The ligand specificity of the G-protein-coupled receptor GPR34

GPR34 is a metabolic immune checkpoint for ILC1-mediated antitumor immunity

Type 1 innate lymphoid cells (ILC1s) are a class of tissue-resident cells with antitumor activity, suggesting its possible role in solid tumor immune surveillance, but it is not clear whether manipulating ILC1s can induce potent antitumor immune responses. Here, we found that G-protein-coupled receptor 34 (GPR34), a receptor for lysophosphatidylserine (LysoPS), was highly expressed on ILC1s but not on conventional natural killer cells in the tumor microenvironment. LysoPS was enriched in the tumor microenvironment and could inhibit ILC1 activation via GPR34. Genetic deletion of LysoPS synthase Abhd16a expression in tumors or Gpr34 expression in ILC1s or antagonizing GPR34 enhanced ILC1 antitumor activity. In individuals with cancer, ABHD16A expression in tumors or GPR34 expression in ILC1s was inversely correlated with the antitumor activity of ILC1s or ILC1-like cells. Thus, our results demonstrate that manipulating ILC1s can induce potent antitumor immunity, and GPR34 is a metabolic immune checkpoint that can be targeted to develop ILC1-based immunotherapy.

Lysophosphatidylserine: A Signaling Lipid with Implications in Human Diseases

Lysophosphatidylserine (lyso-PS) has emerged as yet another important signaling lysophospholipid in mammals, and deregulation in its metabolism has been directly linked to an array of human autoimmune and neurological disorders. It has an indispensable role in several biological processes in humans, and therefore, cellular concentrations of lyso-PS are tightly regulated to ensure optimal signaling and functioning in physiological settings. Given its biological importance, the past two decades have seen an explosion in the available literature toward our understanding of diverse aspects of lyso-PS metabolism and signaling and its association with human diseases. In this Review, we aim to comprehensively summarize different aspects of lyso-PS, such as its structure, biodistribution, chemical synthesis, and SAR studies with some synthetic analogs. From a biochemical perspective, we provide an exhaustive coverage of the diverse biological activities modulated by lyso-PSs, such as its metabolism and the receptors that respond to them in humans. We also briefly discuss the human diseases associated with aberrant lyso-PS metabolism and signaling and posit some future directions that may advance our understanding of lyso-PS-mediated mammalian physiology.

Structural basis for lysophosphatidylserine recognition by GPR34

GPR34 is a recently identified G-protein coupled receptor, which has an immunomodulatory role and recognizes lysophosphatidylserine (LysoPS) as a putative ligand. Here, we report cryo-electron microscopy structures of human GPR34-Gi complex bound with one of two ligands bound: either the LysoPS analogue S3E-LysoPS, or M1, a derivative of S3E-LysoPS in which oleic acid is substituted with a metabolically stable aromatic fatty acid surrogate. The ligand-binding pocket is laterally open toward the membrane, allowing lateral entry of lipidic agonists into the cavity. The amine and carboxylate groups of the serine moiety are recognized by the charged residue cluster. The acyl chain of S3E-LysoPS is bent and fits into the L-shaped hydrophobic pocket in TM4-5 gap, and the aromatic fatty acid surrogate of M1 fits more appropriately. Molecular dynamics simulations further account for the LysoPS-regioselectivity of GPR34. Thus, using a series of structural and physiological experiments, we provide evidence that chemically unstable 2-acyl LysoPS is the physiological ligand for GPR34. Overall, we anticipate the present structures will pave the way for development of novel anticancer drugs that specifically target GPR34.

Multiplex G Protein-Coupled Receptor Screen Reveals Reliably Acting Agonists and a Gq-Phospholipase C Coupling Mode of GPR30/GPER1

