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N-Arachidonyl glycine does not activate G protein-coupled receptor 18 signaling via canonical pathways.
Mol Pharmacol. 2013 Jan; 83(1):267-82.MP

Abstract

Recent studies propose that N-arachidonyl glycine (NAGly), a carboxylic analogue of anandamide, is an endogenous ligand of the Gα(i/o) protein-coupled receptor 18 (GPR18). However, a high-throughput β-arrestin-based screen failed to detect activation of GPR18 by NAGly (Yin et al., 2009; JBC, 18:12328). To address this inconsistency, this study investigated GPR18 coupling in a native neuronal system with endogenous signaling pathways and effectors. GPR18 was heterologously expressed in rat sympathetic neurons, and the modulation of N-type (Ca(v)2.2) calcium channels was examined. Proper expression and trafficking of receptor were confirmed by the "rim-like" fluorescence of fluorescently tagged receptor and the positive staining of external hemagglutinin-tagged GPR18-expressing cells. Application of NAGly on GPR18-expressing neurons did not inhibit calcium currents but instead potentiated currents in a voltage-dependent manner, similar to what has previously been reported (Guo et al., 2008; J Neurophysiol, 100:1147). Other proposed agonists of GPR18, including anandamide and abnormal cannabidiol, also failed to induce inhibition of calcium currents. Mutants of GPR18, designed to constitutively activate receptors, did not tonically inhibit calcium currents, indicating a lack of GPR18 activation or coupling to endogenous G proteins. Other downstream effectors of Gα(i/o)-coupled receptors, G protein-coupled inwardly rectifying potassium channels and adenylate cyclase, were not modulated by GPR18 signaling. Furthermore, GPR18 did not couple to other G proteins tested: Gα(s), Gα(z), and Gα(15). These results suggest NAGly is not an agonist for GPR18 or that GPR18 signaling involves noncanonical pathways not examined in these studies.

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Authors+Show Affiliations

Lu VB
Laboratory of Molecular Physiology, National Institutes of Health/National Institute on Alcohol Abuse and Alcoholism, 5625 Fishers Lane, Room TS-11, MSC 9411, Bethesda, MD 20892, USA. sikeda@mail.nih.gov
Puhl HL
No affiliation info available
Ikeda SR
No affiliation info available

MeSH

AnimalsArachidonic AcidsCalcium Channels, N-TypeCell MembraneCyclic AMPG Protein-Coupled Inwardly-Rectifying Potassium ChannelsGTP-Binding Protein alpha SubunitsGlycineHEK293 CellsHeLa CellsHumansIn Vitro TechniquesMaleMutationNeuronsPatch-Clamp TechniquesRatsRats, WistarReceptors, G-Protein-CoupledSignal TransductionSuperior Cervical Ganglion

Pub Type(s)

Journal Article
Research Support, N.I.H., Intramural

Language

eng

PubMed ID

23104136

Citation

Lu, Van B., et al. "N-Arachidonyl Glycine Does Not Activate G Protein-coupled Receptor 18 Signaling Via Canonical Pathways." Molecular Pharmacology, vol. 83, no. 1, 2013, pp. 267-82.
Lu VB, Puhl HL, Ikeda SR. N-Arachidonyl glycine does not activate G protein-coupled receptor 18 signaling via canonical pathways. Mol Pharmacol. 2013;83(1):267-82.
Lu, V. B., Puhl, H. L., & Ikeda, S. R. (2013). N-Arachidonyl glycine does not activate G protein-coupled receptor 18 signaling via canonical pathways. Molecular Pharmacology, 83(1), 267-82. https://doi.org/10.1124/mol.112.081182
Lu VB, Puhl HL, Ikeda SR. N-Arachidonyl Glycine Does Not Activate G Protein-coupled Receptor 18 Signaling Via Canonical Pathways. Mol Pharmacol. 2013;83(1):267-82. PubMed PMID: 23104136.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - N-Arachidonyl glycine does not activate G protein-coupled receptor 18 signaling via canonical pathways. AU - Lu,Van B, AU - Puhl,Henry L,3rd AU - Ikeda,Stephen R, Y1 - 2012/10/25/ PY - 2012/10/30/entrez PY - 2012/10/30/pubmed PY - 2013/4/10/medline SP - 267 EP - 82 JF - Molecular pharmacology JO - Mol Pharmacol VL - 83 IS - 1 N2 - Recent studies propose that N-arachidonyl glycine (NAGly), a carboxylic analogue of anandamide, is an endogenous ligand of the Gα(i/o) protein-coupled receptor 18 (GPR18). However, a high-throughput β-arrestin-based screen failed to detect activation of GPR18 by NAGly (Yin et al., 2009; JBC, 18:12328). To address this inconsistency, this study investigated GPR18 coupling in a native neuronal system with endogenous signaling pathways and effectors. GPR18 was heterologously expressed in rat sympathetic neurons, and the modulation of N-type (Ca(v)2.2) calcium channels was examined. Proper expression and trafficking of receptor were confirmed by the "rim-like" fluorescence of fluorescently tagged receptor and the positive staining of external hemagglutinin-tagged GPR18-expressing cells. Application of NAGly on GPR18-expressing neurons did not inhibit calcium currents but instead potentiated currents in a voltage-dependent manner, similar to what has previously been reported (Guo et al., 2008; J Neurophysiol, 100:1147). Other proposed agonists of GPR18, including anandamide and abnormal cannabidiol, also failed to induce inhibition of calcium currents. Mutants of GPR18, designed to constitutively activate receptors, did not tonically inhibit calcium currents, indicating a lack of GPR18 activation or coupling to endogenous G proteins. Other downstream effectors of Gα(i/o)-coupled receptors, G protein-coupled inwardly rectifying potassium channels and adenylate cyclase, were not modulated by GPR18 signaling. Furthermore, GPR18 did not couple to other G proteins tested: Gα(s), Gα(z), and Gα(15). These results suggest NAGly is not an agonist for GPR18 or that GPR18 signaling involves noncanonical pathways not examined in these studies. SN - 1521-0111 UR - https://www.unboundmedicine.com/medline/citation/23104136/N_Arachidonyl_glycine_does_not_activate_G_protein_coupled_receptor_18_signaling_via_canonical_pathways_ L2 - http://molpharm.aspetjournals.org/cgi/pmidlookup?view=long&pmid=23104136 DB - PRIME DP - Unbound Medicine ER -