Orphan G Protein-coupled Receptors Research Articles

Orphan GPCRs in Neurodegenerative Disorders: Integrating Structural Biology and Drug Discovery Approaches.

Neurodegenerative disorders, particularly Alzheimer's and Parkinson's diseases, continue to challenge modern medicine despite therapeutic advances. Orphan G-protein-coupled receptors (GPCRs) have emerged as promising targets in the central nervous system, offering new avenues for drug development. This review focuses on the structural biology of orphan GPCRs implicated in these disorders, providing a comprehensive analysis of their molecular architecture and functional mechanisms. We examine recent breakthroughs in structural determination techniques, such as cryo-electron microscopy and X-ray crystallography, which have elucidated the intricate conformations of these receptors. The review highlights how structural insights inform our understanding of orphan GPCR activation, ligand binding and signaling pathways. By integrating structural data with molecular pharmacology, we explore the potential of structure-guided approaches in developing targeted therapeutics toward orphan GPCRs. This structural-biology-centered perspective aims to deepen our comprehension of orphan GPCRs and guide future drug discovery efforts in neurodegenerative disorders.

Virtual screening, molecular docking and dynamics simulation studies to identify potential agonists of orphan receptor GPR78 targeting CNS disorders

G protein-coupled receptors (GPCRs) are important targets in drug discovery because of their roles in physiological and pathological processes. Orphan GPCRs are GPCR proteins for which endogenous ligands have not yet been identified and they present interesting avenues for therapeutic intervention. This study focuses on GPR78, an orphan GPCR that is expressed in the central nervous system and linked to neurological disorders. GPR78 has no reported crystal structure and there is limited research. In this study, we have predicted the three dimensional model of GPR78 and its probable binding pocket. Structure-based virtual screening was carried out using the ChemDiv and Enamine REAL databases, followed by induced-fit docking studies to identify potential lead compounds with favorable interactions. These lead compounds were then embedded into a POPC lipid bilayer for a 200 ns molecular dynamics simulation. Free energy landscapes and MM-PBSA analyses were performed to assess the binding energies and conformational dynamics. The results highlight the dynamic nature of GPR78 in the presence of lead compounds and show favorable binding interactions. This study aims to predict a reliable three dimensional model of GPR78 and identify novel lead compounds through a comprehensive in silico approach. The identification of these potential GPR78 agonists represents a significant step in the development of new therapeutics for neurological disorders, highlighting the therapeutic potential of orphan GPR78 in CNS disorders.

Gz Enhanced Signal Transduction assaY (GZESTY) for GPCR deorphanization.

G protein-coupled receptors (GPCRs) are key pharmacological targets, yet many remain underutilized due to unknown activation mechanisms and ligands. Orphan GPCRs, lacking identified natural ligands, are a high priority for research, as identifying their ligands will aid in understanding their functions and potential as drug targets. Most GPCRs, including orphans, couple to Gi/o/z family members, however current assays to detect their activation are limited, hindering ligand identification efforts. We introduce GZESTY, a highly sensitive, cell-based assay developed in an easily deliverable format designed to study the pharmacology of Gi/o/z-coupled GPCRs and assist in deorphanization. We optimized assay conditions and developed an all-in-one vector employing novel cloning methods to ensure the correct expression ratio of GZESTY components. GZESTY successfully assessed activation of a library of ligand-activated GPCRs, detecting both full and partial agonism, as well as responses from endogenous GPCRs. Notably, with GZESTY we established the presence of endogenous ligands for GPR176 and GPR37 in brain extracts, validating its use in deorphanization efforts. This assay enhances the ability to find ligands for orphan GPCRs, expanding the toolkit for GPCR pharmacologists.

Potent, Selective Agonists for the Cannabinoid-like Orphan GProtein-Coupled Receptor GPR18: A Promising Drug Target forCancer and Immunity.

