A novel signaling mechanism of Progranulin

描述（由申请人提供）：编码分泌糖蛋白的基因前蛋白（PGRN）突变是导致泛素阳性包络体（FTLD-U）的额颞叶变性的主要原因。最近，一种功能未知的II型跨膜蛋白TMEM106B被发现是FTLD-U的危险因素。但PGRN和TMEM106B如何共同作用以防止FTLD-U仍不清楚。我们之前的工作已经确定sortilin是一种PGRN转运受体。我们最近的初步数据进一步表明sortilin在介导PGRN信号传导中起作用。sortilin细胞内区域缺乏信号基序提示存在潜在的“共受体”。我们发现TMEM106B与sortilin物理相互作用，这种相互作用刺激TMEM106B的裂解。此外，TMEM106B是调节膜内蛋白水解（RIP）的底物，已知在神经元信号转导中起关键作用。因此，我们提出sortilin和TMEM106B形成PGRN受体复合物，TMEM106B的裂解介导PGRN信号传导。为了验证这一模型，提出了两个具体目标。目的1：确定sortilin/TMEM106B在PGRN信号传导中的作用。我们将首先通过测量缺乏sortilin或TMEM106B的神经元中PGRN的神经营养效应来测试sortilin和TMEM106B在PGRN信号传导中的重要性。然后，我们将确定PGRN信号是否刺激sortilin/TMEM106B相互作用和TMEM106B切割。目的2：探讨TMEM106B的信号转导机制。我们将首先生成抗切割版本的TMEM106B，以确定PGRN信号是否需要TMEM106B切割。然后将TMEM106B的裂解产物在NSC-34细胞中表达，以确定其是否具有类似于PGRN处理的神经营养作用。我们还计划通过检测TMEM106B切割产物的定位和识别其结合伙伴来探索其下游信号传导机制。综上所述，通过这些研究，我们期望建立sortilin和TMEM106B在PGRN信号传导中的作用，并测试一种涉及TMEM106B切割的新的信号传导机制。我们期望我们提出的研究将显著推进我们对PGRN信号传导机制的理解，并将建立TMEM106B的第一个分子表征并阐明其在神经变性中的作用。

DESCRIPTION (provided by applicant): Mutations in Progranulin (PGRN), a gene encoding a secreted glycoprotein, are the major cause of Frontotemporal Lobar Degeneration with ubiquitin positive inclusions (FTLD-U). More recently, TMEM106B, a type II transmembrane protein of unknown function, was discovered as a risk factor of FTLD-U. But how PGRN and TMEM106B function together to prevent FTLD-U remains unclear. Our previous work has identified sortilin as a PGRN trafficking receptor. Our recent preliminary data further suggests that sortilin plays a role in mediating PGRN signaling. Lack of a signaling motif in sortilin intracellular region suggests the presence of a potential 'co-receptor". We found that TMEM106B physically interacts with sortilin and this interaction stimulates the cleavage of TMEM106B. Furthermore, TMEM106B is a substrate of regulated intramembrane proteolysis (RIP), which is known to play a critical role in neuronal signal transduction. Thus we propose that sortilin and TMEM106B form a receptor complex for PGRN and TMEM106B cleavage mediates PGRN signaling. To test this model, two specific aims are proposed. Aim1: To determine the role of sortilin/TMEM106B in PGRN signaling. We will first test the importance of sortilin and TMEM106B in PGRN signaling by measuring the neurotrophic effects of PGRN in neurons lacking sortilin or TMEM106B. Then we will determine whether PGRN signaling stimulates sortilin/TMEM106B interaction and TMEM106B cleavage. Aim2: To investigate the signaling mechanism of TMEM106B. We will first generate a cleavage resistant version of TMEM106B to determine whether TMEM106B cleavage is required for PGRN signaling. Then the cleavage product of TMEM106B will be expressed in NSC-34 cells to determine whether it has neurotrophic effects similar to PGRN treatment. We also plan to probe the downstream signaling mechanisms of TMEM106B cleavage product by examining its localization and identifying its binding partners. In summary, through these studies, we expect to establish a role of sortilin and TMEM106B in PGRN signaling and test a novel signaling mechanism involving TMEM106B cleavage. We expect our proposed studies will significantly advance our understanding on PGRN signaling mechanisms and will establish the first molecular characterization of TMEM106B and illustrate its role in neurodegeneration.