B Cell Receptor Regulation of Antigen Processing

描述（由申请人提供）：B淋巴细胞捕获、处理和向T细胞呈递抗原的能力是正常体液免疫反应所必需的，并有助于B细胞和T细胞介导的自身免疫性疾病的发病机制。B淋巴细胞优先捕获多价抗原，通过聚集B细胞抗原受体（BCR）并启动信号级联反应，引发一系列协调的细胞反应，确保即使是低亲和力抗原也能被有效捕获。抗原多价性极大地加速了受体的内吞作用和它们通过内吞途径到达内体抗原加工室的转运。与成熟树突状细胞中描述的相似，BCR连接也诱导受体靶向抗原处理室的重塑，从而增强其处理肽并将其装载到MHC II类的能力。尽管BCR信号在决定抗原向T细胞递呈方面很重要，但对于哪些信号通路有助于受体运输以及它们调节的特定细胞过程，人们知之甚少。在本拨款申请中，我们证明了BCR成分Ig？在细胞表面被E3连接酶Itch泛素化，这是早期到晚期内体正常运输所必需的。在没有泛素化的情况下，受体循环回到细胞表面。再往下游，泛素连接酶cl -b是进入抗原加工室所必需的。根据这些观察，我们提出了一个模型，其中在BCR内吞运输中有两个不同的检查点，每个检查点由不同的泛素连接酶控制。基于该模型，我们预测每个检查点的受体运输决定了外周B细胞的反应。我们建议在以下具体目标中对该模型进行检验：确定Itch泛素化Ig？目标2。测定Ig？ubiquitinylation。目标3。确定BLNK和Cbl-b如何参与受体贩运。目的4：确定为什么BCR转运在无能B细胞中异常。

DESCRIPTION (provided by applicant): The ability of B lymphocytes to capture, process and present antigens to T cells is requisite for normal humoral immune responses and contributes to the pathogenesis of both B and T cell mediated autoimmune diseases. B lymphocytes preferentially capture polyvalent antigens which, by aggregating the B cell antigen receptor (BCR) and initiating signaling cascades, elicit a coordinated series of cellular responses that ensure that even low affinity antigens are productively captured. Antigenic polyvalency greatly accelerates both the endocytosis of engaged receptors and their transit through the endocytic pathway to the late endosomal antigen processing compartments. Similar to what has been described in maturing dendritic cells, BCR ligation also induces a remodeling of the receptor targeted antigen processing compartments which enhances their ability to process peptides and load them onto MHC class II. Despite the importance of BCR signaling in determining antigen presentation to T cells, relatively little is known about which signaling pathways contribute to receptor trafficking and what specific cellular processes they regulate. In this grant application, we demonstrate that the BCR constituent Ig? is ubiquitinylated at the cell surface by the E3 ligase Itch and that this is required for normal trafficking from early to late endosomes. In the absence of ubiquitinylation, the receptor recycles back to the cell surface. Farther downstream, the ubiquitin ligase Cbl-b is required for entry into the antigen processing compartments. From these observations, we propose a model in which there are two different checkpoints in BCR endocytic trafficking each controlled by different ubiquitin ligases. Based on this model, we predict that decisions in receptor trafficking made at each checkpoint determine peripheral B cell responses. We propose to test this model in the following Specific Aims: Aim 1. To determine how Itch ubiquitinylates Ig?. Aim 2. To determine the in vivo function of Ig? ubiquitinylation. Aim 3. To determine how BLNK and Cbl-b contribute to receptor trafficking. Aim 4: To determine why BCR trafficking is aberrant in anergic B cells.