Novel human G protein-coupled receptors with long N-terminals containing GPS domains and Ser/Thr-rich regions

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

The adhesion GPCR GPR116/ADGRF5 has a dual function in pancreatic islets regulating somatostatin release and islet development

Glucose homeostasis is maintained by hormones secreted from different cell types of the pancreatic islets and controlled by manifold input including signals mediated through G protein-coupled receptors (GPCRs). RNA-seq analyses revealed expression of numerous GPCRs in mouse and human pancreatic islets, among them Gpr116/Adgrf5. GPR116 is an adhesion GPCR mainly found in lung and required for surfactant secretion. Here, we demonstrate that GPR116 is involved in the somatostatin release from pancreatic delta cells using a whole-body as well as a cell-specific knock-out mouse model. Interestingly, the whole-body GPR116 deficiency causes further changes such as decreased beta-cell mass, lower number of small islets, and reduced pancreatic insulin content. Glucose homeostasis in global GPR116-deficient mice is maintained by counter-acting mechanisms modulating insulin degradation. Our data highlight an important function of GPR116 in controlling glucose homeostasis.

The dimerized pentraxin-like domain of the adhesion G protein-coupled receptor 112 (ADGRG4) suggests function in sensing mechanical forces

Adhesion G protein-coupled receptors (aGPCRs) feature large extracellular regions with modular domains that often resemble protein classes of various function. The pentraxin (PTX) domain, which is predicted by sequence homology within the extracellular region of four different aGPCR members, is well known to form pentamers and other oligomers. Oligomerization of GPCRs is frequently reported and mainly driven by interactions of the seven-transmembrane region and N or C termini. While the functional importance of dimers is well-established for some class C GPCRs, relatively little is known about aGPCR multimerization. Here, we showcase the example of ADGRG4, an orphan aGPCR that possesses a PTX-like domain at its very N-terminal tip, followed by an extremely long stalk containing serine-threonine repeats. Using X-ray crystallography and biophysical methods, we determined the structure of this unusual PTX-like domain and provide experimental evidence for a homodimer equilibrium of this domain which is Ca2+-independent and driven by intermolecular contacts that differ vastly from the known soluble PTXs. The formation of this dimer seems to be conserved in mammalian ADGRG4 indicating functional relevance. Our data alongside of theoretical considerations lead to the hypothesis that ADGRG4 acts as an in vivo sensor for shear forces in enterochromaffin and Paneth cells of the small intestine.

Amelioration of non-alcoholic fatty liver disease by targeting adhesion G protein-coupled receptor F1 (Adgrf1)

Background

Recent research has shown that the adhesion G protein-coupled receptor F1 (Adgrf1; also known as GPR110; PGR19; KPG_012; hGPCR36) is an oncogene. The evidence is mainly based on high expression of Adgrf1 in numerous cancer types, and knockdown Adgrf1 can reduce the cell migration, invasion, and proliferation. Adgrf1 is, however, mostly expressed in the liver of healthy individuals. The function of Adgrf1 in liver has not been revealed. Interestingly, expression level of hepatic Adgrf1 is dramatically decreased in obese subjects. Here, the research examined whether Adgrf1 has a role in liver metabolism.

Methods

We used recombinant adeno-associated virus-mediated gene delivery system, and antisense oligonucleotide was used to manipulate the hepatic Adgrf1 expression level in diet-induced obese mice to investigate the role of Adgrf1 in hepatic steatosis. The clinical relevance was examined using transcriptome profiling and archived biopsy specimens of liver tissues from non-alcoholic fatty liver disease (NAFLD) patients with different degree of fatty liver.

Results

The expression of Adgrf1 in the liver was directly correlated to fat content in the livers of both obese mice and NAFLD patients. Stearoyl-coA desaturase 1 (Scd1), a crucial enzyme in hepatic de novo lipogenesis, was identified as a downstream target of Adgrf1 by RNA-sequencing analysis. Treatment with the liver-specific Scd1 inhibitor MK8245 and specific shRNAs against Scd1 in primary hepatocytes improved the hepatic steatosis of Adgrf1-overexpressing mice and lipid profile of hepatocytes, respectively.