G protein-coupled receptors (GPCRs) constitute the most versatile family of pharmacological target proteins. For some "orphan" GPCRs, no ligand or drug-like modulator is known. In this study, we have established and applied a parallelized assay to coscreen 29 different human GPCRs. Three compounds, chlorhexidine, Lys-05, and 9-aminoacridine, triggered transient Ca²⁺ signals linked to the expression of GPR30. GPR30, also named G protein-coupled estrogen receptor 1 (GPER1), was reported to elicit increases in cAMP in response to 17β-estradiol, 4-hydroxytamoxifen, or G-1. These findings could, however, not be reproduced by other groups, and the deorphanization of GPR30 is, therefore, intensely disputed. The unbiased screen and following experiments in transiently or stably GPR30-overexpressing HEK293 cells did not show responses to 17β-estradiol, 4-hydroxytamoxifen, or G-1. A thorough analysis of the activated signaling cascade revealed a canonical G_q-coupled pathway, including phospholipase C, protein kinase C and ERK activation, receptor internalization, and sensitivity to the G_q inhibitor YM-254890. When expressed in different cell lines, the localization of a fluorescent GPR30 fusion protein appeared variable. An efficient integration into the plasma membrane and stronger functional responses were found in HEK293 and in MCF-7 cells, whereas GPR30 appeared mostly retained in endomembrane compartments in Cos-7 or HeLa cells. Thus, conflicting findings may result from the use of different cell lines. The newly identified agonists and the finding that GPR30 couples to G_q are expected to serve as a starting point for identifying physiologic responses that are controlled by this GPCR. SIGNIFICANCE STATEMENT: This study has identified and thoroughly characterized novel and reliably acting agonists of the G protein-coupled receptor GPER1/GPR30. Applying these agonists, this study demonstrates that GPR30 couples to the canonical G_q-phospholipase C pathway and is rapidly internalized upon continuous exposure to the agonists.

GPR34 in spinal microglia exacerbates neuropathic pain in mice

Background

Neuropathic pain is caused by sensory nerve injury, but effective treatments are currently lacking. Microglia are activated in the spinal dorsal horn after sensory nerve injury and contribute to neuropathic pain. Accordingly, molecules expressed by these cells are considered potential targets for therapeutic strategies. Our previous gene screening study using a mouse model of motor nerve injury showed that the G-protein-coupled receptor 34 gene (GPR34) is induced by nerve injury. Because GPR34 is now considered a microglia-enriched gene, we explored the possibility that it might be involved in microglial activation in the dorsal horn in a mouse model of neuropathic pain.

Methods

mRNA expression of GPR34 and pro-inflammatory molecules was determined by quantitative real-time PCR in wild-type and GPR34-deficient mice with L4 spinal nerve injury. In situ hybridization was used to identify GPR34 expression in microglia, and immunohistochemistry with the microglial marker Iba1 was performed to examine microglial numbers and morphology. Mechanical sensitivity was evaluated by the von Frey hair test. Liquid chromatography–tandem mass spectrometry quantified expression of the ligand for GPR34, lysophosphatidylserine (LysoPS), in the dorsal horn, and a GPR34 antagonist was intrathecally administrated to examine the effect of inhibiting LysoPS-GPR34 signaling on mechanical sensitivity.

Results

GPR34 was predominantly expressed by microglia in the dorsal horn after L4 nerve injury. There were no histological differences in microglial numbers or morphology between WT and GPR34-deficient mice. However, nerve injury-induced pro-inflammatory cytokine expression levels in microglia and pain behaviors were significantly attenuated in GPR34-deficient mice. Furthermore, the intrathecal administration of the GPR34 antagonist reduced neuropathic pain.

Conclusions

Inhibition of GPR34-mediated signal by GPR34 gene deletion reduced nerve injury-induced neuropathic pain by suppressing pro-inflammatory responses of microglia without affecting their morphology. Therefore, the suppression of GPR34 activity may have therapeutic potential for alleviating neuropathic pain.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1458-8) contains supplementary material, which is available to authorized users.

The G protein-coupled receptor GPR34 - The past 20 years of a grownup

Research on GPR34, which was discovered in 1999 as an orphan G protein-coupled receptor of the rhodopsin-like class, disclosed its physiologic relevance only piece by piece. Being present in all recent vertebrate genomes analyzed so far it seems to improve the fitness of species although it is not essential for life and reproduction as GPR34-deficient mice demonstrate. However, closer inspection of macrophages and microglia, where it is mainly expressed, revealed its relevance in immune cell function. Recent data clearly demonstrate that GPR34 function is required to arrest microglia in the M0 homeostatic non-phagocytic phenotype. Herein, we summarize the current knowledge on its evolution, genomic and structural organization, physiology, pharmacology and relevance in human diseases including neurodegenerative diseases and cancer, which accumulated over the last 20 years.

