GPR17 is a P2Y-like receptor that responds to both uracil nucleotides (as UDP-glucose) and cysteinyl-leukotrienes (cysLTs, as LTD4). 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 Gi-proteins and adenylyl cyclase inhibition , both [35S]GTPγS binding and the cAMP assay have been used to investigate receptor functional activity. UDP-glucose was found to enhance LTD4 potency in mediating activation of G proteins, and vice-versa, likely through an allosteric mechanism. Both UDP-glucose and LTD4 induced a time- and concentration-dependent GPR17 loss of response (homologous desensitisation) with similar kinetics. GPR17 homologous desensitisation was accompanied by the internalisation of receptors inside the cells, which occurred in a time-dependent manner with similar kinetics for both agonists. Upon agonist removal, receptor resensitisation 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 desensitisation of LTD4-mediated responses, suggesting that nucleotides have a hierarchy in producing desensitising signals. These findings suggested a functional cross-talk between purinergic and cys-LT 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.
- leukotriene ligands
- purinergic ligands
- receptor heterologous desensitization
- receptor homologous desensitization
- receptor resensitization
- Received December 30, 2010.
- Revision received April 28, 2011.
- Accepted April 28, 2011.
- The American Society for Pharmacology and Experimental Therapeutics