Wong A H, Durbin J E, Li S, Dever T E, Decker T, Koromilas A E
Terry Fox Molecular Oncology Group, Lady Davis Institute, Jewish General Hospital, Montreal H3T 1E2, Canada.
J Biol Chem. 2001 Apr 27;276(17):13727-37. doi: 10.1074/jbc.M011240200. Epub 2001 Jan 25.
We have previously reported a physical association between STAT1 and the protein kinase double-stranded RNA-activated protein kinase (PKR). PKR inhibited STAT1 function in a manner independent of PKR kinase activity. In this report, we have further characterized the properties of both molecules by mapping the sites of their interaction. A STAT1 mutant unable to interact with PKR displays enhanced interferon gamma (IFN-gamma)-induced transactivation capacity compared with STAT1. This effect appears to be mediated by the higher capacity of STAT1 mutant to heterodimerize with STAT3. Furthermore, expression of STAT1 mutant in STAT1(-/-) cells enhances both the antiviral and antiproliferative effects of IFNs as opposed to STAT1. We also provide evidence that STAT1 functions as an inhibitor of PKR in vitro and in vivo. That is, phosphorylation of eIF-2alpha is enhanced in STAT1(-/-) than STAT1(+/+) cells in vivo, and this correlates with higher activation capacity of PKR in STAT1(-/-) cells. Genetic experiments in yeast demonstrate the inhibition of PKR activation and eIF-2alpha phosphorylation by STAT1 but not by STAT1 mutant. These data substantiate our previous findings on the inhibitory effects of PKR on STAT1 and implicate STAT1 in translational control through the modulation of PKR activation and eIF-2alpha phosphorylation.
我们之前报道过信号转导和转录激活因子1（STAT1）与蛋白激酶双链RNA激活蛋白激酶（PKR）之间存在物理关联。PKR以一种独立于其激酶活性的方式抑制STAT1的功能。在本报告中，我们通过绘制它们的相互作用位点进一步表征了这两种分子的特性。与STAT1相比，一种无法与PKR相互作用的STAT1突变体表现出增强的干扰素γ（IFN-γ）诱导的反式激活能力。这种效应似乎是由STAT1突变体与STAT3异源二聚化的更高能力介导的。此外，与STAT1相反，在STAT1基因敲除（STAT1(-/-)）细胞中表达STAT1突变体可增强干扰素的抗病毒和抗增殖作用。我们还提供证据表明，STAT1在体外和体内均作为PKR的抑制剂发挥作用。也就是说，在体内，STAT1基因敲除细胞中真核生物翻译起始因子2α（eIF-2α）的磷酸化比STAT1基因野生型（STAT1(+/+)）细胞中增强，这与STAT1基因敲除细胞中PKR的更高激活能力相关。酵母中的遗传学实验证明，STAT1可抑制PKR激活和eIF-2α磷酸化，而STAT1突变体则不能。这些数据证实了我们之前关于PKR对STAT1抑制作用的发现，并表明STAT1通过调节PKR激活和eIF-2α磷酸化参与翻译控制。