Modeling and Deorphanization of Orphan GPCRs

Despite tremendous efforts, approximately 120 GPCRs remain orphan. Their physiological functions and their potential roles in diseases are poorly understood. Orphan GPCRs are extremely important because they may provide novel therapeutic targets for unmet medical needs. As a complement to experimental approaches, molecular modeling and virtual screening are efficient techniques to discover synthetic surrogate ligands which can help to elucidate the role of oGPCRs. Constitutively activated mutants and recently published active structures of GPCRs provide stimulating opportunities for building active molecular models for oGPCRs and identifying activators using virtual screening of compound libraries. We describe the molecular modeling and virtual screening process we have applied in the discovery of surrogate ligands, and provide examples for CCKA, a simulated oGPCR, and for two oGPCRs, GPR52 and GPR34.

G protein-coupled receptor gpr34l mutation affects thrombocyte function in zebrafish

Haemostasis is a defence mechanism that has evolved to protect organisms from losing their circulating fluid. We have previously introduced zebrafish as a model to study the genetics of haemostasis to identify novel genes that play a role in haemostasis. Here, we identify a zebrafish mutant that showed prolonged time to occlusion (TTO) in the laser injury venous thrombosis assay. By linkage analysis and fine mapping, we found a mutation in the orphan G protein-coupled receptor 34 like gene (gpr34l) causing a change of Val to Glu in the third external loop of Gpr34l. We have shown that injection of zebrafish gpr34l RNA rescues the prolonged TTO defect. The thrombocytes from the mutant showed elevated levels of cAMP that supports the defective thrombocyte function. We also have demonstrated that knockdown of this gene by intravenous Vivo-Morpholino injections yielded a phenotype similar to the gpr34l mutation. These results suggest that the lack of functional Gpr34l leads to increased cAMP levels that result in defective thrombocyte aggregation.

Probing the Hydrophobic Binding Pocket of G-Protein-Coupled Lysophosphatidylserine Receptor GPR34/LPS1 by Docking-Aided Structure-Activity Analysis

The ligands of certain G-protein-coupled receptors (GPCRs) have been identified as endogenous lipids, such as lysophosphatidylserine (LysoPS). Here, we analyzed the molecular basis of the structure-activity relationship of ligands of GPR34, one of the LysoPS receptor subtypes, focusing on recognition of the long-chain fatty acid moiety by the hydrophobic pocket. By introducing benzene ring(s) into the fatty acid moiety of 2-deoxy-LysoPS, we explored the binding site's preference for the hydrophobic shape. A tribenzene-containing fatty acid surrogate with modifications of the terminal aromatic moiety showed potent agonistic activity toward GPR34. Computational docking of these derivatives with a homology modeling/molecular dynamics-based virtual binding site of GPR34 indicated that a kink in the benzene-based lipid surrogates matches the L-shaped hydrophobic pocket of GPR34. A tetrabenzene-based lipid analogue bearing a bulky tert-butyl group at the 4-position of the terminal benzene ring exhibited potent GPR34 agonistic activity, validating the present hydrophobic binding pocket model.

P2Y Receptors in Immune Response and Inflammation

Metabotropic pyrimidine and purine nucleotide receptors (P2Y receptors) are expressed in virtually all cells with implications in very diverse biological functions, including the well-established platelet aggregation (P2Y12), but also immune regulation and inflammation. The classical P2Y receptors bind nucleotides and are encoded by eight genes with limited sequence homology, while phylogenetically related receptors (e.g., P2Y12-like) recognize lipids and peptides, but also nucleotide derivatives. Growing lines of evidence suggest an important function of P2Y receptors in immune cell differentiation and maturation, migration, and cell apoptosis. Here, we give a perspective on the P2Y receptors' molecular structure and physiological importance in immune cells, as well as the related diseases and P2Y-targeting therapies. Extensive research is being undertaken to find modulators of P2Y receptors and uncover their physiological roles. We anticipate the medical applications of P2Y modulators and their immune relevance.

