In vivo functions of Ig-beta ubiquitinylation

描述(由申请人提供)：需要两个协调的信号才能从天然毛囊B细胞中诱导出有效的体液免疫反应。当B细胞抗原受体(BCR)识别多价或膜限制性抗原并启动相互关联的信号级联网络时，第一种信号立即在细胞表面提供。相反，必需的第二信号出现的时间较晚，来自专门化的晚期内小体(MHC II包含间隔室或MIIC)的过程。这些过程包括MHC-II类多肽的负载，以及随后T细胞Help的募集，以及Toll样受体(TLR)7和9与配体的结合。这些信号2使能受体的激活依赖于BCR在细胞表面捕获配体并将其沿着内吞递送的能力 通向它们的受体的途径。然而，BCR靶向晚期内小体，从而将信号1与信号2偶联的分子机制尚不清楚。我们先前已经证明，Ig泛素化在细胞系中是必要的，以将内化的BCR复合体靶向晚期内小体。我们还证明，BCR内吞靶向MIIC不是一个结构性过程，而是一个在外周无能细胞中调节的过程，以防止B细胞的异常激活。我们现在已经得到了免疫泛素化(Ig？)的体内模型。这证实了它在将bcr复合体引入晚期内体中的作用。此外，我们现在证明，免疫泛素化是选择免疫球蛋白高的细胞进入未成熟的B细胞池以及TD和钛的体液免疫反应所必需的。对Ig泛素化的要求与抗原特异性无关，并与基础和BCR诱导的信号转导中的特定缺陷有关。在体外对这些信号缺陷的补充恢复了针对晚期内体的bcr。基于这些和初步结果中提出的其他数据，我们假设BCR泛素化，就像酪氨酸磷酸化一样，在将BCR与B细胞发育和外周血细胞激活所必需的信号过程偶联中发挥关键作用。此外，我们认为泛素化在BCR内稳态以及在选择和维持B细胞方面发挥着额外的作用，而不考虑抗原的特异性。这一中心假设将在以下具体目标中得到检验：目的1.确定Ig泛素化如何促进未成熟B细胞的选择。目的2.确定免疫球蛋白泛素化在外周免疫反应中的作用。目的3.确定Ig调节BCR信号启动和表面动态平衡的机制。好了！

DESCRIPTION (provided by applicant): Two coordinated signals are required to elicit productive humoral immune responses from na¿ve follicular B cells. The first is provided immediately at the cell surface when the B cell antigen receptor (BCR) recognizes polyvalent or membrane-restricted antigens and initiates an interrelated web of signaling cascades. In contrast, the necessary second signals arise later from processes exclusive to specialized late endosomes (the MHC II containing compartment or MIIC). These include the loading of MHC class II with peptides, and subsequent recruitment of T cell help, and ligand binding by toll-like receptors (TLR) 7 and 9. Activation of these signal 2 enabling receptors is dependent upon the abilities of the BCR to capture ligands at the cell surface and to deliver them along the endocytic pathway to their receptors. However, the molecular mechanisms by which the BCR target late endosomes, and thereby couples signal 1 with signal 2, are poorly understood. We have previously demonstrated that Ig¿ ubiquitination is necessary in cell lines for targeting internalized BCR complexes to late endosomes. We have also demonstrated that BCR endocytic targeting to the MIIC is not a constitutive process but one that is regulated in peripheral anergic cells to prevent aberrant B cell activation. We have now gone on to derive an in vivo model of Ig¿ ubiquitination (Ig¿???) that confirms its role in ushering BCR complexes into late endosomes. In addition, we now demonstrate that Ig¿ ubiquitination is required for selection of IgMhigh cells into the immature B cell pool and for both Td and Ti humoral immune responses. The requirement for Ig¿ ubiquitination was independent of antigen specificity and was associated with specific defects in basal and BCR-induced signaling. Complementation of these signaling defects in vitro restored BCR targeting to late endosomes. Based on these and other data presented in Preliminary Results, we hypothesize that BCR ubiquitination, much like tyrosine phosphorylation, plays a critical role in coupling the BCR to signaling processes necessary for B cell development and peripheral activation. Furthermore, we propose that ubiquitination plays additional roles in BCR homeostasis and in selecting and maintaining B cells irrespective of antigenic specificity. This central hypothesis will be tested in the followin Specific Aims: Aim 1. To determine how Ig¿ ubiquitination contributes to immature B cell selection. Aim 2. To determine the role of Ig¿ ubiquitination in peripheral immune responses. Aim 3. Determine the mechanisms by which Ig¿ regulates BCR signal initiation and surface homeostasis. !