Novel human G-protein-coupled receptors

Molecular insights into orphan G protein-coupled receptors relevant to schizophrenia

Schizophrenia remains a sizable socio-economic burden that continues to be treated with therapeutics based on 70-year old science. All currently approved therapeutics primarily target the dopamine D2 receptor to achieve their efficacy. Whilst dopaminergic dysregulation is a key feature in this disorder, the targeting of dopaminergic machinery has yielded limited efficacy and an appreciable side effect burden. Over the recent decades, numerous drugs that engage non-dopaminergic G protein-coupled receptors (GPCRs) have yielded a promise of efficacy without the deleterious side effect profile, yet none have successfully completed clinical studies and progressed to the market. More recently, there has been increased attention around non-dopaminergic GPCR-targeting drugs, which demonstrated efficacy in some schizophrenia symptom domains. This provides renewed hope that effective schizophrenia treatment may lie outside of the dopaminergic space. Despite the potential for muscarinic receptor- (and other well-characterised GPCR families) targeting drugs to treat schizophrenia, they are often plagued with complications such as lack of receptor subtype selectivity and peripheral on-target side effects. Orphan GPCR studies have opened a new avenue of exploration with many demonstrating schizophrenia-relevant mechanisms and a favourable expression profile, thus offering potential for novel drug development. This review discusses centrally expressed orphan GPCRs: GPR3, GPR6, GPR12, GPR52, GPR85, GPR88 and GPR139 and their relationship to schizophrenia. We review their expression, signalling mechanisms and cellular function, in conjunction with small molecule development and structural insights. We seek to provide a snapshot of the growing evidence and development potential of new classes of schizophrenia therapeutics. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

GPR137 Inhibits Cell Proliferation and Promotes Neuronal Differentiation in the Neuro2a Cells

The orphan receptor, G protein-coupled receptor 137 (GPR137), is an integral membrane protein involved in several types of cancer. GPR137 is expressed ubiquitously, including in the central nervous system (CNS). We established a GPR137 knockout (KO) neuro2A cell line to analyze GPR137 function in neuronal cells. KO cells were generated by genome editing using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 and cultured as single cells by limited dilution. Rescue cells were then constructed to re-express GPR137 in GPR137 KO neuro2A cells using an expression vector with an EF1-alpha promoter. GPR137 KO cells increased cellular proliferation and decreased neurite outgrowth (i.e., a lower level of neuronal differentiation). Furthermore, GPR137 KO cells exhibited increased expression of a cell cycle regulator, cyclin D1, and decreased expression of a neuronal differentiation marker, NeuroD1. Additionally, GPR137 KO cells exhibited lower expression levels of the neurite outgrowth markers STAT3 and GAP43. These phenotypes were all abrogated in the rescue cells. In conclusion, GPR137 deletion increased cellular proliferation and decreased neuronal differentiation, suggesting that GPR137 promotes cell cycle exit and neuronal differentiation in neuro2A cells. Regulation of neuronal differentiation by GPR137 could be vital to constructing neuronal structure during brain development.

Orphan G Protein Coupled Receptors in Affective Disorders

G protein coupled receptors (GPCRs) are the main mediators of signal transduction in the central nervous system. Therefore, it is not surprising that many GPCRs have long been investigated for their role in the development of anxiety and mood disorders, as well as in the mechanism of action of antidepressant therapies. Importantly, the endogenous ligands for a large group of GPCRs have not yet been identified and are therefore known as orphan GPCRs (oGPCRs). Nonetheless, growing evidence from animal studies, together with genome wide association studies (GWAS) and post-mortem transcriptomic analysis in patients, pointed at many oGPCRs as potential pharmacological targets. Among these discoveries, we summarize in this review how emotional behaviors are modulated by the following oGPCRs: ADGRB2 (BAI2), ADGRG1 (GPR56), GPR3, GPR26, GPR37, GPR50, GPR52, GPR61, GPR62, GPR88, GPR135, GPR158, and GPRC5B.

GPR137 is a promising novel bio-marker for the prognosis of bladder cancer patients

OBJECTIVES

G protein-coupled receptor 137 (GPR137) was reported to be associated with several cancers, but its role in bladder cancer has not been reported. The purpose of this study was to evaluate clinical significance of GPR137 in bladder cancer.

METHODS

The expressions of GPR137 in pathological tissues and corresponding normal tissues from bladder cancer patients were detected via quantitative real time polymerase chain reaction (qRT-PCR). Western blot was performed to detect GPR137 expression in bladder cancer tissues and adjacent normal tissues. Chi-Squared test analyzed the relationship between GPR137 expression and clinical features of bladder cancer patients. Additionally, Kaplan-Meier method was adopted in estimating overall survival of bladder cancer patients. Prognostic value of GPR137 was evaluated through Cox regression analysis.

RESULTS

The expression of GPR137 mRNA and protein in pathological tissues was significantly higher than that in adjacent normal tissues (P < .001). Moreover, similar result was found for bladder cancer patients and healthy controls (P < .001). And GPR137 expression was associated with tumor size (P = .006) and TNM stage (P = .012). The results of Kaplan-Meier analysis suggested that patients with high expression of GPR137 had shorter overall survival time than those with low expression (Log rank test, P = .001). Cox regression analysis indicated that GPR137 could act as an independent biomarker for bladder cancer prognosis (HR = 1.850, 95% CI = 1.272-2.689, P = .001).

CONCLUSION

Abnormal expression of GPR137 is associated with bladder cancer and GPR137 is a potential biomarker for the therapy and prognosis of bladder cancer.

Down regulation of G protein-coupled receptor 137 expression inhibits proliferation and promotes apoptosis in leukemia cells

Background

G protein-coupled receptors (GPR) are involved in a wide range of physiological processes, some of which, however, can be hijacked by tumor cells. Over-expression of G protein-coupled receptors 137 (GPR137) are associated with the growth of tumor cells, but under-expression of GPR137 has shown to inhibit cell proliferation in several different types of cancers. Currently, the role of GPR137 in leukemia is still unclear. In this study, the effect of under-expression of GPR137 on inhibiting the proliferation of leukemia cells is explored, to identify a novel target for leukemia treatment.

