Regulation of T cell activation and tolerance by Grail

摘要T淋巴细胞的活化受到严格调控，以确保有效消除入侵病原体并维持对自身组织的耐受性。T细胞一方面受细胞外信号的调节，尤其是抗原提呈细胞上的正、负共刺激分子，另一方面也受细胞内精细的信号转导和调节因子的调节。最近，我们发现在缺乏CD28和ICOS共刺激的情况下激活的T细胞变得无功能和无反应，支持共刺激在T细胞激活中的关键作用。这些耐受性T细胞不仅在TCR信号转导方面存在严重缺陷，而且完全缺乏效应特异性转录因子的表达。有趣的是，Grail（淋巴细胞中与能量相关的基因）的表达仅在CD28和ICOS信号缺失时才在T细胞中上调。Grail是一种E3泛素连接酶，其表达在体外和体内均与CD4 T细胞能量相关。阻断负共刺激信号（B7S1， B7-H3或PD-1）恢复T细胞功能，与效应特异性转录因子的表达和Grail表达的下调有关。为了确定Grail在T细胞活化和耐受中的功能，我们建立了Grail突变小鼠模型。我们发现grail缺陷T细胞在体外激活和效应分化中不依赖CD28和ICOS信号。我们目前研究的中心假设是Grail分子对T细胞耐受性和功能的关键调控。我们将首先分析Grail在外周T细胞耐受中的作用。此外，我们将确定Grail调节T细胞耐受性的机制。其次，我们将分析Grail在自然和诱导Treg细胞的产生和功能。最后，我们将评估Grail缺乏是否会导致自身免疫性疾病的易感性，以及这是否是由na - ve和/或Treg细胞缺陷引起的。这些拟议的研究将极大地促进我们对Grail在外周耐受性和自身免疫反应中的功能的了解。

DESCRIPTION (provided by applicant): Abstract T lymphocyte activation is tightly regulated to ensure effective elimination of invading pathogens as well as maintaining tolerance against self-tissues. On one hand, T cells are regulated by extracellular signals, especially the positive and negative costimulatory molecules on antigen-presenting cells, and on the other hand, also by delicate intracellular signal transducers and regulators. Recently, we found that T cells activated in the absence of both CD28 and ICOS costimulation became nonfunctional and nonresponsive, supporting a critical role of costimulation in T cell activation. These tolerant T cells not only were anergic with profound defects in TCR signal transduction but also completely lacked expression of effector-specific transcription factors. Interestingly, expression of Grail (gene related to anergy in lymphocytes), was only upregulated in T cells when both CD28 and ICOS signaling were absent. Grail is an E3 ubiquitin ligase whose expression was previously found to be associated with CD4 T cell anergy in vitro and in vivo. Blocking of negative costimulatory signals (B7S1, B7-H3 or PD-1) restored T cell function, associated with expression of effector-specific transcription factors and down-regulation of Grail expression. To determine the function of Grail in T cell activation and tolerance, we developed a Grail mutant mouse model. We found that Grail-deficient T cells were not dependent on CD28 and ICOS signaling in activation and effector differentiation in vitro. Our central hypothesis for the current study is that Grail molecule critically regulates T cell tolerance and function. We will first analyze the role of Grail in peripheral T cell tolerance. In addition, we will determine the mechanisms whereby Grail regulates T cell tolerance. Secondly, we will analyze the function of Grail in generation and function of natural and inducible Treg cells. Lastly, we will assess whether Grail deficiency will lead to susceptibility to autoimmune diseases and whether this is caused by defects in na¿ve and/or Treg cells. These proposed studies will greatly advance our knowledge on Grail function in peripheral tolerance and autoimmune responses. PUBLIC HEALTH RELEVANCE: T lymphocyte activation is tightly regulated to ensure effective elimination of invading pathogens as well as maintaining tolerance against self-tissues. On one hand, T cells are regulated by extracellular signals, especially the positive and negative costimulatory molecules on antigen-presenting cells, and on the other hand, also by delicate intracellular signal transducers and regulators. Our preliminary analysis of a Grail knockout mouse revealed its essential function in induction of T cell tolerance in vitro. In this project, we propose to continue our analysis on function of Grail in T cells in vitro and in vivo. These proposed studies will greatly advance our knowledge on Grail function in T cells and will provide a novel and unique insight into proper T cell regulation that governs self tolerance and immune function.