Signaling in T Lymphocyte Development

描述（由申请人提供）：也许在发展中很少有问题像不同的细胞命运是如何根据信号梯度而产生的那样难以解决。在许多生物体中，这些模数转换是决定细胞命运的基础。T淋巴细胞发育可能是理解这一普遍问题的最佳系统之一，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够产生正向选择（分化和增殖）的T细胞，这些T细胞能够对胸腺基质细胞的自身mhc作出反应。另一方面，自身抗原产生的强信号导致应答自身抗原的细胞死亡。促凋亡蛋白Bim是阴性选择所必需的，而不是阳性选择所必需的。相反，我们最近发现钙调磷酸酶在T细胞中是阳性选择所必需的，但在阴性选择中是必不可少的。令人惊讶的是，钙调磷酸酶特异性地控制ERK的激活，而不是其他MAP激酶或IkB，这表明胸腺细胞选择的公认信号通路的修订。这些观察结果为从Bim和钙调磷酸酶到分子的生化行军奠定了基础，这些分子随着信号强度的增加，将信号从正选择转移到负选择。目前的研究支持了几种可能的机制，通过这些机制，不同强度的信号可以控制选择。为了避免在生化途径的前向分析中遇到的困难，我们将从Bim和钙调磷酸酶向后工作，以定义在CD4+， CD8+胸腺细胞中控制其活性的生化途径。在这些研究中，我们的目标是确定Bim和钙调磷酸酶激活所需的最低共同介质，从而确定正选择和负选择。然后，我们将确定诱导该分子将高强度信号传递给Bim和低强度信号传递给钙调磷酸酶的机制。我们还将定义钙调磷酸酶介导正选择的下游过程，包括NFATc核输入和输出的机制，在正选择中依赖钙调磷酸酶活性的一组基因，以及这些基因如何产生具有免疫能力的外周淋巴细胞群。确定这些机制将有助于更全面地了解免疫防御，并为开发新疗法提供有用的信息。

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.