GPR55 is a cannabinoid receptor that increases intracellular calcium and inhibits M current

Abstract

The CB1 cannabinoid receptor mediates many of the psychoactive effects of ⌬ 9 THC, the principal active component of cannabis. However, ample evidence suggests that additional non-CB 1/CB2 receptors may contribute to the behavioral, vascular, and immunological actions of ⌬ 9 THC and endogenous cannabinoids. Here, we provide further evidence that GPR55, a G protein-coupled receptor, is a cannabinoid receptor. GPR55 is highly expressed in large dorsal root ganglion neurons and, upon activation by various cannabinoids (⌬ 9 THC, the anandamide analog methanandamide, and JWH015) increases intracellular calcium in these neurons. Examination of its signaling pathway in HEK293 cells transiently expressing GPR55 found the calcium increase to involve G q, G12, RhoA, actin, phospholipase C, and calcium release from IP 3R-gated stores. GPR55 activation also inhibits M current. These results establish GPR55 as a cannabinoid receptor with signaling distinct from CB 1 and CB2.orphan ͉ pain ͉ CB3 ͉ G protein-coupled receptor C annabis has been used and abused for its therapeutic and psychoactive properties for millennia. The effects of cannabinoid compounds are largely mediated by cannabinoid receptors. CB 1 , cloned in 1990 (1), is widely and highly expressed in the CNS, where it likely mediates the majority of the psychotropic and behavioral effects of cannabinoids. CB 2 is primarily expressed in peripheral tissues (2). Both CB 1 and CB 2 are 7-transmembrane G protein-coupled receptors that engage predominantly the G i/o family of G proteins. However, ample evidence suggests that additional receptors may contribute to the behavioral, vascular, and immunological actions of ⌬ 9 tetrahydrocannabinol (THC) and endogenous cannabinoids (3).It has been suggested that GPR55 is a novel cannabinoid receptor (reviewed in ref. 4). GPR55 is only 13.5% identical to CB 1 and 14.4% identical to CB 2 , and its mRNA is present in the brain and periphery (5-7). A recent study found that a variety of cannabinoid compounds stimulated GTP␥S binding in cells stably expressing GPR55 (6). Here, we report GPR55 activation by THC, JWH015, and anandamide increases intracellular calcium by activating signaling pathways quite distinct from those used by CB 1 and CB 2 . Results Activation of GPR55 by Cannabinoids Increases Intracellular Calcium.We first examined the signaling pathways activated by GPR55 in HEK293 cells transiently expressing human GPR55 (hGPR55). Perfusion with 5 M THC evoked a calcium increase (⌬[Ca 2ϩ ] i ) averaging Ϸ100 nM (n ϭ 7, Fig. 1 A and B). Perfusion with 3 M THC evoked a more modest increase (n ϭ 5, 50 nM; Fig. 1B). The agonist-induced calcium response was present in all cells tested, but because it varied in magnitude and time course, concurrent controls were always conducted. GPR55 was essential for the THC-evoked calcium rise because there was minimal calcium rise in nontransfected HEK293 cells exposed to 5 M THC (n ϭ 6, Fig. 1 A and B). A similar calcium increase was seen in CHO cells stably expressing hGPR55 (data not show...

The orphan G protein-coupled receptor GPR55 promotes cancer cell proliferation via ERK

“…This original observation, made in cells ectopically expressing GPR55, was shortly corroborated by other reports (Lauckner et al, 2008;Henstridge et al, 2009;Kapur et al, 2009;Oka et al, 2009Oka et al, , 2010Yin et al, 2009). Moreover, LPI has been found to activate GPR55 in cells in which the receptor is endogenously expressed (large dorsal root ganglion neurons (Lauckner et al, 2008), osteoclasts (Whyte et al, 2009) and lymphoblastoid cells (Oka et al, 2010)), supporting the notion that this phospholipid may be an endogenous GPR55 ligand. Nonetheless, all the functions described so far for LPI on GPR55 come from experiments in which LPI was exogenously added to the cultured cells, and therefore evidence for the role of the naturally occurring lipid in more physiological settings is still missing.…”

“…Nonetheless, all the functions described so far for LPI on GPR55 come from experiments in which LPI was exogenously added to the cultured cells, and therefore evidence for the role of the naturally occurring lipid in more physiological settings is still missing. It has also been shown that several cannabinoid-type compounds modulate this receptor (Ryberg et al, 2007;Lauckner et al, 2008;WaldeckWeiermair et al, 2008;Henstridge et al, 2009Henstridge et al, , 2010Kapur et al, 2009;Yin et al, 2009). However, the inconsistencies among the pharmacological results obtained so far (some compounds being active in some reports and inactive in others, some being agonists in some studies and antagonists in others, and so on) do not entirely clarify whether GPR55 is an actual cannabinoid receptor (Brown and Robin Hiley, 2009;Ross, 2009).…”

“…However, the inconsistencies among the pharmacological results obtained so far (some compounds being active in some reports and inactive in others, some being agonists in some studies and antagonists in others, and so on) do not entirely clarify whether GPR55 is an actual cannabinoid receptor (Brown and Robin Hiley, 2009;Ross, 2009). GPR55 mRNA is highly expressed in the brain, the adrenal glands, parts of the gastrointestinal tract, spleen, tonsils, testes, thymus (Sawzdargo et al, 1999;Ryberg et al, 2007;Oka et al, 2010), large dorsal root ganglion neurons (Lauckner et al, 2008), osteoclasts (Whyte et al, 2009), certain microglial cells (Pietr et al, 2009), endothelial cells and mesenteric arterial smooth muscle cells (Daly et al, 2010), but very little is known about the physiological role of the receptor in these or other tissues. To date, GPR55 has been implicated in the control of pain, specifically in the mechanical hyperalgesia induced by inflammatory and neuropathic pain (Staton et al, 2008), and in the control of bone formation (Whyte et al, 2009).…”

“…Its wide distribution throughout the body suggests, however, that GPR55 might be involved in many other biological functions. As some GPCRs have a prominent role in cancer cell biology (Dorsam and Gutkind, 2007) and, more specifically, GPR55 has been shown to couple to G 12/13 and G q proteins (Ryberg et al, 2007;Lauckner et al, 2008;Henstridge et al, 2009), which drive oncogenic signaling (Dorsam and Gutkind, 2007;Worzfeld et al, 2008), we sought to analyze the physiopathological relevance of this receptor in the context of cancer.…”

Cannabidiol exerts antiepileptic effects by restoring hippocampal interneuron functions in a temporal lobe epilepsy model

“…GPR55 activation also leads to inhibition of http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=564) channels, thereby increasing neuronal excitability (Lauckner et al, 2008). Perhaps by activating http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=561), CBD reduces spontaneous and unitary EPSPs in a voltage‐dependent manner, which would help dampen seizure‐related hyperexcitability in the hippocampus and thus limit the damage associated with excitotoxicity.…”