MHC Class II Transactivator Function and Regulation

描述（由申请人提供）：适当和正常的MHC II类基因调控是健康和活跃的免疫系统的核心，对我们对抗病原体的能力至关重要。II类反激活子CIITA是MHC-II基因表达的主要调控因子。尽管对CIITA进行了广泛的分析，但CIITA生物学和MHC-II调控的重要方面仍然未知。本建议将从结构、监管和功能三个方面展开。CIITA自我结合，这一特性对其功能至关重要，但寡聚化如何促进CIITA激活MHC-II基因的能力尚不清楚。在Aim 1中，我们将验证以下假设，即寡聚化有助于CIITA与MHC-II启动子上的靶蛋白结合，相互作用和控制染色质重塑，和/或连接调节元件。第二个目的是确定生发中心B细胞向浆细胞分化时CIITA基因沉默的机制。我们的数据表明，基因沉默发生在局部染色质结构水平，并由特定组蛋白修饰的变化介导。重要的是，一组全局抑制因子（Blimp-1）和协同抑制因子（MTA-3和BCL-6）已被确定，它们分别介导向浆细胞的转化或B细胞程序的维持。与细胞培养系统一起，这些抑制因子将用于异位控制CIITA的沉默和表达，从而可以阐明染色质控制的分子机制。因此，CIITA将成为这一重要的细胞命运决定的模型。最后，在DC和巨噬细胞中，CIITA是从四个启动子中的第一个（pl）转录的。

DESCRIPTION (provided by applicant): The appropriate and normal regulation of MHC class II genes is central to a healthy and active immune system and critical for our ability to combat pathogens. The class II transactivator, CIITA, is the master regulator of MHC-II gene expression. Despite extensive analysis of CIITA important aspects of CIITA biology and therefore MHC-II regulation remain unknown. This proposal will focus on three aspects of CIITA structure, regulation, and function. CIITA self-associates, a property that is critical to its function, but how oligomerization contributes to CIITA's ability to activate MHC-II genes is not known. In Aim 1, we will test the hypothesis that oligomerization contributes to the ability of CIITA to bind to its target proteins on MHC-II promoters, interact and control chromatin remodeling, and/or serve to link regulatory elements. The second aim seeks to determine the mechanism of CIITA gene silencing that occurs as germinal center B cells differentiate into plasma cells. Our data indicate that gene silencing occurs at the level of the local chromatin structure and is mediated by changes in specific histone modifications. Importantly, a set of global repressers (Blimp-1) and co-repressors (MTA-3 and BCL-6) has been identified that mediate the transition to plasma cells or the maintenance of the B cell program, respectively. Along with cell culture systems, these repressers will be used to ectopically control CIITA silencing and expression such that the molecular mechanism of chromatin control can be elucidated. CIITA will therefore serve as a model for this important cell fate decision. Lastly, in DC and macrophages CIITA is transcribed from the first (pl) of four promoters. This transcript (pl-CIITA) encodes a unique isoform with enhanced transcriptional activity, yet the exact function of this isoform and the specific role of this DC/macrophage specific promoter are unknown. In Aim 3, we will create mice to examine the novel role that this promoter and its isoform play in developing and initiating immune responses. Because DC/macrophages provide the front line defense to pathogens, this model system will provide a clear role for this promoter and isoform. Thus, the central goal of this application is to understand fully the molecular mechanisms by which CIITA functions to regulate the MHC-II gene system. The results of these studies will ultimately identify targets for immune based therapies for the infectious disease, autoimmune disorders, and organ transplantation.