Molecular basis of G protein-coupled receptor function

激动剂与GPCR的结合引起GPCR激酶对活化受体的快速磷酸化。这一过程促进了arrestin蛋白家族成员（-arrestin-1和-2）向活化受体的募集，破坏了受体/G蛋白偶联，并通过将受体靶向网格蛋白包被的小凹来促进GPCR内化。然而，在过去的10-15年中，许多研究表明，-arrestins也可以作为信号分子在自己的权利。这一观察结果不仅具有理论意义，而且具有潜在的临床意义。 在过去的几年中，DREADDs（设计师受体专门激活的设计师药物）已经成为强大的新型化学遗传学工具，以研究由不同功能类别的GPCR激活的信号通路的生理相关性。在结构上，DREADD代表突变的毒蕈碱受体，其可以被氯氮平-N-氧化物（CNO）激活，否则是一种具有高效力和功效的惰性试剂。重要的是，这些新的设计受体不能被内源性毒蕈碱受体激动剂乙酰胆碱激活。 与DREADD的GPCR样性质一致，我们最近证明了基于M3毒蕈碱受体（M3 R）的DREADD不仅激活Gq家族的G蛋白，而且还可以与β-arrestin-1和-2相互作用并触发β-arrestin依赖性下游信号传导。总之，这些发现支持了以下概念：在特定组织或细胞类型中激活特定GPCR（或DREADD）的生理结果代表了由G蛋白和β-抑制蛋白依赖性信号通路激活引起的综合反应。为了深入了解这两个不同的GPCR信号传导分支的生理相关性，重要的是评估G蛋白和β-抑制蛋白依赖性信号传导对特定组织反应的相对贡献。为了阐明这一问题，我们最近产生了基于M3 R的抑制蛋白偏向的DREADD（Nakajima等人，2015）以及缺乏与β-抑制蛋白相互作用的能力的基于M3 R的Gq/11偏向的DREADD（Hu等人，2016）。我们表明，后者DREADD在体内是活跃的，并且新设计受体的细胞类型选择性表达可以导致对G蛋白与β-抑制蛋白依赖性信号传导的生理作用的新见解。这些功能偏向的DREADD代表了研究不同组织和细胞类型中Gq/11与β-抑制蛋白依赖性信号级联的生理相关性的强大新工具。重要的是，这些信息可以用于开发新型的临床有用的药物，包括G蛋白或β-arrestin偏向激动剂。 (Hu J，Stern M，Gimenez LE，Wanka L，Zhu L，Rossi M，Meister J，Inoue A，Beck-Sickinger AG，Gurevich VV，Wess J. A G protein-biased designer G protein-coupled receptor used for the studying the physiological relevance of Gq/11-dependent signaling pathways. J Biol Chem 291，7809-20，2016;本周论文）。 审核： Nakajima K，Gimenea LE，Gurevich VV，Wess J.抑制蛋白偏置DREADD的设计和分析。在：“Designer Receptors Exclusively Activated by Designer Drugs”，Neuromethods Series，Book 108，ed. G. Thiel，Springer Science + Business Media，纽约，NY，pp. 29-48，2015年。 ==

Agonist binding to GPCRs causes rapid phosphorylation of the activated receptors by GPCR kinases. This process promotes the recruitment of members of the arrestin protein family (-arrestin-1 and -2) to the activated receptors, disrupting receptor/G protein coupling and promoting GPCR internalization by targeting the receptors to clathrin-coated pits. However, during the past 10-15 years, many studies have demonstrated that -arrestins can also act as signaling molecules in their own right. This observation is not only of theoretical interest but also of potential clinical relevance. During the past few years, DREADDs (designer receptors exclusively activated by designer drug) have emerged as powerful novel chemogenetic tools to study the physiological relevance of signaling pathways activated by different functional classes of GPCRs. Structurally, DREADDs represent mutant muscarinic receptors that can be activated by clozapine-N-oxide (CNO), an otherwise pharmacologically inert agent, with high potency and efficacy. Importantly, these new designer receptors cannot be activated by acetylcholine, the endogenous muscarinic receptor agonist. Consistent with the GPCR-like properties of DREADDs, we recently demonstrated that an M3 muscarinic receptor (M3R)-based DREADD does not only activate G proteins of the Gq family but can also interact with beta-arrestin-1 and -2 and trigger beta-arrestin-dependent downstream signaling. Taken together, these findings support the concept that the physiological outcome of activating a specific GPCR (or DREADD) in a particular tissue or cell type represents an integrated response caused by the activation of both G protein- and beta-arrestin-dependent signaling pathways. To gain insight into the physiological relevance of these two distinct GPCR signaling branches, it is important to assess the relative contribution of G protein- and beta-arrestin-dependent signaling to a particular tissue response. To shed light on this issue, we recently generated an M3R-based -arrestin-biased DREADD (Nakajima et al., 2015) as well as an M3R-based Gq/11-biased DREADD that lacks the ability to interact with beta-arrestins (Hu et al., 2016). We showed that this latter DREADD is active in vivo and that cell type-selective expression of the new designer receptors can lead to novel insights into the physiological roles of G protein- vs. beta-arrestin-dependent signaling. These functionally biased DREADDs represent powerful new tools to study the physiological relevance of Gq/11- vs. beta-arrestin-dependent signaling cascades in distinct tissues and cell types. Importantly, such information could be exploited for developing novel classes of clinically useful drugs, including G protein- or beta-arrestin-biased agonists. (Hu J, Stern M, Gimenez LE, Wanka L, Zhu L, Rossi M, Meister J, Inoue A, Beck-Sickinger AG, Gurevich VV, Wess J. A G protein-biased designer G protein-coupled receptor useful for studying the physiological relevance of Gq/11-dependent signaling pathways. J Biol Chem 291, 7809-20, 2016;paper of the week). Review: Nakajima K, Gimenea LE, Gurevich VV, Wess J. Design and analysis of an arrestin-biased DREADD. In: "Designer Receptors Exclusively Activated by Designer Drugs", Neuromethods Series, Book 108, ed. G. Thiel, Springer Science + Business Media, New York, NY, pp. 29-48, 2015. ==