Materials and methods

In this study, lentivirus-mediated RNA interference (RNAi) was employed to investigate the role of GPR137 in two leukemia cell lines K562 and HL60. The gene expression of GPR137 was analyzed by RT-PCR and its protein expression was determined by Western blot. Flow cytometry and Annexin V/7-AAD Apoptosis Detection Kit was used respectively in cell cycle and apoptosis analysis. The protein expression of CyclinD1, CDK4, BCL-2 and caspase-3 were also determined.

Results

There was high level of constitutive expression of GPR137 in leukemia cancer cell lines K562 and HL60. Lentivirus-mediated RNAi could significantly down-regulate gene and protein expression of GPR137 in both cell lines. Down regulation of GPR137 was associated with the reduction in proliferation rate and colony forming capacity. In addition, down regulation of GPR137 arrested cells in the G0/G1 phase of cell cycle and induced apoptosis in both leukemia cell lines K562 and HL60.

Conclusions

The expression of GPR137 is associated with the proliferation of leukemia cell lines. Down regulation of GPR137 could inhibit proliferation and promote apoptosis in leukemia cells, which makes it a promising bio-marker and therapeutic target to treat patients with leukemia.

The ESRP1-GPR137 axis contributes to intestinal pathogenesis

Aberrant alternative pre-mRNA splicing (AS) events have been associated with several disorders. However, it is unclear whether deregulated AS directly contributes to disease. Here, we reveal a critical role of the AS regulator epithelial splicing regulator protein 1 (ESRP1) for intestinal homeostasis and pathogenesis. In mice, reduced ESRP1 function leads to impaired intestinal barrier integrity, increased susceptibility to colitis and altered colorectal cancer (CRC) development. Mechanistically, these defects are produced in part by modified expression of ESRP1-specific Gpr137 isoforms differently activating the Wnt pathway. In humans, ESRP1 is downregulated in inflamed biopsies from inflammatory bowel disease patients. ESRP1 loss is an adverse prognostic factor in CRC. Furthermore, generation of ESRP1-dependent GPR137 isoforms is altered in CRC and expression of a specific GPR137 isoform predicts CRC patient survival. These findings indicate a central role of ESRP1-regulated AS for intestinal barrier integrity. Alterations in ESRP1 function or expression contribute to intestinal pathology.

An epigenome-wide association analysis of cardiac autonomic responses among a population of welders

DNA methylation is one of the potential epigenetic mechanisms associated with various adverse cardiovascular effects; however, its association with cardiac autonomic dysfunction, in particular, is unknown. In the current study, we aimed to identify epigenetic variants associated with alterations in cardiac autonomic responses. Cardiac autonomic responses were measured with two novel markers: acceleration capacity (AC) and deceleration capacity (DC). We examined DNA methylation levels at more than 472,506 CpG probes through the Illumina Infinium HumanMethylation450 BeadChip assay. We conducted separate linear mixed models to examine associations of DNA methylation levels at each CpG with AC and DC. One CpG (cg26829071) located in the GPR133 gene was negatively associated with DC values after multiple testing corrections through false discovery rate. Our study suggests the potential functional importance of methylation in cardiac autonomic responses. Findings from the current study need to be replicated in future studies in a larger population.

GPR133 (ADGRD1), an adhesion G-protein-coupled receptor, is necessary for glioblastoma growth

Glioblastoma (GBM) is a deadly primary brain malignancy with extensive intratumoral hypoxia. Hypoxic regions of GBM contain stem-like cells and are associated with tumor growth and angiogenesis. The molecular mechanisms that regulate tumor growth in hypoxic conditions are incompletely understood. Here, we use primary human tumor biospecimens and cultures to identify GPR133 (ADGRD1), an orphan member of the adhesion family of G-protein-coupled receptors, as a critical regulator of the response to hypoxia and tumor growth in GBM. GPR133 is selectively expressed in CD133+ GBM stem cells (GSCs) and within the hypoxic areas of PPN in human biospecimens. GPR133 mRNA is transcriptionally upregulated by hypoxia in hypoxia-inducible factor 1α (Hif1α)-dependent manner. Genetic inhibition of GPR133 with short hairpin RNA reduces the prevalence of CD133+ GSCs, tumor cell proliferation and tumorsphere formation in vitro. Forskolin rescues the GPR133 knockdown phenotype, suggesting that GPR133 signaling is mediated by cAMP. Implantation of GBM cells with short hairpin RNA-mediated knockdown of GPR133 in the mouse brain markedly reduces tumor xenograft formation and increases host survival. Analysis of the TCGA data shows that GPR133 expression levels are inversely correlated with patient survival. These findings indicate that GPR133 is an important mediator of the hypoxic response in GBM and has significant protumorigenic functions. We propose that GPR133 represents a novel molecular target in GBM and possibly other malignancies where hypoxia is fundamental to pathogenesis.

The emerging roles of human trace amines and human trace amine-associated receptors (hTAARs) in central nervous system

Human trace amines (TAs) are endogenous compounds, previously almost ignored in human pathology for many reasons (difficulty of their measurement in biological fluids, unknown receptors for elusive amines), are now considered to play a significant role in synaptic transmission within the central nervous system (CNS) acting as neuromodulators. The recent discovery of a novel family of G-protein-coupled receptors (GPCRs) that includes individual members that are highly specific for TAs indicates a potential role for TAs as vertebrate neurotransmitters or neuromodulators, although the majority of these GPCRs so far have not been demonstrated to be activated by TAs. Human trace amine receptors (including TAAR1 TAAR2 TAAR5 TAAR6 TAAR8 TAAR9) are expressed in the brain and play significant physiological and neuropathological roles by activation of trace amines. We herein discuss the recent findings that provide insights into the functional roles of human trace amines (including P-Octopamine, β phenylethylamine, Tryptamine, Tyramine, Synephrine, 3-Iodothyronamine, 3-Methoxytyramine, N-Methyltyramine, N-Methylphenethylamine) in brain. Furthermore, we discuss the known functions of human trace amine receptors in brain.