The human orphan G protein-coupled receptor GPR18, activated by Δ9-tetrahydrocannabinol (THC), constitutes a promising drug target in immunology and cancer. However, studies on GPR18 are hampered by the lack of suitable tool compounds. In the present study, potent and selective GPR18 agonists were developed showing low nanomolar potency at human and mouse GPR18, determined in β-arrestin recruitment assays. Structure-activity relationships were analyzed, and selectivity versus cannabinoid (CB) and CB-like receptors was assessed. Compound 51 (PSB-KK1415, EC50 19.1 nM) was the most potent GPR18 agonist showing at least 25-fold selectivity versus CB receptors. The most selective GPR18 agonist 50 (PSB-KK1445, EC50 45.4 nM) displayed >200-fold selectivity versus both CB receptor subtypes, GPR55, and GPR183. The new GPR18 agonists showed minimal species differences, while THC acted as a weak partial agonist at the mouse receptor. The newly discovered compounds represent the most potent and selective GPR18 agonists reported to date.

ERNEST COST action overview on the (patho)physiology of GPCRs and orphan GPCRs in the nervous system.

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that play a critical role in nervous system function by transmitting signals between cells and their environment. They are involved in many, if not all, nervous system processes, and their dysfunction has been linked to various neurological disorders representing important drug targets. This overview emphasises the GPCRs of the nervous system, which are the research focus of the members of ERNEST COST action (CA18133) working group 'Biological roles of signal transduction'. First, the (patho)physiological role of the nervous system GPCRs in the modulation of synapse function is discussed. We then debate the (patho)physiology and pharmacology of opioid, acetylcholine, chemokine, melatonin and adhesion GPCRs in the nervous system. Finally, we address the orphan GPCRs, their implication in the nervous system function and disease, and the challenges that need to be addressed to deorphanize them.

Cardiomyocyte-specific overexpression of GPR22 ameliorates cardiac injury in mice with acute myocardial infarction

BackgroundThe activation of G protein-coupled receptors (GPCR) signaling by external stimuli has been implicated in inducing cardiac stress and stress responses. GPR22 is an orphan GPCR expressed in brains and hearts, while its expression level is associated with cardiovascular damage in diabetes. Previous studies have suggested a protective role of GPR22 in mechanical cardiac stress, as loss of its expression increases susceptibility to heart failure post-ventricular pressure overload. However, the involvement and underlying signaling of GPR22 in cardiac stress response to ischemic stress remains unexplored.MethodsIn this study, we used cultured cells and a transgenic mouse model with cardiomyocyte-specific GPR22 overexpression to investigate the impact of ischemic stress on GPR22 expression and to elucidate its role in myocardial ischemic injury. Acute myocardial infarction (AMI) was induced by left coronary artery ligation in eight-week-old male GPR22 transgenic mice, followed by histopathological and biochemical examination four weeks post-AMI induction.ResultsGPR22 expression in H9C2 and RL-14 cells, two cardiomyocyte cell lines, was decreased by cobalt chloride (CoCl2) treatment. Similarly, reduced expression of myocardial GPR22 was observed in mice with AMI. Histopathological examinations revealed a protective effect of GPR22 overexpression in attenuating myocardial infarction in mice with AMI. Furthermore, myocardial levels of Bcl-2 and activation of PI3K-Akt signaling were downregulated by ischemic stress and upregulated by GPR22 overexpression. Conversely, the expression levels of caspase-3 and phosphorylated ERK1/2 in the infarcted myocardium were downregulated with GPR22 overexpression.ConclusionMyocardial ischemic stress downregulates cardiac expression of GPR22, whereas overexpression of GPR22 in cardiomyocytes upregulates Akt signaling, downregulates ERK activation, and mitigates ischemia-induced myocardial injury.

Is the Serpin-Enzyme Complex Receptor an Orphan G-Protein Coupled Receptor?

