title: Agonist-induced desensitization/resensitization of human G protein-coupled receptor 17: a functional cross-talk between purinergic and cysteinyl-leukotriene ligands.
abstract: 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.
authors.affiliation: Department of Psychiatry, Neurobiology, Pharmacology and Biotechnology, University of Pisa, Via Bonanno 6, 56126 Pisa, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Daniele
authors.forename: M L
authors.initials: ML
authors.lastname: Trincavelli
authors.forename: P
authors.initials: P
authors.lastname: Gabelloni
authors.forename: D
authors.initials: D
authors.lastname: Lecca
authors.forename: P
authors.initials: P
authors.lastname: Rosa
authors.forename: M P
authors.initials: MP
authors.lastname: Abbracchio
authors.forename: C
authors.initials: C
authors.lastname: Martini
mesh_terms: D006801:Humans; D017998:Leukotriene D4 / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D011485:Protein Binding / Q000502:physiology; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology*; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000378:metabolism* / Q000502:physiology; D018077:Receptors, Leukotriene / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D014407:Tumor Cells, Cultured; D014532:Uridine Diphosphate Glucose / Q000378:metabolism* / Q000494:pharmacology
chemical_list: C121670:GPR17 protein, human; D008024:Ligands; D043562:Receptors, G-Protein-Coupled; D018077:Receptors, Leukotriene; D017998:Leukotriene D4; D014532:Uridine Diphosphate Glucose