Bandyopadhyay S K, Leonard G T, Bandyopadhyay T, Stark G R, Sen G C
Department of Molecular Biology, Cleveland Clinic Foundation, Ohio 44195, USA.
J Biol Chem. 1995 Aug 18;270(33):19624-9. doi: 10.1074/jbc.270.33.19624.
Many genes induced by type I interferons (IFNs) are also induced by double-stranded (ds)RAN. In this study, we investigated the mechanism of this induction process. Using cell lines from which the type I IFN genes have been deleted, we established that induction by dsRNA of the IFN-inducible 561 gene is direct and not mediated by the intermediate synthesis of IFN. Unlike 561 mRNA, the IFN-inducible 6-16 mRNA was induced poorly by dsRNA. Transfection studies demonstrated that the sequence difference between the core IFN-stimulated response elements (ISREs) of these two genes is not responsible for their differential inducibility by dsRNA. A point mutation in the 561 ISRE that abolished its response to IFN-alpha also made it unresponsive to dsRNA, thus demonstrating that the ISRE is the relevant cis-acting element for dsRNA signaling. The roles of different known ISRE-binding protein and tyrosine kinases in transducing the signal elicited by dsRNA were evaluated in genetically altered cell lines. dsRNA failed to induce 561 mRNA in cells expressing an anti-sense RNA for interferon regulatory factor 1, whereas it was induced strongly in cells expressing the corresponding sense mRNA. 561 mRNA was also induced strongly by dsRNA, but not by IFN-alpha, in mutant cell lines that do not express functional tyrosine kinases Tyk2 or JAK1 or ISRE binding protein, p48, or STAT2, all of which are required for IFN-alpha signaling. However, in cells devoid of functional STAT1, which is also required for IFN-alpha signaling, the induction of 561 mRNA by dsRNA was very low. Expression of transfected STAT1 alpha protein, but not of STAT 1beta protein, in these cells greatly enhanced the dsRNA inducibility of the 561 gene. These studies indicated that the major ISRE-mediated signaling pathway used by dsRNA requires interferon regulatory factor 1 and STAT alpha. This pathway, however, does not require the other known cytoplasmic components used for IFN-alpha signaling.
许多由I型干扰素（IFN）诱导的基因也可由双链（ds）RNA诱导。在本研究中，我们调查了这种诱导过程的机制。利用已缺失I型IFN基因的细胞系，我们确定dsRNA对IFN诱导型561基因的诱导是直接的，并非由IFN的中间合成介导。与561 mRNA不同，IFN诱导型6 - 16 mRNA受dsRNA的诱导较弱。转染研究表明，这两个基因的核心IFN刺激反应元件（ISRE）之间的序列差异并非其受dsRNA诱导能力不同的原因。561 ISRE中的一个点突变消除了其对IFN-α的反应，同时也使其对dsRNA无反应，从而证明ISRE是dsRNA信号传导的相关顺式作用元件。在基因改造的细胞系中评估了不同已知ISRE结合蛋白和酪氨酸激酶在转导dsRNA引发的信号中的作用。dsRNA在表达干扰素调节因子1反义RNA的细胞中无法诱导561 mRNA，而在表达相应正义mRNA的细胞中可强烈诱导。在不表达功能性酪氨酸激酶Tyk2或JAK1、ISRE结合蛋白p48或STAT2的突变细胞系中，dsRNA也可强烈诱导561 mRNA，但IFN-α不能，而这些都是IFN-α信号传导所必需的。然而，在同样是IFN-α信号传导所必需的缺乏功能性STAT1的细胞中，dsRNA对561 mRNA的诱导非常低。在这些细胞中表达转染的STAT1α蛋白而非STAT1β蛋白，可大大增强561基因对dsRNA的诱导能力。这些研究表明，dsRNA使用的主要ISRE介导的信号通路需要干扰素调节因子1和STATα。然而，该通路不需要用于IFN-α信号传导的其他已知细胞质成分。
