Ligand Directed Functional Selectivity of G-Protein Coupled Receptor Signalling

描述（由申请人提供）：所有组织中的细胞对许多外部刺激（例如光、气味、神经递质、激素）的转导是通过称为G蛋白偶联受体（GPCR）的大基因超家族成员的激活发生的，所述GPCR通过大量且不断扩大的细胞内和膜结合蛋白将受体激活与信号传导事件的复杂级联反应偶联。GPCR转导过程的共同特征是异源三聚体G蛋白的中介作用。在激动剂与GPCR结合后，同源G1和G23亚基的解离或重排被认为触发各种酶、离子通道和其他效应分子的刺激或抑制。经典受体理论表明，特定GPCR的任何激动剂都将诱导相同的构象变化，并且激动剂之间的功效和效力的差异仅反映偶联效率（信号强度）和相对结合亲和力。最近的一些GPCR的证据也表明存在配体特异性构象，优先交通受体激活选择子集的信号传导途径，导致不同的激动剂通过相同的GPCR亚型的不同的信号级联。在人D2多巴胺受体的情况下，我们已经发现了选择性激活模式（效力和内在活性）的K和Ca通道，腺苷酸环化酶，MAP激酶暴露于激动剂喹吡罗，DHX，和NPA。激动剂作用的这种“功能选择性”的潜在分子机制尚不清楚。在本研究中，我们将通过四个具体的目标来研究神经内分泌AtT 20细胞系和原代大鼠神经元中功能性受体-信号复合物的机制：（1）确定与五种效应物偶联的D2和D3多巴胺受体的配体依赖性选择性;腺苷酸环化酶（AC）、Kir3.0通道、CaV2.0通道、p42/44 MAP激酶（Erk 1/2）和2-抑制蛋白易位。(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)测试跨膜结构域（TM 2、TM 5、TM 7）和细胞内环中的保守残基对通过D2受体的激动剂信号传导的功能选择性的贡献，这些保守残基先前在其他GPCR中显示为信号开关。(4)检验特异性受体/G1蛋白复合物赋予激动剂依赖性功能选择性的假设。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功效中的作用的理解，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。 公共卫生相关性：这项研究探索了一种新的信号传导现象的分子基础，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指导非常不同的信号传导结果。我们将重点关注一类重要的多巴胺受体，它们与药物滥用行为以及几种精神疾病（如精神分裂症）有着广泛的联系。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和更特异的药物，用于这些疾病，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.