Duan Hai Ou, Simpson-Haidaris Patricia J
Department of Medicine, University of Rochester School of Medicine and Dentistry Rochester, New York 14642, USA.
J Biol Chem. 2003 Oct 17;278(42):41270-81. doi: 10.1074/jbc.M304210200. Epub 2003 Aug 4.
Several families of transcription factors play important roles in modulating liver-specific gene expression during an acute phase response (APR). Stat3/APR factor is the main transactivator of gene expression by the interleukin (IL)-6 family of cytokines signaling through gp130. During an APR, fibrinogen (FBG) genes are coordinately up-regulated by IL-6 and glucocorticoids. Except for rat gammaFBG, attempts to demonstrate direct binding of IL-6-activated Stat3 to FBG CTGGGAA promoter elements have not been successful. Herein we show the presence of three functional type II IL-6 response elements (IL-6REs) on the human gammaFBG promoter and that the magnitude of Stat3 binding to these elements correlates negatively with their functional activity in reporter gene assays. Stat3-specific binding to gammaFBG IL-6REs was confirmed by cross-competition with alpha2-macroglobulin IL-6RE and specific interactions with anti-Stat3 in electrophoretic mobility shift assays. All type II IL-6REs contributed to full promoter activity; however, transactivation from Site II at -306 to -301 was strongest. In contrast to a previous report, IL-6 failed to induce activation of serum amyloid A-activating factor-1/c-Myc-associated zinc finger protein (SAF-1/MAZ), and mutation of the SAF-1RE had little effect on IL-6 induction of gammaFBG promoter activity. In the absence of a functional glucocorticoid receptor response element, dexamethasone potentiated IL-6-induced gammaFBG promoter activity 2-fold, requiring promoter-proximal Site I and Site II; the promoter-distal Site III had no effect on dexamethasone potentiation of IL-6-induced promoter activity. Notably the propensity for Stat3 binding to human gammaFBG IL-6REs was low compared with Stat3 binding to the alpha2-macroglobulin IL-6RE. Together these data suggest that Stat3 transactivation via IL-6REs on FBG promoters likely involves participation of additional transcription factors and/or coactivators to achieve optimal coordinated up-regulation during an APR.
在急性期反应（APR）期间，几个转录因子家族在调节肝脏特异性基因表达方面发挥着重要作用。Stat3/APR因子是白细胞介素（IL）-6家族细胞因子通过gp130信号传导激活基因表达的主要反式激活因子。在APR期间，纤维蛋白原（FBG）基因由IL-6和糖皮质激素协同上调。除大鼠γFBG外，试图证明IL-6激活的Stat3与FBG CTGGGAA启动子元件直接结合均未成功。在此我们展示了人类γFBG启动子上存在三个功能性II型IL-6反应元件（IL-6REs），并且在报告基因分析中，Stat3与这些元件的结合强度与其功能活性呈负相关。通过与α2-巨球蛋白IL-6RE的交叉竞争以及在电泳迁移率变动分析中与抗Stat3的特异性相互作用，证实了Stat3与γFBG IL-6REs的特异性结合。所有II型IL-6REs均有助于启动子的完全活性；然而，位于-306至-301的位点II的反式激活作用最强。与先前的报道相反，IL-6未能诱导血清淀粉样蛋白A激活因子-1/c-Myc相关锌指蛋白（SAF-1/MAZ）的激活，并且SAF-1RE的突变对IL-6诱导的γFBG启动子活性影响很小。在缺乏功能性糖皮质激素受体反应元件的情况下，地塞米松使IL-6诱导的γFBG启动子活性增强2倍，这需要启动子近端的位点I和位点II；启动子远端的位点III对地塞米松增强IL-6诱导的启动子活性没有影响。值得注意的是，与Stat3与α2-巨球蛋白IL-6RE的结合相比，Stat3与人γFBG IL-6REs的结合倾向较低。这些数据共同表明，Stat3通过FBG启动子上的IL-6REs进行反式激活可能涉及其他转录因子和/或共激活因子的参与，以在APR期间实现最佳的协同上调。
