Multiple Pathways of CD28 Costimulation

描述(由申请人提供)：众所周知，通过CD28的共刺激可以对T细胞的激活、存活、耐受和分化产生显著影响。然而，尽管有相当大的兴趣和努力，CD28的这些不同功能是否都是通过简单地通过扩增TCR信号或通过诱导一个或多个不同的信号通路来调节的，目前还不清楚。我们最近发现CD28可以转导两条独立的信号通路，导致IL-2分泌上调。一种途径依赖于CD28激活磷脂酰肌醇3-激酶(PI3K)的能力，导致PKCtheta特异性地募集到免疫突触的cSMAC区域，导致核因子-kappaB的核转位，以及IL-2转录的上调。这一途径可能是通过TCR和CD28信号之间的近端信号整合在免疫突触内蛋白质特定定位的背景下介导的。第二种途径在没有CD28介导的PI3K激活的情况下起作用，并且不会诱导PKCtheta重新招募到免疫突触或上调IL-2转录。然而，不能激活PI3K的CD28共刺激仍能诱导正常水平的IL-2分泌，主要是通过稳定IL-2mRNA来实现的。当CD28共刺激以反式方式提供时，这一途径似乎也发挥了作用，因此可能是通过质膜下游的信号整合来介导的。这项建议的总体目标是定义细胞生物学、生化和分子步骤，这些步骤介导了CD28共刺激的这两个独立途径。 我们将通过两个具体目标实现这些目标： 1.确定CD28及其相关信号分子靶向cSMAC对CD28共刺激IL-2转录的影响。 2.确定导致IL-2mRNA稳定的PI3-激酶非依赖性CD28信号通路的组成成分。

DESCRIPTION (provided by applicant): It is well established that costimulation through CD28 can have a dramatic effect on T cell activation, survival, tolerance, and differentiation. However, in spite of considerable interest and effort, it has been unclear whether these different functions of CD28 are all mediated simply through amplification of TCR signaling or through the induction of one or more distinct signaling pathways. We have recently found that CD28 can transduce two independent signaling pathways that result in the upregulation of IL-2 secretion. One pathway is dependent in the ability of CD28 to activate phosphatidylinositol 3-kinase (PI3K) and results in the specific recruitment of PKCtheta to the cSMAC region of the immunological synapse, nuclear translocation of NF-kappaB, and upregulation of IL-2 transcription. This pathway may be mediated through proximal signal integration between TCR and CD28 signaling within the context of specific localization of proteins within the immunological synapse. The second pathway functions in the absence of CD28-mediated activation of PI3K and does not induce recruitment of PKCtheta to the immunological synapse or upregulation of IL-2 transcription. Nevertheless, costimulation through CD28 that cannot activate PI3K still induces normal levels of IL-2 secretion primarily through stabilization of IL-2 mRNA. This pathway also appears to function when CD28 costimulation is provided in trans and so may be mediated by signal integration downstream from the plasma membrane. The overall goal of this proposal is to define the cell biological, biochemical, and molecular steps that mediate these two independent pathways of CD28 costimulation. We will accomplish these goals through two specific aims: 1. Determine how targeting of CD28 and associated signaling molecules to the cSMAC impacts on CD28 costimulation of IL-2 transcription. 2. Identify the components of the PI3-kinase-independent CD28 signaling pathway that lead to IL-2 mRNA stabilization.