An Ancient Pseudoknot in TNF-α Pre-mRNA Activates PKR, Inducing eIF2α Phosphorylation that Potently Enhances Splicing
An Ancient Pseudoknot in TNF-α Pre-mRNA Activates PKR, Inducing eIF2α Phosphorylation that Potently Enhances Splicing
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DOI：
10.1016/j.celrep.2017.06.035
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发表时间：
2017-07-05
期刊：
影响因子：
8.8
通讯作者：
Kaempfer, Raymond
中科院分区：
文献类型：
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作者：
Namer, Lise Sarah;Osman, Farhat;Kaempfer, Raymond
肿瘤坏死因子α（TNF-α）在炎症反应期间迅速表达。有效的 TNF-a mRNA 剪接是通过激活 RNA 依赖性 eIF2 α 蛋白激酶 (PKR) 的 3' UTR 元件实现的。我们发现，TNF-a RNA 激活剂折叠成从硬骨鱼到人类都保守的假结，对于 PKR 激活和 mRNA 剪接至关重要。假结将 RNA 限制为两个具有平行轴的双螺旋堆叠，从而允许轻松进行 PKR 二聚化和激酶激活所需的反式自磷酸化。突变表明 PKR 激活剂可有效增强剪接而不抑制翻译。 eIF2 α 磷酸化会抑制翻译，对于应对细胞应激至关重要，但 PKR 启用的 TNF mRNA 剪接严格依赖于 eIF2 α 磷酸化。事实上，eIF2 Serine51 α 磷酸化对于实现高效剪接是必要且充分的，将其作用从翻译的负控制扩展到剪接的正控制。这种机制是可操作的非人外周血单核细胞 (PBMC)，通过 TNF mRNA 剪接将应激信号与保护性免疫联系起来，而 TNF mRNA 剪接在 eIF2 α 磷酸化后变得有效。
Tumor necrosis factor alpha (TNF-alpha) is expressed promptly during inflammatory responses. Efficient TNF-a mRNA splicing is achieved through a 3' UTR element that activates RNA-dependent eIF2 alpha protein kinase (PKR). The TNF-a RNA activator, we show, folds into a pseudoknot conserved from teleost fish to humans, critical for PKR activation and mRNA splicing. The pseudoknot constrains the RNA into two double-helical stacks having parallel axes, permitting facile PKR dimerization and trans-autophosphorylation needed for kinase activation. Mutations show that the PKR activator potently enhances splicing without inhibiting translation. eIF2 alpha phosphorylation represses translation and is essential for coping with cellular stress, yet PKR-enabled TNF mRNA splicing depends strictly on eIF2 alpha phosphorylation. Indeed, eIF2 alpha phosphorylation at Serine51 is necessary and sufficient to achieve highly efficient splicing, extending its role from negative control of translation to positive control of splicing. This mechanism, operational inhuman peripheral blood mononuclear cells (PBMCs), links stress signaling to protective immunity through TNF mRNA splicing rendered efficient upon eIF2 alpha phosphorylation.