FcRn-dependent sorting of IgG and IgG-opsinized antigens by epithelial cells

描述(由申请人提供)：本项目的主要目标是阐明Ig G MHC类Fc3受体FcRN如何将Ig G和Ig G调理抗原转运到肠道屏障内和穿过肠屏障。FcRN在上皮细胞中转运免疫球蛋白及其相关的免疫球蛋白复合体，对宿主和共生微生物群之间的对话，从而对粘膜表面的上皮维持、炎症反应和宿主防御具有重要的影响。我们将验证假设：1)肠上皮细胞利用FcRN中和免疫球蛋白调理的微生物和微生物产物，并引发炎症反应；2)与共同/顶端循环内小体相关的特定细胞因子调节FcRN的运输；以及3)FcRN中的膜近端两亲性基序-细胞质尾部感觉(或诱导)膜曲率或表面电位，从而影响受体的运输。目的1描述免疫球蛋白调理颗粒如何将FcRN从跨细胞和循环途径转移到降解途径。在这一分选步骤中，我们还将使用在FcRN细胞质尾部区域突变的FcRN-异构体来检查FcRN细胞质尾部的结构-功能关系。AIM 2将跟进我们最近的研究中提出的想法，即小GTP酶Rab25调节指定跨细胞作用的分选步骤。我们的目标是鉴定和表征共同的/顶端循环内小体的细胞因子，这些内小体调控FcRN在极化细胞中的运输。将要研究的蛋白质包括Rab11a/Rab25效应器的FIP家族、Rab10、Rab8、ACAP1和胞外复合体。我们将尝试使用酵母双杂交系统对FcRN相互作用的蛋白质进行无偏筛选，我们将检查顶端和基侧膜陷阱，看看这些分子是否标记含有FcRN的囊泡，以便通过极化细胞进行载体运输。目的3将聚焦于FcRN细胞质尾部的膜近端区域，以测试一种通过感受(或诱导)膜曲率或表面电位的两亲性1-螺旋结构域来分选膜蛋白的新想法。我们认为，这个基序的寡聚解释了FcRN如何内化免疫球蛋白调理颗粒，并将运输途径从回收和跨细胞作用切换到降解的隔室。与公共卫生相关：我们的目标是了解肠道与位于肠腔(腔)中的巨大而复杂的微生物群和微生物产物相互作用的一种方式。肠腔中的微生物在健康和疾病，包括慢性炎症性肠病中，对肠道功能的调节有很大的作用。在这里，我们研究了运送免疫球蛋白G(人类最主要的抗体形式)的肠道受体如何决定这种相互作用的结果。

DESCRIPTION (provided by applicant): The overarching goal of this project is to elucidate how the IgG MHC Class I-like Fc3-receptor FcRn transports IgG and IgG-opsonized antigens into and across the intestinal barrier. Trafficking of IgG and associated IgG- complexes by FcRn in epithelial cells has important consequences on the dialogue between host and commensal microflora, and thus on epithelial maintenance, inflammatory responses and host defense at mucosal surfaces. We will test the hypotheses: 1) that intestinal epithelial cells utilize FcRn to neutralize IgG- opsonized microbes and microbial products and to raise an inflammatory response; 2) that specific cellular factors associated with the common/apical recycling endosome, a compartment unique to polarized epithelial cells, regulate the trafficking of FcRn; and 3) that a membrane proximal amphipathic motif in the FcRn- cytoplasmic tail senses (or induces) membrane curvature or surface potential so as to affect receptor trafficking. AIM 1 will characterize how IgG-opsonized particles divert FcRn from the transcytotic and recycling pathways, which typify FcRn trafficking, into the degradative pathway. We also will examine structure-function relationships of the FcRn cytoplasmic tail in this sorting step using FcRn-isoforms mutated in its cytoplasmic tail domain. AIM 2 will follow-up on ideas raised in our recent studies indicating that the small GTPase Rab25 regulates a sorting step that specifies transcytosis. We aim to identify and characterize the cellular factors of the common/apical recycling endosomes that regulate FcRn trafficking in polarized cells. Proteins to be studied include the FIP family of Rab11a/Rab25 effectors, Rab10, Rab8, ACAP1, and the exocyst complex. We will attempt an unbiased screen for FcRn-interacting proteins using a yeast two-hybrid system, and we will examine the apical and basolateral membrane SNAREs to see if these molecules mark FcRn-containing vesicles for vectorial transport across polarized cells. AIM 3 will focus on the membrane proximal region of the FcRn cytoplasmic tail to test a new idea for sorting of membrane proteins by amphipathic 1-helical domains that sense (or induce) membrane curvature or surface potential. We propose that oligomerization of this motif explains how FcRn can internalize IgG-opsonized particles and switch pathways of trafficking away from recycling and transcytosis into degradative compartments. PUBLIC HEALTH RELEVANCE: We aim to understand one way that the intestine interacts with the vast and complex microflora and microbial products located in the intestinal lumen (cavity). Microbes in the intestinal lumen are strongly implicated in regulating intestinal function in health and disease, including the chronic inflammatory bowel diseases. Here, we study how an intestinal receptor for transporting immunoglobulin G (the most dominant form of antibodies in humans) dictates the outcome of this interaction.