Reineke Lucas C, Lloyd Richard E
Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA.
Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
J Virol. 2015 Mar;89(5):2575-89. doi: 10.1128/JVI.02791-14. Epub 2014 Dec 17.
Stress granules (SGs) are cytoplasmic storage sites containing translationally silenced mRNPs that can be released to resume translation after stress subsides. We previously showed that poliovirus 3C proteinase cleaves the SG-nucleating protein G3BP1, blocking the ability of cells to form SGs late in infection. Many other viruses also target G3BP1 and inhibit SG formation, but the reasons why these functions evolved are unclear. Previously, we also showed a link between G3BP1-induced SGs and protein kinase R (PKR)-mediated translational control, but the mechanism of PKR interplay with SG and the antiviral consequences are unknown. Here, we show that G3BP1 exhibits antiviral activity against several enteroviruses, whereas truncated G3BP1 that cannot form SGs does not. G3BP1-induced SGs are linked to activation of innate immune transcriptional responses through NF-κB and JNK. The G3BP1-induced SGs also recruit PKR and other antiviral proteins. We show that the PXXP domain within G3BP1 is essential for the recruitment of PKR to SGs, for eIF2α phosphorylation driven by PKR, and for nucleating SGs of normal composition. We also show that deletion of the PXXP domain in G3BP1 compromises its antiviral activity. These findings tie PKR activation to its recruitment to SGs by G3BP1 and indicate that G3BP1 promotes innate immune responses at both the transcriptional and translational levels and integrates cellular stress responses and innate immunity.
Stress granules appear during virus infection, and their importance is not well understood. Previously, it was assumed that they were nonfunctional artifacts associated with cellular stress. PKR is a well-known antiviral protein; however, its regulation in cells is not well understood. Our work links cellular stress granules with activation of PKR and other innate immune pathways through the activity of G3BP1, a critical stress granule component. The ability of stress granules and G3BP1 to activate PKR and other innate immune transcriptional responses indicates that G3BP1 is an antiviral protein. This work helps to refine a longstanding paradigm indicating stress granules are inert structures and explains why G3BP1 is subverted by many viruses to promote a productive infection.
应激颗粒（SGs）是细胞质中的储存位点，包含翻译沉默的mRNA-蛋白质复合物（mRNPs），在应激消退后可释放以恢复翻译。我们之前表明，脊髓灰质炎病毒3C蛋白酶切割应激颗粒成核蛋白G3BP1，在感染后期阻断细胞形成应激颗粒的能力。许多其他病毒也靶向G3BP1并抑制应激颗粒形成，但这些功能进化的原因尚不清楚。之前，我们还表明G3BP1诱导的应激颗粒与蛋白激酶R（PKR）介导的翻译控制之间存在联系，但PKR与应激颗粒相互作用的机制以及抗病毒后果尚不清楚。在这里，我们表明G3BP1对几种肠道病毒具有抗病毒活性，而不能形成应激颗粒的截短型G3BP1则没有。G3BP1诱导的应激颗粒通过核因子κB（NF-κB）和应激活化蛋白激酶（JNK）与先天免疫转录反应的激活相关联。G3BP1诱导的应激颗粒还招募PKR和其他抗病毒蛋白。我们表明，G3BP1中的脯氨酸-XX-脯氨酸（PXXP）结构域对于将PKR招募到应激颗粒、PKR驱动的真核翻译起始因子2α（eIF2α）磷酸化以及形成正常组成的应激颗粒至关重要。我们还表明，G3BP1中PXXP结构域的缺失会损害其抗病毒活性。这些发现将PKR的激活与其被G3BP1招募到应激颗粒联系起来，并表明G3BP1在转录和翻译水平上促进先天免疫反应，并整合细胞应激反应和先天免疫。
应激颗粒在病毒感染期间出现，其重要性尚未得到充分理解。以前，人们认为它们是与细胞应激相关的无功能假象。PKR是一种著名的抗病毒蛋白；然而，其在细胞中的调节尚不清楚。我们的工作通过关键应激颗粒成分G3BP1的活性将细胞应激颗粒与PKR和其他先天免疫途径的激活联系起来。应激颗粒和G3BP1激活PKR和其他先天免疫转录反应的能力表明G3BP1是一种抗病毒蛋白。这项工作有助于完善一个长期存在的范式，即应激颗粒是惰性结构，并解释了为什么G3BP1被许多病毒利用以促进有效感染。
