Lazennec G, Katzenellenbogen B S
Department of Molecular and Integrative Physiology, University of Illinois, Urbana 61801, USA.
Mol Cell Endocrinol. 1999 Mar 25;149(1-2):93-105. doi: 10.1016/s0303-7207(98)00254-8.
Estrogen receptor (ER)-negative breast carcinomas are often difficult to treat as they do not respond to hormone therapy. In an attempt to determine if expressing the human estrogen receptor in an ectopic manner could restore the hormone responsiveness of these cells, we have expressed the human ER in ER-negative MDA-MB 231 breast cancer cells using a recombinant adenovirus gene delivery system that allows high level expression of ER in essentially all cells. In these cells, the ER was correctly translated, had a wild type hormone binding affinity (Kd = 0.6 nM), bound well to estrogen response element-containing DNA, and showed an activation pattern of estrogen response element-reporter gene activity by estrogen and antiestrogens very similar to that observed in MCF-7 breast cancer cells containing endogenous ER (stimulation by estrogen, no stimulation by the antiestrogens trans-hydroxytamoxifen or ICI 164384, and blockade of estradiol stimulation by trans-hydroxytamoxifen or ICI 164384). Intriguingly, estradiol stimulation of these cells was also able to induce expression of pS2, an estrogen regulated gene considered to be a favorable prognostic marker for endocrine therapy in ER-positive breast cancer cells. Expression of the ER had no effect by itself on the proliferation rate of MDA-MB 231 cells. However, treatment of the ER-containing cells with estradiol or with the pure antiestrogen ICI 164 384 suppressed proliferation of the cells while the antiestrogen trans-hydroxytamoxifen had little effect on proliferation; and cotreatment with trans-hydroxytamoxifen reversed the estradiol- or ICI 164 384-evoked suppression of proliferation. To understand the mechanism underlying the inhibition of proliferation by estradiol, we examined the expression of several growth related endogenous genes. c-Myc protooncogene expression was strongly inhibited by treatment with estradiol as was expression of BRCA1 and BRCA2 genes, which is in agreement with their mitogenic-dependent expression, while expression of beta-actin, a housekeeping gene, was not affected by hormone treatment. Together, these data suggest that reexpressing the human ER in breast cancer cells that no longer express this protein renders them sensitive to hormone treatment. The ability of the antiestrogen ICI 164 384 to suppress the proliferation of ER-negative breast cancer cells that reexpress ER might be useful ultimately as an endocrine gene therapy approach for controlling the growth of ER-negative breast cancer cells. The application of recombinant adenoviruses expressing the human ER presents interesting features which might be used as a basis for designing more powerful and effective treatments for ER-negative breast cancers.
雌激素受体（ER）阴性的乳腺癌通常难以治疗，因为它们对激素疗法无反应。为了确定以异位方式表达人雌激素受体是否能恢复这些细胞的激素反应性，我们使用重组腺病毒基因递送系统在ER阴性的MDA-MB 231乳腺癌细胞中表达人ER，该系统能使ER在基本上所有细胞中高水平表达。在这些细胞中，ER被正确翻译，具有野生型激素结合亲和力（Kd = 0.6 nM），能很好地结合含雌激素反应元件的DNA，并且通过雌激素和抗雌激素显示出与在含有内源性ER的MCF-7乳腺癌细胞中观察到的非常相似的雌激素反应元件-报告基因活性激活模式（雌激素刺激，反式羟基他莫昔芬或ICI 164384无刺激，反式羟基他莫昔芬或ICI 164384阻断雌二醇刺激）。有趣的是，雌二醇对这些细胞的刺激还能够诱导pS2的表达，pS2是一种雌激素调节基因，被认为是ER阳性乳腺癌细胞内分泌治疗的良好预后标志物。ER的表达本身对MDA-MB 231细胞的增殖率没有影响。然而，用雌二醇或纯抗雌激素ICI 164 384处理含ER的细胞会抑制细胞增殖，而抗雌激素反式羟基他莫昔芬对增殖几乎没有影响；与反式羟基他莫昔芬共同处理可逆转雌二醇或ICI 164 384引起的增殖抑制。为了了解雌二醇抑制增殖的潜在机制，我们检测了几种与生长相关的内源性基因的表达。用雌二醇处理强烈抑制了c-Myc原癌基因的表达以及BRCA1和BRCA2基因的表达，这与它们的促有丝分裂依赖性表达一致，而管家基因β-肌动蛋白的表达不受激素处理的影响。总之，这些数据表明在不再表达该蛋白的乳腺癌细胞中重新表达人ER可使它们对激素治疗敏感。抗雌激素ICI 164 384抑制重新表达ER的ER阴性乳腺癌细胞增殖的能力最终可能作为一种内分泌基因治疗方法用于控制ER阴性乳腺癌细胞的生长。表达人ER的重组腺病毒的应用呈现出一些有趣的特征，可作为设计更强大、更有效的ER阴性乳腺癌治疗方法的基础。