Knockdown of GPR137,G Protein-coupled receptor 137, Inhibits the Proliferation and Migration of Human Prostate Cancer Cells

GPR137 belongs to the G protein-coupled receptor family involving the regulation of transmembrane signal transduction that launches pivotal cellular functions. However, its function in prostate cancer (PCa) has been rarely reported. It was found in this study that GPR137 was upregulated in PCa tissues as compared with that in paracancerous tissues. To see whether GPR137 could serve as a potential therapeutic target for PCa, GPR137 was knocked down to verify its biological function in PCa cells. Lentivirus-introduced short hairpin RNA (shRNA) was designed to silence GPR137 gene. It was found that silencing of GPR137 gene suppressed the proliferation and colony formation of PCa cell lines PC-3 and DU145. Further study indicated that growth inhibition by GPR137 knockdown was associated with cell cycle arrest at G0/G1 phase. Furthermore, silencing of GPR137 repressed the invasion and migration abilities of PC-3 cells via downregulating slug and snail and upregulating E-cadherin. Collectively, these findings imply that GPR137 plays an important role in the occurrence and progression of PCa and may prove to be a potential therapeutic target for the treatment of advanced PCa.

G-protein-coupled receptor 137 accelerates proliferation of urinary bladder cancer cells in vitro

Urinary bladder cancer is a worldwide concern because of its level of incidence and recurrence. To search an effective therapeutic strategy for urinary bladder cancer, it is important to identify proteins involved in tumorigenesis that could serve as potential targets for diagnosis and treatment. G-protein-coupled receptors (GPRs) constitute a large protein family of receptors that sense molecules outside the cell and activate signal transduction pathways and cellular responses inside the cell. GPR137 is a newly discovered human gene encoding orphan GPRs. In this study, we aimed to investigate the physiological role of GPR137 in urinary bladder cancer. The effect of GPR137 on cell growth was examined via an RNA interference (RNAi) lentivirus system in two human urinary bladder cancer cell lines BT5637 and T24. Lentivirus-mediated RNAi could specifically suppressed GPR137 expression in vitro, resulting in alleviated cell viability and impaired colony formation, as well as blocks G0/G1 and S phases of the cell cycle. These results suggested GPR137 as an essential player in urinary bladder cancer cell growth, and it may serve as a potential target for gene therapy in the treatment of urinary bladder cancer.

Inhibition of GPR137 suppresses proliferation of medulloblastoma cells in vitro

Medulloblastoma is the most common malignant pediatric brain tumor in children. GPR137 is a ubiquitously expressed gene in the central nervous system. It has been reported that GPR137 modulates malignant proliferation of glioma cells. However, the relationship between GPR137 and medulloblastoma is still unknown. In this study, we knocked down GPR137 in the medulloblastoma cell line Daoy via a lentivirus-based RNA interference system to explore its role in medulloblastoma. Functional analyses showed that cell proliferation and colony formation were obviously restrained in Daoy cells after GPR137 knockdown. Furthermore, knockdown of GPR137 in Daoy cells led to a significant increase in cell percentage in the G0/G1 phase but a decrease in the S phase. Additionally, the cell population in the sub-G1 phase, which represents apoptotic cells, was remarkably increased in GPR137 knockdown cells. GPR137 inhibition induced a strong proapoptotic effect in Daoy cells, as confirmed by annexin V-APC/7-AAD double staining. In conclusion, GPR137 knockdown inhibited growth of Daoy medulloblastoma cells via disturbing cell cycle progression and inducing apoptosis. Our investigation suggested that GPR137 could be a potential oncogene in medulloblastoma cells and might serve as a target for the treatment of medulloblastoma.

Knockdown of GPR137 by RNAi inhibits pancreatic cancer cell growth and induces apoptosis

G-protein-coupled receptors (GPCRs), the largest family of cell-surface molecules involved in a number of biological and pathological processes, have recently emerged as key players in carcinogenesis and cancer progression. Orphan G protein-coupled receptors (oGPCRs) are a group of proteins lacking endogenous ligands. GPR137, one of the novel oGPCR genes, was discovered by homology screening. However, the biological role of GPR137 in cancers has not yet been discussed and is of great therapeutic interest. In this study, we knocked down GPR137 via a lentivirus system in two human pancreatic cancer cell lines BXPC-3 and PANC-1. Knockdown of GPR137 strongly inhibited cell proliferation and colony formation. Flow cytometry showed that cell cycle was arrested in the sub-G1 phase and apoptotic cells were significantly increased after GPR137 knockdown. Western blotting confirmed that GPR137 silencing induced apoptosis due to cleavage of PARP (poly ADP-ribose polymerase) and upregulation of caspase 3. Furthermore, lentivirus-mediated overexpression of GPR137 promoted the proliferation of PANC-1 cells, suggesting GPR137 as a potential oncogene in pancreatic cancer cells. Taken together, our results prove the importance of GPR137 as a crucial regulator in controlling cancer cell growth and apoptosis.

Identification and SAR of Glycine Benzamides as Potent Agonists for the GPR139 Receptor

A focused high throughput screening for GPR139 was completed for a select 100K compounds, and new agonist leads were identified. Subsequent analysis and structure-activity relationship studies identified (S)-3-chloro-N-(2-oxo-2-((1-phenylethyl)amino)ethyl)benzamide 7c as a potent and selective agonist of hGPR139 with an EC50 = 16 nM. The compound was found to cross the blood-brain barrier and have good drug-like properties amenable for oral dosing in rat.

High-throughput screening of antagonists for the orphan G-protein coupled receptor GPR139

AIM

To discover antagonists of the orphan G-protein coupled receptor GPR139 through high-throughput screening of a collection of diverse small molecules.

METHODS

Calcium mobilization assays were used to identify initial hits and for subsequent confirmation studies.

RESULTS

Five small molecule antagonists, representing 4 different scaffolds, were identified following high-throughput screening of 16 000 synthetic compounds.