Alpha-1 antitrypsin (α1-AT) is a member of serine proteinase inhibitors, collectively known as serpins, that inactivate their target enzymes by forming a stabilized serpin-enzyme complex. α1-AT molecules interact with elastase, forming biologically active complexes. It was suggested that the formation of α1-AT-elastase complex would expose a domain from α1-AT molecule that is recognized by a specific cell receptor. Thus, a synthetic peptide, called 105Y, was made based on the sequence of the exposed domain. The peptide binds specifically to human hepatoma HepG2 cells, human monocytes, human neutrophils, and rat pheochromocytoma cells (PC12). This binding is blocked by α1-AT-elastase complex and other serpin-enzyme complexes, suggesting an existence of a specific cell surface receptor, termed SEC receptor, that recognizes serpin enzyme complexes. However, the identity of SEC receptor is still unknown. Thus, we decided to use the Deductive Reasoning Strategy approach to investigate if the SEC receptor belongs to G-protein-coupled receptor (GPCR) family. We measured responsiveness of HepG2 cells as well as human neuroblastoma SHSY5Y cells to 105Y peptide by quantifying their expression of an early response gene c-Fos using real time quantitative polymerase chain reaction (qPCR) and measured their expression of orphan GPCRs using polymerase chain reaction (PCR) followed by gel electrophoresis. Our results indicate that the cells were responding to 105Y peptide and express certain orphan GPCRs. Our goal is to evaluate the necessity of these oGPCRs in 105Y peptide signaling in order to determine the best candidate(s) for the 105Y receptor. These results would shed light on the identity of the SEC receptor for better understanding of the molecular biology and physiology of the serpin-enzyme complexes and their receptors. National Institute of Health. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Orphan GPCR GPRC5C Facilitates Angiotensin II-Induced Smooth Muscle Contraction.

GPCRs (G-protein-coupled receptors) play a central role in the regulation of smooth muscle cell (SMC) contractility, but the function of SMC-expressed orphan GPCR class C group 5 member C (GPRC5C) is unclear. The aim of this project is to define the role of GPRC5C in SMC in vitro and in vivo. We studied the role of GPRC5C in the regulation of SMC contractility and differentiation in human and murine SMC in vitro, as well as in tamoxifen-inducible, SMC-specific GPRC5C knockout mice under basal conditions and in vascular disease in vivo. Mesenteric arteries from tamoxifen-inducible, SMC-specific GPRC5C knockout mice showed ex vivo significantly reduced angiotensin II (Ang II)-dependent calcium mobilization and contraction, whereas responses to other relaxant or contractile factors were normal. In vitro, the knockdown of GPRC5C in human aortic SMC resulted in diminished Ang II-dependent inositol phosphate production and lower myosin light chain phosphorylation. In line with this, tamoxifen-inducible, SMC-specific GPRC5C knockout mice showed reduced Ang II-induced arterial hypertension, and acute inactivation of GPRC5C was able to ameliorate established arterial hypertension. Mechanistically, we show that GPRC5C and the Ang II receptor AT1 dimerize, and knockdown of GPRC5C resulted in reduced binding of Ang II to AT1 receptors in HEK293 cells, human and murine SMC, and arteries from tamoxifen-inducible, SMC-specific GPRC5C knockout mice. Our data show that GPRC5C regulates Ang II-dependent vascular contraction by facilitating AT1 receptor-ligand binding and signaling.

Abstract 197: The GPR52-MCAM axis as a novel regulatory mechanism of breast cancer cell clustering and metastatic potential

