VLGR1 signaling at focal adhesions and ICD release as a non-canonical signaling pathway of aGPCRs

VLGR1(超大G蛋白偶联受体-1)，又称ADGRV1、GPR98和MASS，是迄今为止最大的黏附性GPCR(AGPCR)。虽然VLGR1的表达几乎无处不在，但它主要集中在神经系统。人类VLGR1基因的突变导致了人类亚瑟综合征(USH)，这是最常见的遗传性失聪形式。此外，越来越多的证据表明，VLGR1缺陷也与癫痫有关。到目前为止，人们对其在膜黏附和信号传导中的双重功能知之甚少。在目前的资助期间，我们通过应用亲和蛋白质组学(TAP)结合质谱学，确定了与VLGR1和其他几个aGPCRs相关的相互作用伙伴和蛋白质簇。这些aGPCRs相互作用的生物信息学分析定义了基因本体论(GO)术语和与突变的aGPCR功能相关的细胞模块。对于第二个授权期，我们已经选择了特定的功能模块来进一步评估和深入描述它们在VLGR1和GPCRs中的信号功能。(1)我们将阐明VLGR1在局灶性粘连(FAs)中的作用，FAs是ECM和细胞外生长和迁移所必需的放线细胞骨架之间的信号枢纽。我们将利用包括不同类型神经细胞在内的不同类型的VLGR1缺陷细胞模型，测试VLGR1在脂肪酸周转的时空控制、细胞迁移调控和细胞骨架调控中的作用。(2)我们将破译VLGR1和其他aGPCRs与γ-分泌酶复合体的相互作用，这是一个常见的非典型的aGPCR信号通路。为此，我们将测试aGPCRs是否是伽马分泌酶的底物，以及它们的胞内域(ICD)是如何释放到细胞质中的。此外，我们还将评估GPCRs的核功能。我们确信，我们的结果将有助于理解GPCRs是如何工作的。我们还希望对与GPCRs功能障碍相关的疾病的发病机制有新的认识，并看到为这些疾病的治疗寻找新的治疗靶点的机会。

VLGR1 (very large G protein-coupled receptor-1), also known asADGRV1, GPR98 and MASS is by far the largest adhesion GPCR(aGPCR). Although VLGR1 expression is almost ubiquitous, it ishighly concentrated in the nervous system. Mutations in the humanVLGR1 gene cause the human Usher syndrome (USH), the mostcommon form of hereditary deaf-blindness. In addition, there isgrowing evidence that defects in VLGR1 are also associated withepilepsy. So far, little is known about its dual function in membranemembraneadhesion and signaling. In the current funding period, weidentified interaction partners and protein clusters related to VLGR1,and to several other aGPCRs by applying affinity proteomics (tandemaffinity purifications (TAPs) in combination with mass spec).Bioinformatics analyses of the interactomes of these aGPCRs havedefined Gene Ontology (GO) terms and cell modules related toputative aGPCR function. For the second grant period, we haveselected specific functional modules for further evaluation and indepthcharacterization of their signaling function for VLGR1 and foraGPCRs. (1) We will elucidate the role of VLGR1 in focal adhesions(FAs) which act as signaling hubs between the ECM and the actincytoskeleton essential for cell outgrowth and migration. We will testVLGR1´s contribution to the spatial and temporal control of FAturnover, the regulation of cell migration and the modulation of thecytoskeleton using divers VLGR1 deficient cellular models includingdifferent types of neural cell. (2) We will decipher the interaction ofVLGR1 and other aGPCRs with the gamma-secretase complex as acommon non-canonical aGPCR signaling pathway. For this, we willtest whether aGPCRs are substrates of the gamma-secretase andhow their intracellular domains (ICDs) are released into thecytoplasm. Furthermore, we will evaluate nuclear functions ofaGPCRs. We are certain that our results will help to understand howaGPCRs work. We also hope to gain new insights into thepathomechanisms of diseases associated with the dysfunction ofaGPCRs and see opportunities to identify new therapeutic targets forthe treatment of these diseases.