CONCLUSION

The findings provide important tools for further study of this orphan G-protein coupled receptor.

Inverse agonistic action of 3-iodothyronamine at the human trace amine-associated receptor 5

OBJECTIVE

Application of 3-iodothyronamine (3-T1AM) results in decreased body temperature and body weight in rodents. The trace amine-associated receptor (TAAR) 1, a family A G protein-coupled receptor, is a target of 3-T1AM. However, 3-T1AM effects still persist in mTaar1 knockout mice, which suggest so far unknown further receptor targets that are of physiological relevance. TAAR5 is a highly conserved TAAR subtype among mammals and we here tested TAAR5 as a potential 3-T1AM target. First, we investigated mouse Taar5 (mTaar5) expression in several brain regions of the mouse in comparison to mTaar1. Secondly, to unravel the full spectrum of signaling capacities, we examined the distinct Gs-, Gi/o-, G12/13-, Gq/11- and MAP kinase-mediated signaling pathways of mouse and human TAAR5 under ligand-independent conditions and after application of 3-T1AM. We found overlapping localization of mTaar1 and mTaar5 in the amygdala and ventromedial hypothalamus of the mouse brain. Second, the murine and human TAAR5 (hTAAR5) display significant basal activity in the Gq/11 pathway but show differences in the basal activity in Gs and MAP kinase signaling. In contrast to mTaar5, 3-T1AM application at hTAAR5 resulted in significant reduction in basal IP3 formation and MAP kinase signaling. In conclusion, our data suggest that the human TAAR5 is a target for 3-T1AM, exhibiting inhibitory effects on IP3 formation and MAP kinase signaling pathways, but does not mediate Gs signaling effects as observed for TAAR1. This study also indicates differences between TAAR5 orthologs with respect to their signaling profile. In consequence, 3-T1AM-mediated effects may differ between rodents and humans.

Down-regulation of G protein-coupled receptor 137 by RNA interference inhibits cell growth of two hepatoma cell lines

G protein-coupled receptors (GPCRs) are important signal transduction mediators and pharmacological therapeutic targets. G protein-coupled receptor 137 (GPR137) was initially reported as a novel orphan GPCR around 10 years ago. Some orphan GPCRs have been implicated in cancer cell proliferation and migration. The aim of this study is to investigate the role of GPR137 in hepatocellular carcinoma (HCC). GPR137 is widely expressed in several human HCC cell lines, as determined by real-time PCR. We then applied lentivirus mediated RNA interference (RNAi) to knock down GPR137 expression in two HCC cell lines HepG2 and Bel7404. Depletion of GPR137 remarkably inhibited cell proliferation and colony formation capacity. Knockdown of GPR137 in HepG2 cells led to cell cycle arrest at G0/G1 phase and G2/M phase, and induced cell apoptosis, as determined by flow cytometry analysis, which contributed to cell growth inhibition. Our findings suggested that GPR137 could facilitate HCC cell proliferation and thus promote hepatocarcinogenesis.

RNA interference-mediated silencing of G protein-coupled receptor 137 inhibits human gastric cancer cell growth

G protein-coupled receptor 137 (GPR137) is an integral membrane protein, which belongs to the GPR137 family of cell surface mediators of signal transduction. GPF137 was recently identified; however, its role in human disease onset has remained to be elucidated. GPR137 is highly expressed in multiple human gastric cancer cell lines. A GPR137 short hairpin RNA (shRNA)-expressing vector was transfected into AGS and MGC80-3 gastric cancer cells, and the subsequent depletion of GPR137 resulted in a significant reduction in cell proliferation and colony formation, as determined by MTT and colony formation assays. In addition, cell cycle analysis indicated that GPR137 knockdown arrested MGC80-3 cells in G₂/M phase. To the best of our knowledge, the present study was the first to investigate the role of GPR137 in gastric tumorigenesis and revealed that knockdown of GPR137 by lentivirus-mediated shRNA transfection inhibited the growth of gastric cancer cells in vitro. These results indicated that GPR137 may present a novel target for the development of pharmacological therapeutics for human gastric cancer.

Analysis of human TAAR8 and murine Taar8b mediated signaling pathways and expression profile

The thyroid hormone derivative 3-iodothyronamine (3-T₁AM) exerts metabolic effects in vivo that contradict known effects of thyroid hormones. 3-T₁AM acts as a trace amine-associated receptor 1 (TAAR1) agonist and activates G_s signaling in vitro. Interestingly, 3-T₁AM-meditated in vivo effects persist in Taar1 knockout-mice indicating that further targets of 3-T₁AM might exist. Here, we investigated another member of the TAAR family, the only scarcely studied mouse and human trace-amine-associated receptor 8 (Taar8b, TAAR8). By RT-qPCR and locked-nucleic-acid (LNA) in situ hybridization, Taar8b expression in different mouse tissues was analyzed. Functionally, we characterized TAAR8 and Taar8b with regard to cell surface expression and signaling via different G-protein-mediated pathways. Cell surface expression was verified by ELISA, and cAMP accumulation was quantified by AlphaScreen for detection of G_s and/or G_i/o signaling. Activation of G-proteins G_q/11 and G_12/13 was analyzed by reporter gene assays. Expression analyses revealed at most marginal Taar8b expression and no gender differences for almost all analyzed tissues. In heart, LNA-in situ hybridization demonstrated the absence of Taar8b expression. We could not identify 3-T₁AM as a ligand for TAAR8 and Taar8b, but both receptors were characterized by a basal G_i/o signaling activity, a so far unknown signaling pathway for TAARs.

