Department of Psychiatry, Neurobiology, Pharmacology and Biotechnology, University of Pisa, Via Bonanno 6, 56126 Pisa, Italy.
J Pharmacol Exp Ther. 2011 Aug;338(2):559-67. doi: 10.1124/jpet.110.178715. Epub 2011 Apr 29.
G protein-coupled receptor (GPR) 17 is a P2Y-like receptor that responds to both uracil nucleotides (as UDP-glucose) and cysteinyl-leukotrienes (cysLTs, as LTD(4)). By bioinformatic analysis, two distinct binding sites have been hypothesized to be present on GPR17, but little is known on their putative cross-regulation and on GPR17 desensitization/resensitization upon agonist exposure. In this study, we investigated in GPR17-expressing 1321N1 cells the cross-regulation between purinergic- and cysLT-mediated responses and analyzed GPR17 regulation after prolonged agonist exposure. Because GPR17 receptors couple to G(i) proteins and adenylyl cyclase inhibition, both guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPγS) binding and the cAMP assay have been used to investigate receptor functional activity. UDP-glucose was found to enhance LTD(4) potency in mediating activation of G proteins and vice versa, possibly through an allosteric mechanism. Both UDP-glucose and LTD(4) induced a time- and concentration-dependent GPR17 loss of response (homologous desensitization) with similar kinetics. GPR17 homologous desensitization was accompanied by internalization of receptors inside cells, which occurred in a time-dependent manner with similar kinetics for both agonists. Upon agonist removal, receptor resensitization occurred with the typical kinetics of G protein-coupled receptors. Finally, activation of GPR17 by UDP-glucose (but not vice versa) induced a partial heterologous desensitization of LTD(4)-mediated responses, suggesting that nucleotides have a hierarchy in producing desensitizing signals. These findings suggest a functional cross-talk between purinergic and cysLT ligands at GPR17. Because of the recently suggested key role of GPR17 in brain oligodendrogliogenesis and myelination, this cross-talk may have profound implications in fine-tuning cell responses to demyelinating and inflammatory conditions when these ligands accumulate at lesion sites.
G 蛋白偶联受体（GPR）17 是一种 P2Y 样受体，对尿嘧啶核苷酸（如 UDP-葡萄糖）和半胱氨酰白三烯（cysLTs，如 LTD(4)）均有反应。通过生物信息学分析，假设 GPR17 上存在两个不同的结合位点，但对于它们的假定交叉调节以及激动剂暴露后 GPR17 的脱敏/再敏化知之甚少。在这项研究中，我们在表达 GPR17 的 1321N1 细胞中研究了嘌呤能和 cysLT 介导的反应之间的交叉调节，并分析了长时间暴露于激动剂后 GPR17 的调节。由于 GPR17 受体与 G(i) 蛋白和腺苷酸环化酶偶联，因此使用鸟苷 5'-O-(3-[(35)S]硫代)三磷酸 ([(35)S]GTPγS) 结合和 cAMP 测定来研究受体功能活性。发现 UDP-葡萄糖可增强 LTD(4) 在介导 G 蛋白激活中的效力，反之亦然，可能通过变构机制。UDP-葡萄糖和 LTD(4) 均诱导 GPR17 反应的时间和浓度依赖性丧失（同源脱敏），具有相似的动力学。GPR17 同源脱敏伴随着受体在细胞内内化，这在两种激动剂的时间依赖性方式下以相似的动力学发生。激动剂去除后，受体再敏化发生，具有 G 蛋白偶联受体的典型动力学。最后，UDP-葡萄糖激活 GPR17（而不是相反）诱导 LTD(4) 介导的反应的部分异源脱敏，表明核苷酸在产生脱敏信号方面具有优先级。这些发现表明嘌呤能和 cysLT 配体在 GPR17 之间存在功能交叉对话。由于 GPR17 在大脑少突胶质细胞发生和髓鞘形成中的关键作用，当这些配体在病变部位积累时，这种交叉对话可能对脱髓鞘和炎症条件下细胞反应的精细调节具有深远影响。
