IL2 RECEPTORS--MOLECULAR REGULATION

人们正在研究人类白介素2受体，以了解正常细胞和肿瘤细胞中T细胞免疫反应的关键成分。T细胞激活后，IL-2和IL-2受体被诱导；T细胞免疫反应的大小和持续时间由IL-2的生成量、受体的表达水平和这些事件的时间进程控制。IL-2受体存在三条链，即IL-2Ra、IL-2Rb和GC，其中IL-2Ra和IL-2Rb在转录水平上受到显著调控。该小组主要关注IL-2诱导的信号类型，特别是STAT蛋白的激活，以及调节IL-2ra基因表达以响应丝裂原和IL-2的机制。在分析IL-2诱导的STAT蛋白(信号转导和转录激活因子)方面已经取得了相当大的进展。IL-2可激活新鲜人外周血淋巴细胞(PBL)中的Stat5a和Stat5b(两种氨基酸同源性为90%的密切相关蛋白)，还可激活植物血凝素预激活的PBL中的STAT3。继续对Stat5a和Stat5b基因敲除小鼠进行分析。此前，有研究表明，与Stat5a基因敲除小鼠一样，Stat5b基因敲除小鼠也表现出自然杀伤细胞增殖和杀细胞活性的实质性缺陷。在过去的一年里，研究表明，Stat5a和Stat5b都是抗原诱导的嗜酸性粒细胞和T细胞重新聚集到组织中所必需的。与IL-2ra基因5‘调控区存在IL-2反应元件一致，先前的研究表明，与Stat5a基因敲除小鼠一样，Stat5b基因敲除小鼠在IL-2诱导的IL-2ra表达方面存在缺陷。转基因方法正被用来进一步研究Stat5a和Stat5b的独特作用和重叠作用。在合作研究中，该小组报告了HMG-I(Y)蛋白对IL-2受体α链启动子上的定位核小体赋予结构特异性的作用。此外，现在已经确定了IL-2ra基因中的一个额外的调节元件。此外，据报道，从杆状病毒表达系统中纯化的Stat5a和Stat5b蛋白被用于结合位点选择分析。这表明Stat5a和Stat5b二聚体都与类似的TTCN3GAA基序结合，而Stat5a四聚体表现出与比预期更大的位点结合。具体地说，研究表明，除了典型的气体基序外，不同的“半气体”基序或甚至不太相似的序列对结合起重要作用。更大的位点库也可能作为实现特定STAT蛋白与特定启动子结合的更高特异性的基础。该实验室还致力于建立系统，以确定底物丝氨酸磷酸化在IL-2反应中的作用，并评估Stat5蛋白丝氨酸磷酸化的功能意义。总之，这些研究大大增强了我们对IL-2R表达的基础以及IL-2依赖的基因调控的理解。

The human interleukin-2 receptor is 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. The group has focused primarily on the types of signals induced by IL-2, particularly the activation of STAT proteins, and the mechanism of regulating IL-2Ra gene expression in response to mitogen and IL-2. Considerable progress has been made in analyzing the STAT proteins (signal transducers and activators of transcription) induced by IL-2. IL-2 can activate both Stat5a and Stat5b (two closely related proteins with >90% amino acid identity) in fresh human peripheral blood lymphocytes (PBL) and additionally activates Stat3 in PBL preactivated with phytohemagglutinin. The analysis of Stat5a and Stat5b knockout mice was continued. Previously, it was shown that like Stat5a knockout mice, Stat5b knockout mice also exhibit a substantial defect in the proliferative and cytolytic activities of natural killer cells. In the past year, it was demonstrated that both Stat5a and Stat5b are required for antigen-induced eosinophil and T-cell recruitment into tissue. Consistent with the presence of an IL-2 response element in the 5' regulatory region of the IL-2Ra gene, it was previously shown that like Stat5a knockout mice, Stat5b knockout mice are defective in IL-2-induced IL-2Ra expression. Transgenic approaches are being used to further investigate distinctive vs. overlapping roles of Stat5a and Stat5b. In collaborative studies, the group reported the effect of HMG-I(Y) proteins on imparting architectural specificity to a positioned nucleosome on the IL-2 receptor alpha chain promoter. Moreover, an additional regulatory element in the IL-2Ra gene has now been characterized. Furthermore, it was reported that Stat5a and Stat5b proteins purified from a baculovirus expression system were used in a binding site-selection analysis. This has revealed that both Stat5a and Stat5b dimers bind to similar TTCN3GAA motifs, whereas Stat5a tetramers exhibit binding to a larger repertoire of sites than was expected. Specifically, it was demonstrated that in addition to canonical GAS motifs, divergent "half-GAS" motifs or even less similar sequences importantly contributed to binding. The larger repertoire of sites also likely serves as a basis for achieving greater specificity of binding of particular STAT proteins to particular promoters. The lab has also worked to set up systems to define the role of serine phosphorylation of substrates in response to IL-2, and to evaluate the functional significance of serine phosphorylation of stat5 proteins. Together, these studies substantially enhance our understanding of the basis for IL-2R expression as well as IL-2-dependent gene regulation.