Tag Archives: G-Protein coupled receptors

Endocannabinoids in the gut.

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“The endocannabinoid system mainly consists of endogenously produced cannabinoids (endocannabinoids) and two G protein-coupled receptors (GPCRs), cannabinoid receptors 1 and 2 (CB1 and CB2). This system also includes enzymes responsible for the synthesis and degradation of endocannabinoids and molecules required for the uptake and transport of endocannabinoids. In addition, endocannabinoid-related lipid mediators and other putative endocannabinoid receptors, such as transient receptor potential channels and other GPCRs have been identified. Accumulating evidence indicates that the endocannabinoid system is a key modulator of gastrointestinal physiology, influencing satiety, emesis, immune function, mucosal integrity, motility, secretion, and visceral sensation. In light of therapeutic benefits of herbal and synthetic cannabinoids, the vast potential of the endocannabinoid system for the treatment of gastrointestinal diseases has been demonstrated. This review focuses on the role of the endocannabinoid system in gut homeostasis and in the pathogenesis of intestinal disorders associated with intestinal motility, inflammation and cancer. Finally, links between gut microorganisms and the endocannabinoid system are briefly discussed.”

http://www.ncbi.nlm.nih.gov/pubmed/27538961

Endocannabinoid dysregulation in cognitive and stress-related brain regions in the Nrg1 mouse model of schizophrenia.

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“The endocannabinoid system is dysregulated in schizophrenia.

These results demonstrate for the first time in vivo interplay between Nrg1 and endocannabinoids in the brain.

Our results demonstrate that aberrant Nrg1 and endocannabinoid signalling may cooperate in the hippocampus to impair cognition in schizophrenia, and that Nrg1 deficiency alters endocannabinoid signalling in brain stress circuitry.”

http://www.ncbi.nlm.nih.gov/pubmed/27521758

CB1 cannabinoid receptor activity is modulated by the cannabinoid receptor interacting protein CRIP 1a.

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“The CB1 cannabinoid receptor is a G-protein coupled receptor that has important physiological roles in synaptic plasticity, analgesia, appetite, and neuroprotection.

We report the discovery of two structurally related CB1 cannabinoid receptor interacting proteins (CRIP1a and CRIP1b) that bind to the distal C-terminal tail of CB1. CRIP1a and CRIP1b are generated by alternative splicing of a gene located on chromosome 2 in humans, and orthologs of CRIP1a occur throughout the vertebrates, whereas CRIP1b seems to be unique to primates.

CRIP1a coimmunoprecipitates with CB1receptors derived from rat brain homogenates, indicating that CRIP1a and CB1 interact in vivo. Furthermore, in superior cervical ganglion neurons coinjected with CB1 and CRIP1a or CRIP1b cDNA, CRIP1a, but not CRIP1b, suppresses CB1-mediated tonic inhibition of voltage-gated Ca2+ channels.

Discovery of CRIP1a provides the basis for a new avenue of research on mechanisms of CB1 regulation in the nervous system and may lead to development of novel drugs to treat disorders where modulation of CB1 activity has therapeutic potential (e.g., chronic pain, obesity, and epilepsy).”

http://www.ncbi.nlm.nih.gov/pubmed/17895407

Cannabinoid receptor interacting protein (CRIP1a) attenuates CB1R signaling in neuronal cells.

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“CB1 cannabinoid receptors (CB1R) are one of the most abundantly expressed G protein coupled receptors (GPCR) in the CNS and regulate diverse neuronal functions.

The identification of GPCR interacting proteins has provided additional insight into the fine-tuning and regulation of numerous GPCRs.

The cannabinoid receptor interacting protein 1a (CRIP1a) binds to the distal carboxy terminus of CB1R, and has been shown to alter CB1R-mediated neuronal function.

The mechanisms by which CRIP1a regulates CB1R activity have not yet been identified; therefore the focus of this investigation is to examine the cellular effects of CRIP1a on CB1R signaling using neuronal N18TG2 cells stably transfected with CRIP1a over-expressing and CRIP1a knockdown constructs.

These studies suggest a mechanism by which endogenous levels of CRIP1a modulate CB1R-mediated signal transduction by facilitating a Gi/o protein subtype preference for Gi1 and Gi2, accompanied by an overall suppression of G-protein-mediated signaling in neuronal cells.”

http://www.ncbi.nlm.nih.gov/pubmed/25446256

Cannabinoid Receptor Interacting Protein (CRIP1a) suppresses agonist-driven CB1 receptor internalization, and regulates receptor replenishment in an agonist-biased manner.

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“Cannabinoid Receptor Interacting Protein1a (CRIP1a) is a CB1 receptor (CB1 R) distal C-terminus-associated protein that modulates CB1 R signaling via G proteins, and CB1 R down-regulation but not desensitization.

In the present study, we determined the involvement of CRIP1a in CB1 R plasma membrane trafficking.

These studies demonstrate a novel role for CRIP1a in agonist-driven CB1 R cell surface regulation postulated to occur by two mechanisms: attenuating agonist-mediated but not internalization in the absence of exogenous agonists, and biased agonist-dependent trafficking of de novo synthesized receptor to the cell surface.”

http://www.ncbi.nlm.nih.gov/pubmed/27513693

Modulation of L-α-lysophosphatidylinositol/GPR55 mitogen-activated protein kinase (MAPK) signaling by cannabinoids.

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“This study has implications for developing new therapeutics for the treatment of cancer, pain, and metabolic disorders.

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.

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.

Here, we report that the little investigated cannabis constituents CBDV, CBGA, and CBGV are potent inhibitors of LPI-induced GPR55 signaling.

