Regulator of G protein signaling proteins differentially control opioid analgesia

描述（由申请人提供）：G蛋白信号（RGS）蛋白调控因子是G蛋白偶联受体（GPCR）辅助蛋白家族，对细胞信号传导的时间和空间控制至关重要，包括mu-阿片受体（MOR）下游的信号传导。RGS蛋白是GTPase加速蛋白（gap），它加速Galpha结合GTP的水解，促进无活性Galpha GDP的形成，从而关闭gpcr的信号传导。我们已经证明RGS蛋白可以终止MOR向腺苷酸环化酶和MAP激酶途径的信号传导。另一方面，MOR释放细胞内钙的有效信号需要RGS蛋白的GAP活性。因此，RGS的活性控制着单个细胞内信号通路的平衡。我们最近使用了一种新的工具来探索RGS蛋白对GPCR信号传导的调节：一种转基因敲入小鼠，其表达的Galpha蛋白对RGS蛋白的GAP活性不敏感。在这些小鼠中，抗痛觉依赖于阿片激动剂和所用的疼痛测定。例如，在热板试验中，RGS调节的丧失使吗啡增强，而不影响美沙酮的抗避孕作用。相反，在尾断试验中，去除RGS活性会降低吗啡和美沙酮抗避孕作用。这表明参与这两种行为的不同神经元通路对RGS蛋白的作用表现出不同的敏感性。我们建议继续对这些小鼠进行探索，以解决一系列关于MOR信号传导及其与抗感觉的关系的基本问题。例如：抗感觉试验之间的差异是由于RGS作用的部位特异性差异造成的吗？观察到的激动剂差异的基础是什么？这种差异可以用细胞信号水平的影响来解释吗？其他使用Galpha蛋白的神经递质系统的作用是什么？更多临床相关的疼痛模型是否也受RGS蛋白调控？我们的总体概念框架如下：1)RGS活性控制GPCR信号传导到多个通路的平衡，这种平衡可能在疼痛时被破坏；2)RGS诱导的mor介导的抗痛觉的变化可能反映了神经递质系统之间平衡的改变，特别是痛觉肽（NOP）系统。拟议的研究将促进我们对阿片信号通路及其由RGS蛋白调控的理解，并在行为改变的背景下解释这些作用。本研究结果可用于开发更好的镇痛药物。

DESCRIPTION (provided by applicant): Regulators of G protein Signaling (RGS) proteins are a family of G protein-coupled receptor (GPCR) accessory proteins that are essential for the temporal and spatial control of cell signaling, including signaling downstream of the mu-opioid receptor (MOR). RGS proteins are GTPase accelerating proteins (GAPs) that accelerate the hydrolysis of Galpha bound GTP and promote the formation of inactive Galpha GDP to switch off signaling by GPCRs. We have shown that RGS proteins serve to terminate signaling of MOR to adenylate cyclase and the MAP kinase pathway. On the other hand, efficient signaling of MOR to release intracellular calcium requires RGS protein GAP activity. Thus, RGS activity controls the balance of signaling pathways within a single cell. We recently used a novel tool to explore regulation of GPCR signaling by RGS proteins: a transgenic knock-in mouse that expresses Galpha proteins that are insensitive to the GAP activity of RGS proteins. In these mice antinociception is dependent on the opioid agonist and pain assay employed. For example, in the hot-plate assay loss of RGS regulation potentiates morphine, without affecting methadone, antinociception. In contrast, in the tail-withdrawal assay removal of RGS activity decreases both morphine and methadone antinociception. This suggests the different neuronal pathways involved in these two behaviors show differential sensitivity to RGS protein action. We propose to continue our exploration of these mice to tackle a series of fundamental questions concerning MOR signaling and its relationship to antinociception. For example: Are the differences between antinociceptive tests due to site-specific variation in RGS action? What is the basis of the observed agonist differences? Can the differences be explained by effects at the level of cell signaling? What is the role of other neurotransmitter systems that also use Galpha proteins? Are more clinically-related pain models also regulated by RGS proteins? Our overall conceptual framework is as follows: 1) RGS activity controls the balance of GPCR signaling to multiple pathways and this balance may be disrupted in pain and 2) RGS-induced changes in MOR-mediated-antinociception may reflect an alteration in the balance between neurotransmitter systems, particularly the nociceptin (NOP) system. The proposed studies will advance our understanding of opioid signaling pathways and their regulation by RGS proteins and explain these actions in the context of altered behaviors. Results from this study may be exploited to develop better analgesic drugs.