How Stress Controls the Inflammatory Cytokine Response

我们检验了一个新的概念，即整合的细胞应激反应在调节炎症细胞因子基因表达方面起着关键作用。具体地说，我们的目标是研究应激如何调节编码肿瘤坏死因子(TNF-α)和细胞因子信号抑制因子3(SOCS3)的基因，SOCS3是一种广泛的炎症信号负面调节因子。我们将共同研究炎症细胞因子IL-6(急性时相反应的主要介质)和免疫抑制糖皮质激素如何影响这一调节。这项工作是基于我们的发现，即多个炎性细胞因子基因包含有效的PKR基因内RNA激活物。EIF2-α被包括RNA激活的蛋白激酶(PKR)在内的激酶磷酸化，抑制翻译，对整合细胞应激反应是必不可少的。干扰素-γ通过5-近端的RNA结构局部激活PKR，从而减弱自身的翻译。有效的剪接需要一个激活PKR的短3-UTR元件；PKR的激活诱导eIF2-α磷酸化，这是剪接该mRNA所必需的，揭示了eIF2-α磷酸化在mRNA剪接中的新的积极作用。SOCS3通过PKR和eIF2-α的磷酸化受胁迫信号的调节。SOCS3蛋白是非常短暂的，然而，一个更稳定和更有效的N末端截断的异构体-增量N-SOCS3，被PKR和促进eIF2-α磷酸化的条件强烈诱导。我们最近发现，糖皮质激素通过抑制SOCS3蛋白的表达而增加IL-6依赖基因的诱导，而不影响SOCS3蛋白的稳定性或SOCS3 mRNA的水平和稳定性，提示存在翻译抑制。我们在这里询问PKR的稳定合成所需的PKR的激活是否通过PKR的基因内SOCS3 RNA激活剂实现，以及糖皮质激素是否通过PKR的激活和eIF2-α的磷酸化来影响调控。PKR的激活和eIF2-α的磷酸化控制SOCS3和TNF-α的基因表达，SOCS3和TNF-α都受IL-6和糖皮质激素的调节，为联合研究创造了坚实的基础。这项侧重于应激信号机制的联合基础生物学研究的结果将影响对许多疾病的核心和保护性免疫所必需的炎症过程的基本理解。

We examine the novel concept that the integrated cellular stress response plays a critical role in regulating inflammatory cytokine gene expression. Specifically, we aim to study how stress regulates the genes encoding tumor necrosis factor (TNF-alpha) and suppressor of cytokine signaling 3 (SOCS3), a broad negative regulator of inflammatory signaling. Jointly, we will investigate how this regulation is affected by the inflammatory cytokine IL-6, a major mediator of the acute-phase response, and by immunosuppressive glucocorticoids. The work is based on our discovery that multiple inflammatory cytokine genes contain potent intragenic RNA activators of PKR. Phosphorylation of eIF2-alpha by kinases, including the RNA-activated kinase, PKR, represses translation and is essential for mounting the integrated cellular stress response. IFN-gamma mRNA attenuates its own translation by locally activating PKR through a 5-proximal RNA structure. Efficient splicing of TNF-alpha mRNA requires a short 3-UTR element that activates PKR; activation of PKR induces eIF2-alpha phosphorylation strictly needed for splicing of this mRNA, revealing a novel, positive role for eIF2-alpha phosphorylation in mRNA splicing. SOCS3 is regulated by stress signaling via PKR and eIF2-alpha phosphorylation. SOCS3 protein is very short-lived, however, a more stable and more potent N-terminally truncated isoform, delta N-SOCS3, is induced strongly by PKR and by conditions that promote eIF2-alpha phosphorylation. We showed recently that glucocorticoids increase IL-6-dependent gene induction by inhibiting expression of SOCS3 protein while not affecting SOCS3 protein stability or level and stability of SOCS3 mRNA, suggestive of translational repression. We ask here whether the activation of PKR needed for stable delta N-SOCS3 synthesis is achieved through an intragenic SOCS3 RNA activator of PKR and whether glucocorticoids influence control via PKR and phosphorylation of eIF2-alpha.Activation of PKR and phosphorylation of eIF2-alpha control SOCS3 and TNF-alpha gene expression and both SOCS3 and TNF-alpha are regulated by IL-6 and glucocorticoids, creating a solid basis for this joint research. Findings emanating from this joint basic biological research focused on the mechanisms of stress signaling will impact on basic understanding of inflammatory processes essential for protective immunity and at the heart of many diseases.