Conclusions

These results indicate Adgrf1 regulates hepatic lipid metabolism through controlling the expression of Scd1. Downregulation of Adgrf1 expression can potentially serve as a protective mechanism to stop the overaccumulation of fat in the liver in obese subjects. Overall, the above findings not only reveal a new mechanism regulating the progression of NAFLD, but also proposed a novel therapeutic approach to combat NAFLD by targeting Adgrf1.

Funding

This work was supported by the National Natural Science Foundation of China (81870586), Area of Excellence (AoE/M-707/18), and General Research Fund (15101520) to CMW, and the National Natural Science Foundation of China (82270941, 81974117) to SJ.

Tethered agonist activated ADGRF1 structure and signalling analysis reveal basis for G protein coupling

Adhesion G Protein Coupled Receptors (aGPCRs) have evolved an activation mechanism to translate extracellular force into liberation of a tethered agonist (TA) to effect cell signalling. We report here that ADGRF1 can signal through all major G protein classes and identify the structural basis for a previously reported Gα_q preference by cryo-EM. Our structure shows that Gα_q preference in ADGRF1 may derive from tighter packing at the conserved F569 of the TA, altering contacts between TM helix I and VII, with a concurrent rearrangement of TM helix VII and helix VIII at the site of Gα recruitment. Mutational studies of the interface and of contact residues within the 7TM domain identify residues critical for signalling, and suggest that Gα_s signalling is more sensitive to mutation of TA or binding site residues than Gα_q. Our work advances the detailed molecular understanding of aGPCR TA activation, identifying features that potentially explain preferential signal modulation.

GPR116 receptor regulates the antitumor function of NK cells via Gαq/HIF1α/NF-κB signaling pathway as a potential immune checkpoint

BACKGROUND

NK cell is one of innate immune cells and can protect the body from cancer-initiating cells. It has been reported that GPR116 receptor is involved in inflammation and tumors. However, the effect of GPR116 receptor on the NK cells remains largely unclear.

RESULTS

We discovered that GPR116^-/- mice could efficiently eliminate pancreatic cancer through enhancing the proportion and function of NK cells in tumor. Moreover, the expression of GPR116 receptor was decreased upon the activation of the NK cells. Besides, GPR116^-/- NK cells showed higher cytotoxicity and antitumor activity in vitro and in vivo by producing more GzmB and IFNγ than wild-type (WT) NK cells. Mechanistically, GPR116 receptor regulated the function of NK cells via Gαq/HIF1α/NF-κB signaling pathway. Furthermore, downregulation of GPR116 receptor promoted the antitumor activity of NKG2D-CAR-NK92 cells against pancreatic cancer both in vitro and in vivo.

CONCLUSIONS

Our data indicated that GPR116 receptor had a negatively effect on NK cell function and downregulation of GPR116 receptor in NKG2D-CAR-NK92 cells could enhance the antitumor activity, which provides a new idea to enhance the antitumor efficiency of CAR NK cell therapy.

Functions of G protein-coupled receptor 56 in health and disease

Human G protein-coupled receptor 56 (GPR56) is encoded by gene ADGRG1 from chromosome 16q21 and is homologously encoded in mice, at chromosome 8. Both 687 and 693 splice forms are present in humans and mice. GPR56 has a 381 amino acid-long N-terminal extracellular segment and a GPCR proteolysis site upstream from the first transmembrane domain. GPR56 is mainly expressed in the heart, brain, thyroid, platelets, and peripheral blood mononuclear cells. Accumulating evidence indicates that GPR56 promotes the formation of myelin sheaths and the development of oligodendrocytes in the cerebral cortex of the central nervous system. Moreover, GPR56 contributes to the development and differentiation of hematopoietic stem cells, induces adipogenesis, and regulates the function of immune cells. The lack of GPR56 leads to nervous system dysfunction, platelet disorders, and infertility. Abnormal expression of GPR56 is related to the malignant transformation and tumor metastasis of several cancers including melanoma, neuroglioma, and gastrointestinal cancer. Metabolic disorders and cardiovascular diseases are also associated with dysregulation of GPR56 expression, and GPR56 is involved in the pharmacological resistance to some antidepressant and cancer drug treatments. In this review, the molecular structure, expression profile, and signal transduction of GPR56 are introduced, and physiological and pathological functions of GRP56 are comprehensively summarized. Attributing to its significant biological functions and its long N-terminal extracellular region that interacts with multiple ligands, GPR56 is becoming an attractive therapeutic target in treating neurological and hematopoietic diseases.