Prostaglandin E2 glyceryl ester is an endogenous agonist of the nucleotide receptor P2Y6

Cyclooxygenase-2 catalyses the biosynthesis of prostaglandins from arachidonic acid but also the biosynthesis of prostaglandin glycerol esters (PG-Gs) from 2-arachidonoylglycerol. Previous studies identified PG-Gs as signalling molecules involved in inflammation. Thus, the glyceryl ester of prostaglandin E2, PGE2-G, mobilizes Ca2+ and activates protein kinase C and ERK, suggesting the involvement of a G protein-coupled receptor (GPCR). To identify the endogenous receptor for PGE2-G, we performed a subtractive screening approach where mRNA from PGE2-G response-positive and -negative cell lines was subjected to transcriptome-wide RNA sequencing analysis. We found several GPCRs that are only expressed in the PGE2-G responder cell lines. Using a set of functional readouts in heterologous and endogenous expression systems, we identified the UDP receptor P2Y6 as the specific target of PGE2-G. We show that PGE2-G and UDP are both agonists at P2Y6, but they activate the receptor with extremely different EC50 values of ~1 pM and ~50 nM, respectively. The identification of the PGE2-G/P2Y6 pair uncovers the signalling mode of PG-Gs as previously under-appreciated products of cyclooxygenase-2.

G protein-coupled receptor 34 in ovarian granulosa cells of cattle: changes during follicular development and potential functional implications

Abundance of G protein-coupled receptor 34 (GPR34) mRNA is greater in granulosa cells (GCs) of cystic vs normal follicles of cattle. The present experiments were designed to determine if GPR34 mRNA in granulosa cell [GC] changes during selection and growth of dominant follicles in cattle as well as to investigate the hormonal regulation of GPR34 mRNA in bovine GC in vitro. In Exp. 1, estrous cycles of nonlactating cows were synchronized and then ovariectomized on either day 3-4 or 5-6 after ovulation. GPR34 mRNA abundance in GC was 2.8- to 3.8-fold greater (P < 0.05) in small (1-5 mm) and large (≥8 mm) estrogen-inactive dominant follicles than in large estrogen-active follicles. Also, GPR34 mRNA tended to be greater (P < 0.10) in F2 than F1 follicles on day 3-4 postovulation. In Exp. 2-7, ovaries were collected at an abattoir and GC were isolated and treated in vitro. Expression of GPR34 was increased (P < 0.05) 2.2-fold by IGF1. Tumor necrosis factor (TNF)-α decreased (P < 0.05) the IGF1-induced GPR34 mRNA abundance in small-follicle GC, whereas IGF1 decreased (P < 0.05) GPR34 expression by 45% in large-follicle GC. Treatment of small-follicle GC with either IL-2, prostaglandin E2 or angiogenin decreased (P < 0.05) GPR34 expression, whereas FSH, cortisol, wingless 3A, or hedgehog proteins did not affect (P > 0.10) GPR34 expression. In Exp. 6 and 7, 2 presumed ligands of GPR34, L-a-lysophosphatidylserine (LPPS) and LPP-ethanolamine, increased (P < 0.05) GC numbers and estradiol production by 2-fold or more in small-follicle GC, and this response was only observed in IGF1-treated GC. In conclusion, GPR34 is a developmentally and hormonally regulated gene in GC, and its presumed ligands enhance IGF1-induced proliferation and steroidogenesis of bovine GC.

Topogenesis and cell surface trafficking of GPR34 are facilitated by positive-inside rule that effects through a tri-basic motif in the first intracellular loop

Protein folding, topogenesis and intracellular targeting of G protein-coupled receptors (GPCRs) must be precisely coordinated to ensure correct receptor localization. To elucidate how different steps of GPCR biosynthesis work together, we investigated the process of membrane topology determination and how it relates to the acquisition of cell surface trafficking competence in human GPR34. By monitoring a fused FLAG-tag and a conformation-sensitive native epitope during the expression of GPR34 mutant panel, a tri-basic motif in the first intracellular loop was identified as the key topogenic signal that dictates the orientation of transmembrane domain-1 (TM1). Charge disruption of the motif perturbed topogenic processes and resulted in the conformational epitope loss, post-translational processing alteration, and trafficking arrest in the Golgi. The placement of a cleavable N-terminal signal sequence as a surrogate topogenic determinant overcame the effects of tri-basic motif mutations and rectified the TM1 orientation; thereby restored the conformational epitope, post-translational modifications, and cell surface trafficking altogether. Progressive N-tail truncation and site-directed mutagenesis revealed that a proline-rich segment of the N-tail and all four cysteines individually located in the four separate extracellular regions must simultaneously reside in the ER lumen to muster the conformational epitope. Oxidation of all four cysteines was necessary for the epitope formation, but the cysteine residues themselves were not required for the trafficking event. The underlying biochemical properties of the conformational epitope was therefore the key to understand mechanistic processes propelled by positive-inside rule that simultaneously regulate the topogenesis and intracellular trafficking of GPR34.

