SIGNIFICANCE OF THE MULTIFUNCTIONAL INSULIN-LIKE GROWTH FACTOR-II RECEPTOR IN REGULATING NORMAL BRAIN FUNCTION

多功能胰岛素样生长因子 II 受体在调节正常脑功能中的意义

• 批准号: RGPIN-2017-05729
• 负责人: Kar, Satyabrata
• 金额: $ 1.89万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=681670
• 关键词: SIGNIFICANCE; MULTIFUNCTIONAL; INSULIN; LIKE; GROWTH

The insulin-like growth factor-II (IGF-II) receptor is a single-pass multifunctional glycoprotein containing a large extracellular domain and a small cytoplasmic tail. The receptor interacts with IGF-II and mannose 6-phosphate (M6P)-bearing ligands, such as lysosomal enzymes via two distinct sites. Majority of the receptors are expressed within trans-Golgi/endosomal compartments and are involved in the segregation of newly synthesized lysosomal enzymes for sorting to endosomes/lysosomes. A subset of receptors located on the plasma membrane regulates internalization of IGF-II and M6P-containing ligands for their clearance or activation. Receptor dimerization has been suggested to play a role in optimal binding and internalization of M6P-bearing ligands. There is also evidence that the IGF-II receptor participates in mediating certain biological actions of IGF-II by activating specific intracellular signaling pathways. At present, while the trafficking role of the receptor is well established, its significance in transmembrane signaling in response to IGF-II binding remains controversial. Using a variety of approaches, we have reported that i) the single-pass IGF-II receptor is coupled to a G-protein and its activation by Leu27IGF-II, an IGF-II analog that binds preferentially to the receptor, potentiates acetylcholine release but attenuates GABA release from adult rat hippocampus by a pertussis toxin (PTX)-sensitive pathway and ii) activation of the receptor leads to its translocation from detergent-resistant to detergent-soluble membrane fractions and stimulation of extracellular signal-related kinase 1/2 via a PTX-dependent pathway. Our recent preliminary data further indicate that i) binding of [125I]IGF-II but not the M6P ligand [125I]PMB-BSA to the IGF-II receptor is inhibited by GTP analogue GTPS, ii) PTX treatment attenuates internalization of [125I]IGF-II in hippocampal cultured neurons, iii) Leu27IGF-II potentiates hippocampal glutamate release and enhances spatial learning in adult arts. Thus, we hypothesize that single transmembrane domain IGF-II receptor, by interaction with a G-protein, can directly regulate biological functions of IGF-II in the adult rat brain. To address this issue we propose: i) to determine whether IGF-II receptor-mediated G-protein signaling can occur in the presence of M6P-ligands, ii) to establish if dimerization of the IGF-II receptor is necessary for its signaling effects, iii) to determine the fate of the IGF-II receptor following induction of G-protein-mediated signaling cascade and iv) to establish the role of glutamate and acetylcholine in IGF-II-mediated enhancement of cognitive function. We believe that this study should generate original data regarding specificity of interactions between the IGF-II receptor and G protein and help to define its significance in regulating normal brain functions.

胰岛素样生长因子- ii （IGF-II）受体是一种单代多功能糖蛋白，含有一个大的细胞外结构域和一个小的细胞质尾部。该受体通过两个不同的位点与IGF-II和携带甘露糖6-磷酸（M6P）的配体（如溶酶体酶）相互作用。大多数受体在反式高尔基体/内体室中表达，并参与新合成的溶酶体酶的分离，以便分选到内体/溶酶体。位于质膜上的受体亚群调节IGF-II和含m6p配体的内化以清除或激活它们。受体二聚化已被认为在携带m6p配体的最佳结合和内化中发挥作用。也有证据表明，IGF-II受体通过激活特定的细胞内信号通路，参与介导IGF-II的某些生物学作用。目前，虽然该受体的转运作用已经确定，但其在响应IGF-II结合的跨膜信号传导中的意义仍存在争议。使用多种方法，我们已经报道了i)单通道IGF-II受体与g蛋白偶联并被Leu27IGF-II激活，Leu27IGF-II是一种优先结合受体的IGF-II类似物；通过百日破毒素（PTX）敏感途径增强乙酰胆碱释放，但减弱GABA从成年大鼠海马的释放；ii)受体的激活导致其从洗涤剂抗性转移到洗涤剂可溶性膜部分，并通过PTX依赖途径刺激细胞外信号相关激酶1/2。我们最近的初步数据进一步表明，i) [125I]IGF-II而不是M6P配体[125I]PMB-BSA与IGF-II受体的结合被GTP类似物GTPS抑制，ii) PTX治疗减弱海马培养神经元中[125I]IGF-II的内化，iii) Leu27IGF-II增强海马谷氨酸释放并增强成人艺术的空间学习。因此，我们假设单个跨膜结构域IGF-II受体通过与g蛋白相互作用，可以直接调节成年大鼠脑中IGF-II的生物学功能。为了解决这一问题，我们提出：i)确定IGF-II受体介导的g蛋白信号传导是否可以在m6p配体存在的情况下发生，ii)确定IGF-II受体的二聚化是否对其信号传导作用是必要的，iii)确定诱导g蛋白介导的信号级联后IGF-II受体的命运，iv)确定谷氨酸和乙酰胆碱在IGF-II介导的认知功能增强中的作用。我们认为，这项研究应该产生关于IGF-II受体和G蛋白之间相互作用特异性的原始数据，并有助于确定其在调节正常脑功能中的意义。