GPR110, a receptor for synaptamide, expressed in osteoclasts negatively regulates osteoclastogenesis

Bone remodeling is precisely regulated mainly by osteoblasts and osteoclasts. Although some G-protein coupled receptors (GPCRs) were reported to play roles in osteoblast function, little is known about the roles in osteoclasts. In this study, we found, for the first time, that the expression of GPR110 increased during osteoclastogenesis. GPR110 belongs to adhesion GPCR and was the functional receptor of N-docosahexaenoyl ethanolamine (also called synaptamide). Synaptamide suppressed osteoclastogenesis induced by receptor activator of nuclear factor-kappa B ligand. Considering that synaptamide is the endogenous metabolite of DHA, we hypothesized that DHA may inhibit osteoclastogenesis by affecting synaptamide/GPR110 signaling. But GPR110 knockout and subsequent rescue experiments revealed a pivotal role of GPR110 in the attenuation of osteoclastogenesis by synaptamide but not by DHA. These results suggest that synaptamide/GPR110 signaling negatively regulates osteoclastogenesis. Our study suggested that ligands of GPR110, such as synaptamide, might be a useful drug for osteoporotic patients.

Emerging roles of adhesion G protein-coupled receptors

Adhesion G protein-coupled receptors (aGPCRs) form a sub-group within the GPCR superfamily. Their distinctive structure contains an abnormally large N-terminal, extracellular region with a GPCR autoproteolysis-inducing (GAIN) domain. In most aGPCRs, the GAIN domain constitutively cleaves the receptor into two fragments. This process is often required for aGPCR signalling. Over the last two decades, much research has focussed on aGPCR-ligand interactions, in an attempt to deorphanize the family. Most ligands have been found to bind to regions N-terminal to the GAIN domain. These receptors may bind a variety of ligands, ranging across membrane-bound proteins and extracellular matrix components. Recent advancements have revealed a conserved method of aGPCR activation involving a tethered ligand within the GAIN domain. Evidence for this comes from increased activity in receptor mutants exposing the tethered ligand. As a result, G protein-coupling partners of aGPCRs have been more extensively characterised, making use of their tethered ligand to create constitutively active mutants. This has led to demonstrations of aGPCR function in, for example, neurodevelopment and tumour growth. However, questions remain around the ligands that may bind many aGPCRs, how this binding is translated into changes in the GAIN domain, and the exact mechanism of aGPCR activation following GAIN domain conformational changes. This review aims to examine the current knowledge around aGPCR activation, including ligand binding sites, the mechanism of GAIN domain-mediated receptor activation and how aGPCR transmembrane domains may relate to activation. Other aspects of aGPCR signalling will be touched upon, such as downstream effectors and physiological roles.

Evidences of G Coupled-Protein Receptor (GPCR) Signaling in the human Malaria Parasite Plasmodium falciparum for Sensing its Microenvironment and the Role of Purinergic Signaling in Malaria Parasites

The nucleotides were discovered in the early 19th century and a few years later, the role of such molecules in energy metabolism and cell survival was postulated. In 1972, a pioneer work by Burnstock and colleagues suggested that ATP could also work as a neurotransmitter, which was known as the "purinergic hypothesis". The idea of ATP working as a signaling molecule faced initial resistance until the discovery of the receptors for ATP and other nucleotides, called purinergic receptors. Among the purinergic receptors, the P2Y family is of great importance because it comprises of G proteincoupled receptors (GPCRs). GPCRs are widespread among different organisms. These receptors work in the cells' ability to sense the external environment, which involves: to sense a dangerous situation or detect a pheromone through smell; the taste of food that should not be eaten; response to hormones that alter metabolism according to the body's need; or even transform light into an electrical stimulus to generate vision. Advances in understanding the mechanism of action of GPCRs shed light on increasingly promising treatments for diseases that have hitherto remained incurable, or the possibility of abolishing side effects from therapies widely used today.

