Lau Wai-Sum, Chan Robbie Yat-Kan, Guo De-An, Wong Man-Sau
Central Laboratory of the Institute of Molecular Technology for Drug Discovery and Synthesis, Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, PR China.
J Steroid Biochem Mol Biol. 2008 Jan;108(1-2):64-71. doi: 10.1016/j.jsbmb.2007.06.005. Epub 2007 Sep 8.
Ginsenoside Rg1, an active ingredient commonly found in ginseng root, was previously demonstrated to be a phytoestrogen that exerted estrogen-like activity without direct interaction with estrogen receptors (ERs) in human breast cancer (MCF-7) cells. The present study was designed to determine the molecular mechanism by which Rg1 exerted estrogenic effects. Co-incubation of MCF-7 cells with 1 microM of ER antagonist ICI182780 abolished the inductive effects of Rg1 on pS2 expression as well as ERE-luciferase activity, suggesting that the estrogenic effects of Rg1 were mediated through the endogenous ERs. To evaluate the relative involvement of ERalpha and ERbeta in mediating the actions of Rg1, ER-negative human embryonic kidney (HEK293) cells were co-transfected with the ERE-luciferase reporter construct and either ERalpha or ERbeta construct. The results showed that Rg1 could activate ERE-luciferase activity via the ERalpha-mediated pathway in a dose-dependent manner (10(-14) to 10(-6)M); whereas, the activation of ERbeta-mediated ERE-luciferase activity by Rg1 only occur at high concentration (10(-6)M). Furthermore, the results showed that 1pM Rg1 could rapidly induce phosphorylation of the AF-1 domain of ERalpha at serine 118 residue within the first 5 min of incubation, suggesting that Rg1 activates ERalpha in a ligand-independent manner. Taken together, our results indicate that Rg1 preferentially activates ERalpha via phosphorylation of AF-1 domain in the absence of receptor binding. This study is the first to provide evidence that ginsenoside Rg1 exerts estrogen-like actions via ligand-independent activation of ERalpha pathway.
人参皂苷Rg1是人参根中常见的一种活性成分，先前已证明它是一种植物雌激素，在人乳腺癌（MCF-7）细胞中发挥雌激素样活性，且不与雌激素受体（ERs）直接相互作用。本研究旨在确定Rg1发挥雌激素作用的分子机制。MCF-7细胞与1微摩尔的ER拮抗剂ICI182780共同孵育，消除了Rg1对pS2表达以及ERE-荧光素酶活性的诱导作用，这表明Rg1的雌激素作用是通过内源性ERs介导的。为了评估ERα和ERβ在介导Rg1作用中的相对参与度，将ER阴性的人胚肾（HEK293）细胞与ERE-荧光素酶报告基因构建体以及ERα或ERβ构建体共转染。结果表明，Rg1可通过ERα介导的途径以剂量依赖性方式（10^(-14)至10^(-6)M）激活ERE-荧光素酶活性；而Rg1对ERβ介导的ERE-荧光素酶活性的激活仅在高浓度（10^(-6)M）时发生。此外，结果表明，1皮摩尔Rg1在孵育的前5分钟内可迅速诱导ERα的AF-1结构域在丝氨酸118残基处磷酸化，这表明Rg1以非配体依赖的方式激活ERα。综上所述，我们的结果表明，Rg1在没有受体结合的情况下通过AF-1结构域的磷酸化优先激活ERα。本研究首次提供证据表明人参皂苷Rg1通过非配体依赖的ERα途径激活发挥雌激素样作用。