Down-regulation of GPR137 expression inhibits proliferation of colon cancer cells

G protein-coupled receptors (GPRs) are highly related to oncogenesis and cancer metastasis. G protein-coupled receptor 137 (GPR137) was initially reported as a novel orphan GPR about 10 years ago. Some orphan GPRs have been implicated in human cancers. The aim of this study is to investigate the role of GPR137 in human colon cancer. Expression levels of GRP137 were analyzed in different colon cancer cell lines by quantitative polymerase chain reaction and western blot analysis. Lentivirus-mediated short hairpin RNA was specifically designed to knock down GPR137 expression in colon cancer cells. Cell viability was measured by methylthiazoletetrazolium and colony formation assays. In addition, cell cycle characteristic was investigated by flow cytometry. GRP137 expression was observed in all seven colon cancer cell lines at different levels. The mRNA and protein levels of GPR137 were down-regulated in both HCT116 and RKO cells after lentivirus infection. Lentivirus-mediated silencing of GPR137 reduced the proliferation rate and colonies numbers. Knockdown of GPR137 in both cell lines led to cell cycle arrest in the G0/G1 phase. These results indicated that GPR137 plays an important role in colon cancer cell proliferation. A better understanding of GPR137's effects on signal transduction pathways in colon cancer cells may provide insights into the novel gene therapy of colon cancer.

Inhibition of GPR137 expression reduces the proliferation and colony formation of malignant glioma cells

GPR137 are ubiquitously expressed in the central nervous system. However, the role o f GPR137 in human malignant glioma is still poorly known. In the present study, we firstly detected the expression of GPR137 in 29 human glioma tissue specimens by immunohistochemistry and in 5 malignant glioma cell lines by quantitative RT-PCR. The expression of GPR137 was much stronger in high-grade gliomas than in low-grade gliomas. Lentivirus-mediated small interfering RNAs (siRNAs) were employed to knock down GPR137 expression in glioma cells. Inhibition of GPR137 expression by RNAi significantly inhibited the proliferation and colony-forming capacity of U251, A172 and U373 cells. Moreover, flow cytometry analysis showed that knockdown of GPR137 led to the cell-cycle arrest at the S phase. Our results indicated that GPR137 is involved in the progression of human glioma, suggesting GPR137 as a potential oncogene of glioma cells.

Profiling of olfactory receptor gene expression in whole human olfactory mucosa

Olfactory perception is mediated by a large array of olfactory receptor genes. The human genome contains 851 olfactory receptor gene loci. More than 50% of the loci are annotated as nonfunctional due to frame-disrupting mutations. Furthermore haplotypic missense alleles can be nonfunctional resulting from substitution of key amino acids governing protein folding or interactions with signal transduction components. Beyond their role in odor recognition, functional olfactory receptors are also required for a proper targeting of olfactory neuron axons to their corresponding glomeruli in the olfactory bulb. Therefore, we anticipate that profiling of olfactory receptor gene expression in whole human olfactory mucosa and analysis in the human population of their expression should provide an opportunity to select the frequently expressed and potentially functional olfactory receptors in view of a systematic deorphanization. To address this issue, we designed a TaqMan Low Density Array (Applied Biosystems), containing probes for 356 predicted human olfactory receptor loci to investigate their expression in whole human olfactory mucosa tissues from 26 individuals (13 women, 13 men; aged from 39 to 81 years, with an average of 67±11 years for women and 63±12 years for men). Total RNA isolation, DNase treatment, RNA integrity evaluation and reverse transcription were performed for these 26 samples. Then 384 targeted genes (including endogenous control genes and reference genes specifically expressed in olfactory epithelium for normalization purpose) were analyzed using the same real-time reverse transcription PCR platform. On average, the expression of 273 human olfactory receptor genes was observed in the 26 selected whole human olfactory mucosa analyzed, of which 90 were expressed in all 26 individuals. Most of the olfactory receptors deorphanized to date on the basis of sensitivity to known odorant molecules, which are described in the literature, were found in the expressed olfactory receptors gene set.

Olfactory receptor 51E1 as a novel target for diagnosis in somatostatin receptor-negative lung carcinoids

Somatostatin receptors (SSTRs) may be used in lung carcinoids (LCs) for diagnosis and therapy, although additional targets are clearly warranted. This study aimed to investigate whether olfactory receptor 51E1 (OR51E1) may be a potential target for LCs. OR51E1 coding sequence was analyzed in LC cell lines, NCI-H727 and NCI-H720. OR51E1 transcript expression was investigated in LC cell lines and frozen specimens by quantitative real-time PCR. OR51E1, SSTR2, SSTR3, and SSTR5 expression was evaluated by immunohistochemistry on paraffin-embedded sections of 73 typical carcinoids (TCs), 14 atypical carcinoids (ACs), and 11 regional/distant metastases and compared with OctreoScan data. Immunohistochemistry results were rendered semiquantitatively on a scale from 0 to 3, taking into account the cellular compartmentalization (membrane vs cytoplasm) and the percentage of tumor cells (<50 vs >50%). Our results showed that WT OR51E1 transcript was expressed in both LC cell lines. OR51E1 mRNA was expressed in 9 out of 12 TCs and 7 out of 9 ACs (P=NS). Immunohistochemically, OR51E1, SSTR2, SSTR3, and SSTR5 were detected in 85, 71, 25, and 39% of TCs and in 86, 79, 43, and 36% of ACs respectively. OR51E1 immunohistochemical scores were higher or equal than those of SSTRs' in 79% of TCs and 86% of ACs. Furthermore, in the LC cases where all SSTR subtypes were lacking, membrane OR51E1 expression was detected in 10 out of 17 TCs and 1 out of 2 ACs. Moreover, higher OR51E1 immunohistochemical scores were detected in 5 out of 6 OctreoScan-negative LC lesions. Therefore, the high expression of OR51E1 in LCs makes it a potential novel diagnostic target in SSTR-negative tumors.

Olfactory receptor 51E1 protein as a potential novel tissue biomarker for small intestine neuroendocrine carcinomas

OBJECTIVE

Late diagnosis hinders proper management of small intestine neuroendocrine carcinoma (SI-NEC) patients. The olfactory receptor, family 51, subfamily E, member 1 (OR51E1) has been reported as a potential novel SI-NEC marker, without protein expression recognition. Thus, we further studied whether the encoded protein may be a novel SI-NEC clinical biomarker.

