Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario K7L3N6, Canada.
Cell Signal. 2018 Mar;43:71-84. doi: 10.1016/j.cellsig.2017.12.006. Epub 2017 Dec 24.
G protein-coupled receptors (GPCR) can participate in a number of signaling pathways, and this property led to the concept of biased GPCR agonism. Agonists, antagonists and allosteric modulators can bind to GPCRs in different ways, creating unique conformations that differentially modulate signaling through one or more G proteins. A unique neuromedin B (NMBR) GPCR-signaling platform controlling mammalian neuraminidase-1 (Neu1) and matrix metalloproteinase-9 (MMP9) crosstalk has been reported in the activation of the insulin receptor (IR) through the modification of the IR glycosylation. Here, we propose that there exists a biased GPCR agonism as small diffusible molecules in the activation of Neu1-mediated insulin receptor signaling. GPCR agonists bombesin, bradykinin, angiotensin I and angiotensin II significantly and dose-dependently induce Neu1 sialidase activity and IR activation in human IR-expressing rat hepatoma cell lines (HTC-IR), in the absence of insulin. Furthermore, the GPCR agonist-induced Neu1 sialidase activity could be specifically blocked by the NMBR inhibitor, BIM-23127. Protein expression analyses showed that these GPCR agonists significantly induced phosphorylation of IRβ and insulin receptor substrate-1 (IRS1). Among these, angiotensin II was the most potent GPCR agonist capable of promoting IRβ phosphorylation in HTC-IR cells. Interestingly, treatment with BIM-23127 and Neu1 inhibitor oseltamivir phosphate were able to block GPCR agonist-induced IR activation in HTC cells in vitro. Additionally, we found that angiotensin II receptor (type I) exists in a multimeric receptor complex with Neu1, IRβ and NMBR in naïve (unstimulated) and stimulated HTC-IR cells with insulin, bradykinin, angiotensin I and angiotensin II. This complex suggests a molecular link regulating the interaction and signaling mechanism between these molecules on the cell surface. These findings uncover a biased GPCR agonist-induced IR transactivation signaling axis, mediated by Neu1 sialidase and the modification of insulin receptor glycosylation.
G 蛋白偶联受体 (GPCR) 可参与多种信号通路，这一特性导致了偏 GPCR 激动剂的概念。激动剂、拮抗剂和变构调节剂可以以不同的方式与 GPCR 结合，形成独特的构象，通过一种或多种 G 蛋白差异调节信号转导。已经报道了一种独特的神经肽 B (NMB) GPCR 信号平台，通过胰岛素受体 (IR) 糖基化的修饰来控制哺乳动物神经氨酸酶-1 (Neu1) 和基质金属蛋白酶-9 (MMP9) 的串扰，从而激活胰岛素受体。在这里，我们提出，在 Neu1 介导的胰岛素受体信号转导的激活中，存在作为小扩散分子的偏 GPCR 激动剂。GPCR 激动剂蛙皮素、缓激肽、血管紧张素 I 和血管紧张素 II 显著且剂量依赖性地诱导 Neu1 神经氨酸酶活性和人胰岛素受体表达的大鼠肝癌细胞系 (HTC-IR) 中 IR 的激活，而无需胰岛素。此外，NMBR 抑制剂 BIM-23127 可特异性阻断 GPCR 激动剂诱导的 Neu1 神经氨酸酶活性。蛋白表达分析表明，这些 GPCR 激动剂显著诱导了 IRβ 和胰岛素受体底物-1 (IRS1) 的磷酸化。其中，血管紧张素 II 是最有效的 GPCR 激动剂，能够促进 HTC-IR 细胞中 IRβ 的磷酸化。有趣的是，用 BIM-23127 和 Neu1 抑制剂奥司他韦磷酸盐处理能够阻断 HTC 细胞中 GPCR 激动剂诱导的 IR 激活。此外，我们发现血管紧张素 II 受体 (I 型) 存在于 Neu1、IRβ 和 NMBR 的多聚体受体复合物中，在未刺激 (未刺激) 和用胰岛素、缓激肽、血管紧张素 I 和血管紧张素 II 刺激的 HTC-IR 细胞中。该复合物表明，在细胞表面上，存在调节这些分子相互作用和信号转导机制的分子联系。这些发现揭示了一个由 Neu1 神经氨酸酶和胰岛素受体糖基化修饰介导的偏 GPCR 激动剂诱导的 IR 转激活信号轴。
