Foxo1 is an essential transcription factor required for the survival and differentiation of memory CD8 T cells, yet it is unclear whether these Foxo1-dependent functions are inherently coupled. To address this question, we examined the effects of different Foxo1 posttranslational modifications. Phosphorylation of Foxo1 by Akt kinases at three distinct residues is well characterized to inhibit Foxo1 transcriptional activity. However, the effect of Foxo1 phosphorylation within its DNA-binding domain at serine 209 by Mst1 kinase is not fully understood. In this study, we show that an S209A phospho-null Foxo1 exhibited Akt-dependent nuclear trafficking in mouse CD8 T cells and augmented the expression of canonical Foxo1 target genes such as Il7r and Sell In contrast, an S209D phosphomimetic Foxo1 (SD-Foxo1) was largely excluded from the nucleus of CD8 T cells and failed to transactivate these genes. RNA sequencing analysis revealed that SD-Foxo1 was associated with a distinct Foxo1-dependent transcriptional profile, including genes mediating CD8 effector function and cell survival. Despite defective transactivation of canonical target genes, SD-Foxo1 promoted IL-15-mediated CD8 T cell survival in vitro and survival of short-lived effector cells in vivo in response to Listeria monocytogenes infection. However, SD-Foxo1 actively repressed CD127 expression and failed to generate memory precursors and long-lived memory T cells. Together, these data indicate that S209 is a critical residue for the regulation of Foxo1 subcellular localization and for balancing CD8 T cell differentiation and survival.

中文翻译：

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Foxo1 丝氨酸 209 是 CD8 T 细胞分化和存活的关键调控位点

Foxo1 是记忆 CD8 T 细胞存活和分化所需的重要转录因子，但尚不清楚这些 Foxo1 依赖性功能是否固有耦合。为了解决这个问题，我们检查了不同 Foxo1 翻译后修饰的影响。Akt 激酶在三个不同的残基处对 Foxo1 的磷酸化具有很好的特征，可抑制 Foxo1 的转录活性。然而，Mst1 激酶对其 DNA 结合域 209 位丝氨酸的 Foxo1 磷酸化的影响尚不完全清楚。在这项研究中，我们发现 S209A 磷酸缺失 Foxo1 在小鼠 CD8 T 细胞中表现出 Akt 依赖性核转运，并增强了经典 Foxo1 靶基因（如 Il7r 和 Sell）的表达。S209D phosphomimetic Foxo1 (SD-Foxo1) 在很大程度上被排除在 CD8 T 细胞的细胞核之外，并且未能反式激活这些基因。RNA 测序分析显示 SD-Foxo1 与独特的 Foxo1 依赖性转录谱相关，包括介导 CD8 效应器功能和细胞存活的基因。尽管经典靶基因的反式激活存在缺陷，SD-Foxo1 促进了 IL-15 介导的 CD8 T 细胞体外存活和体内短寿命效应细胞的存活，以响应单核细胞增生李斯特菌感染。然而，SD-Foxo1 主动抑制 CD127 表达，未能产生记忆前体和长寿命记忆 T 细胞。总之，这些数据表明 S209 是调节 Foxo1 亚细胞定位和平衡 CD8 T 细胞分化和存活的关键残基。