Abstract Background: Breast cancer is the most diagnosed cancer worldwide and is the second leading cause of cancer death among women in the United States. Despite breakthroughs in targeted therapies for breast cancer, the 5-year survival rate for women with metastatic breast cancer is 30%. There is a strong rationale to explore the therapeutic potential of G-protein coupled receptors (GPCRs), which comprise the largest class of proteins successfully targeted by FDA-approved drugs. Importantly, at least one-third of GPCRs are “orphans” and remain largely uncharacterized. One of these orphan GPCRs is GPR52. To date, there is no literature on the role of GPR52 in any cancer type, but we find from publicly available clinical data that low mRNA expression of GPR52 in breast tumors correlates with reduced overall survival (hazard ratio=0.67 [0.53-0.83], logrank P= 0.00035) and that GPR52 mRNA levels tend to be lower in tumor metastases compared to primary tumor (n>80, p=4.45e-17). Therefore, we hypothesize that loss of GPR52 may support breast cancer metastasis. Results: We used CRISPR-Cas9 to knockout (KO) GPR52 in triple-negative breast cancer cell lines MDA-MB-468 and MDA-MB-231, and in the non-cancerous breast epithelial cell line MCF10A, and confirmed the generation of frameshift mutations by Sanger sequencing. Interestingly, we observed that GPR52 KO cells clustered together in vitro in 2D and hypothesized that this characteristic may allow GPR52 KO breast cancer cells to increase their metastatic potential. We conducted invasion assays though Matrigel and found that GPR52 KO cells were more likely to invade as sheets or clusters. To determine the in vivo impact of GPR52 loss, we injected MDA-MB-468 GPR52 KO cells in zebrafish (Danio rerio) two days post-fertilization and observed that GPR52 loss led to increased metastatic foci and total cancer surface area thirty hours post-injection (n≥12, p<0.05). We determined from RNA-sequencing (n=3, p<.0001) and confirmed with western blotting that the melanoma cell adhesion molecule (MCAM) is upregulated in the MCF10A and MDA-MB-468 GPR52 KO cells. Increased mRNA expression of MCAM has been associated with reduced overall survival in breast cancer patients (hazard ratio=1.33 [1.05-1.62], logrank P= 0.02) Conclusion: Knockout of GPR52 from breast cancer cells promotes increased cell clustering in vitro and metastasis in zebrafish. These data support the investigation of GPR52 as a biomarker of cancer aggression and a potential therapeutic target for breast cancer patients whose tumors express GPR52. Citation Format: Sarah Z. Hanif, CheukMan C. Au, Ingrid Torregroza, Bhavneet Bhinder, Lukas Dow, Olivier Elemento, Todd Evans, Kristy A. Brown. The GPR52-MCAM axis as a novel regulatory mechanism of breast cancer cell clustering and metastatic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 197.

Orphan G protein-coupled receptors: the ongoing search for a home.

G protein-coupled receptors (GPCRs) make up the largest receptor superfamily, accounting for 4% of protein-coding genes. Despite the prevalence of such transmembrane receptors, a significant number remain orphans, lacking identified endogenous ligands. Since their conception, the reverse pharmacology approach has been used to characterize such receptors. However, the multifaceted and nuanced nature of GPCR signaling poses a great challenge to their pharmacological elucidation. Considering their therapeutic relevance, the search for native orphan GPCR ligands continues. Despite limited structural input in terms of 3D crystallized structures, with advances in machine-learning approaches, there has been great progress with respect to accurate ligand prediction. Though such an approach proves valuable given that ligand scarcity is the greatest hurdle to orphan GPCR deorphanization, the future pairings of the remaining orphan GPCRs may not necessarily take a one-size-fits-all approach but should be more comprehensive in accounting for numerous nuanced possibilities to cover the full spectrum of GPCR signaling.

Lipid-Dependent Activation of the Orphan G Protein-Coupled Receptor, GPR3.

The class A orphan G protein-coupled receptor (GPCR), GPR3, has been implicated in a variety of conditions, including Alzheimer's and premature ovarian failure. GPR3 constitutively couples with Gαs, resulting in the production of cAMP in cells. While tool compounds and several putative endogenous ligands have emerged for the receptor, its endogenous ligand, if it exists, remains a mystery. As novel potential drug targets, the structures of orphan GPCRs have been of increasing interest, revealing distinct modes of activation, including autoactivation, presence of constitutively activating mutations, or via cryptic ligands. Here, we present a cryo-electron microscopy (cryo-EM) structure of the orphan GPCR, GPR3 in complex with DNGαs and Gβ1γ2. The structure revealed clear density for a lipid-like ligand that bound within an extended hydrophobic groove, suggesting that the observed "constitutive activity" was likely due to activation via a lipid that may be ubiquitously present. Analysis of conformational variance within the cryo-EM data set revealed twisting motions of the GPR3 transmembrane helices that appeared coordinated with changes in the lipid-like density. We propose a mechanism for the binding of a lipid to its putative orthosteric binding pocket linked to the GPR3 dynamics.