G-Protein-Coupled Receptor and Ion Channel Genes Used by Influenza Virus for Replication

Influenza virus causes epidemics and sporadic pandemics resulting in morbidity, mortality, and economic losses. Influenza viruses require host genes to replicate. RNA interference (RNAi) screens can identify host genes coopted by influenza virus for replication. Targeting these proinfluenza genes can provide therapeutic strategies to reduce virus replication. Nineteen proinfluenza G-protein-coupled receptor (GPCR) and 13 proinfluenza ion channel genes were identified in human lung (A549) cells by use of small interfering RNAs (siRNAs). These proinfluenza genes were authenticated by testing influenza virus A/WSN/33-, A/CA/04/09-, and B/Yamagata/16/1988-infected A549 cells, resulting in the validation of 16 proinfluenza GPCR and 5 proinfluenza ion channel genes. These findings showed that several GPCR and ion channel genes are needed for the production of infectious influenza virus. These data provide potential targets for the development of host-directed therapeutic strategies to impede the influenza virus productive cycle so as to limit infection.IMPORTANCE Influenza epidemics result in morbidity and mortality each year. Vaccines are the most effective preventive measure but require annual reformulation, since a mismatch of vaccine strains can result in vaccine failure. Antiviral measures are desirable particularly when vaccines fail. In this study, we used RNAi screening to identify several GPCR and ion channel genes needed for influenza virus replication. Understanding the host genes usurped by influenza virus during viral replication can help identify host genes that can be targeted for drug repurposing or for the development of antiviral drugs. The targeting of host genes is refractory to drug resistance generated by viral mutations, as well as providing a platform for the development of broad-spectrum antiviral drugs.

Druggable Lipid GPCRs: Past, Present, and Prospects

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

Recurrent novel THBS1-ADGRF5 gene fusion in a new tumor subtype "Acral FibroChondroMyxoid Tumors"

Acral soft tissue tumors are common neoplasms, a subset of which pose a diagnostic challenge. We report 10 cases of a previously unrecognized acral benign soft tissue tumor. These tumors arose on the fingers and toes and involved bone in half of cases. Histologically, the tumors were lobulated and displayed an abundant stroma made of variable fibrous, chondroid and myxoid material reminiscent of cartilaginous or myoepithelial differentiation. Tumor cells harbored small round to reniform nuclei with clear chromatin and inconspicuous nucleoli along with scant eosinophilic cytoplasm. The cells were mostly arranged haphazardly in the stroma but also in small clusters. No mitotic activity was detected. No specific feature was identified in recurrent cases. By immunohistochemistry, the cells consistently stained for CD34 (10/10), ERG (9/10), and SOX9 (7/10). Whole RNA sequencing identified a previously undescribed recurrent in frame THBS1-ADGRF5 gene fusion in all cases. The transcript was confirmed by RT-PCR and was not found in the control group of mimickers including soft tissue chondromas. We propose the name of Acral FibroChondroMyxoid Tumors for this new entity.

The role of GPR110 in lung cancer progression

Background

G protein-coupled receptors (GPCRs) are involved in several signaling pathways. However, the roles of many GPCRs in tumor oncogenesis and progression are not fully understood. In our previous study, we concluded that the absence of Gpr110 decelerates the development of liver brosis/cirrhosis into tumorigenesis. In our current study, the role of GPR110 in the oncogenesis and progression of lung cancer was observed.

Methods

After collecting tumor tissues from lung cancer patients, the expression of GPR110 was analyzed by both Western blotting and real-time PCR. Immunofluorescence was used to observe GPR110 expression in human lung cancer cells. A CCK8 kit was used to analyze the proliferation of human lung cancer cells transfected with Gpr110. Changes in cell migration were evaluated with wound healing and Transwell assays. A nude mouse xenograft model was constructed. Lung cancer model was induced in Gpr110^-/- mice with urethane.

Results

GPR110 mRNA and protein expression was significantly higher in lung cancer tissue. GPR110 was barely expressed in H460, A549, H1299, and SPC-A1 cells, but its expression in PC-9 and QG56 cells was significantly higher. Overexpression of GPR110 promoted the proliferation and cell aggregation of H1299 cells and H1299 cell migration was also enhanced. Overexpression of GPR110 in H1299 cells significantly promoted tumor development in the nude mice tumor xenograft model. There was no statistical significance between the Gpr110^+/+ and Gpr110^-/- mice despite the lesions in the Gpr110^-/- mice group decreasing at 35 and 40 weeks after the initial injection of urethane.

