Multiple Pathways of CD28 Costimulation

描述（由申请人提供）：已经证实，通过CD28共刺激可以对T细胞的激活、存活、耐受和分化产生巨大影响。然而，尽管有相当大的兴趣和努力，但尚不清楚CD28的这些不同功能是否都是通过TCR信号的扩增或通过诱导一种或多种不同的信号通路来介导的。我们最近发现CD28可以转导两种独立的信号通路，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，并导致PKCtheta特异性募集到免疫突触的cmac区域，NF-kappaB的核易位以及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介导的，在免疫突触中蛋白质的特定定位。第二种途径在没有cd28介导的PI3K激活的情况下发挥作用，并且不会诱导PKCtheta向免疫突触募集或上调IL-2转录。然而，不能激活PI3K的CD28共刺激仍然主要通过稳定IL-2 mRNA诱导正常水平的IL-2分泌。在反式中提供CD28共刺激时，这一途径似乎也起作用，因此可能是由质膜下游的信号整合介导的。本提案的总体目标是确定介导CD28共刺激这两种独立途径的细胞生物学、生化和分子步骤。

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.