Chon S Y, Hassanain H H, Gupta S L
Hipple Cancer Research Center, Dayton, Ohio 45439, USA.
J Biol Chem. 1996 Jul 19;271(29):17247-52. doi: 10.1074/jbc.271.29.17247.
Interferon (IFN)-gamma induces the expression of the indoleamine 2, 3-dioxygenase (INDO) gene in human cells, which plays a role in the inhibitory effect of IFN-gamma on intracellular pathogens and on cell proliferation. Earlier studies established that the IFN-gamma-inducible expression of the INDO gene was dependent on two upstream elements: (i) a 14-base pair sequence homologous to an interferon-stimulated response element (ISRE) sequence found in IFN-alpha-inducible genes and (ii) a 9-base pair palindromic sequence (palindromic element (PE) II) homologous to an interferon-gamma-activated site (GAS) element found in IFN-gamma-inducible genes. A second GAS element (PE I), between ISRE and PE II, was ineffective in supporting a response to IFN-gamma. Studies were carried out to determine the distinction between the two GAS elements and the relative role of the two elements (ISRE and PE II) required for a response to IFN-gamma. The PE I element was able to form a complex with IFN-gamma-activated p91 (STAT1) factor but with lower efficiency than the complex formed with PE II sequence. However, switching the positions of PE I and II sequences in reporter plasmid constructs (containing chloramphenicol acetyltransferase gene) showed that both PE I and PE II were able to support a response to IFN-gamma if located at the position of PE II but not at the position of PE I. Increasing the distance between the ISRE and PE II also affected the level of response, suggesting that the relative position of the two elements is important for optimal stimulus. To explore whether an interaction between the IFN-gamma-regulated factors (IRF-1 and p91) binding to the ISRE and PE II might be important, we tested whether the ISRE sequence could be replaced by another response element, NF-kappaB. The plasmid construct with NF-kappaB element in place of the ISRE was responsive to IFN-gamma, indicating that an interaction between the IRF-1 and p91 factors was not required. The results indicate that the response of INDO gene to IFN-gamma depends on a cooperative role of IFN-gamma-responsive factors binding to the ISRE and GAS elements.
干扰素（IFN）-γ可诱导人细胞中吲哚胺2,3-双加氧酶（INDO）基因的表达，该基因在IFN-γ对细胞内病原体和细胞增殖的抑制作用中发挥作用。早期研究表明，INDO基因的IFN-γ诱导型表达依赖于两个上游元件：（i）一个与IFN-α诱导型基因中发现的干扰素刺激反应元件（ISRE）序列同源的14个碱基对序列，以及（ii）一个与IFN-γ诱导型基因中发现的干扰素-γ激活位点（GAS）元件同源的9个碱基对回文序列（回文元件（PE）II）。位于ISRE和PE II之间的第二个GAS元件（PE I）在支持对IFN-γ的反应方面无效。开展了研究以确定这两个GAS元件之间的区别以及对IFN-γ反应所需的两个元件（ISRE和PE II）的相对作用。PE I元件能够与IFN-γ激活的p91（STAT1）因子形成复合物，但效率低于与PE II序列形成的复合物。然而，在报告质粒构建体（含有氯霉素乙酰转移酶基因）中交换PE I和II序列的位置表明，如果位于PE II的位置，PE I和PE II都能够支持对IFN-γ的反应，但位于PE I的位置则不能。增加ISRE和PE II之间的距离也会影响反应水平，这表明这两个元件的相对位置对于最佳刺激很重要。为了探究与ISRE和PE II结合的IFN-γ调节因子（IRF-1和p91）之间的相互作用是否重要，我们测试了ISRE序列是否可以被另一个反应元件NF-κB取代。用NF-κB元件取代ISRE的质粒构建体对IFN-γ有反应，表明IRF-1和p91因子之间不需要相互作用。结果表明，INDO基因对IFN-γ的反应取决于与ISRE和GAS元件结合的IFN-γ反应因子的协同作用。