The phytocannabinoids Δ9-tetrahydrocannabivarin, cannabidivarin, and cannabigerovarin are also potent inhibitors of LPI.

Our findings also suggest that GPR55 may be a new pharmacological target for the following C. sativa constituents: Δ9-THCV, CBDV, CBGA, and CBGV.

These Cannabis sativa constituents may represent novel therapeutics targeting GPR55.”  http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249141/

“Lysophosphatidylinositol (LPI) is a bioactive lipid generated by phospholipase A2 which is believed to play an important role in several diseases.”  http://www.ncbi.nlm.nih.gov/pubmed/22285325

 “The putative cannabinoid receptor GPR55 promotes cancer cell proliferation.  In this issue of Oncogene, two groups demonstrated that GPR55 is expressed in various cancer types in an aggressiveness-related manner, suggesting a novel cancer biomarker and a potential therapeutic target.” http://www.ncbi.nlm.nih.gov/pubmed/21057532
“The orphan G protein-coupled receptor GPR55 promotes cancer cell proliferation via ERK. These findings reveal the importance of GPR55 in human cancer, and suggest that it could constitute a new biomarker and therapeutic target in oncology.” http://www.ncbi.nlm.nih.gov/pubmed/20818416
“The putative cannabinoid receptor GPR55 defines a novel autocrine loop in cancer cell proliferation. These findings may have important implications for LPI as a novel cancer biomarker and for its receptor GPR55 as a potential therapeutic target.”  http://www.ncbi.nlm.nih.gov/pubmed/20838378
“L-α-lysophosphatidylinositol meets GPR55: a deadly relationship. Evidence points to a role of L-α-lysophosphatidylinositol (LPI) in cancer.”  http://www.ncbi.nlm.nih.gov/pubmed/21367464

Scotopic vision in the monkey is modulated by the G protein-coupled receptor 55.

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“The endogenous cannabinoid system plays important roles in the retina of mice and monkeys via their classic CB1 and CB2 receptors.

We have previously reported that the G protein-coupled receptor 55 (GPR55), a putative cannabinoid receptor, is exclusively expressed in rod photoreceptors in the monkey retina, suggesting its possible role in scotopic vision.

These results support the hypothesis that GPR55 plays an instrumental role in mediating scotopic vision.”

http://www.ncbi.nlm.nih.gov/pubmed/27485069

Endocannabinoid system as a regulator of tumor cell malignancy – biological pathways and clinical significance.

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“The endocannabinoid system (ECS) comprises cannabinoid receptors (CBs), endogenous cannabinoids, and enzymes responsible for their synthesis, transport, and degradation of (endo)cannabinoids.

To date, two CBs, CB1 and CB2, have been characterized; however, orphan G-protein-coupled receptor GPR55 has been suggested to be the third putative CB.

Several different types of cancer present abnormal expression of CBs, as well as other components of ECS, and this has been shown to correlate with the clinical outcome.

Although most effects of (endo)cannabinoids are mediated through stimulation of classical CBs, they also interact with several molecules, either prosurvival or proapoptotic molecules.

It should be noted that the mode of action of exogenous cannabinoids differs significantly from that of endocannabinoid and results from the studies on their activity both in vivo and in vitro could not be easily compared.

This review highlights the main signaling pathways involved in the antitumor activity of cannabinoids and the influence of their activation on cancer cell biology.

We also discuss changes in the expression pattern of the ECS in various cancer types that have an impact on disease progression and patient survival.

A growing amount of experimental data imply possible exploitation of cannabinoids in cancer therapy.”

http://www.ncbi.nlm.nih.gov/pubmed/27486335

Allosteric modulation of heterodimeric G-protein-coupled receptors.

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“G-protein-coupled receptors (GPCRs) are, and will probably remain, the most tractable class of targets for the development of small-molecule therapeutic medicines.

Currently, all approved GPCR-directed medicines are agonists or antagonists at orthosteric binding sites – except for the calcimimetic cinacalcet, which is a positive allosteric modulator of Ca(2+)-sensing receptors, and maraviroc, an allosteric inhibitor of CC-chemokine receptor (CCR) 5.

It is now widely accepted that GPCRs exist and might function as dimers, and there is growing evidence for the physiological presence and relevance of GPCR heterodimers.

Molecules that can regulate a GPCR within a heterodimer, through allosteric effects between the two protomers of the dimer or between a protomer or protomers and the associated G protein, offer the potential to function in a highly selective and tissue-specific way.

Despite the conceptual attraction of such allosteric regulators of GPCR heterodimers as drugs, they cannot be identified by screening approaches that routinely use a ‘one GPCR target at a time’ strategy.

In our opinion, this will require the development of new approaches for screening and a return to the use of physiologically relevant cell systems at an early stage in compound identification.”

http://www.ncbi.nlm.nih.gov/pubmed/18022255

Cannabidiol is an allosteric modulator at mu- and delta-opioid receptors.

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“The mechanism of action of cannabidiol, one of the major constituents of cannabis, is not well understood but a noncompetitive interaction with mu opioid receptors has been suggested on the basis of saturation binding experiments.

The aim of the present study was to examine whether cannabidiol is an allosteric modulator at this receptor, using kinetic binding studies, which are particularly sensitive for the measurement of allosteric interactions at G protein-coupled receptors.

In addition, we studied whether such a mechanism also extends to the delta opioid receptor. For comparison, (-)-Delta9-tetrahydrocannabinol (THC; another major constituent of cannabis) and rimonabant (a cannabinoid CB1 receptor antagonist) were studied.

The present study shows that cannabidiol is an allosteric modulator at mu and delta opioid receptors. This property is shared by THC but not by rimonabant.”

http://www.ncbi.nlm.nih.gov/pubmed/16489449