Treeck Oliver, Pfeiler Georg, Horn Felicitas, Federhofer Bettina, Houlihan Helena, Vollmer Angelika, Ortmann Olaf
Department of Obstetrics and Gynecology, University Regensburg, 93053 Regensburg, Germany.
Mol Cell Endocrinol. 2007 Jan 29;264(1-2):50-60. doi: 10.1016/j.mce.2006.10.003. Epub 2006 Nov 13.
Estrogen receptor (ER) beta gene codes for different transcript variants resulting from alternative splicing. In this study, we report identification of the two novel human exon-skipped ERbeta transcript isoforms ERbetaDelta125 and ERbetaDelta1256 in MDA-MD-231 breast cancer cells. Both transcripts could also be detected in a variety of human tissues. We further report the results of an in vitro attempt to characterize their function in regulation of cell growth, motility, apoptosis and gene expression. COS-1 cells stably transfected with the novel ERbeta transcripts exhibited a notably slower growth even in the absence of estradiol when compared to vector-transfected control cells. Like ERbeta1, both novel ERbeta transcript isoforms raised the basal apoptosis rate of COS-1 cells in a ligand-independent manner. Whereas introduction of ERbetaDelta1256 notably increased the sensitivity of COS-1 cells towards lower concentrations of selective estrogen receptor modulator tamoxifen, presence of ERbeta1 and ERbetaDelta125 transcripts further weakened the growth-inhibitory effect of tamoxifen on this cell line. Furthermore, expression of ERbetaDelta1256 variant was demonstrated to reduce transcript levels of estrogen-responsive genes like cyclin A2, IGFBP-4 and fibulin 1c in COS-1 cells in a ligand-independent manner. Though we were not able to detect the predicted 29 and 34kDa proteins by means of western blot analysis, our data strongly suggest the biological functionality of both isoforms on molecular level. With this report increasing the multitude of existing ERbeta mRNA isoforms, we provide further evidence that their synthesis has to be considered as an important level of estrogen signaling.
雌激素受体（ER）β基因通过可变剪接编码不同的转录变体。在本研究中，我们报告了在MDA-MD-231乳腺癌细胞中鉴定出两种新的人类外显子跳跃型ERβ转录异构体ERβDelta125和ERβDelta1256。在多种人类组织中也能检测到这两种转录本。我们还进一步报告了一项体外实验的结果，该实验旨在表征它们在调节细胞生长、运动、凋亡和基因表达方面的功能。与载体转染的对照细胞相比，稳定转染了新型ERβ转录本的COS-1细胞即使在没有雌二醇的情况下生长也明显较慢。与ERβ1一样，这两种新型ERβ转录异构体均以配体非依赖的方式提高了COS-1细胞的基础凋亡率。虽然引入ERβDelta1256显著增加了COS-1细胞对较低浓度选择性雌激素受体调节剂他莫昔芬的敏感性，但ERβ1和ERβDelta125转录本的存在进一步削弱了他莫昔芬对该细胞系的生长抑制作用。此外，已证明ERβDelta1256变体的表达以配体非依赖的方式降低了COS-1细胞中雌激素反应性基因如细胞周期蛋白A2、胰岛素样生长因子结合蛋白4和纤连蛋白1c的转录水平。尽管我们无法通过蛋白质印迹分析检测到预测的29 kDa和34 kDa蛋白，但我们的数据强烈表明这两种异构体在分子水平上具有生物学功能。随着本报告增加了现有ERβ mRNA异构体的种类，我们提供了进一步的证据，表明它们的合成必须被视为雌激素信号传导的一个重要层面。
