Department of Neurology and the Molecular Pharmacology Program, Memorial Sloan Kettering Cancer Center, 1275 York Ave, New York, NY, 10065, USA.
Eurofins DiscoverX, Fremont, CA, USA.
Cell Mol Neurobiol. 2021 Jul;41(5):1059-1074. doi: 10.1007/s10571-020-00973-5. Epub 2020 Oct 8.
The biased signaling has been extensively studied in the original mu opioid receptor (MOR-1), particularly through G protein and β-arrestin2 signaling pathways. The concept that the G protein pathway is often linked to the therapeutic effect of the drug, while the β-arrestin pathway is associated to the side effects has been proposed to develop biased analgesic compounds with limited side-effects associated with traditional opiates. The mu opioid receptor gene, OPRM1, undergoes extensive alternative pre-mRNA splicing, generating multiple splice variants or isoforms that are conserved from rodent to human. One type of the Oprm1 splice variants are the full-length 7 transmembrane (7TM) C-terminal splice variants, which have identical receptor structures including entire binding pocket, but contain a different intracellular C-terminal tail resulted from 3' alternative splicing. Increasing evidence suggest that these full-length 7TM C-terminal variants play important roles in mu opioid pharmacology, raising questions regarding biased signaling at these multiple C-terminal variants. In the present study, we investigated the effect of different C-terminal variants on mu agonist-induced G protein coupling, β-arrestin2 recruitment, and ultimately, signaling bias. We found that mu agonists produced marked differences in G protein activation and β-arrestin2 recruitment among various C-terminal variants, leading to biased signaling at various level. Particularly, MOR-1O, an exon 7-associated variant, showed greater β-arrestin2 bias for most mu agonists than MOR-1, an exon 4-associated variant. Biased signaling of G protein-coupled receptors has been defined by evidences that different agonists can produce divergent signaling transduction pathways through a single receptor. Our findings that a single mu agonist can induce differential signaling through multiple 7TM splice variants provide a new perspective on biased signaling at least for Oprm1, which perhaps is important for our understanding of the complex mu opioid actions in vivo where all the 7TM splice variants co-exist.
偏态信号已在原始 μ 阿片受体 (MOR-1) 中得到广泛研究，特别是通过 G 蛋白和β-arrestin2 信号通路。人们提出了这样一种概念，即 G 蛋白通路通常与药物的治疗效果有关，而β-arrestin 通路则与副作用有关，这为开发具有有限副作用的偏向性镇痛化合物提供了思路，这些化合物与传统阿片类药物相关的副作用有关。μ 阿片受体基因 OPRM1 经历广泛的选择性前体 mRNA 剪接，生成多种从啮齿动物到人类都保守的剪接变体或同工型。Oprm1 剪接变体的一种类型是全长 7 跨膜 (7TM) C 端剪接变体，其受体结构完全相同，包括整个结合口袋，但由于 3'选择性剪接，包含不同的细胞内 C 端尾部。越来越多的证据表明，这些全长 7TM C 端变体在 μ 阿片药理学中发挥重要作用，这引发了关于这些多种 C 端变体的偏向信号的问题。在本研究中，我们研究了不同 C 端变体对 μ 激动剂诱导的 G 蛋白偶联、β-arrestin2 募集以及最终信号偏向的影响。我们发现，μ 激动剂在各种 C 端变体之间产生了明显的 G 蛋白激活和β-arrestin2 募集差异，导致不同水平的偏向信号。特别是，与外显子 4 相关的变体 MOR-1 相比，与外显子 7 相关的变体 MOR-1O 对大多数 μ 激动剂表现出更大的β-arrestin2 偏向性。G 蛋白偶联受体的偏向信号已通过不同激动剂可通过单个受体产生不同的信号转导途径的证据来定义。我们的发现表明，单个 μ 激动剂可以通过多个 7TM 剪接变体诱导不同的信号转导，这为至少对于 Oprm1 的偏向信号提供了一个新的视角，这也许对于我们理解体内所有 7TM 剪接变体共存时 μ 阿片类药物的复杂作用很重要。
