Strehlow I, Decker T
Department of Immunobiology, Fraunhofer Institute for Toxikology and Molecular Biology, Hannover, Germany.
Nucleic Acids Res. 1992 Aug 11;20(15):3865-72. doi: 10.1093/nar/20.15.3865.
The 9/27 and GBP mRNAs are both inducible by Interferon-gamma (IFN-gamma). The promoters of both genes contain an Interferon Stimulation Response Element (ISRE), but while the GBP gene is strongly induced transcriptionally by IFN-gamma the response of the 9/27 promoter is very weak. We investigated the molecular basis for this difference. The different IFN-gamma-responsiveness was found to have more than one reason. First, 9/27 promoter DNA was unable to bind the Gamma Interferon Activation Factor (GAF) with a single high affinity site. It efficiently competed for the association of the GAF with the GBP promoter but this competition was due to the presence of two low affinity sites, the ISRE and an ISRE-like sequence, suggesting that the GAS and ISRE, though both having clear preferences for specific proteins, may nevertheless share a certain degree of structural homology. Second, the 9/27 and GBP ISREs differed markedly in their affinities for regulatory proteins (ISGFs 1,2,3) and the GBP ISRE was more potent in mediating IFN-gamma-induced promoter activity in transient transfection. Third and most importantly, however, the strong difference between the IFN-gamma response of the two promoters was mainly due to the sequences surrounding the ISRE: the positive-acting GAS on one side and sequences with silencing properties 5' and 3' of the 9/27 ISRE on the other side. The data thus show mechanisms to both up- and down-regulate the activity of the ISRE.
9/27和GBP的信使核糖核酸（mRNA）均可被γ干扰素（IFN-γ）诱导。这两个基因的启动子都包含一个干扰素刺激反应元件（ISRE），但GBP基因可被IFN-γ强烈转录诱导，而9/27启动子的反应则非常微弱。我们研究了这种差异的分子基础。发现不同的IFN-γ反应性有不止一个原因。首先，9/27启动子DNA无法通过单个高亲和力位点结合γ干扰素激活因子（GAF）。它能有效竞争GAF与GBP启动子的结合，但这种竞争是由于存在两个低亲和力位点，即ISRE和一个类ISRE序列，这表明GAS和ISRE虽然对特定蛋白质都有明确的偏好，但可能仍存在一定程度的结构同源性。其次，9/27和GBP的ISRE对调节蛋白（ISGFs 1、2、3）的亲和力明显不同，并且GBP的ISRE在瞬时转染中介导IFN-γ诱导的启动子活性方面更强效。然而，第三点也是最重要的一点，两个启动子的IFN-γ反应之间的强烈差异主要是由于ISRE周围的序列：一侧是起正作用的GAS，另一侧是9/27 ISRE 5'和3'端具有沉默特性的序列。因此，这些数据展示了上调和下调ISRE活性的机制。
