Signaling in T Lymphocyte Development

描述(由申请人提供)：也许在发育过程中，很少有问题像信号梯度产生不同细胞命运的方法那样难以解决。这些从模拟到数字的开关是决定许多生物体细胞命运的基础。T淋巴细胞发育可能是理解这一普遍问题的最好系统之一，因为关键信号是在生化、遗传和细胞生物学方法都可以发挥作用的阶段给出的。在淋巴细胞中，微弱或短暂的信号被认为能产生阳性选择(分化和增殖)T细胞，能够对胸腺基质细胞上的自身MHC产生反应。另一方面，自身抗原产生的强烈信号会导致对自身抗原反应的细胞死亡。促凋亡蛋白Bim是负选择所必需的，但不是正选择所必需的。相反，我们最近发现，钙调神经磷酸酶在T细胞中对于正选择是必不可少的，但对于负选择是必不可少的。令人惊讶的是，钙调神经磷酸酶专门控制ERK的激活，而不是其他MAP激酶或IKB的激活，这表明胸腺细胞选择的公认信号通路的修改。这些观察为从Bim和钙调神经磷酸酶到分子(S)的生化进行曲奠定了基础，该分子随着信号强度的增加将信号从正选择转移到负选择。目前的研究支持几种可能的机制，通过这些机制，不同强度的信号可以控制选择。为了避免正向分析生化途径所遇到的困难，我们将从Bim和Calcineurin向后工作，以定义控制它们在CD4+、CD8+胸腺细胞中活动的生化途径。我们在这些研究中的目标将是确定BIM和钙调神经磷酸酶激活所需的最低公共介质，从而确定积极和消极选择。然后，我们将确定这种分子被诱导将高强度信号引导到BIM，将低强度信号引导到钙调神经磷酸酶的机制。我们还将定义钙调神经磷酸酶下游介导正选择的过程，包括NFATc核输入和输出的机制，在正选择中依赖钙调神经磷酸酶活性的一组基因，以及这些基因如何产生具有免疫活性的外周淋巴细胞。明确这些机制应该会导致对免疫防御的更全面的理解，并为新疗法的开发提供有用的信息。

DESCRIPTION (provided by applicant): Perhaps few questions in development have been so intractable as the means by which different cell fates are produced in response to a gradient of signals. These analogue-to-digital switches underlie the determination of cell fates in many organisms. T Lymphocyte development may be one of the best systems to understand this general problem because the critical signals are given at a stage where biochemical, genetic and cell biologic methods can all be brought to play. In lymphocytes, weak or transient signals are thought to produce positive selection (differentiation and proliferation) of T cells capable of reacting to self-MHC on thymic stromal cells. On the other hand, strong signals produced by self-antigen lead to death of cells responding to self-antigen. The pro-apoptotic protein Bim is required for negative selection but is not necessary for positive selection. Conversely, we have recently found that calcineurin is essential in T cells for positive selection, but dispensable for negative selection. Surprisingly calcineurin specifically controls the activation of ERK but not other MAP kinases or IkB, suggesting a revision of the accepted signaling pathways of thymocyte selection. These observations set the stage for a biochemical march from Bim and calcineurin to the molecule(s) that divert signals from positive to negative selection with increasing signal intensity. Current studies support several possible mechanisms by which signals of different intensity could control selection. To avoid the difficulties encountered with forward analysis of biochemical pathways we will work backward from Bim and calcineurin to define the biochemical pathways that control their activity in CD4+, CD8+ thymocytes. Our goal in these studies will be to define the lowest common mediator necessary for activation of both Bim and calcineurin and hence positive and negative selection. We will then determine the mechanism by which this molecule is induced to channel high intensity signals to Bim and low intensity signals to calcineurin. We will also define the processes downstream of calcineurin that mediate positive selection including the mechanism of NFATc nuclear import and export, the set of genes that are dependent on calcineurin activity in positive selection and how these genes give rise to a population of immunologically competent peripheral lymphocytes. Defining these mechanisms should lead to a more complete understanding of immune defense and provide useful information for development of new therapies.