Lee J W, Joshi S, Chan J S, Wong Y H
Department of Biology and Biotechnology Research Institute, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, China.
J Neurochem. 1998 May;70(5):2203-11.
The mu-opioid receptor has recently been shown to stimulate phosphoinositide-specific phospholipase C via the pertussis toxin-sensitive G16 protein. Given the promiscuous nature of G16 and the high degree of resemblance of signaling properties of the three opioid receptors, both delta- and kappa-opioid receptors are likely to activate G16. Interactions of delta- and kappa-opioid receptors with G16 were examined by coexpressing the opioid receptors and G alpha16 in COS-7 cells. The delta-selective agonist [D-Pen2,D-Pen5] enkephalin potently stimulated the formation of inositol phosphates in cells coexpressing the delta-opioid receptor and G alpha16. The delta-opioid receptor-mediated stimulation of phospholipase C was absolutely dependent on the coexpression of G alpha16 and exhibited appropriate ligand selectivity and dose dependency. Similar transfection studies revealed only weak stimulation by the mu-opioid receptor, whereas the kappa-opioid receptor produced moderate phospholipase C activity. G alpha16 thus appeared to interact differentially with the three opioid receptors. Radioligand binding assays indicate that the mu-opioid receptor was expressed at a lower level than those of the delta- and kappa-opioid receptors. To examine if differential coupling to G alpha16 is prevalent, a panel of Gs- or Gi-coupled receptors was coexpressed with G alpha16 in COS-7 cells and assayed for agonist-induced stimulation of phospholipase C. Activation of alpha2- and beta2-adrenergic, dopamine D1 and D2, adenosine A1, somatostatin-1 and -2, C5a, formyl peptide, and luteinizing hormone receptors all resulted in stimulation of phospholipase C, with maximal stimulations ranging from 1.5- to almost 17-fold. These findings suggest that the promiscuous G alpha16 can in fact discriminate among different receptors and that such preferential interaction might in part be due to the abundance of receptors.
最近研究表明，μ-阿片受体可通过百日咳毒素敏感的G16蛋白刺激磷酸肌醇特异性磷脂酶C。鉴于G16性质的混杂性以及三种阿片受体信号特性的高度相似性，δ-和κ-阿片受体都可能激活G16。通过在COS-7细胞中共表达阿片受体和Gα16，研究了δ-和κ-阿片受体与G16的相互作用。δ-选择性激动剂[D-Pen2，D-Pen5]脑啡肽可有效刺激共表达δ-阿片受体和Gα16的细胞中肌醇磷酸的形成。δ-阿片受体介导的磷脂酶C刺激绝对依赖于Gα16的共表达，并表现出适当的配体选择性和剂量依赖性。类似的转染研究表明，μ-阿片受体的刺激作用较弱，而κ-阿片受体产生中等程度的磷脂酶C活性。因此，Gα16似乎与三种阿片受体存在不同的相互作用。放射性配体结合试验表明，μ-阿片受体的表达水平低于δ-和κ-阿片受体。为了研究与Gα16的差异偶联是否普遍存在，将一组与Gs或Gi偶联的受体与Gα16在COS-7细胞中共表达，并检测激动剂诱导的磷脂酶C刺激情况。α2-和β2-肾上腺素能受体、多巴胺D1和D2受体、腺苷A1受体、生长抑素-1和-2受体、C5a受体、甲酰肽受体和促黄体生成素受体的激活均导致磷脂酶C的刺激，最大刺激倍数在1.5至近17倍之间。这些发现表明，混杂的Gα16实际上可以区分不同的受体，这种优先相互作用可能部分归因于受体的丰度。
