Role of the DR/DQ super enhancer in MHC-II expression

主要组织相容性复合体II类（MHC-II）蛋白由HLA-DR、-DQ和-DP三种HLA基因编码 通过将加工的抗原肽呈递给CD 4 + T细胞，从而启动和/或维持 适应性免疫反应MHC-II表达受转录调节，并在细胞中组成型表达。 抗原呈递细胞，如B细胞，但也可在非免疫细胞中被IFN γ诱导。因此，MHC-II- 介导的免疫应答和适应性免疫主要在转录水平上受到控制。所有MHC- II基因受一组共同的近端启动子转录元件和因子的共调控， CIITA是细胞类型限制性的，由IFN γ诱导。几年前，我们发现MHC-II基因的表达是 也受到一系列转录绝缘子元件的调节，这些元件与CTCF和粘附素结合， 元件是彼此与MHC-II启动子之间的长距离染色质相互作用的焦点 地区这些元件一起形成了一个三维染色质结构，有利于基因的表达。 表情事实上，当B细胞分化为浆细胞并失去MHC-II表达时，这种结构被破坏。 也失去了。虽然这个模型是正确的，并已站在过去5年，我们现在提供令人兴奋的新证据 它是不完整的。本文提出的新数据鉴定了位于HLA-10之间的超级增强子（SE）。 DRB 1和-DQA 1基因（称为DR/DQ-SE）是系统最大表达和 它的“3D”架构。CRISPR/Cas9介导的Raji B细胞中DR/DQ-SE的缺失导致细胞凋亡率降低。 HLA-DR和-DQ的表达，刺激同种异体CD 4 T细胞应答的能力降低，以及HLA-DR和-DQ的丧失。 启动子相关的组蛋白修饰和所有局部CTCF-绝缘子相互作用。此外，虽然 接受MHC蛋白质是高度多态性的，非编码多态性的顺式调节区域内的 MHC-II基因座更广泛且与MHC-II表达和疾病紧密相关，这表明 DR/DQ-SE对MHC-II表达的转录调节是免疫和疾病的关键组成部分。 除了我们所介绍的，没有其他关于这个地区及其工作原理的信息。为了填补这一空白， 本申请试图了解该SE如何起作用以控制MHC-II表达， 免疫力目的1将阐明DR/DQ-SE的基本分子和生化成分， 确定多态性如何影响其功能。目标2将确定SE影响和测试的范围 一个如何运作的模型。目标3将研究如何建立和退役SE。在一起， 我们的研究将深入了解人类（SNP）的多样性如何影响免疫力，以及最终如何影响免疫力。 一组至关重要的免疫系统基因受到调控。获得的知识将具有广泛的 对基因调控的影响，并将提供新的见解如何适应性免疫的初始步骤， 可以控制响应。我们的研究结果可能对未来的免疫疗法产生重要影响 和疫苗接种，以及用于治疗传染病、自身免疫、癌症和移植。

Major histocompatibility complex class-II (MHC-II) proteins are encoded by HLA-DR, -DQ, and -DP  gene pairs and function by presenting processed antigenic peptides to CD4+ T cells thereby initiating and/or sustaining adaptive immune responses. MHC-II expression is transcriptionally regulated and expressed constitutively in antigen-presenting cells, such as B cells, but may be induced in non-immune cells by IFN. Thus, MHC-II- mediated immune responses and adaptive immunity is controlled primarily at the level of transcription. All MHC- II genes are coregulated by a common set of proximal promoter transcription elements and factors of which only CIITA is cell type limiting and induced by IFN. Several years ago, we showed that MHC-II gene expression was also modulated by a series of transcriptional insulator elements that bound CTCF and cohesin and that these elements were the focal points of long-range chromatin interactions between each other and MHC-II promoter regions. Together these elements formed a three-dimensional chromatin architecture that favored gene expression. Indeed, as B cells differentiated into plasma cells and lost MHC-II expression, this architecture was also lost. While this model is correct and has stood for the last 5 years, we now provide exciting new evidence that it is incomplete. New data presented herein identifies a super enhancer (SE) located between the HLA- DRB1 and -DQA1 genes (termed the DR/DQ-SE) that is required for maximal expression of the system and for its “3D” architecture. CRISPR/Cas9 mediated deletion of the DR/DQ-SE in Raji B cells resulted in decreased expression of HLA-DR and -DQ, reduced ability to stimulate an allogenic CD4 T cell response, and loss of promoter associated histone modifications and all local CTCF-insulator interactions. Additionally, while it is accepted that MHC proteins are highly polymorphic, non-coding polymorphisms within cis-regulatory regions of the MHC-II locus are more extensive and strongly linked to MHC-II expression and disease, suggesting that transcriptional regulation of MHC-II expression by the DR/DQ-SE is a key component of immunity and disease. Aside from what we present, nothing else is known about this region and how it works. To fill this gap in knowledge, this application seeks to understand how this SE functions to control MHC-II expression and immunity. Aim 1 will elucidate fundamental molecular and biochemical components of the DR/DQ-SE and determine how polymorphisms affect its function. Aim 2 will determine the range of the SE’s influence and test a model of how it may operate. Aim 3 will examine how the SE is established, and decommissioned. Together, our studies will provide insight into how human (SNP) diversity influences immunity, and ultimately how this critically important set of immune system genes are regulated. The knowledge gained will have broad implications on gene regulation and will provide new insight into how the initial steps of adaptive immune responses may be controlled. Our results could have important implications for future immune-based therapies and vaccinations, and for treatments of infectious disease, autoimmunity, cancer, and transplantation.