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: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=710810
• 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）受体是一种单通道多功能糖蛋白，含有一个大的胞外结构域和一个小的胞质尾区。该受体通过两个不同的位点与IGF-II和甘露糖6-磷酸（M6 P）-承载配体（如溶酶体酶）相互作用。大多数受体在反式高尔基体/内体区室中表达，并参与新合成的溶酶体酶的分离，用于分选内体/溶酶体。位于质膜上的受体亚群调节IGF-II和含M6 P的配体的内化，用于其清除或活化。已经提出受体二聚化在携带M6 P的配体的最佳结合和内化中起作用。也有证据表明IGF-II受体通过激活特定的细胞内信号传导途径参与介导IGF-II的某些生物学作用。目前，虽然该受体的运输作用已得到充分证实，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。使用各种方法，我们已经报道了i）单程IGF-II受体与G蛋白偶联，并且其被Leu 27 IGF-II激活，Leu 27 IGF-II是一种优先结合受体的IGF-II类似物，增强乙酰胆碱释放，但减弱GABA释放从成年大鼠海马通过百日咳毒素（PTX）敏感途径和ii）受体的激活导致其易位从去污剂-对洗涤剂可溶性膜组分具有抗性，并通过PTX依赖性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）GTP类似物GTPS抑制[125 I]IGF-II而非M6 P配体[125 I]PMB-BSA与IGF-II受体的结合，ii）PTX处理减弱海马培养神经元中[125 I]IGF-II的内化，iii）Leu 27 IGF-II增强海马谷氨酸释放并增强成人艺术中的空间学习。因此，我们推测，单跨膜结构域IGF-II受体，通过与G蛋白的相互作用，可以直接调节IGF-II在成年大鼠脑中的生物学功能。为解决这一问题，我们建议：i）确定IGF-II受体介导的G蛋白信号传导是否可以在M6 P-配体存在下发生，ii）确定IGF-II受体的二聚化是否是其信号传导作用所必需的，iii）确定IGF-II受体在G蛋白介导的信号级联反应诱导后的命运，和iv）确定谷氨酸和乙酰胆碱在IGF-II受体介导的信号级联反应中的作用。介导的认知功能增强。我们相信，这项研究应该产生原始数据的特异性IGF-II受体和G蛋白之间的相互作用，并帮助确定其在调节正常的大脑功能的意义。