Defining how T cells measure the strength of T cell receptor signals

摘要 T细胞是适应性免疫反应的介体。为了正确地建立反应，T细胞使用细胞外 受体感知它们的环境并将信号传递给细胞内的信号网络。虽然很多人 与T细胞功能相关的信号通路已经建立，但对这些通路是如何发挥作用的知之甚少 调制以区分不同类型的信号，因此代表着我们的 知识库。这些知识将有助于控制T细胞在多发性硬化中的激活和分化 治疗环境。一个主要的信号输入是T细胞受体(TCR)信号强度，它调节T 细胞分化、胸腺发育和细胞因子信号转导。在之前的工作中，我们发现了 T细胞受体信号的差异性调控AKT/mTOR信号轴。调整TCR信号强度 AKT的磷酸化进而控制AKT底物的特异性，从而使不同的TCR信号强度 使用不同的AKT信令网络。虽然这些结果很耐人寻味，但基础生化 将TCR信号强度耦合到下行信令网络的机制，包括差分AKT 激活仍然定义不清。一条可以将TCR信号强度与细胞内信号联系起来的途径 网络是磷脂酰肌醇(PIP)的代谢。许多PIP物种具有生物活性并调节信号， 转录、代谢和RNA剪接。在pMHC与TCR结合后，PI3K将PI(4，5)P2磷酸化为 在细胞膜上产生PIP3。PIP3之所以引起人们的兴趣，是因为它激活了对 免疫功能，包括AKT和PDK1。然而，还会产生其他具有生物活性的PIP类脂物种，它们的 T细胞的功能尚未完全确定。基于我们建立的研究AKT激活的计算模型 T细胞，我们的模拟意外地预测到不同的TCR信号强度会产生不同的PIP。 在实验上，我们发现除了PIP3之外，其他生物活性的PIP在 测试细胞激活和不同TCR信号强度产生不同的PIP种类。我们的蛋白质组筛查 识别T细胞中与特定PIP结合的蛋白质，这使我们能够识别新的途径 在T细胞激活过程中被激活。这一新结果是T细胞通过产生TCR信号来传递信号强度 不同的PIP有可能阐明T细胞如何解释细胞外的基本生化机制 信号。这些初步数据是我们中心假设的基础，即T细胞编码TCR信号 通过产生不同的磷脂酰肌醇来控制T细胞命运决定的强度，这将通过以下几个方面进行测试：1) 识别响应TCR信号控制磷脂酰肌醇差异产生的机制 强度和2)确定差异生成的磷脂酰肌醇如何在Treg和T中发挥作用 辅助性细胞命运选择和Th1与Th2细胞命运选择。总而言之，这项工作的结果将提供 受体信号在分子水平整合的新机制及识别差异功能 磷脂酰肌醇的产生在CD4+T细胞命运选择的背景下。

Abstract T cells are mediators of the adaptive immune response. To properly mount a response, T cells use extracellular receptors to sense their environment and transduce signals to intracellular signaling networks. While many signaling pathways relevant to T cell function are established, less is known about how these pathways are modulated to discriminate between different types of signals and thus represents a significant gap in our knowledge base. Such knowledge would aid in controlling T cell activation and differentiation in multiple therapeutic settings. One dominant signaling input is T cell receptor (TCR) signaling strength, which regulates T cell differentiation, thymic development and cytokine signaling. In previous work, we identified that the strength of the T cell receptor signal differentially regulated the AKT/mTOR signaling axis. TCR signal strength regulated the phosphorylation of AKT which in turn controls AKT substrate specificity so that different TCR signal strengths engage qualitatively different AKT signaling networks. While these results are intriguing, the basic biochemical mechanisms that couple TCR signal strength to downstream signaling networks including differential AKT activation remains ill defined. One pathway that could couple TCR signal strength to intracellular signaling networks is phosphatidylinositol (PIP) metabolism. Many PIP species are bioactive and regulate signaling, transcription, metabolism and RNA splicing. Following pMHC binding to TCR, PI3K phosphorylates PI(4,5)P2 to generate PIP3 at the cell membrane. PIP3 has garnered interest because it activates kinases important for immune function, including AKT and PDK1. However, other bioactive PIP lipid species are generated and their functions in T cells are ill established. Based on a computational model we built to study the AKT activation in a T cell, our simulation unexpectedly predicted that different TCR signal strengths would generate different PIPs. Experimentally, we found that other bioactive PIPs in addition to PIP3 are generated at appreciable levels during T cell activation and that different TCR signal strengths generate different PIP species. Our proteomic screen identified proteins in a T cell that bind to specific PIPs, which positions us to identify novel pathways that are engaged during T cell activation. The novel result that T cells transduce TCR signal strength by generating different PIPs has the potential to illuminate a basic biochemical mechanism for how T cell interprets extracellular signals. These preliminary data serve as the basis of our central hypothesis that T cells encode TCR signal strength by generating different phosphatidylinositols to control T cell fate decisions, which will be tested by: 1) identifying mechanisms that control differential generation of phosphatidylinositols in response to TCR signal strength and 2) identifying how differential generation of phosphatidylinositols functions in the Treg versus T helper cell fate choice and the Th1 versus Th2 cell fate choice. Taken together, results from this work will provide novel mechanisms of receptor signal integration at the molecular level and identify functions of differential phosphatidylinositol generation in the context of CD4+ T cell fate choices.