Abstract
GPR55 is activated by l-α-lysophosphatidylinositol (LPI) but also by certain cannabinoids. In this study, we investigated the GPR55 pharmacology of various cannabinoids, including analogues of the CB1 receptor antagonist Rimonabant®, CB2 receptor agonists, and Cannabis sativa constituents. To test ERK1/2 phosphorylation, a primary downstream signaling pathway that conveys LPI-induced activation of GPR55, a high throughput system, was established using the AlphaScreen® SureFire® assay. Here, we show that CB1 receptor antagonists can act both as agonists alone and as inhibitors of LPI signaling under the same assay conditions. This study clarifies the controversy surrounding the GPR55-mediated actions of SR141716A; some reports indicate the compound to be an agonist and some report antagonism. In contrast, we report that the CB2 ligand GW405833 behaves as a partial agonist of GPR55 alone and enhances LPI signaling. GPR55 has been implicated in pain transmission, and thus our results suggest that this receptor may be responsible for some of the antinociceptive actions of certain CB2 receptor ligands. The phytocannabinoids Δ9-tetrahydrocannabivarin, cannabidivarin, and cannabigerovarin are also potent inhibitors of LPI. These Cannabis sativa constituents may represent novel therapeutics targeting GPR55.
Highlights
Studying the Pharmacology of GPR55 Using AlphaScreen Surefire pERK1/2 Assay—The phosphorylation of ERK1/2 protein has been reported as one of the main signaling pathways initiated upon stimulation of the GPR55 receptor; we focused our research on phosphorylated ERK1/2 protein and established a high throughput system using the AlphaScreen SureFire phospho-ERK assay
LPI and Certain Cannabinoids Induce Sustained GPR55-mediated ERK1/2 Phosphorylation—Studies have shown that GPR55 induces maximal ERK1/2 phosphorylation response after 10 –20 min; here we show that both basal and LPI-induced stimulation levels are reduced at 60 min (Fig. 1 compared with 20 min) the percent stimulation is sustained, but the potency of LPI is significantly decreased after 60 min
We have established a rapid and sensitive method to study the pharmacology of the GPCR GPR55 using the AlphaScreen SureFire ERK assay
Summary
Results: Structural analogues of SR141716A act both as agonists alone and as inhibitors of L-␣-lysophosphatidylinositol. Certain CB2 receptor agonists modulate GPR55 activity. Conclusion: Certain cannabinoids can both activate GPR55 and attenuate L-␣-lysophosphatidylinositol-mediated phosphorylated ERK1/2 activation. This has mechanistic implications for the antinociceptive effects of certain CB2 agonists. Significance: Cannabinoid ligands have complex interactions with the L-␣-lysophosphatidylinositol/GPR55 signaling system
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
