Centro Sanitario, University of Calabria, Arcavacata di Rende, Italy.
Oncogene. 2011 Sep 29;30(39):4129-40. doi: 10.1038/onc.2011.124. Epub 2011 Apr 18.
Tamoxifen (Tam) treatment is a first-line endocrine therapy for estrogen receptor-α-positive breast cancer patients. Unfortunately, resistance frequently occurs and is often related with overexpression of the membrane tyrosine kinase receptor HER2. This is the rationale behind combined treatments with endocrine therapy and novel inhibitors that reduce HER2 expression and signaling and thus inhibit Tam-resistant breast cancer cell growth. In this study, we show that activation of farnesoid X receptor (FXR), by the primary bile acid chenodeoxycholic acid (CDCA) or the synthetic agonist GW4064, inhibited growth of Tam-resistant breast cancer cells (termed MCF-7 TR1), which was used as an in vitro model of acquired Tam resistance. Our results demonstrate that CDCA treatment significantly reduced both anchorage-dependent and anchorage-independent epidermal growth factor (EGF)-induced growth in MCF-7 TR1 cells. Furthermore, results from western blot analysis and real-time reverse transcription-PCR revealed that CDCA treatment reduced HER2 expression and inhibited EGF-mediated HER2 and p42/44 mitogen-activated protein kinase (MAPK) phosphorylation in these Tam-resistant breast cancer cells. Transient transfection experiments, using a vector containing the human HER2 promoter region, showed that CDCA treatment downregulated basal HER2 promoter activity. This occurred through an inhibition of nuclear factor-κB transcription factor binding to its specific responsive element located in the HER2 promoter region as revealed by mutagenesis studies, electrophoretic mobility shift assay and chromatin immunoprecipitation analysis. Collectively, these data suggest that FXR ligand-dependent activity, blocking HER2/MAPK signaling, may overcome anti-estrogen resistance in human breast cancer cells and could represent a new therapeutic tool to treat breast cancer patients that develop resistance.
他莫昔芬（Tam）治疗是雌激素受体-α阳性乳腺癌患者的一线内分泌治疗方法。不幸的是，经常会发生耐药，并且常常与膜酪氨酸激酶受体 HER2 的过度表达有关。这就是联合内分泌治疗和新型抑制剂治疗的原理，这些抑制剂可降低 HER2 的表达和信号传导，从而抑制他莫昔芬耐药的乳腺癌细胞生长。在这项研究中，我们表明，初级胆汁酸鹅脱氧胆酸（CDCA）或合成激动剂 GW4064 激活法尼酯 X 受体（FXR），可抑制他莫昔芬耐药乳腺癌细胞（称为 MCF-7 TR1）的生长，该细胞被用作获得性他莫昔芬耐药的体外模型。我们的结果表明，CDCA 处理可显着降低 MCF-7 TR1 细胞中依赖锚定和非依赖锚定的表皮生长因子（EGF）诱导的生长。此外，Western blot 分析和实时逆转录-PCR 的结果表明，CDCA 处理可降低 HER2 表达，并抑制这些他莫昔芬耐药乳腺癌细胞中 EGF 介导的 HER2 和 p42/44 丝裂原活化蛋白激酶（MAPK）磷酸化。使用包含人 HER2 启动子区域的载体进行的瞬时转染实验表明，CDCA 处理可下调基础 HER2 启动子活性。这是通过抑制核因子-κB 转录因子与其位于 HER2 启动子区域的特定反应元件结合来实现的，这是通过突变研究，电泳迁移率变动分析和染色质免疫沉淀分析揭示的。总的来说，这些数据表明，FXR 配体依赖性活性可阻断 HER2/MAPK 信号传导，可能克服人类乳腺癌细胞中的抗雌激素耐药性，并可能成为治疗发生耐药的乳腺癌患者的新治疗工具。
