GPR55

Last updated
GPR55
Identifiers
Aliases GPR55 , LPIR1, G protein-coupled receptor 55
External IDs OMIM: 604107 MGI: 2685064 HomoloGene: 36184 GeneCards: GPR55
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_005683

NM_001033290

RefSeq (protein)

NP_005674

NP_001028462

Location (UCSC) Chr 2: 230.91 – 230.96 Mb Chr 1: 85.94 – 85.96 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

G protein-coupled receptor 55 also known as GPR55 is a G protein-coupled receptor that in humans is encoded by the GPR55 gene. [5]

Contents

GPR55, along with GPR119 and GPR18, have been implicated as novel cannabinoid receptors. [6] [7]

History

GPR55 was identified and cloned for the first time in 1999. [8] Later it was identified by an in silico screen as a putative cannabinoid receptor because of a similar amino acid sequence in the binding region. [9] Research groups from Glaxo Smith Kline and Astra Zeneca characterized the receptor extensively because it was hoped to be responsible for the blood pressure lowering properties of cannabinoids. GPR55 is indeed activated by endogenous and exogenous cannabinoids such as plant and synthetic cannabinoids but GPR-55 knockout mice generated by a research group from Glaxo Smith Kline showed no altered blood pressure regulation after administration of the cannabidiol-derivative abnormal cannabidiol. [10]

Signal cascade

GPR55 is coupled to the G-protein G13 and activation of the receptor leads to stimulation of rhoA, cdc42 and rac1. [11]

Pharmacology

GPR55 is activated by the plant cannabinoids Δ9-THC [12] and the endocannabinoids anandamide, 2-AG and noladin ether in the low nanomolar range. Exocannabinoids such as the synthetic cannabinoid CP-55940 are also able to activate the receptor [12] while the structurally unrelated cannabinoid mimic WIN 55,212-2 fails to activate the receptor. [10] Recent research suggests that lysophosphatidylinositol and its 2-arachidonoyl derivative, 2-arachidonoyl lysophosphatidylinositol (2-ALPI), may be the endogenous ligands for GPR55 [13] [14] [15] and the receptor appears likely to be a possible target for treatment of inflammation and pain as with the other cannabinoid receptors. [16] [17]

This profile as a distinct non-CB1/CB2 receptor which responds to a variety of both endogenous and exogenous cannabinoid ligands has led some groups to suggest GPR55 should be categorised as the CB3 receptor, and this re-classification may follow in time. [18] [19] [20] [21] However this is complicated by the fact that another possible CB3 receptor has been discovered in the hippocampus, although its gene has not yet been cloned, [22] suggesting that there may be at least four cannabinoid receptors which will eventually be characterised. Evidence accumulated during the last few years suggests that GPR55 plays a relevant role in cancer and opens the possibility of considering this orphan receptor as a new therapeutic target and potential biomarker in oncology. [23]

Ligands

Agonists

Ligands found to bind to GPR55 as agonists include:

Antagonists

Physiological function

The physiological role of GPR55 is unclear. Mice with a target deletion of the GPR55 gene show no specific phenotype. [10] GPR55 is widely expressed in the brain, especially in the cerebellum. It is expressed in the jejunum and ileum but apparently not more generally in the periphery. [12] Osteoblasts and osteoclasts express GPR55 and this has been shown to regulate bone cell function. [27]

Related Research Articles

Cannabinoid Compounds found in cannabis

Cannabinoids are compounds found in the cannabis plant or synthetic compounds that can interact with the endocannabinoid system. The most notable cannabinoid is the phytocannabinoid tetrahydrocannabinol (THC) (Delta-9-THC), the primary intoxicating compound in cannabis. Cannabidiol (CBD) is another major constituent of the some cannabis plants. At least 113 distinct cannabinoids have been isolated from cannabis. It was reported in 2020 that cannabinoids can be found in other plants such as rhododendron, licorice and liverwort, and earlier in Echinacea.

Cannabinoid receptor Group of receptors to cannabinoid compounds

Cannabinoid receptors, located throughout the body, are part of the endocannabinoid system, which is involved in a variety of physiological processes including appetite, pain-sensation, mood, and memory.

The endocannabinoid system (ECS) is a biological system composed of endocannabinoids, which are endogenous lipid-based retrograde neurotransmitters that bind to cannabinoid receptors (CBRs), and cannabinoid receptor proteins that are expressed throughout the vertebrate central nervous system and peripheral nervous system. The endocannabinoid system remains under preliminary research, but may be involved in regulating physiological and cognitive processes, including fertility, pregnancy, pre- and postnatal development, various activity of immune system, appetite, pain-sensation, mood, and memory, and in mediating the pharmacological effects of cannabis. The ECS plays an important role in multiple aspects of neural functions, including the control of movement and motor coordination, learning and memory, emotion and motivation, addictive-like behavior and pain modulation, among others.

