Memory CD8 + T cells are characterized by their ability to persist long after the initial antigen encounter and their capacity to generate a rapid recall response. Recent studies have identified a role for metabolic reprogramming and mitochondrial function in promoting the longevity of memory T cells. However, detailed mechanisms involved in promoting their rapid recall response are incompletely understood. Here, we identify a role for the initial and continued activation of the trifunctional rate-limiting enzyme of the de novo pyrimidine synthesis pathway CAD (carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase) as critical in promoting the rapid recall response of previously activated CD8 + T cells. We found that CAD was rapidly phosphorylated upon naïve T cell activation in an mTORC1-dependent manner, yet remained phosphorylated long after initial activation. Previously activated CD8 + T cells displayed continued de novo pyrimidine synthesis in the absence of mitogenic signals, and interfering with this pathway diminished the speed and magnitude of cytokine production upon rechallenge. Inhibition of CAD did not affect cytokine transcript levels but diminished available pre-rRNA (ribosomal RNA), the polycistronic rRNA precursor whose synthesis is the rate-limiting step in ribosomal biogenesis. CAD inhibition additionally decreased levels of detectable ribosomal proteins in previously activated CD8 + T cells. Conversely, overexpression of CAD improved both the cytokine response and proliferation of memory T cells. Overall, our studies reveal a critical role for CAD-induced pyrimidine synthesis and ribosomal biogenesis in promoting the rapid recall response characteristic of memory T cells.

中文翻译：

---

记忆 CD8 + T 细胞中持续存在的 CAD 活性支持再次攻击所需的 rRNA 合成和核糖体生物合成

内存CD8+T 细胞的特点是它们在初次遇到抗​​原后仍能持续很长时间，并能产生快速回忆反应。最近的研究已经确定了代谢重编程和线粒体功能在促进记忆 T 细胞寿命方面的作用。然而，尚未完全了解促进其快速回忆反应所涉及的详细机制。在这里，我们确定了从头嘧啶合成途径 CAD（氨甲酰磷酸合成酶 2、天冬氨酸转氨甲酰酶和二氢乳清酶）的三功能限速酶的初始和持续激活的作用，这对于促进先前的快速回忆反应至关重要激活的CD8+T 细胞。我们发现 CAD 在幼稚 T 细胞激活后以 mTORC1 依赖性方式迅速磷酸化，但在初始激活后很长时间内仍保持磷酸化。先前激活的 CD8+在没有促有丝分裂信号的情况下，T 细胞显示出持续的从头嘧啶合成，并且干扰该途径会降低再次攻击时细胞因子产生的速度和幅度。抑制 CAD 不影响细胞因子转录水平，但减少了可用的 pre-rRNA（核糖体 RNA），这是一种多顺反子 rRNA 前体，其合成是核糖体生物发生中的限速步骤。CAD 抑制还降低了先前激活的 CD8 中可检测核糖体蛋白的水平+T 细胞。相反，CAD 的过度表达改善了记忆 T 细胞的细胞因子反应和增殖。总体而言，我们的研究揭示了 CAD 诱导的嘧啶合成和核糖体生物发生在促进记忆 T 细胞的快速回忆反应特征方面的关键作用。