Constitutive activation mechanism of a class C GPCR.

Class C G-protein-coupled receptors (GPCRs) are activated through binding of agonists to the large extracellular domain (ECD) followed by rearrangement of the transmembrane domains (TMDs). GPR156, a class C orphan GPCR, is unique because it lacks an ECD and exhibits constitutive activity. Impaired GPR156-Gi signaling contributes to loss of hearing. Here we present the cryo-electron microscopy structures of human GPR156 in the Go-free and Go-coupled states. We found that an endogenous phospholipid molecule is located within each TMD of the GPR156 dimer. Asymmetric binding of Gα to the phospholipid-bound GPR156 dimer restructures the first and second intracellular loops and the carboxy-terminal part of the elongated transmembrane 7 (TM7) without altering dimer conformation. Our findings reveal that GPR156 is a transducer for phospholipid signaling. Constant binding of abundant phospholipid molecules and the G-protein-induced reshaping of the cytoplasmic face provide a basis for the constitutive activation of GPR156.

Decrypting orphan GPCR drug discovery via multitask learning

The drug discovery of G protein-coupled receptors (GPCRs) superfamily using computational models is often limited by the availability of protein three-dimensional (3D) structures and chemicals with experimentally measured bioactivities. Orphan GPCRs without known ligands further complicate the process. To enable drug discovery for human orphan GPCRs, multitask models were proposed for predicting half maximal effective concentrations (EC50) of the pairs of chemicals and GPCRs. Protein multiple sequence alignment features, and physicochemical properties and fingerprints of chemicals were utilized to encode the protein and chemical information, respectively. The protein features enabled the transfer of data-rich GPCRs to orphan receptors and the transferability based on the similarity of protein features. The final model was trained using both agonist and antagonist data from 200 GPCRs and showed an excellent mean squared error (MSE) of 0.24 in the validation dataset. An independent test using the orphan dataset consisting of 16 receptors associated with less than 8 bioactivities showed a reasonably good MSE of 1.51 that can be further improved to 0.53 by considering the transferability based on protein features. The informative features were identified and mapped to corresponding 3D structures to gain insights into the mechanism of GPCR-ligand interactions across the GPCR family. The proposed method provides a novel perspective on learning ligand bioactivity within the diverse human GPCR superfamily and can potentially accelerate the discovery of therapeutic agents for orphan GPCRs.

The orphan G protein-coupled receptor 141 expressed in myeloid cells functions as an inflammation suppressor.

G protein-coupled receptors (GPCRs) regulate many cellular processes in response to various stimuli, including light, hormones, neurotransmitters, and odorants, some of which play critical roles in innate and adaptive immune responses. However, the physiological functions of many GPCRs and the involvement of them in autoimmune diseases of the central nervous system remain unclear. Here, we demonstrate that GPR141, an orphan GPCR belonging to the class A receptor family, suppresses immune responses. High GPR141 messenger RNA levels were expressed in myeloid-lineage cells, including neutrophils (CD11b + Gr1+), monocytes (CD11b + Gr1-Ly6C+ and CD11b + Gr1-Ly6C-), macrophages (F4/80+), and dendritic cells (CD11c+). Gpr141 -/- mice, which we independently generated, displayed almost no abnormalities in myeloid cell differentiation and compartmentalization in the spleen and bone marrow under steady-state conditions. However, Gpr141 deficiency exacerbated disease conditions of experimental autoimmune encephalomyelitis, an autoimmune disease model for multiple sclerosis, with increased inflammation in the spinal cord. Gpr141 -/- mice showed increased CD11b + Gr1+ neutrophils, CD11b + Gr1- monocytes, CD11c+ dendritic cells, and CD4+ T cell infiltration into the experimental autoimmune encephalomyelitis-induced spinal cord compared with littermate control mice. Lymphocytes enriched from Gpr141 -/- mice immunized with myelin oligodendrocyte glycoprotein 35-55 produced high amounts of interferon-γ, interleukin-17A, and interleukin-6 compared with those from wild-type mice. Moreover, CD11c+ dendritic cells (DCs) purified from Gpr141 -/- mice increased cytokine production of myelin oligodendrocyte glycoprotein 35-55-specific T cells. These findings suggest that GPR141 functions as a negative regulator of immune responses by controlling the functions of monocytes and dendritic cells and that targeting GPR141 may be a possible therapeutic intervention for modulating chronic inflammatory diseases.

