Ligand Directed Functional Selectivity of G-Protein Coupled Receptor Signalling

描述(申请人提供)：所有组织中的细胞对许多外部刺激(如光、气味、神经递质、激素)的转导都是通过激活被称为G蛋白偶联受体(GPCRs)的大基因超家族的成员来实现的，GPCRs通过大量和不断扩大的细胞内和膜结合蛋白将受体激活与复杂的信号事件级联。GPCRs转导过程的一个共同特征是异源三聚体G蛋白的中介作用。当激动剂与GPCRs结合后，同源的G1和G23亚基的解离或重排被认为触发了对各种酶、离子通道和其他效应器分子的刺激或抑制。经典受体理论认为，特定gpr的任何激动剂都会引起相同的构象变化，激动剂之间的效力和效力的差异仅反映了偶联效率(信号强度)和相对结合亲和力。最近一些GPCRs的证据表明，存在配体特异的构象，它优先激活交通受体来选择信号通路的子集，导致不同激动剂通过相同的GPCR异构体产生不同的信号级联。在人类D2多巴胺受体的情况下，我们发现了K和Ca通道、腺苷环化酶和MAPK的选择性激活模式(效力和内在活性)，当暴露于激动剂奎比罗、DHX和NPA时。激动剂作用的这种“功能选择性”的潜在分子机制尚不清楚。在拟议的研究中，我们将通过四个特定目标来研究神经内分泌AtT20细胞系和原代大鼠神经元中功能性受体-信号复合体的机制：(1)确定D2和D3多巴胺受体与五个效应器偶联的配体依赖的选择性；腺酰环化酶(AC)、Kir3.0通道、CaV2.0通道、p42/44 MAPK(ERK1/2)和2-arrestin易位。(2)评估大鼠中脑神经元天然D2受体信号的功能选择性参数。(3)检测跨膜区(TM2、TM5、TM7)的保守残基和其他GPCRs中已被证明是信号开关的胞内环对D2受体激动剂信号选择性的贡献。(4)验证特异性受体/G1蛋白复合体具有激动剂依赖性功能选择性的假说。这些实验将增加对分子间相互作用在指定多巴胺能配体的效力和效率方面的作用的理解，并反过来将对针对几种神经精神和内分泌疾病的药物的开发产生影响。 与公共健康相关：这项研究探索了一种新的信号现象的分子基础，这种现象被称为“功能选择性”，通过这种现象，不同的药物和神经递质可以通过相同的神经递质受体亚型来引导非常不同的信号结果。我们将集中在一类重要的多巴胺受体，广泛涉及药物滥用行为以及几种精神障碍，如精神分裂症。由于受体是药物治疗的重要靶点，我们的研究结果将指导开发更精细、更特异的药物来治疗这些疾病，副作用更少。

DESCRIPTION (provided by applicant): Transduction of many external stimuli (e.g. light, odorants, neurotransmitters, hormones) by cells in all tissues occurs through activation of members of a large gene superfamily called G-protein coupled receptors (GPCRs) that couple receptor activation to complex cascades of signaling events through a vast and expanding array of intracellular and membrane bound proteins. A common feature of the transduction process for GPCRs is the intermediation of heterotrimeric G-proteins. Upon agonist binding to GPCRs, dissociation or rearrangement of the cognate G1 and G23 subunits is thought to trigger stimulation or inhibition of various enzymes, ion channels, and other effector molecules. Classical receptor theory suggests that any agonist of a specific GPCR will induce the same conformational changes, and that differences in efficacy and potency among agonists reflect only the coupling efficiency (strength of signal) and relative binding affinity. Recent evidence for a number of GPCRs has alternatively suggested the existence of ligand-specific conformations that preferentially traffic receptor activation to select subsets of signaling pathways resulting in distinct signal cascades for different agonists through the same GPCR isoform. In the case of the human D2 dopamine receptor, we have discovered selective activation patterns (potency and intrinsic activity) for K and Ca channels, adenylyl cyclase, and MAP kinase upon exposure to the agonists quinpirole, DHX, and NPA. The underlying molecular mechanisms for this "functional selectivity" of agonist action are unknown. In the proposed research we will examine mechanisms underlying functional receptor-signal complexes in the neuroendocrine AtT20 cell line and primary rat neurons through four specific aims: (1) To define ligand- dependent selectivity of D2 and D3 dopamine receptors coupled to five effectors; adenylyl cyclase (AC), Kir3.0 channels, CaV2.0 channels, p42/44 MAP kinase (Erk1/2), and 2-arrestin translocation. (2) To assess the parameters of functional selectivity for native D2 receptor signaling in rat midbrain neurons. (3) To test the contribution of conserved residues in transmembrane domains (TM2, TM5, TM7) and intracellular loops previously shown to be signal switches in other GPCRs to functional selectivity of agonist signaling through D2 receptors. (4) To test the hypothesis that specific receptor/G1-protein complexes confer agonist-dependent functional selectivity. These experiments will increase understanding of the role of intermolecular interactions in specifying the potency and efficacy of dopaminergic ligands and, in turn, will have impact on the development of drugs targeted toward several neuropsychiatric and endocrine disorders. PUBLIC HEALTH RELEVANCE: This research explores the molecular basis for a novel signaling phenomenon, termed "functional selectivity", by which different drugs and neurotransmitters can direct very different signaling outcomes through the same isoform of neurotransmitter receptor. We will focus on an important class of dopamine receptors widely implicated in substance abuse behaviors as well as several psychiatric disorders such as schizophrenia. As the receptors are important targets for pharmaco-therapies, the outcome of our research will guide the development of more refined and specific drugs for these disorders with fewer side effects.