Chen D, Ganapathy P, Zhu L J, Xu X, Li Q, Bagchi I C, Bagchi M K
Population Council and The Rockefeller University, New York, New York 10021, USA.
Mol Endocrinol. 1999 Jun;13(6):993-1004. doi: 10.1210/mend.13.6.0287.
The steroid hormone estrogen profoundly influences the early events in the uterus leading to embryo implantation. It is thought that estrogen triggers the expression of a unique set of genes in the preimplantation endometrium that in turn control implantation. To identify these estrogen-induced genes, we used a delayed implantation model system in which embryo attachment to endometrium is dependent on estrogen administration. Using a mRNA differential display (DD) method, we isolated a number of cDNAs representing mRNAs whose expression is either turned on or turned off in response to an implantation-inducing dose of estrogen. We identified one of these cDNAs as that encoding rab11, a p21ras-like GTP-binding protein (G protein), which functions in the targeting of transport vesicles to the plasma membrane. In normal pregnant rats, rab11 mRNA was expressed at low levels on days 1-2 of pregnancy, but its expression was markedly enhanced (approximately 6- to 8-fold) between days 3-5 immediately before implantation. In situ hybridization and immunocytochemistry revealed that rab11 expression in the uterus was predominantly in the glandular epithelium. In ovariectomized rats, the expression of rab11 mRNA was induced in the endometrium in response to estrogen. To determine whether this effect of estrogen was mediated through its nuclear receptors, we examined rab11 expression in a transformed endometrial cell line, Ishikawa. In transient transfection experiments, we observed that overexpression of estrogen receptor (ER) alpha or beta induced endogenous rab11 mRNA in a hormone-dependent manner. ER bound to an antagonist, ICI 182,780, failed to activate this gene expression. These findings, together with the observation that ER alpha but not ER beta is detected in the glands of the preimplantation uterus, indicate that rab11 is one of the proteins that are specifically induced by estrogen-complexed ER alpha in rat endometrium at the onset of implantation. Our results imply that estrogen, which induces the synthesis of many growth factors and their receptors and other secretory proteins that are thought to be critical for implantation, may also facilitate their transport to the membrane and/or secretion by stimulating the expression of rab11, a component of the membrane-trafficking pathway. This study therefore provides novel insights into the diverse cellular mechanisms by which estrogen, acting via its nuclear receptors, may influence blastocyst implantation.
类固醇激素雌激素对子宫内导致胚胎着床的早期事件有深远影响。据认为，雌激素会触发着床前子宫内膜中一组独特基因的表达，进而控制着床过程。为了鉴定这些雌激素诱导的基因，我们使用了一种延迟着床模型系统，在该系统中胚胎与子宫内膜的附着依赖于雌激素的施用。利用mRNA差异显示（DD）方法，我们分离出了一些代表mRNA的cDNA，这些mRNA的表达在给予诱导着床剂量的雌激素后会开启或关闭。我们鉴定出其中一个cDNA编码rab11，它是一种p21ras样GTP结合蛋白（G蛋白），在将运输小泡靶向质膜中发挥作用。在正常怀孕大鼠中，rab11 mRNA在怀孕第1 - 2天表达水平较低，但在着床前第3 - 5天其表达显著增强（约6至8倍）。原位杂交和免疫细胞化学显示，子宫中rab11的表达主要位于腺上皮。在去卵巢大鼠中，雌激素可诱导子宫内膜中rab11 mRNA的表达。为了确定雌激素的这种作用是否通过其核受体介导，我们检测了转化的子宫内膜细胞系 Ishikawa 中rab11的表达。在瞬时转染实验中，我们观察到雌激素受体（ER）α或β的过表达以激素依赖的方式诱导内源性rab11 mRNA。与拮抗剂ICI 182,780结合的ER未能激活该基因表达。这些发现，连同在着床前子宫腺体中检测到ERα而非ERβ的观察结果，表明rab11是在着床开始时大鼠子宫内膜中由雌激素复合的ERα特异性诱导的蛋白质之一。我们的结果表明，雌激素诱导许多生长因子及其受体以及其他被认为对着床至关重要的分泌蛋白的合成，它可能还通过刺激膜运输途径的一个组成部分rab11的表达来促进它们向膜的运输和/或分泌。因此，本研究为雌激素通过其核受体发挥作用可能影响胚泡着床的多种细胞机制提供了新的见解。