Global and endothelial G-protein coupled receptor 75 (GPR75) knockout relaxes pulmonary artery and mitigates hypoxia-induced pulmonary hypertension

RationalePulmonary hypertension (PH) is a multifactorial disease with a poor prognosis and inadequate treatment options. We found two-fold higher expression of the orphan G-Protein Coupled Receptor 75 (GPR75) in leukocytes and pulmonary arterial smooth muscle cells from idiopathic PH patients and from lungs of C57BL/6 mice exposed to hypoxia. We therefore postulated that GPR75 signaling is critical to the pathogenesis of PH. MethodsTo test this hypothesis, we exposed global (Gpr75−/−) and endothelial cell (EC) GPR75 knockout (EC-Gpr75−/−) mice and wild-type (control) mice to hypoxia (10% oxygen) or normal atmospheric oxygen for 5 weeks. We then recorded echocardiograms and performed right heart catheterizations. ResultsChronic hypoxia increased right ventricular systolic and diastolic pressures in wild-type mice but not Gpr75−/− or EC-Gpr75−/− mice. In situ hybridization and qPCR results revealed that Gpr75 expression was increased in the alveoli, airways and pulmonary arteries of mice exposed to hypoxia. In addition, levels of chemokine (CC motif) ligand 5 (CCL5), a low affinity ligand of GPR75, were increased in the lungs of wild-type, but not Gpr75−/−, mice exposed to hypoxia, and CCL5 enhanced hypoxia-induced contraction of intra-lobar pulmonary arteries in a GPR75-dependent manner. Gpr75 knockout also increased pulmonary cAMP levels and decreased contraction of intra-lobar pulmonary arteries evoked by endothelin-1 or U46619 in cAMP-protein kinase A-dependent manner. ConclusionThese results suggest GPR75 has a significant role in the development of hypoxia-induced PH.

Specific binding of GPR174 by endogenous lysophosphatidylserine leads to high constitutive Gs signaling

Many orphan G protein-coupled receptors (GPCRs) remain understudied because their endogenous ligands are unknown. Here, we show that a group of class A/rhodopsin-like orphan GPCRs including GPR61, GPR161 and GPR174 increase the cAMP level similarly to fully activated D1 dopamine receptor (D1R). We report cryo-electron microscopy structures of the GPR61‒Gs, GPR161‒Gs and GPR174‒Gs complexes without any exogenous ligands. The GPR174 structure reveals that endogenous lysophosphatidylserine (lysoPS) is copurified. While GPR174 fails to respond to exogenous lysoPS, likely owing to its maximal activation by the endogenous ligand, GPR174 mutants with lower ligand binding affinities can be specifically activated by lysoPS but not other lipids, in a dose-dependent manner. Moreover, GPR174 adopts a non-canonical Gs coupling mode. The structures of GPR161 and GPR61 reveal that the second extracellular loop (ECL2) penetrates into the orthosteric pocket, possibly contributing to constitutive activity. Our work definitively confirms lysoPS as an endogenous GPR174 ligand and suggests that high constitutive activity of some orphan GPCRs could be accounted for by their having naturally abundant ligands.

Orphan G Protein-Coupled Receptor GPR37 as an Emerging Therapeutic Target.