2-Arachidonoylglycerol Chemical compound

2-Arachidonoylglycerol (2-AG) is an endocannabinoid, an endogenous agonist of the CB1 receptor and the primary endogenous ligand for the CB2 receptor. It is an ester formed from the omega-6 fatty acid arachidonic acid and glycerol. It is present at relatively high levels in the central nervous system, with cannabinoid neuromodulatory effects. It has been found in maternal bovine and human milk. The chemical was first described in 1994-1995, although it had been discovered some time before that. The activities of phospholipase C (PLC) and diacylglycerol lipase (DAGL) mediate its formation. 2-AG is synthesized from arachidonic acid-containing diacylglycerol (DAG).

TRPV1 Receptor responsible for regulation of body temperature

The transient receptor potential cation channel subfamily V member 1 (TrpV1), also known as the capsaicin receptor and the vanilloid receptor 1, is a protein that, in humans, is encoded by the TRPV1 gene. It was the first isolated member of the transient receptor potential vanilloid receptor proteins that in turn are a sub-family of the transient receptor potential protein group. This protein is a member of the TRPV group of transient receptor potential family of ion channels.

NAGly receptor Protein-coding gene in the species Homo sapiens

N-Arachidonyl glycine receptor, also known as G protein-coupled receptor 18 (GPR18), is a protein that in humans is encoded by the GPR18 gene. Along with the other previously "orphan" receptors GPR55 and GPR119, GPR18 has been found to be a receptor for endogenous lipid neurotransmitters, several of which also bind to cannabinoid receptors. It has been found to be involved in the regulation of intraocular pressure.

GPR52 Protein-coding gene in the species Homo sapiens

Probable G-protein coupled receptor 52 is a protein that in humans is encoded by the GPR52 gene.

Cannabinoid receptor type 1 Mammalian protein found in Homo sapiens

Cannabinoid receptor type 1 (CB1), also known as cannabinoid receptor 1, is a G protein-coupled cannabinoid receptor that in humans is encoded by the CNR1 gene. The human CB1 receptor is expressed in the peripheral nervous system and central nervous system. It is activated by: endocannabinoids, a group of retrograde neurotransmitters that include anandamide and 2-arachidonoylglycerol (2-AG); plant phytocannabinoids, such as the compound THC which is an active ingredient of the psychoactive drug cannabis; and, synthetic analogs of THC. CB1 is antagonized by the phytocannabinoid tetrahydrocannabivarin (THCV).

Cannabinoid receptor type 2 Mammalian protein found in Homo sapiens

The cannabinoid receptor type 2, abbreviated as CB2, is a G protein-coupled receptor from the cannabinoid receptor family that in humans is encoded by the CNR2 gene. It is closely related to the cannabinoid receptor type 1 (CB1), which is largely responsible for the efficacy of endocannabinoid-mediated presynaptic-inhibition, the psychoactive properties of tetrahydrocannabinol (THC), the active agent in cannabis, and other phytocannabinoids (plant cannabinoids). The principal endogenous ligand for the CB2 receptor is 2-Arachidonoylglycerol (2-AG).

GPR119 Protein-coding gene in the species Homo sapiens

G protein-coupled receptor 119 also known as GPR119 is a G protein-coupled receptor that in humans is encoded by the GPR119 gene.

GPR3

G-protein coupled receptor 3 is a protein that in humans is encoded by the GPR3 gene. The protein encoded by this gene is a member of the G protein-coupled receptor family of transmembrane receptors and is involved in signal transduction.

<i>N</i>-Arachidonoyl dopamine Chemical compound

N-Arachidonoyl dopamine (NADA) is an endocannabinoid that acts as an agonist of the CB1 receptor and the transient receptor potential V1 (TRPV1) ion channel. NADA was first described as a putative endocannabinoid (agonist for the CB1 receptor) in 2000 and was subsequently identified as an endovanilloid (agonist for TRPV1) in 2002. NADA is an endogenous arachidonic acid based lipid found in the brain of rats, with especially high concentrations in the hippocampus, cerebellum, and striatum. It activates the TRPV1 channel with an EC50 of approximately of 50 nM which makes it the putative endogenous TRPV1 agonist.

A cannabinoid receptor antagonist, also known simply as a cannabinoid antagonist or as an anticannabinoid, is a type of cannabinoidergic drug that binds to cannabinoid receptors (CBR) and prevents their activation by endocannabinoids. They include antagonists, inverse agonists, and antibodies of CBRs. The discovery of the endocannabinoid system led to the development of CB1 receptor antagonists. The first CBR inverse agonist, rimonabant, was described in 1994. Rimonabant blocks the CB1 receptor selectively and has been shown to decrease food intake and regulate body-weight gain. The prevalence of obesity worldwide is increasing dramatically and has a great impact on public health. The lack of efficient and well-tolerated drugs to cure obesity has led to an increased interest in research and development of CBR antagonists. Cannabidiol (CBD), a naturally occurring cannabinoid, is a non-competitive CB1/CB2 receptor antagonist. And Δ9-tetrahydrocannabivarin (THCV), a naturally occurring cannabinoid, modulate the effects of THC via direct blockade of cannabinoid CB1 receptors, thus behaving like first-generation CB1 receptor inverse agonists, such as rimonabant. CBD is a very low-affinity CB1 ligand, that can nevertheless affect CB1 receptor activity in vivo in an indirect manner, while THCV is a high-affinity CB1 receptor ligand and potent antagonist in vitro and yet only occasionally produces effects in vivo resulting from CB1 receptor antagonism. THCV has also high affinity for CB2 receptors and signals as a partial agonist, differing from both CBD and rimonabant.