Conclusions

Our findings indicate that GPR110 promotes the progression of lung cancer through accelerating cell proliferation and migration.

Comparing the effects of vitamin E tocotrienol-rich fraction supplementation and α-tocopherol supplementation on gene expression in healthy older adults

OBJECTIVES

This study aims to compare the differential gene expression resulting from tocotrienol-rich fraction and α-tocopherol supplementation in healthy older adults.

METHODS

A total of 71 eligible subjects aged 50 to 55 years from Gombak and Kuala Lumpur, Malaysia, were divided into three groups and supplemented with placebo (n=23), α-tocopherol (n=24) or tocotrienol-rich fraction (n=24). Blood samples were collected at baseline and at 3 and 6 months of supplementation for microarray analysis.

RESULTS

The number of genes altered by α-tocopherol was higher after 6 months (1,410) than after 3 months (273) of supplementation. α-Tocopherol altered the expression of more genes in males (952) than in females (731). Similarly, tocotrienol-rich fraction modulated the expression of more genes after 6 months (1,084) than after 3 months (596) and affected more genes in males (899) than in females (781). α-Tocopherol supplementation modulated pathways involving the response to stress and stimuli, the immune response, the response to hypoxia and bacteria, the metabolism of toxins and xenobiotics, mitosis, and synaptic transmission as well as activated the mitogen-activated protein kinase and complement pathways after 6 months. However, tocotrienol-rich fraction supplementation affected pathways such as the signal transduction, apoptosis, nuclear factor kappa B kinase, cascade extracellular signal-regulated kinase-1 and extracellular signal-regulated kinase-2, immune response, response to drug, cell adhesion, multicellular organismal development and G protein signaling pathways.

CONCLUSION

Supplementation with either α-tocopherol or tocotrienol-rich fraction affected the immune and drug response and the cell adhesion and signal transduction pathways but modulated other pathways differently after 6 months of supplementation, with sex-specific responses.

The 17β-estradiol induced upregulation of the adhesion G-protein coupled receptor (ADGRG7) is modulated by ESRα and SP1 complex

The physiological role and the regulation of ADGRG7 are not yet elucidated. The functional involvement of this receptor was linked with different physiological process such as reduced body weight, gastrointestinal function and recently, a gene variant in ADGRG7 was observed in patients with adolescent idiopathic scoliosis. Here, we identify the ADGRG7 as an estrogen-responsive gene under the regulation of estrogen receptor ERα in scoliotic osteoblasts and other cells lines. We found that ADGRG7 expression was upregulated in response to estrogen (E2) in adolescent idiopathic scoliosis (AIS) cells. ADGRG7 promoter studies indicate the presence of an ERα response half site in close vicinity of a specificity protein 1 (SP1) binding site. Mutation of the SP1 site completely abrogated the response to E2, indicating its essential requirement. ChIP confirmed the binding of SP1 and ERα to the ADGRG7 promoter. Our results identify the ADGRG7 gene as an estrogen-responsive gene under the control of ERα and SP1 tethered actions, suggesting a possible role of estrogens in the regulation of ADGRG7 This article has an associated First Person interview with the first author of the paper.

N-Docosahexaenoylethanolamine: A neurotrophic and neuroprotective metabolite of docosahexaenoic acid

N-Docosahexaenoylethanolamine (synaptamide) is an endocannabinoid-like metabolite endogenously synthesized from docosahexaenoic acid (DHA, 22:6n-3), the major omega-3 polyunsaturated fatty acid present in the brain. Although its biosynthetic mechanism has yet to be established, there is a closely linked relationship between the levels of synaptamide and its precursor DHA in the brain. Synaptamide at nanomolar concentrations promotes neurogenesis, neurite outgrowth and synaptogenesis in developing neurons. Synaptamide also attenuates the lipopolysaccharide-induced neuroinflammatory response and reduces the deleterious effects of ethanol on neurogenic differentiation of neural stem cells (NSCs). These actions are mediated by a specific target receptor of synaptamide GPR110 (ADGRF1), a G-protein coupled receptor that is highly expressed in NSCs and the brain during development. Synaptamide binding to GPR110 induces cAMP production and phosphorylation of protein kinase A (PKA) and the cAMP response element binding protein (CREB). This signaling pathway leads to the expression of neurogenic and synaptogenic genes and suppresses the expression of proinflammatory genes. The GPR110-dependent cellular effects of synaptamide are recapitulated in animal models, suggesting that synaptamide-derived mechanisms may have translational implications. The synaptamide bioactivity transmitted by newly deorphanized GPR110 provides a novel target for neurodevelopmental and neuroprotective control as well as new insight into mechanisms for DHA's beneficial effects on the central nervous system.

