IL-2 Family Cytokines and their Receptors-- Molecular Regulation via GABP

白细胞介素-2受体和相关的细胞因子/细胞因子受体系统正在研究，以了解正常和肿瘤细胞中T细胞免疫应答的关键组成部分。T细胞活化后，IL-2和IL-2受体被诱导; T细胞免疫应答的幅度和持续时间由产生的IL-2的量、表达的受体水平和这些事件的时间过程控制。存在IL-2受体的三条链，IL-2 Ra、IL-2 Rb和gc，其中IL-2 Ra和IL-2 Rb在转录水平上受到显著调节。gc是IL-4、IL-7、IL-9、IL-15和IL-21的受体也使用的共享链，并且是在XSCID中突变的蛋白质。我们主要关注这些细胞因子诱导的信号类型，以及这些细胞因子及其受体的调节基础。 以前，我们证明了IL-7受体α链表达受IL-2负调控。虽然关于B细胞中IL-7受体的调节基础有一些信息，但在T细胞中基本上一无所知。在B细胞中，Ets家族转录因子PU. 1对于基因的控制至关重要。我们先前发现，在B细胞中结合PU. 1的相同Ets结合位点对于T细胞中的IL-7 Ra表达也是必需的，但是在T细胞中，关键因子是GA结合蛋白（GABP）。此外，通过基因捕获方法产生GABP α链水平降低的小鼠。GABPa表达减少的胚胎表现出胸腺细胞数量明显减少，这些细胞上的IL-7 Ra表达较低。在上一个报告期，我们观察到GABP也是B细胞发育的关键调节因子，部分通过调节Pax 5和Pax 5靶基因起作用，并且GABP和PU.1控制巨核细胞生成的成熟阶段特异性调节。 在今年，我们报道了GABP调节编码丝氨酸-苏氨酸激酶的基因的表达，表示KIS，磷酸化p27 Kip 1，细胞周期蛋白依赖性激酶抑制剂，是重要的细胞迁移和细胞周期进程。有趣的是，在血管平滑肌细胞中通过siRNA敲低GABPa表达减少了KIS基因表达并减少了细胞迁移。此外，在血清刺激后，KIS基因表达在GABPa KO细胞中减少，S期细胞减少。此外，在体内血管损伤后，GABPa杂合子小鼠动脉病变内KIS表达减少。这些结果总体上强调了GABPa对KIS表达和功能的重要作用。 GABP包含α和β链，β链具有长和短同种型。L型可以形成α-β异四聚体，而S型不能。为了更多地了解GABPb的功能，我们选择性地靶向被认为是GABP作用所必需的长形式，并产生仍保留GABPb-S形式表达的GABPb-L形式KO小鼠。出乎意料的是，淋巴发育没有缺陷，T和B细胞发育正常，成熟T和B细胞对各种刺激的反应正常，而不是具有严重的表型。相比之下，靶向L和S形式导致早期胚胎致死。这些数据表明，与先前的信念相反，GABPb-S也是功能性的，而不是作为显性阴性。 我们还研究了IL-7 Ra在CD 8 + T细胞中的表达。病毒特异性CD 8 T细胞通常会降低IL-7 Ra的水平，并且寿命短，但有些会逃逸并成为记忆前体效应细胞。我们发现GABPa是记忆前体效应细胞中IL-7 Ra表达所需的，而Gfi-I是效应T细胞中稳定的IL-7 Ra抑制所需的。因此，IL-7 Ra的表达受到GABP和Gfi-1相反功能的调节，证实了我们之前关于GABP的报道，并确定Gfi-1是一种平衡因子。 总的来说，上述发现增强了我们对细胞因子的共同细胞因子受体家族控制基因表达以调节免疫应答的机制的理解。

The interleukin-2 receptor and related cytokine/cytokine receptor systems are being studied to understand critical components of the T cell immune response in normal and neoplastic cells. Following T-cell activation, IL-2 and IL-2 receptors are induced; the magnitude and duration of the T-cell immune response is controlled by the amount of IL-2 produced, the levels of receptors expressed, and the time course of these events. Three chains of the IL-2 receptor exist, IL-2Ra, IL-2Rb, and gc, with IL-2Ra and IL-2Rb being significantly regulated at the level of transcription. gc is a shared chain also used by the receptors for IL-4, IL-7, IL-9, IL-15, and IL-21, and is the protein that is mutated in XSCID. We have focused primarily on the types of signals induced by some of these cytokines, and the basis for regulation of these cytokines and their receptors. Previously, we demonstrated that IL-7 receptor alpha chain expression is negatively regulated by IL-2. Although some information was available regarding the basis for regulation of the IL-7 receptor in B cells, essentially nothing was known in T cells. In B cells, an Ets family transcription factor, PU.1, is critical for control of the gene. We previously discovered that the same Ets binding site that binds PU.1 in B cells is also essential for IL-7Ra expression in T cells, but that in T cells, the critical factor is GA binding protein (GABP). Additionally, mice with diminished levels of the GABP alpha chain were generated by a gene-trap methodology. Embryos with diminished expression of GABPa exhibited markedly decreased numbers of thymocytes and lower IL-7Ra expression on those cells. In the previous reporting period, we observed that GABP was also a critical regulator of B cell development, acting in part by regulating Pax5 and Pax5 target genes and that GABP and PU.1 control maturation stage-specific regulation of megakaryopoiesis. In the current year, we reported that GABP regulates expression of the gene encoding a serine-threonine kinase, denoted KIS, that phosphorylates p27Kip1, a cyclin-dependent kinase inhibitor, and is important for cell migration and cell cycle progression. Interestingly, knocking down GABPa expression by siRNA in vascular smooth muscle cells diminished KIS gene expression and reduced cell migration. Moreover, after serum stimulation, KIS gene expression was diminished in the GABPa KO cells, with decreased cells in S-phase. Furthermore, after vascular injury in vivo, mice heterozygous for GABPa had diminished KIS expression within arterial lesions. These results overall underscored an important role for GABPa for KIS expression and function. GABP comprises both alpha and beta chains, with the beta chain having both long and short isoforms. The L form can form alpha-beta heterotetramers whereas the S form cannot. To learn more about the function of GABPb, we selectively targeted the long form that was believed to be essential for GABP action and generated GABPb-L form KO mice that still retained expression of the GABPb-S form. Unexpectedly, rather than having a severe phenotype, there was no defect in lymphoid development, with normal T and B cell development and normal mature T and B cell responses to various stimuli. In contrast, targeting both the L and S forms resulted in early embryonic lethality. These data indicate that contrary to prior belief, GABPb-S is also functional rather than serving as a dominant negative. We also studied IL-7Ra expression in CD8+ T cells. Virus-specific CD8 T cells typically diminish levels of IL-7Ra and are short lived, but some escape and become memory precursor effector cells. We found that GABPa was required for IL-7Ra expression in memory precursor effector cells whereas Gfi-I was needed for stable IL-7Ra repression in effector T cells. Thus, expression of IL-7Ra is regulated by opposing functions of GABP and Gfi-1, confirming our own earlier reports on GABP and identifying Gfi-1 as being a counterbalancing factor. Overall, the above findings enhance our understanding of mechanisms by which the common cytokine receptor family of cytokines control gene expression to regulate the immune response.