Beyond apoptosis: the mechanism and function of phosphatidylserine asymmetry in the membrane of activating mast cells

Loss of plasma membrane asymmetry is a hallmark of apoptosis, but lipid bilayer asymmetry and loss of asymmetry can contribute to numerous cellular functions and responses that are independent of programmed cell death. Exofacial exposure of phosphatidylserine occurs in lymphocytes and mast cells after antigenic stimulation and in the absence of apoptosis, suggesting that there is a functional requirement for phosphatidylserine exposure in immunocytes. In this review we examine current ideas as to the nature of this functional role in mast cell activation. Mechanistically, there is controversy as to the candidate proteins responsible for phosphatidylserine translocation from the internal to external leaflet, and here we review the candidacies of mast cell PLSCR1 and TMEM16F. Finally we examine the potential relationship between functionally important mast cell membrane perturbations and phosphatidylserine exposure during activation.

Structure-activity relationships of lysophosphatidylserine analogs as agonists of G-protein-coupled receptors GPR34, P2Y10, and GPR174

Lysophosphatidylserine (LysoPS) is an endogenous lipid mediator generated by hydrolysis of membrane phospholipid phosphatidylserine. Recent ligand screening of orphan G-protein-coupled receptors (GPCRs) identified two LysoPS-specific human GPCRs, namely, P2Y10 (LPS2) and GPR174 (LPS3), which, together with previously reported GPR34 (LPS1), comprise a LysoPS receptor family. Herein, we examined the structure-activity relationships of a series of synthetic LysoPS analogues toward these recently deorphanized LysoPS receptors, based on the idea that LysoPS can be regarded as consisting of distinct modules (fatty acid, glycerol, and l-serine) connected by phosphodiester and ester linkages. Starting from the endogenous ligand (1-oleoyl-LysoPS, 1), we optimized the structure of each module and the ester linkage. Accordingly, we identified some structural requirements of each module for potency and for receptor subtype selectivity. Further assembly of individually structure-optimized modules yielded a series of potent and LysoPS receptor subtype-selective agonists, particularly for P2Y10 and GPR174.

Lysophospholipid receptor nomenclature review: IUPHAR Review 8

Lysophospholipids encompass a diverse range of small, membrane-derived phospholipids that act as extracellular signals. The signalling properties are mediated by 7-transmembrane GPCRs, constituent members of which have continued to be identified after their initial discovery in the mid-1990s. Here we briefly review this class of receptors, with a particular emphasis on their protein and gene nomenclatures that reflect their cognate ligands. There are six lysophospholipid receptors that interact with lysophosphatidic acid (LPA): protein names LPA1 - LPA6 and italicized gene names LPAR1-LPAR6 (human) and Lpar1-Lpar6 (non-human). There are five sphingosine 1-phosphate (S1P) receptors: protein names S1P1 -S1P5 and italicized gene names S1PR1-S1PR5 (human) and S1pr1-S1pr5 (non-human). Recent additions to the lysophospholipid receptor family have resulted in the proposed names for a lysophosphatidyl inositol (LPI) receptor - protein name LPI1 and gene name LPIR1 (human) and Lpir1 (non-human) - and three lysophosphatidyl serine receptors - protein names LyPS1 , LyPS2 , LyPS3 and gene names LYPSR1-LYPSR3 (human) and Lypsr1-Lypsr3 (non-human) along with a variant form that does not appear to exist in humans that is provisionally named LyPS2L . This nomenclature incorporates previous recommendations from the International Union of Basic and Clinical Pharmacology, the Human Genome Organization, the Gene Nomenclature Committee, and the Mouse Genome Informatix.