GPCRs profiling and identification of GPR110 as a potential new target in HER2+ breast cancer

PURPOSE

G protein-coupled receptors (GPCRs) represent the largest family of druggable targets in human genome. Although several GPCRs can cross-talk with the human epidermal growth factor receptors (HERs), the expression and function of most GPCRs remain unknown in HER2+ breast cancer (BC). In this study, we aimed to evaluate gene expression of GPCRs in tumorigenic or anti-HER2 drug-resistant cells and to understand the potential role of candidate GPCRs in HER2+ BC.

METHODS

Gene expression of 352 GPCRs was profiled in Aldeflur+ tumorigenic versus Aldeflur- population and anti-HER2 therapy-resistant derivatives versus parental cells of HER2+ BT474 cells. The GPCR candidates were confirmed in 7 additional HER2+ BC cell line models and publicly available patient dataset. Anchorage-dependent and anchorage-independent cell growth, mammosphere formation, and migration/invasion were evaluated upon GPR110 knockdown by siRNA in BT474 and SKBR3 parental and lapatinib+ trastuzumab-resistant (LTR) cells.

RESULTS

Adhesion and class A GPCRs were overexpressed in Aldeflur+ and anti-HER2 therapy-resistant population of BT474 cells, respectively. GPR110 was the only GPCR overexpressed in Aldeflur+ and anti-HER2 therapy-resistant population in BT474, SKBR3, HCC1569, MDA-MB-361, AU565, and/or HCC202 cells and in HER2+ BC subtype in patient tumors. Using BT474 and SKBR3 parental and LTR cells, we found that GPR110 knockdown significantly reduced anchorage-dependent/independent cell growth as well as migration/invasion of parental and LTR cells and mammosphere formation in LTR derivatives and not in parental cells.

CONCLUSION

Our data suggest a potential role of GPR110 in tumorigenicity and in tumor cell dissemination in HER2+ BC.

STAT6, PBX2, and PBRM1 Emerge as Predicted Regulators of 452 Differentially Expressed Genes Associated With Puberty in Brahman Heifers

The liver plays a central role in metabolism and produces important hormones. Hepatic estrogen receptors and the release of insulin-like growth factor 1 (IGF1) are critical links between liver function and the reproductive system. However, the role of liver in pubertal development is not fully understood. To explore this question, we applied transcriptomic analyses to liver samples of pre- and post-pubertal Brahman heifers and identified differentially expressed (DE) genes and genes encoding transcription factors (TFs). Differential expression of genes suggests potential biological mechanisms and pathways linking liver function to puberty. The analyses identified 452 DE genes and 82 TF with significant contribution to differential gene expression by using a regulatory impact factor metric. Brain-derived neurotrophic factor was observed as the most down-regulated gene (P = 0.003) in post-pubertal heifers and we propose this gene influences pubertal development in Brahman heifers. Additionally, co-expression network analysis provided evidence for three TF as key regulators of liver function during pubertal development: the signal transducer and activator of transcription 6, PBX homeobox 2, and polybromo 1. Pathway enrichment analysis identified transforming growth factor-beta and Wnt signaling pathways as significant annotation terms for the list of DE genes and TF in the co-expression network. Molecular information regarding genes and pathways described in this work are important to further our understanding of puberty onset in Brahman heifers.

