Shehu Aurora, Albarracin Constance, Devi Y Sangeeta, Luther Kristin, Halperin Julia, Le Jamie, Mao Jifang, Duan Rachel W, Frasor Jonna, Gibori Geula
Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
Mol Endocrinol. 2011 May;25(5):754-66. doi: 10.1210/me.2010-0261. Epub 2011 Mar 3.
Our laboratory has previously cloned and purified an ovarian protein found to be a novel 17β-hydroxysteroid dehydrogenase type 7 enzyme (HSD17B7) (formerly prolactin receptor-associated protein) that converts the weak estrogen, estrone, to the highly potent estradiol. The regulation of this enzyme has not yet been explored. In this report, we show high expression of HSD17B7 in human ductal carcinoma and breast cancer cell lines and present evidence for a strong up-regulation of this enzyme by estradiol at the level of mRNA, protein expression, and promoter activity in MCF-7 cells. The effect of estradiol is mediated by estrogen receptor (ER)α, whereas ERβ prevents this stimulation. ER antagonists, ICI 182,780 and 4-hydroxytamoxifen, prevent estradiol-induced stimulation of the endogenously expressed HSD17B7, suggesting that these inhibitors not only block estradiol action but also its production. We have identified a -185-bp region of the hsd17b7 promoter that is highly conserved among rat, mouse, and human and confers regulation by estradiol in MCF-7 cells. This region is devoid of a classical estradiol-response element but contains a nuclear factor 1 (NF1) site that is essential for estradiol action. We found that estradiol stimulates the recruitment and DNA binding of NF1 to this region of the hsd17b7 promoter. Furthermore, knockdown of NF1 family members, NF1B, NF1A, and NF1X, completely prevents induction of this gene by estradiol. In summary, our findings demonstrate that estradiol stimulates HSD17B7 transcriptional activity in breast cancer cells through a novel mechanism requiring NF1 and strongly suggest a positive feedback mechanism to increase local estradiol synthesis causing growth of estrogen-dependent breast cancers.
我们实验室之前克隆并纯化了一种卵巢蛋白，该蛋白被发现是一种新型的7型17β-羟基类固醇脱氢酶（HSD17B7）（以前称为催乳素受体相关蛋白），它可将弱雌激素雌酮转化为高效能的雌二醇。该酶的调控机制尚未得到研究。在本报告中，我们展示了HSD17B7在人导管癌和乳腺癌细胞系中的高表达，并提供证据表明在MCF-7细胞中，雌二醇在mRNA、蛋白质表达和启动子活性水平上强烈上调该酶。雌二醇的作用由雌激素受体（ER）α介导，而ERβ则阻止这种刺激。ER拮抗剂ICI 182,780和4-羟基他莫昔芬可阻止雌二醇诱导的内源性表达的HSD17B7的刺激，这表明这些抑制剂不仅阻断雌二醇的作用，还阻断其产生。我们已经鉴定出hsd17b7启动子的一个-185 bp区域，该区域在大鼠、小鼠和人类中高度保守，并赋予MCF-7细胞中雌二醇的调控作用。该区域没有经典的雌二醇反应元件，但含有一个对雌二醇作用至关重要的核因子1（NF1）位点。我们发现雌二醇刺激NF1募集并与hsd17b7启动子的该区域结合。此外，敲低NF1家族成员NF1B、NF1A和NF1X可完全阻止雌二醇对该基因的诱导。总之，我们的研究结果表明，雌二醇通过一种需要NF1的新机制刺激乳腺癌细胞中HSD17B7的转录活性，并强烈提示存在一种正反馈机制，可增加局部雌二醇合成，从而导致雌激素依赖性乳腺癌的生长。