DESIGN

OR51E1 coding sequence was cloned using total RNA from SI-NEC patient specimens. Quantitative real-time PCR analysis explored OR51E1 expression in laser capture microdissected SI-NEC cells and adjacent microenvironment cells. Moreover, immunohistochemistry investigated OR51E1 protein expression on operation and biopsy material from primary SI-NECs, mesentery, and liver metastases from 70 patients. Furthermore, double immunofluorescence studies explored the potential co-localization of the vesicular monoamine transporter 1 (SLC18A1, generally referred to as VMAT1) and OR51E1 in the neoplastic cells and in the intestinal mucosa adjacent to the tumor.

RESULTS

OR51E1 coding sequence analysis showed absence of mutation in SI-NEC patients at different stages of disease. OR51E1 expression was higher in microdissected SI-NEC cells than in the adjacent microenvironment cells. Furthermore, both membranous and cytoplasmic OR51E1 immunostaining patterns were detected in both primary SI-NECs and metastases. Briefly, 18/43 primary tumors, 7/28 mesentery metastases, and 6/18 liver metastases were 'positive' for OR51E1 in more than 50% of the tumor cells. In addition, co-localization studies showed that OR51E1 was expressed in >50% of the VMAT1 immunoreactive tumor cells and of the enterochromaffin cells in the intestinal mucosa adjacent to the tumor.

CONCLUSION

OR51E1 protein is a potential novel clinical tissue biomarker for SI-NECs. Moreover, we suggest its potential therapeutic molecular target development using solid tumor radioimmunotherapy.

An association and haplotype analysis of porcine maternal infanticide: a model for human puerperal psychosis?

An association analysis using the Illumina porcine SNP60 beadchip was performed to identify SNPs significantly associated with porcine maternal infanticide. We previously hypothesised that this was a good animal model for human puerperal psychosis, an extreme form of postnatal mood disorder. Animals were selected from carefully phenotyped unrelated infanticide and control groups (representing extremes of the phenotypic spectrum), from four different lines. Permutation and sliding window analyses and an analysis to see which haplotypes were in linkage disequilibrium (LD) were compared to identify concordant regions. Across all analyses, intervals on SSCs 1, 3, 4, 10, and 13 were constant, contained genes associated with psychiatric or neurological disorders and were significant in multiple lines. The strongest (near GWS) consistent candidate region across all analyses and all breeds was the one located on SSC3 with one peak at 23.4 Mb, syntenic to a candidate region for bipolar disorder and another at 31.9 Mb, syntenic to a candidate region for human puerperal psychosis (16p13). From the haplotype/LD analysis, two regions reached genome wide significance (GWS): the first on SSC4 (KHDRBS3 to FAM135B), which was significant (-logP 5.57) in one Duroc based breed and is syntenic to a region in humans associated with cognition and neurotism; the second on SSC15, which was significant (-log10P 5.68) in two breeds and contained PAX3, which is expressed in the brain.

Differential modulation of Beta-adrenergic receptor signaling by trace amine-associated receptor 1 agonists

Trace amine-associated receptors (TAAR) are rhodopsin-like G-protein-coupled receptors (GPCR). TAAR are involved in modulation of neuronal, cardiac and vascular functions and they are potentially linked with neurological disorders like schizophrenia and Parkinson's disease. Subtype TAAR1, the best characterized TAAR so far, is promiscuous for a wide set of ligands and is activated by trace amines tyramine (TYR), phenylethylamine (PEA), octopamine (OA), but also by thyronamines, dopamine, and psycho-active drugs. Unfortunately, effects of trace amines on signaling of the two homologous β-adrenergic receptors 1 (ADRB1) and 2 (ADRB2) have not been clarified yet in detail. We, therefore, tested TAAR1 agonists TYR, PEA and OA regarding their effects on ADRB1/2 signaling by co-stimulation studies. Surprisingly, trace amines TYR and PEA are partial allosteric antagonists at ADRB1/2, whereas OA is a partial orthosteric ADRB2-antagonist and ADRB1-agonist. To specify molecular reasons for TAAR1 ligand promiscuity and for observed differences in signaling effects on particular aminergic receptors we compared TAAR, tyramine (TAR) octopamine (OAR), ADRB1/2 and dopamine receptors at the structural level. We found especially for TAAR1 that the remarkable ligand promiscuity is likely based on high amino acid similarity in the ligand-binding region compared with further aminergic receptors. On the other hand few TAAR specific properties in the ligand-binding site might determine differences in ligand-induced effects compared to ADRB1/2. Taken together, this study points to molecular details of TAAR1-ligand promiscuity and identified specific trace amines as allosteric or orthosteric ligands of particular β-adrenergic receptor subtypes.

Cell adhesion receptor GPR133 couples to Gs protein

Adhesion G protein-coupled receptors (GPCR), with their very large and complex N termini, are thought to participate in cell-cell and cell-matrix interactions and appear to be highly relevant in several developmental processes. Their intracellular signaling is still poorly understood. Here we demonstrate that GPR133, a member of the adhesion GPCR subfamily, activates the G(s) protein/adenylyl cyclase pathway. The presence of the N terminus and the cleavage at the GPCR proteolysis site are not required for G protein signaling. G(s) protein coupling was verified by Gα(s) knockdown with siRNA, overexpression of Gα(s), co-expression of the chimeric Gq(s4) protein that routes GPR133 activity to the phospholipase C/inositol phosphate pathway, and missense mutation within the transmembrane domain that abolished receptor activity without changing cell surface expression. It is likely that not only GPR133 but also other adhesion GPCR signal via classical receptor/G protein-interaction.

Focus on the splicing of secretin GPCRs transmembrane-domain 7

The family of G-protein coupled receptors (GPCRs) is one of the largest protein families in the mammalian genome with a fundamental role in cell biology. GPCR activity is finely tuned by various transcriptional, post-transcriptional and post-translational mechanisms. Alternative pre-mRNA splicing is now emerging as a crucial process regulating GPCR biological function. Intriguingly, this mechanism appears to extensively target the Secretin family of GPCRs, especially the exon that encodes a 14 amino acid sequence that forms the distal part of 7th transmembrane helix, and exhibits an unusually high level of sequence conservation among most Secretin GPCRs. Do the "TMD7-short" receptor variants have a role as novel regulators of GPCR signallng and, if so, what are the implications for hormonal actions and physiology?