Expansion of divergent SEA domains in cell surface proteins and nucleoporin 54

SEA (sea urchin sperm protein, enterokinase, agrin) domains, many of which possess autoproteolysis activity, have been found in a number of cell surface and secreted proteins. Despite high sequence divergence, SEA domains were also proposed to be present in dystroglycan based on a conserved autoproteolysis motif and receptor-type protein phosphatase IA-2 based on structural similarity. The presence of a SEA domain adjacent to the transmembrane segment appears to be a recurring theme in quite a number of type I transmembrane proteins on the cell surface, such as MUC1, dystroglycan, IA-2, and Notch receptors. By comparative sequence and structural analyses, we identified dystroglycan-like proteins with SEA domains in Capsaspora owczarzaki of the Filasterea group, one of the closest single-cell relatives of metazoans. We also detected novel and divergent SEA domains in a variety of cell surface proteins such as EpCAM, α/ε-sarcoglycan, PTPRR, collectrin/Tmem27, amnionless, CD34, KIAA0319, fibrocystin-like protein, and a number of cadherins. While these proteins are mostly from metazoans or their single cell relatives such as choanoflagellates and Filasterea, fibrocystin-like proteins with SEA domains were found in several other eukaryotic lineages including green algae, Alveolata, Euglenozoa, and Haptophyta, suggesting an ancient evolutionary origin. In addition, the intracellular protein Nucleoporin 54 (Nup54) acquired a divergent SEA domain in choanoflagellates and metazoans.

Orphan GPR110 (ADGRF1) targeted by N-docosahexaenoylethanolamine in development of neurons and cognitive function

Docosahexaenoic acid (DHA, 22:6n-3) is an omega-3 fatty acid essential for proper brain development. N-docosahexaenoylethanolamine (synaptamide), an endogenous metabolite of DHA, potently promotes neurogenesis, neuritogenesis and synaptogenesis; however, the underlying molecular mechanism is not known. Here, we demonstrate orphan G-protein coupled receptor 110 (GPR110, ADGRF1) as the synaptamide receptor, mediating synaptamide-induced bioactivity in a cAMP-dependent manner. Mass spectrometry-based proteomic characterization and cellular fluorescence tracing with chemical analogues of synaptamide reveal specific binding of GPR110 to synaptamide, which triggers cAMP production with low nM potency. Disruption of this binding or GPR110 gene knockout abolishes while GPR110 overexpression enhances synaptamide-induced bioactivity. GPR110 is highly expressed in fetal brains but rapidly decreases after birth. GPR110 knockout mice show significant deficits in object recognition and spatial memory. GPR110 deorphanized as a functional synaptamide receptor provides a novel target for neurodevelopmental control and new insight into mechanisms by which DHA promotes brain development and function.

7TM Domain Structure of Adhesion GPCRs

Schematic presentation of the overall adhesion G Protein-Coupled Receptor (aGPCR) structure and functional domains, covering an extracellular N-terminal fragment (NTF), a membrane-spanning C-terminal fragment (CTF) and a GPCR proteolysis site (GPS). (Left side) aGPCR model constructed based on the seven-transmembrane (7TM) structure (blue) of secretin family glucagon receptor (GCGR) (PDB, 4L6R) [11] and the GPCR autoproteolysis inducing (GAIN) domain (magenta) structure of latrophilin 1 (PDB, 4DLQ) [9]. The β-13 strand residues are depicted in green. (Right side) The experimentally validated full-length secretin family GCGR structure combining structural and experimental information from the GCGR 7TM crystal structure (PDB, 4L6R) (blue), the GCGR extracellular domain (ECD) structure (PDB, 4ERS) (magenta) and the ECD structure of glucagon-like peptide-1 (GLP-1)-bound glucagon-like peptide-1 receptor (GLP-1R) (PDB, 3IOL) (green), complemented by site-directed mutagenesis, electron microscopy (EM), hydrogen-deuterium exchange (HDX) and cross-linking studies [11-13]) Despite the recent breakthroughs in the elucidation of the three-dimensional structures of the seven transmembrane (7TM) domain of the G protein-coupled receptor (GPCR) superfamily, a corresponding structure of a member of the adhesion GPCR (aGPCR) family has not yet been solved. In this chapter, we give an overview of the current knowledge of the 7TM domain of aGPCRs by comparative structure-based sequence similarity analyses between aGPCRs and GPCRs with known crystal structure. Of the GPCR superfamily, only the secretin family shares some sequence similarity with aGPCRs. This chapter will therefore emphasize on the comparison of these two GPCR families. Two 7TM domain structures of secretin family GPCRs are known that provide insight into the structure-function relationships of conserved sequence motifs that play important roles and are also present in most aGPCRs. This suggests that the 7TM domains of aGPCRs and secretin family GPCRs share a similar structural fold and that the conserved residues in both families may be involved in similar intermolecular interaction networks and facilitate similar conformational changes. Comparison of the residues that line the large peptide hormone binding pocket in the 7TM domain of secretin family GPCRs with corresponding residues in aGPCRs indicates that in the latter, the corresponding pocket in the 7TM domain is relatively hydrophobic and may be even larger. Improved knowledge on these conserved sequence motifs will help to understand the interactions of the aGPCR 7TM domain with ligands and gain insight into the activation mechanism of aGPCRs.

