERalpha expression and supports the development of WT1 inhibitors as a potential means of restoring antiestrogen responsiveness in breast cancer therapy.
抗雌激素药物他莫昔芬已用于激素反应性乳腺癌的治疗达十余年。雌激素受体（ER）表达缺失是原发性抗雌激素耐药的最常见机制。威尔姆斯瘤1抑制基因（WT1）是一种具有临床实用价值的标志物，与乳腺癌患者的不良预后相关；在雌激素和孕激素受体阴性的乳腺癌病例中经常观察到其高水平表达。这些受体表达的缺失是肿瘤细胞对激素操纵无反应的特征。为了确定WT1表达与乳腺癌细胞抗雌激素耐药之间是否存在联系，我们研究了WT1对雌激素受体α（ERα）阳性的MCF-7细胞中他莫昔芬反应性的影响。我们发现，WT1在MCF-7细胞中的过表达显著消除了他莫昔芬诱导的细胞凋亡以及17β-雌二醇（E₂）介导的细胞增殖。WT1过表达后，ERα及其下游靶基因的表达被显著抑制，而WT1短发夹RNA（shRNA）下调WT1可增强ERα表达以及ERα阴性、WT1高表达的MDA468和HCC1954细胞对他莫昔芬治疗的敏感性。此外，我们已证实WT1蛋白可与ERα近端启动子中的内源性WT1共有位点结合，从而以WT1位点序列特异性方式抑制ERα启动子的转录活性。我们的研究清楚地表明，WT1通过下调ERα表达而成为乳腺癌抗雌激素耐药的介导因子，并支持开发WT1抑制剂作为恢复乳腺癌治疗中抗雌激素反应性的潜在手段。