A genome-wide association scan of RR and QT interval duration in 3 European genetically isolated populations: the EUROSPAN project

BACKGROUND

We set out to identify common genetic determinants of the length of the RR and QT intervals in 2325 individuals from isolated European populations.

METHODS AND RESULTS

We analyzed the heart rate at rest, measured as the RR interval, and the length of the corrected QT interval for association with 318 237 single-nucleotide polymorphisms. The RR interval was associated with common variants within GPR133, a G-protein-coupled receptor (rs885389, P=3.9 x 10(-8)). The QT interval was associated with the earlier reported NOS1AP gene (rs2880058, P=2.00 x 10(-10)) and with a region on chromosome 13 (rs2478333, P=4.34 x 10(-8)), which is 100 kb from the closest known transcript LOC730174 and has previously not been associated with the length of the QT interval.

CONCLUSIONS

Our results suggested an association between the RR interval and GPR133 and confirmed an association between the QT interval and NOS1AP.

Expression patterns of the opsin 5-related genes in the developing chicken retina

The opsin gene family encodes G protein-coupled seven-transmembrane proteins that bind to a retinaldehyde chromophore for photoreception. It has been reported that opsin 5 is expressed in mammalian neural tissue, but its function has been elusive. As a first step to understand the function for opsin 5 in the developing eye, we searched for chicken opsin 5-related genes in the genome by a bioinformatic approach and isolated opsin 5 cDNA fragments from the embryonic retina by RT-PCR. We found that there are three opsin 5-related genes, designated cOpn5m (chicken opsin 5, mammalian type), cOpn5L1 (chicken opsin 5-like 1), and cOpn5L2 (chicken opsin 5-like 2), in the chicken genome. Quantitative PCR analysis has revealed that cOpn5m is the most abundant in the developing and early posthatching neural retina. In situ hybridization analysis has shown that cOpn5m is specifically expressed in subsets of differentiating ganglion cells and amacrine cells. These results suggest that the mammalian type opsin 5 may contribute to the development of these retinal cells in the chicken.

Analysis of the goldfish Carassius auratus olfactory epithelium transcriptome reveals the presence of numerous non-olfactory GPCR and putative receptors for progestin pheromones

Background

The goldfish (Carassius auratus) uses steroids and prostaglandins as pheromone cues at different stages of the reproductive cycle to facilitate spawning synchronization. Steroid progestin pheromone binding has been detected in goldfish olfactory membranes but the receptors responsible for this specific binding remain unknown. In order to shed some light on the olfactory epithelium transcriptome and search for possible receptor candidates a large set of EST from this tissue were analysed and compared to and combined with a similar zebrafish (Danio rerio) resource.

Results

We generated 4,797 high quality sequences from a normalized cDNA library of the goldfish olfactory epithelium, which were clustered in 3,879 unique sequences, grouped in 668 contigs and 3,211 singletons. BLASTX searches produced 3,243 significant (E-value < e^-10) hits and Gene Ontology (GO) analysis annotated a further 1,223 of these genes (37.7%). Comparative analysis with zebrafish olfactory epithelium ESTs revealed 1,088 identical unigenes. The transcriptome size of both species was estimated at about 16,400 unigenes, based on the proportion of genes identified involved in Glucose Metabolic Process. Of 124 G-protein coupled receptors identified in the olfactory epithelium of both species, 56 were olfactory receptors. Beta and gamma membrane progestin receptors were also isolated by subcloning of RT-PCR products from both species and an olfactory epithelium specific splice form identified.

Conclusion

The high similarity between the goldfish and zebrafish olfactory systems allowed the creation of a 'cyprinid' olfactory epithelium library estimated to represent circa 70% of the transcriptome. These results are an important resource for the identification of components of signalling pathways involved in olfaction as well as putative targets for pharmacological and histochemical studies. The possible function of the receptors identified in the olfactory system is described. Moreover, the role of olfactory epithelium specific isoforms of classical membrane progestin receptor genes as candidates for preovulatory pheromone sensing is discussed.

Adhesion-GPCRs: emerging roles for novel receptors

The G protein-coupled receptor (GPCR) family comprises the largest class of cell surface receptors found in metazoan proteomes. Within the novel GPCR subfamily of adhesion-GPCRs, approximately 150 distinct orthologues, from invertebrates to mammals, have been identified to date. All members of this family contain a large extracellular region, often containing common protein modules, coupled to a seven-transmembrane domain via a stalk region that seems to be crucial for functionality. Owing to their unique structure, restricted expression profile and involvement in several human diseases, adhesion-GPCRs have long been proposed to have vital dual roles in cellular adhesion and signalling. More recent studies have provided structural, evolutionary, developmental and immunological insights in relation to the adhesion-GPCR family.

De novo and complex imbalanced chromosomal rearrangements revealed by array CGH in a patient with an abnormal phenotype and apparently "balanced" paracentric inversion of 14(q21q23)

Paracentric inversions are one of the common chromosomal rearrangements typically associated with a normal phenotype. However, if dosage-sensitive genes are disrupted by the breakpoints, an abnormal phenotype could result. Detection of paracentric inversions often relies on careful high resolution banding, which has limited sensitivity. We report here cytogenetic studies performed on a 4-year-old female patient with global developmental delay, hypotonia, and dysmorphic features. The initial cytogenetic evaluation by G-banding revealed a de novo inversion of chromosome 14. Subsequent array CGH analysis using both a targeted BAC array and a high-resolution oligonucleotide array revealed microdeletions at the breakpoints of 14q21.1 (0.8 Mb) and 14q23.1 (0.9 Mb). Unexpectedly, a microdeletion in the region of 16q23.1 (1.3 Mb) was also identified, which overlaps with the common fragile site FRA16D. Parental chromosome and FISH analyses were normal, supporting the conclusion that these microdeletions were de novo in the patient and likely contributed to her abnormal phenotype. The case report presented illustrates the value of using high-resolution microarray analysis for phenotypically abnormal individuals with apparently balanced chromosomal rearrangements, including inversions.