Action and Signaling of Lysophosphatidylethanolamine in MDA-MB-231 Breast Cancer Cells

Previously, we reported that lysophosphatidylethanolamine (LPE), a lyso-type metabolite of phosphatidylethanolamine, can increase intracellular Ca²⁺ ([Ca²⁺]_i) via type 1 lysophosphatidic acid (LPA) receptor (LPA₁) and CD97, an adhesion G-protein-coupled receptor (GPCR), in MDA-MB-231 breast cancer cells. Furthermore, LPE signaling was suggested as like LPA₁/CD97-G_i/o proteins-phospholipase C-IP₃-Ca²⁺ increase in these cells. In the present study, we further investigated actions of LPE not only in the [Ca²⁺]_i increasing effect but also in cell proliferation and migration in MDA-MB-231 breast cancer cells. We utilized chemically different LPEs and a specific inhibitor of LPA₁, AM-095 in comparison with responses in SK-OV3 ovarian cancer cells. It was found that LPE-induced Ca²⁺ response in MDA-MB-231 cells was evoked in a different manner to that in SK-OV3 cells in terms of structural requirements. AM-095 inhibited LPE-induced Ca²⁺ response and cell proliferation in MDA-MB-231 cells, but not in SK-OV3 cells, supporting LPA₁ involvement only in MDA-MB-231 cells. LPA had significant effects on cell proliferation and migration in MDA-MB-231 cells, whereas LPE had less or no significant effect. However, LPE modulations of MAPKs (ERK1/2, JNK and p38 MAPK) was not different to those by LPA in the cells. These data support the involvement of LPA₁ in LPE-induced Ca²⁺ response and cell proliferation in breast MDA-MB-231 cells but unknown GPCRs (not LPA₁) in LPE-induced responses in SK-OV3 cells. Furthermore, although LPE and LPA utilized LPA₁, LPA utilized more signaling cascades than LPE, resulting in stronger responses by LPA in proliferation and migration than LPE in MDA-MB-231 cells.

Intercellular Lipid Mediators and GPCR Drug Discovery

G-protein-coupled receptors (GPCR) are the largest superfamily of receptors responsible for signaling between cells and tissues, and because they play important physiological roles in homeostasis, they are major drug targets. New technologies have been developed for the identification of new ligands, new GPCR functions, and for drug discovery purposes. In particular, intercellular lipid mediators, such as, lysophosphatidic acid and sphingosine 1-phosphate have attracted much attention for drug discovery and this has resulted in the development of fingolimod (FTY-720) and AM095. The discovery of new intercellular lipid mediators and their GPCRs are discussed from the perspective of drug development. Lipid GPCRs for lysophospholipids, including lysophosphatidylserine, lysophosphatidylinositol, lysophosphatidylcholine, free fatty acids, fatty acid derivatives, and other lipid mediators are reviewed.

Lysophosphatidylethanolamine utilizes LPA(1) and CD97 in MDA-MB-231 breast cancer cells

Lysophosphatidylethanolamine (LPE) is a lyso-type metabolite of phosphatidylethanolamine (a plasma membrane component), and its intracellular Ca(2+) ([Ca(2+)]i) increasing actions may be mediated through G-protein-coupled receptor (GPCR). However, GPCRs for lysophosphatidic acid (LPA), a structurally similar representative lipid mediator, have not been implicated in LPE-mediated activities in SK-OV3 or OVCAR-3 ovarian cancer cells or in receptor over-expression systems. In the present study, LPE-induced [Ca(2+)]i increase was observed in MDA-MB-231 cells but not in other breast cancer cell lines. In addition, LPE- and LPA-induced responses showed homologous and heterologous desensitization. Furthermore, VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases, and knockdown of LPA1 by transfection with LPA1 siRNA completely inhibited LPE-induced [Ca(2+)]i increases. Furthermore, the involvement of CD97 (an adhesion GPCR) in the action of LPA1 in MDA-MB-231 cells was demonstrated by siRNA transfection. Pertussis toxin (a specific inhibitor of Gi/o proteins), edelfosine (an inhibitor of phospholipase C), or 2-APB (an inhibitor of IP3 receptor) completely inhibited LPE-induced [Ca(2+)]i increases, whereas HA130, an inhibitor of autotaxin/lysophospholipase D, did not. Therefore, LPE is supposed to act on LPA1-CD97/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise in MDA-MB-231 breast cancer cells.

