The biology of the beige-like protein LRBA in health and disease

我们在2012年发现，人类基因LRBA的突变导致免疫失调综合征（López-Herrera et al.，AJHG）。这种疾病的特点是慢性炎症性肠病，严重的自身免疫性和感染易感性增加。关于LRBA的生物学功能知之甚少：-LRBA普遍表达（Wu C等人，2009)-其表达在细胞活化后增加（Wang X等人，2000)-从用荧光显微镜进行的共定位研究，我们知道LRBA位于内体和溶酶体（Wang JW等人，2001)-来自相同家族的蛋白质（海滩蛋白）介导细胞囊泡和肌动蛋白细胞骨架之间的连接（Cullinane等人，2013）-公开了海滩蛋白和自噬之间的联系（Rahman等人，2012）在这个项目中，我们建议进一步研究LRBA的遗传学和生物学，以了解其在免疫系统中的作用，并确定治疗炎症性肠病、严重自身免疫和感染易感性的可能新靶点。在WP 1中，我们将探讨为什么缺乏普遍表达的蛋白质会导致仅限于免疫系统的表型。我们将研究LRBA及其同源物在不同细胞群体中的表达和剪接变体以及各种刺激。此外，我们将研究LRBA缺陷细胞的基因表达谱。我们的初步数据表明，LRBA（320 kDa的大小）形成880 kDa的复合物。在WP 2中，我们希望确定LRBA的互动伙伴。我们建议通过两种方法来做到这一点：假设驱动的方法，通过免疫共沉淀确定潜在的相互作用伙伴;和无假设的方法，通过SILAC质谱。我们将通过验证或证伪以下假设来研究LRBA在WP 3中的功能：-LRBA对淋巴细胞的趋化性很重要-LRBA在免疫受体再循环中起着关键作用-LRBA在自噬中起着关键作用-LRBA干扰mTOR信号传导途径关于人类免疫系统的基因/蛋白质的功能的发现，其表现为单基因人类疾病特征，对于转化研究特别有趣，因为这些基因/蛋白质定义了免疫系统的阿基里斯脚跟，特别是与治疗靶向相关。

We discovered in 2012 that mutations in the gene LRBA in humans lead to an immune dysregulation syndrome (López-Herrera et al., AJHG). This disease is characterized by a chronic inflammatory bowel disease, severe autoimmunity and an increased infection susceptibility. Not much is know on the biological functions of LRBA:-LRBA is expressed ubiquitously (Wu C et al., 2009)-Its expression increases following cell activation (Wang X et al., 2000)-From co-localization studies with fluorescence microscopy we know that LRBA is located at endosomes and lysosomes (Wang JW et al., 2001)-Proteins from the same family (BEACH proteins) mediate the link between cellular vesicles and the actin cytoskeleton (Cullinane et al., 2013)-A link between BEACH proteins and autophagy is published (Rahman et al., 2012) In this project we suggest to further study the genetics and the biology of LRBA to learn about its role in the immune system and to identify possible novel targets for the treatment of inflammatory bowel disease, severe autoimmunity and infection susceptibility.In WP1 we will approach the question why the lack of an ubiquitously expressed protein leads to a phenotype limited to the immune system. We will study the expression and splice variants of LRBA and its homologs in different cell populations and following various stimuli. Moreover, we will study the gene expression profile of LRBA-deficient cells. Our preliminary data show that LRBA (320 kDa in size) forms complexes of 880 kDa. In WP2 we wish to identify interaction partners of LRBA. We propose to do this by two means: The hypothesis-driven approach, by identifying potential interaction partners by co-immunoprecipitation; and the hypothesis-free approach, by SILAC-mass spectroscopy. We will study the function of LRBA in WP3 by verifying or falsifying the following hypotheses:-LRBA is important for the chemotaxis of lymphocytes-LRBA plays a critical role in immune receptor recycling-LRBA plays a critical role in autophagy-LRBA interferes with the mTOR signaling pathwayDiscoveries on the function of genes/proteins of the human immune system, which manifest as monogenetic human disease traits, are especially interesting for translational research, as these genes/proteins define Achilles heels of the immune system, specifically relevant for therapeutic targeting.