Prostate--specific G protein couple receptor genes and STAG1/PMEPA1 in peripheral blood from patients with prostatic cancer

We investigated whether prostate - specific G protein couple receptor genes and STAG1/PMEPA1 gene expression in peripheral- blood could be useful as a diagnostic or prognostic marker of prostate cancer. Circulating cells were identified by reverse transcription-polymerase chain reaction (RT-PCR) to detect PSGR and STAG1/PMEPA1 mRNA in peripheral blood (PB) from 11 patients with treated prostate cancer (CaP), 11 with newly-diagnosed untreated CaP and 20 with benign prostatic hyperplasia (BPH) (controls). RT-PCR amplified PSGR in 8 of 11 untreated and in 9 of 11 treated patients with CaP and in 16 of 20 with BPH; whereas it amplified PMEPA1 in 1 of 11 untreated and in 7 of 11 treated patients with CaP and in 4 of 20 with BPH. In our control tissues and cell lines nearly all the prostatic and non- prostatic tissues and cell lines expressed PSGR mRNA, whereas only one prostatic neoplastic tissue and the androgen-responsive (LNCaP) and androgen non-responsive (PC3) prostatic cell lines expressed PMEPA1. These findings suggest that the investigated genes are poorly specific and probably of little use as diagnostic or prognostic markers in peripheral blood for monitoring prostate cancer progression and recurrence.

Quantitative expression profile of PSGR in prostate cancer

PSGR is a novel member of the G-protein-coupled olfactory receptor family. Our initial report showed predominant expression of the PSGR in human prostate gland and significant alterations of PSGR expression in primary prostate cancer (CaP) specimens. The aim of this study was to provide in-depth evaluations of the expression profile of PSGR in prostatic epithelial cells of CaP patients and to evaluate the association of PSGR expression characteristics with clinico-pathologic features. In total, 220 RNA specimens, from laser capture microdissected paired benign and malignant prostatic epithelial cells of 110 CaP patients, were analyzed for PSGR expression by quantitative real-time PCR. The differential expression of PSGR between the prostatic epithelial cells of malignant and benign glands was statistically significant (P<0.0001). Comparison of PSGR expression between paired benign and tumor cells revealed prostate tumor cell-specific overexpression in 67.2% of tumor specimens (74 of 110), decreased expression in 20.9% of tumor specimens (23 of 110) and no difference of PSGR expression between tumor and normal cells in 11.8% of specimens (13 of 110). In representative cases, PSGR expression patterns were independently confirmed by in situ RNA hybridization. The PSGR overexpression associated with higher percentage of pathologic stage, pT3, and a higher level of preoperative serum PSA. CaP cells of African-American CaP patients exhibited about two-fold increase of PSGR expression in comparison to the Caucasian American CaP patients. Strikingly high-percentage CaP cells overexpress PSGR warrants further studies of PSGR expression alterations to define subsets of CaPs.

Regulation of human prostate-specific G-protein coupled receptor, PSGR, by two distinct promoters and growth factors

PSGR is a newly identified human prostate tissue-specific gene belonging to the G-protein coupled receptor (GPCR) family. Overexpression of PSGR is associated with human prostate intraepithelial neoplasia (PIN) and prostate tumors, suggesting PSGR may play an important role in early prostate cancer development and progression. To understand the regulation of tissue-specific expression of human PSGR and its upregulation mechanism in prostate cancers, we characterized the promoter region of PSGR and analyzed the control mechanism for PSGR expression in human prostate tissues/cells. In this report, we demonstrate that two distinct promoters control the transcriptional regulation of PSGR in human prostate cells. The first promoter region includes exon 1 and a TATA box at -31 site. The minimal DNA sequence with promoter activity is about 123 bp upstream of exon 1. Exon 1 contains tissue specific regulatory activity for the first promoter of PSGR gene. The second promoter is located in the upstream region of exon 2, which is a TATA-less and non-GC-rich promoter. Primer extension and RNA protection assays (RPA) revealed that the transcription driven by the second promoter is initiated at the junction of intron and exon 2 within a cluster of nucleotides located about 250 bp upstream from the junction. Both promoters show prostate cell-specific characteristics in our luciferase assays in transfected cells. Furthermore, we investigated the regulation of the promoter activities of the PSGR gene by different growth factors and cytokines, and demonstrated that interleukin-6 (IL-6) activates the promoter activities of PSGR in human prostate cancer cells. These data suggest that two functional promoters regulate the transcriptional expression of PSGR in human prostate tissues and PSGR is a new target for IL-6 transcriptional regulation.

PSGR2, a novel G-protein coupled receptor, is overexpressed in human prostate cancer

The G-protein coupled receptors (GPCRs) recognize a large variety of extracellular molecules (such as hormones, neurotransmitters, growth and developmental factors) and several sensory messages (such as light, odors and pain). GPCRs and their signal transduction pathway represent important specific targets for a variety of human diseases. To investigate the potential roles of GPCRs in human normal prostate and prostate cancers, we identified and characterized a novel human G-protein coupled receptor, PSGR2, which is highly overexpressed in human prostate cancers. Although PSGR2 shares sequence homology with human olfactory G-protein coupled receptors, the expression of PSGR2 is highly restricted to human prostate tissue, and no expression was detected in 22 normal and 10 tumor tissues examined using Northern blot and PCR analysis. Furthermore, we investigated the expression levels of PSGR2 in 133 human prostate samples with real-time quantitative reverse transcription-PCR and in situ hybridization method. We demonstrated that PSGR2 expression increased significantly in human high grade prostate intraepithelial neoplasia (PIN) and prostate cancers (approximately 10-fold) as compared to normal and BPH (benign prostatic hyperplasia) tissues (p < 0.001), suggesting PSGR2 may play an important role in human prostate cancer development and progression. Together, our results suggest that PSGR2 is a novel prostate specific G-protein coupled receptor and may be useful as a tissue marker and molecular target for the early detection and treatment of human prostate cancers.