Alvarez-Baron Claudia P, Jonsson Philip, Thomas Christoforos, Dryer Stuart E, Williams Cecilia
Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5001, USA.
Mol Endocrinol. 2011 Aug;25(8):1326-36. doi: 10.1210/me.2011-0045. Epub 2011 Jun 16.
The growth of many human breast tumors requires the proliferative effect of estrogen acting via the estrogen receptor α (ERα). ERα signaling is therefore a clinically important target for breast cancer prevention and therapeutics. Although extensively studied, the mechanism by which ERα promotes proliferation remains to be fully established. We observed an up-regulation of transcript encoding the pH-sensitive two-pore domain potassium channel KCNK5 in a screen for genes stimulated by 17β-estradiol (E2) in the ERα(+) breast cancer cell lines MCF-7 and T47D. KCNK5 mRNA increased starting 1 h after the onset of E2 treatment, and protein levels followed after 12 h. Estrogen-responsive elements are found in the enhancer region of KCNK5, and chromatin immunoprecipitation assays revealed binding of ERα to the KCNK5 enhancer in E2-treated MCF-7 cells. Cells treated with E2 also showed increases in the amplitude of pH-sensitive potassium currents, as assessed by whole-cell recordings. These currents are blocked by clofilium. Although confocal microscopy suggested that most of the channels are located in intracellular compartments, the increase in macroscopic currents suggests that E2 treatment increases the number of active channels at the cell surface. Application of small interfering RNA specific for KCNK5 decreased pH-sensitive potassium currents and also reduced the estrogen-induced proliferation of T47D cells. We conclude that E2 induces the expression of KCNK5 via ERα(+) in breast cancer cells, and this channel plays a role in regulating proliferation in these cell lines. KCNK5 may therefore represent a useful target for treatment, for example, of tamoxifen-resistant breast cancer.
许多人类乳腺肿瘤的生长需要雌激素通过雌激素受体α（ERα）发挥增殖作用。因此，ERα信号传导是乳腺癌预防和治疗的一个重要临床靶点。尽管已进行了广泛研究，但ERα促进增殖的机制仍有待全面阐明。我们在对ERα(+)乳腺癌细胞系MCF-7和T47D中受17β-雌二醇（E2）刺激的基因进行筛选时，观察到编码pH敏感双孔域钾通道KCNK5的转录本上调。E2处理开始1小时后，KCNK5 mRNA增加，12小时后蛋白质水平随之增加。在KCNK5的增强子区域发现了雌激素反应元件，染色质免疫沉淀试验显示在E2处理的MCF-7细胞中ERα与KCNK5增强子结合。通过全细胞膜片钳记录评估，用E2处理的细胞也显示pH敏感钾电流幅度增加。这些电流被氯非铵阻断。尽管共聚焦显微镜显示大多数通道位于细胞内区室，但宏观电流的增加表明E2处理增加了细胞表面活性通道的数量。应用针对KCNK5的小干扰RNA可降低pH敏感钾电流，并减少雌激素诱导的T47D细胞增殖。我们得出结论，E2通过乳腺癌细胞中的ERα(+)诱导KCNK5的表达，并且该通道在调节这些细胞系的增殖中起作用。因此，KCNK5可能是治疗例如他莫昔芬耐药乳腺癌的一个有用靶点。