G protein-coupled receptors (GPCRs) are successful druggable targets, making up around 35% of all FDA-approved medications. However, a large number of receptors remain orphaned, with no known endogenous ligand, representing a challenging but untapped area to discover new therapeutic targets. Among orphan GPCRs (oGPCRs) of interest, G protein-coupled receptor 37 (GPR37) is highly expressed in the central nervous system (CNS), particularly in the spinal cord and oligodendrocytes. While its cellular signaling mechanisms and endogenous receptor ligands remain elusive, GPR37 has been implicated in several important neurological conditions, including Parkinson's disease (PD), inflammation, pain, autism, and brain tumors. GPR37 structure, signaling, emerging physiology, and pharmacology are reviewed while integrating a discussion on potential therapeutic indications and opportunities.

RNAi-mediated knockdown of two orphan G protein-coupled receptors reduces fecundity in the yellow fever mosquito Aedes aegypti.

G protein-coupled receptors (GPCRs) control numerous physiological processes in insects, including reproduction. While many GPCRs have known ligands, orphan GPCRs do not have identified ligands in which they bind. Advances in genomic sequencing and phylogenetics provide the ability to compare orphan receptor protein sequences to sequences of characterized GPCRs, and thus gain a better understanding of the potential functions of orphan GPCRs. Our study sought to investigate the functions of two orphan GPCRs, AAEL003647 and AAEL019988, in the yellow fever mosquito, Aedes aegypti. From our phylogenetic investigation, we found that AAEL003647 is orthologous to the SIFamide-2/SMYamide receptor. We also found that AAEL019988 is orthologous to the Trapped in endoderm (Tre1) receptor of Drosophila melanogaster. Next, we conducted a tissue-specific expression analysis and found that both receptors had highest expression in the ovaries, suggesting they may be important for reproduction. We then used RNA interference (RNAi) to knock down both genes and found a significant reduction in the number of eggs laid per individual female mosquito, suggesting both receptors are important for Ae. aegypti reproduction.

G protein-coupled receptors as targets for transformative neuropsychiatric therapeutics.

G protein-coupled receptors (GPCRs) constitute the largest family of druggable genes in the human genome. Even though perhaps 30% of approved medications target GPCRs, they interact with only a small number of them. Here, we consider whether there might be new opportunities for transformative therapeutics for neuropsychiatric disorders by specifically targeting both known and understudied GPCRs. Using psychedelic drugs that target serotonin receptors as an example, we show how recent insights into the structure, function, signaling, and cell biology of these receptors have led to potentially novel therapeutics. We next focus on the possibility that nonpsychedelic 5-HT2A receptor agonists might prove to be safe and rapidly acting antidepressants. Finally, we examine understudied and orphan GPCRs using the MRGPR family of receptors as an example.

High expression of GPR50 promotes the proliferation, migration and autophagy of hepatocellular carcinoma cells in vitro.

G protein-coupled receptors (GPCRs) play important roles in tumorigenesis and the development of hepatocellular carcinoma (HCC). GPR50 is an orphan GPCR. Previous studies have indicated that GPR50 could protect against breast cancer development and decrease tumor growth in a xenograft mouse model. However, its role in HCC remains indistinct. To detect the role and the regulation mechanism of GPR50 in HCC, GPR50 expression was analyzed in HCC patients (gene expression omnibus database (GEO) (GSE45436)) and detected in HCC cell line CBRH-7919, and the results showed that GPR50 was significantly up-regulated in HCC patients and CBRH-7919 cell line compared to the corresponding normal control. Gpr50 cDNA was transfected into HCC cell line CBRH-7919, and we found that Gpr50 promoted the proliferation, migration, and autophagy of CBRH-7919. The regulation mechanism of GPR50 in HCC was detected by isobaric tags for relative and absolute quantification (iTRAQ) analysis, and we found that GPR50 promoted HCC was closely related to CCT6A and PGK1. Taken together, GPR50 may promote HCC progression via CCT6A-induced proliferation and PGK1-induced migration and autophagy, and GPR50 could be an important target for HCC.