Sigma-1 receptor (S1R) is a multimodal chaperone protein which is implicated in various pathophysiological conditions including drug addiction, Alzheimer's disease and amyotrophic lateral sclerosis (ALS). S1R interacts with various ion channels and receptors on endoplasmic reticulum or plasma membrane (PM). It has been reported that S1R colocalizes with the M2-muscarinic acetylcholine receptor (M2R) on the soma of motoneurons, although a functional interaction between these two proteins hasn't been established. Here, we investigated the regulation of M2R signalling by S1R using electrophysiological recordings of GIRK currents in HEK293T cells. We observed that S1R strongly inhibited M2R-mediated activation of GIRK1/2, but the disease mutant linked to ALS, S1R E102Q, did not. The inhibitory effect of S1R was selective for M2R and wasn't seen when S1R was co-expressed with other Gi/o coupled receptors including M4R. Chimeric and mutant receptors of M2R and M4R were generated and analysed, and this highlighted Ala401 in the transmembrane 6 domain (TM6) of M2R and Glu172 as well as Glu175 in the extracellular loop 2 region of M2R, as essential for the inhibition by S1R. Co-immunoprecipitation confirmed the physical interaction between M2R and S1R. Immunocytochemical labelling of M2R and S1R expressed in HeLa cells, HEK293T cells and cultured hippocampal neurons, showed clear PM expression of M2R throughout the cell which was decreased by coexpression with S1R but was still apparent. Taken together, our results show that S1R interacts with M2R to reduce both its PM expression and function, and this involves TM6 and the extracellular loop 2.

中文翻译：

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M2R 的结构决定因素参与 Sigma-1R 的抑制。


Sigma-1 受体 （S1R） 是一种多模式伴侣蛋白，与各种病理生理状况有关，包括药物成瘾、阿尔茨海默病和肌萎缩侧索硬化症 （ALS）。S1R 与内质网或质膜 （PM） 上的各种离子通道和受体相互作用。据报道，S1R 与运动神经元胞体上的 M2-毒蕈碱乙酰胆碱受体 （M2R） 共定位，尽管这两种蛋白质之间的功能相互作用尚未确定。在这里，我们使用 HEK293T 细胞中 GIRK 电流的电生理记录研究了 S1R 对 M2R 信号传导的调节。我们观察到 S1R 强烈抑制 M2R 介导的 GIRK1/2 激活，但与 ALS 相关的疾病突变体 S1R E102Q 没有。S1R 的抑制作用对 M2R 具有选择性，当 S1R 与其他 Gi/o 偶联受体（包括 M4R）共表达时未观察到。生成和分析 M2R 和 M4R 的嵌合和突变受体，这突出了 M2R 和 Glu172 跨膜 6 结构域 （TM6） 中的 Ala401 以及 M2R 细胞外环 2 区域的 Glu175，这对 S1R 的抑制至关重要。免疫共沉淀证实了 M2R 和 S1R 之间的物理相互作用。在 HeLa 细胞、HEK293T 细胞和培养的海马神经元中表达的 M2R 和 S1R 的免疫细胞化学标记显示 M2R 在整个细胞中表达的明显 PM 表达，与 S1R 共表达降低，但仍然明显。综上所述，我们的结果表明 S1R 与 M2R 相互作用以降低其 PM 表达和功能，这涉及 TM6 和细胞外环 2。