Oesterreich S, Zhang P, Guler R L, Sun X, Curran E M, Welshons W V, Osborne C K, Lee A V
Breast Center, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
Cancer Res. 2001 Aug 1;61(15):5771-7.
Estrogen can increase insulin-like growth factor-I receptor (IGF-IR) and insulin receptor substrate-1 (IRS-1) expression, two key components of IGF-I-mediated signaling. The result is sensitization of breast cancer cells to IGF-I and synergistic growth in the presence of estrogen and IGF-I. We hypothesized that loss of estrogen receptor alpha (ERalpha) would result in reduced IGF-mediated signaling and growth. To test this hypothesis, we examined IGF-I effects in MCF-7 breast cancer cell sublines that have been selected for loss of ERalpha (C4 and C4-12 cells are ERalpha-negative) by long-term estrogen withdrawal. C4 and C4-12 cells had reduced IGF-IR and IRS-1 mRNA and protein expression (compared with MCF-7 cells) that was not inducible by estrogen. Furthermore, C4 and C4-12 cells showed reduced IGF-I signaling and failed to show any growth response to either estrogen or IGF-I. To prove that loss of IGF and estrogen-mediated signaling and growth was a consequence of loss of ERalpha, we re-expressed ERalpha in C4-12 cells by stable transfection with HA-tagged ERalpha. Three independent C4-12 ERalpha-HA clones expressed a functional ERalpha that (a) was down-regulated by estrogen, (b) conferred estrogen-induction of cyclin D1 expression, and (c) caused estrogen-mediated increase in the number of cells in S phase. All of the effects were completely blocked by antiestrogens. Interestingly, ERalpha-HA expression in C4-12 cells did not restore estrogen induction of progesterone receptor expression. However, ERalpha-positive C4-12 cells now exhibited estrogen-induction of IGF-IR and IRS-1 levels and responded mitogenically to both estrogen and IGF-I. These data show that ERalpha is a critical requirement for IGF signaling, and to our knowledge this is the first report of functional ERalpha expression that confers estrogen-mediated growth of an ER-negative breast cancer cell line.
雌激素可增加胰岛素样生长因子-I受体（IGF-IR）和胰岛素受体底物-1（IRS-1）的表达，这是IGF-I介导信号传导的两个关键组成部分。结果是乳腺癌细胞对IGF-I敏感，并在雌激素和IGF-I共同存在时协同生长。我们推测雌激素受体α（ERα）的缺失会导致IGF介导的信号传导和生长减少。为了验证这一假设，我们检测了长期撤除雌激素后已筛选出缺失ERα的MCF-7乳腺癌细胞亚系（C4和C4-12细胞为ERα阴性）中IGF-I的作用。C4和C4-12细胞中IGF-IR和IRS-1的mRNA及蛋白表达降低（与MCF-7细胞相比），且不受雌激素诱导。此外，C4和C4-12细胞显示出IGF-I信号传导减弱，对雌激素或IGF-I均未表现出任何生长反应。为了证明IGF和雌激素介导的信号传导及生长缺失是ERα缺失的结果，我们通过用HA标签的ERα进行稳定转染，在C4-12细胞中重新表达ERα。三个独立的C4-12 ERα-HA克隆表达了功能性的ERα，其（a）受雌激素下调，（b）赋予雌激素对细胞周期蛋白D1表达的诱导作用，（c）导致雌激素介导的S期细胞数量增加。所有这些作用均被抗雌激素完全阻断。有趣的是，C4-12细胞中ERα-HA的表达并未恢复雌激素对孕激素受体表达的诱导作用。然而，ERα阳性的C4-12细胞现在表现出雌激素对IGF-IR和IRS-1水平的诱导作用，并对雌激素和IGF-I均有丝裂原反应。这些数据表明ERα是IGF信号传导的关键需求，据我们所知，这是首次报道功能性ERα表达赋予雌激素介导的ER阴性乳腺癌细胞系生长的研究。