International Union of Basic and Clinical Pharmacology. LXXXVIII. G protein-coupled receptor list: recommendations for new pairings with cognate ligands

In 2005, the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) published a catalog of all of the human gene sequences known or predicted to encode G protein-coupled receptors (GPCRs), excluding sensory receptors. This review updates the list of orphan GPCRs and describes the criteria used by NC-IUPHAR to recommend the pairing of an orphan receptor with its cognate ligand(s). The following recommendations are made for new receptor names based on 11 pairings for class A GPCRs: hydroxycarboxylic acid receptors [HCA₁ (GPR81) with lactate, HCA₂ (GPR109A) with 3-hydroxybutyric acid, HCA₃ (GPR109B) with 3-hydroxyoctanoic acid]; lysophosphatidic acid receptors [LPA₄ (GPR23), LPA₅ (GPR92), LPA₆ (P2Y5)]; free fatty acid receptors [FFA4 (GPR120) with omega-3 fatty acids]; chemerin receptor (CMKLR1; ChemR23) with chemerin; CXCR7 (CMKOR1) with chemokines CXCL12 (SDF-1) and CXCL11 (ITAC); succinate receptor (SUCNR1) with succinate; and oxoglutarate receptor [OXGR1 with 2-oxoglutarate]. Pairings are highlighted for an additional 30 receptors in class A where further input is needed from the scientific community to validate these findings. Fifty-seven human class A receptors (excluding pseudogenes) are still considered orphans; information has been provided where there is a significant phenotype in genetically modified animals. In class B, six pairings have been reported by a single publication, with 28 (excluding pseudogenes) still classified as orphans. Seven orphan receptors remain in class C, with one pairing described by a single paper. The objective is to stimulate research into confirming pairings of orphan receptors where there is currently limited information and to identify cognate ligands for the remaining GPCRs. Further information can be found on the IUPHAR Database website (http://www.iuphar-db.org).

Novel bioactive glycerol-based lysophospholipids: new data -- new insight into their function

Based on the results of research conducted over last two decades, lysophospholipids (LPLs) were observed to be not only structural components of cellular membranes but also biologically active molecules influencing a broad variety of processes such as carcinogenesis, neurogenesis, immunity, vascular development or regulation of metabolic diseases. With a growing interest in the involvement of extracellular lysophospholipids in both normal physiology and pathology, it has become evident that those small molecules may have therapeutic potential. While lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) have been studied in detail, other LPLs such as lysophosphatidylglycerol (LPG), lysophosphatidylserine (LPS), lysophosphatidylinositol (LPI), lysophosphatidylethanolamine (LPE) or even lysophosphatidylcholine (LPC) have not been elucidated to such a high degree. Although information concerning the latter LPLs is sparse as compared to LPA and S1P, within the last couple of years much progress has been made. Recently published data suggest that these compounds may regulate fundamental cellular activities by modulating multiple molecular targets, e.g. by binding to specific receptors and/or altering the structure and fluidity of lipid rafts. Therefore, the present review is devoted to novel bioactive glycerol-based lysophospholipids and recent findings concerning their functions and possible signaling pathways regulating physiological and pathological processes.

Identification of determinants required for agonistic and inverse agonistic ligand properties at the ADP receptor P2Y12

The ADP receptor P2Y(12) belongs to the superfamily of G protein-coupled receptors (GPCRs), and its activation triggers platelet aggregation. Therefore, potent antagonists, such as clopidogrel, are of high clinical relevance in prophylaxis and treatment of thromboembolic events. P2Y(12) displays an elevated basal activity in vitro, and as such, inverse agonists may be therapeutically beneficial compared with antagonists. Only a few inverse agonists of P2Y(12) have been described. To expand this limited chemical space and improve understanding of structural determinants of inverse agonist-receptor interaction, this study screened a purine compound library for lead structures using wild-type (WT) human P2Y(12) and 28 constitutively active mutants. Results showed that ATP and ATP derivatives are agonists at P2Y(12). The potency at P2Y(12) was 2-(methylthio)-ADP > 2-(methylthio)-ATP > ADP > ATP. Determinants required for agonistic ligand activity were identified. Molecular docking studies revealed a binding pocket for the ATP derivatives that is bordered by transmembrane helices 3, 5, 6, and 7 in human P2Y(12,) with Y(105), E(188), R(256), Y(259), and K(280) playing a particularly important role in ligand interaction. N-Methyl-anthraniloyl modification at the 3'-OH of the 2'-deoxyribose leads to ligands (mant-deoxy-ATP [dATP], mant-deoxy-ADP) with inverse agonist activity. Inverse agonist activity of mant-dATP was found at the WT human P2Y(12) and half of the constitutive active P2Y(12) mutants. This study showed that, in addition to ADP and ATP, other ATP derivatives are not only ligands of P2Y(12) but also agonists. Modification of the ribose within ATP can result in inverse activity of ATP-derived ligands.