GPR55 ligands promote receptor coupling to multiple signalling pathways.
OBJECTIVE
Although GPR55 is potently activated by the endogenous lysophospholipid, L-alpha-lysophosphatidylinositol (LPI), it is also thought to be sensitive to a number of cannabinoid ligands, including the prototypic CB1 receptor antagonists AM251 and SR141716A (Rimonabant). In this study we have used a range of functional assays to compare the pharmacological activity of selected cannabinoid ligands, AM251, AM281 and SR141716A with LPI in a HEK293 cell line engineered to stably express recombinant, human GPR55.


METHODS
We evaluated Ca(2+) signalling, stimulation of extracellular signal regulated kinase (ERK1/2) mitogen activated kinase MAP-kinases, induction of transcriptional regulators that are downstream of GPR55, including nuclear factor of activated T cells (NFAT), nuclear factor-kappaB (NF-kappaB) and cAMP response element binding protein (CREB), as well as receptor endocytosis. In addition, we assessed the suitability of a novel, label-free assay for GPR55 ligands that involves optical measurement of dynamic mass redistribution following receptor activation.


RESULTS
GPR55 linked to a range of downstream signalling events and that the activity of GPR55 ligands was influenced by the functional assay employed, with differences in potency and efficacy observed.


CONCLUSIONS
Our data help to resolve some of the issues surrounding the pharmacology of cannabinoid ligands at GPR55 and highlight some differences in effector coupling associated with distinct GPR55 ligands.
Division of Medical Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK.
Christopher M
CM
Henstridge
Nariman Ab
NA
Balenga
Ralf
R
Schröder
Julia K
JK
Kargl
Wolfgang
W
Platzer
Lene
L
Martini
Simon
S
Arthur
June
J
Penman
Jennifer L
JL
Whistler
Evi
E
Kostenis
Maria
M
Waldhoer
Andrew J
AJ
Irving
D001681:Biological Assay / Q000379:methods; D002186:Cannabinoids / Q000494:pharmacology*; D002461:Cell Line, Transformed; D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D008024:Ligands; D008246:Lysophospholipids / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043882:Receptors, Cannabinoid; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects* / Q000378:metabolism; D000077285:Rimonabant; D015398:Signal Transduction / Q000187:drug effects*
D002186:Cannabinoids; C524885:GPR55 protein, human; D008024:Ligands; D008246:Lysophospholipids; D009025:Morpholines; D010880:Piperidines; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D043562:Receptors, G-Protein-Coupled; C025449:lysophosphatidylinositol; C103505:AM 251; D000077285:Rimonabant; C109925:AM 281