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 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 guanosine 5′-O-(3-[35S]thio)triphosphate ([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, possibly through an allosteric mechanism. Both UDP-glucose and LTD4 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 LTD4-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.
Footnotes
This work was supported by the Italian Ministry of Education (Project of National Research Interest) PRIN-COFIN Project [2008XFMEA3] (to M.L.T. and M.P.A.).
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.178715.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
-
ABBREVIATIONS:
- GPR
- G protein-coupled receptor
- cysLT
- cysteinyl-leukotriene
- CysLT
- cysteinyl-leukotriene receptor
- DTT
- dithiothreitol
- FK
- forskolin
- hGPR17
- human GPR17
- OPC
- oligodendrocyte precursor cell
- P2YR
- P2Y receptor
- PBS
- phosphate-buffered saline
- PCR
- polymerase chain reaction
- RT
- reverse transcription
- bp
- base pair.
- Received December 30, 2010.
- Accepted April 28, 2011.
- Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|