Tremblay G B, Tremblay A, Copeland N G, Gilbert D J, Jenkins N A, Labrie F, Giguère V
Molecular Oncology Group, Boyal Victoria Hospital Montréal, Québec, Canada.
Mol Endocrinol. 1997 Mar;11(3):353-65. doi: 10.1210/mend.11.3.9902.
Estrogen receptor beta (ER beta) is a novel steroid receptor that is expressed in rat prostate and ovary. We have cloned the mouse homolog of ER beta and mapped the gene, designated Estrb, to the central region of chromosome 12. The cDNA encodes a protein of 485 amino acids that shares, respectively, 97% and 60% identity with the DNA- and ligand-binding domains of mouse (m) ER alpha. Mouse ER beta bind to an inverted repeat spaced by three nucleotides in a gel mobility shift assay and transactivates promoters containing synthetic or natural estrogen response elements in an estradiol (E2)-dependent manner. Scatchard analysis indicates that mER beta has slightly lower affinity for E2 [dissociation constant (Kd) = 0.5 nM] when compared with mER alpha (Kd = 0.2 nM). Antiestrogens, including 4-hydroxytamoxifen (OHT), ICI 182,780, and a novel compound, EM-800, inhibit E2-dependent transactivation efficiently. However, while OHT displays partial agonistic activity with ER alpha on a basal promoter linked to estrogen response elements in Cos-1 cells, this effect is not observed with mER beta. Cotransfection of mER beta and H-RasV12 causes enhanced activation in the presence of E2. Mutagenesis of a serine residue (position 60), located within a mitogen-activated protein kinase consensus phosphorylation site abolishes the stimulatory effect of Ras, suggesting that the activity of mER beta is also regulated by the mitogen-activated protein kinase pathway. Surprisingly, the coactivator SRC-1 up-regulates mER beta transactivation both in the absence and presence of E2, and in vitro interaction between SRC-1 and the ER beta ligand-binding domain is enhanced by E2. Moreover, the ligand-independent stimulatory effect of SRC-1 on ER beta transcriptional activity is abolished by ICI 182,780, but not by OHT. Our results demonstrate that while ER beta shares many of the functional characteristics of ER alpha, the molecular mechanisms regulating the transcriptional activity of mER beta may be distinct from those of ER alpha.
雌激素受体β（ERβ）是一种新的类固醇受体，在大鼠前列腺和卵巢中表达。我们已克隆出小鼠ERβ的同源物，并将该基因（命名为Estrb）定位到12号染色体的中央区域。该cDNA编码一个由485个氨基酸组成的蛋白质，它与小鼠（m）ERα的DNA结合域和配体结合域分别具有97%和60%的同源性。在凝胶迁移率变动分析中，小鼠ERβ能与间隔三个核苷酸的反向重复序列结合，并以雌二醇（E2）依赖的方式激活含有合成或天然雌激素反应元件的启动子。Scatchard分析表明，与mERα（解离常数Kd = 0.2 nM）相比，mERβ对E2的亲和力略低（Kd = 0.5 nM）。抗雌激素药物，包括4-羟基他莫昔芬（OHT）、ICI 182,780和一种新型化合物EM-800，能有效抑制E2依赖的转录激活。然而，虽然OHT在Cos-1细胞中与ERα在与雌激素反应元件相连的基础启动子上表现出部分激动活性，但mERβ未观察到这种效应。mERβ和H-RasV12的共转染在有E2存在时会导致激活增强。位于丝裂原活化蛋白激酶共有磷酸化位点内的一个丝氨酸残基（第60位）的诱变消除了Ras的刺激作用，这表明mERβ的活性也受丝裂原活化蛋白激酶途径的调节。令人惊讶的是，共激活因子SRC-1在有无E2的情况下均上调mERβ的转录激活，并且E2增强了SRC-1与ERβ配体结合域之间的体外相互作用。此外，ICI 182,780可消除SRC-1对ERβ转录活性的非配体依赖性刺激作用，但OHT不能。我们的结果表明，虽然ERβ具有许多ERα的功能特征，但调节mERβ转录活性的分子机制可能与ERα不同。