AM-1241 Chemical compound

AM-1241 (1-(methylpiperidin-2-ylmethyl)-3-(2-iodo-5-nitrobenzoyl)indole) is a chemical from the aminoalkylindole family that acts as a potent and selective agonist for the cannabinoid receptor CB2, with a Ki of 3.4 nM at CB2 and 80 times selectivity over the related CB1 receptor. It has analgesic effects in animal studies, particularly against "atypical" pain such as hyperalgesia and allodynia. This is thought to be mediated through CB2-mediated peripheral release of endogenous opioid peptides, as well as direct activation of the TRPA1 channel. It has also shown efficacy in the treatment of amyotrophic lateral sclerosis in animal models.

Abnormal cannabidiol Synthetic, cannabinoid-like compound

Abnormal cannabidiol (Abn-CBD) is a synthetic regioisomer of cannabidiol, which unlike most other cannabinoids produces vasodilator effects, lowers blood pressure, and induces cell migration, cell proliferation and mitogen-activated protein kinase activation in microglia, but without producing any psychoactive effects.

<i>N</i>-Arachidonylglycine Chemical compound

N-Arachidonylglycine (NAGly) is a carboxylic metabolite of the endocannabinoid anandamide (AEA). Since it was first synthesized in 1996, NAGly has been a primary focus of the relatively contemporary field of lipidomics due to its wide range of signaling targets in the brain, the immune system and throughout various other bodily systems. In combination with 2‐arachidonoyl glycerol (2‐AG), NAGly has enabled the identification of a family of lipids often referred to as endocannabinoids. Recently, NAGly has been found to bind to G-protein coupled receptor 18 (GPR18), the putative abnormal cannabidiol receptor. NaGly is an endogenous inhibitor of fatty acid amide hydrolase (FAAH) and thereby increases the ethanolamide endocannabinoids AEA, oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) levels. NaGly is found throughout the body and research on its explicit functions is ongoing.

O-1602 Chemical compound

O-1602 is a synthetic compound most closely related to abnormal cannabidiol, and more distantly related in structure to cannabinoid drugs such as THC. O-1602 does not bind to the classical cannabinoid receptors CB1 or CB2 with any significant affinity, but instead is an agonist at several other receptors which appear to be related to the cannabinoid receptors, particularly GPR18 and GPR55. These previously orphan receptors have been found to be targets for a number of endogenous and synthetic cannabinoid compounds, and are thought to be responsible for most of the non-CB1, non-CB2 mediated effects that have become evident in the course of cannabinoid research. O-1602 produces some effects shared with classical cannabinoid compounds such as analgesic and antiinflammatory effects and appetite stimulation, but it does not produce sedation or psychoactive effects, and has several actions in the gut and brain that are not shared with typical cannabinoid agonists.

O-1918 Chemical compound

O-1918 is a synthetic compound related to cannabidiol, which is an antagonist at two former orphan receptors GPR18 and GPR55, that appear to be related to the cannabinoid receptors. O-1918 is used in the study of these receptors, which have been found to be targets for a number of endogenous and synthetic cannabinoid compounds, and are thought to be responsible for most of the non-CB1, non-CB2 mediated effects that have become evident in the course of cannabinoid research.

Lysophosphatidylinositol, or L-α-lysophosphatidylinositol, is an endogenous lysophospholipid and endocannabinoid neurotransmitter. LPI, along with its 2-arachidonoyl- derivative, 2-arachidonoyl lysophosphatidylinositol (2-ALPI), have been proposed as the endogenous ligands of GPR55.

CID16020046 Chemical compound

CID16020046 is a compound which acts as an inverse agonist at the former orphan receptor GPR55, and may be the first selective inverse agonist characterised for this receptor. It was found to block a number of GPR55 mediated responses such as wound healing and activation of immune system T-cells and B-cells, as well as showing inverse agonist activity in the absence of GPR55 agonist stimulation. However while it was found to have good selectivity over the related CB1 and CB2 cannabinoid receptors as well as a number of other targets, CID16020046 has not yet been tested against another related receptor GPR18, so its selectivity for GPR55 over this target has not been established. It has antiinflammatory actions, has been used to study the interaction between GPR55 mediated and CB1 mediated activity, and research using this compound has revealed a role for GPR55 in learning and memory.

References

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Further reading