Classification, Nomenclature, and Structural Aspects of Adhesion GPCRs

Representation of the nine distinct aGPCR subfamilies and their unique N-terminal domain architecture. The illustration also shows the extracellular structural feature shared by all aGPCRs (except ADGRA1), known as the GPCR autoproteolysis-inducing (GAIN) domain, that mediates autoproteolysis and subsequent attachment of the cleaved NTF and CTF fragments The adhesion family of G protein-coupled receptors (aGPCRs) is unique among all GPCR families with long N-termini and multiple domains that are implicated in cell-cell and cell-matrix interactions. Initially, aGPCRs in the human genome were phylogenetically classified into nine distinct subfamilies based on their 7TM sequence similarity. This phylogenetic grouping of genes into subfamilies was found to be in congruence in closely related mammals and other vertebrates as well. Over the years, aGPCR repertoires have been mapped in many species including model organisms, and, currently, there is a growing interest in exploring the pharmacological aspects of aGPCRs. Nonetheless, the aGPCR nomenclature has been highly diverse because experts in the field have used different names for different family members based on their characteristics (e.g., epidermal growth factor-seven-span transmembrane (EGF-TM7)), but without harmonization with regard to nomenclature efforts. In order to facilitate naming of orthologs and other genetic variants in different species in the future, the Adhesion-GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposed a unified nomenclature for aGPCRs. Here, we review the classification and the most recent/current nomenclature of aGPCRs and as well discuss the structural topology of the extracellular domain (ECD)/N-terminal fragment (NTF) that is comparable with this 7TM subfamily classification. Of note, we systematically describe the structural domains in the ECD of aGPCR subfamilies and highlight their role in aGPCR-protein interactions.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G protein-coupled receptors

The Adhesion family forms a large branch of the pharmacologically important superfamily of G protein-coupled receptors (GPCRs). As Adhesion GPCRs increasingly receive attention from a wide spectrum of biomedical fields, the Adhesion GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposes a unified nomenclature for Adhesion GPCRs. The new names have ADGR as common dominator followed by a letter and a number to denote each subfamily and subtype, respectively. The new names, with old and alternative names within parentheses, are: ADGRA1 (GPR123), ADGRA2 (GPR124), ADGRA3 (GPR125), ADGRB1 (BAI1), ADGRB2 (BAI2), ADGRB3 (BAI3), ADGRC1 (CELSR1), ADGRC2 (CELSR2), ADGRC3 (CELSR3), ADGRD1 (GPR133), ADGRD2 (GPR144), ADGRE1 (EMR1, F4/80), ADGRE2 (EMR2), ADGRE3 (EMR3), ADGRE4 (EMR4), ADGRE5 (CD97), ADGRF1 (GPR110), ADGRF2 (GPR111), ADGRF3 (GPR113), ADGRF4 (GPR115), ADGRF5 (GPR116, Ig-Hepta), ADGRG1 (GPR56), ADGRG2 (GPR64, HE6), ADGRG3 (GPR97), ADGRG4 (GPR112), ADGRG5 (GPR114), ADGRG6 (GPR126), ADGRG7 (GPR128), ADGRL1 (latrophilin-1, CIRL-1, CL1), ADGRL2 (latrophilin-2, CIRL-2, CL2), ADGRL3 (latrophilin-3, CIRL-3, CL3), ADGRL4 (ELTD1, ETL), and ADGRV1 (VLGR1, GPR98). This review covers all major biologic aspects of Adhesion GPCRs, including evolutionary origins, interaction partners, signaling, expression, physiologic functions, and therapeutic potential.

Novel functional complexity of polycystin-1 by GPS cleavage in vivo: role in polycystic kidney disease

Polycystin-1 (Pc1) cleavage at the G protein-coupled receptor (GPCR) proteolytic site (GPS) is required for normal kidney morphology in humans and mice. We found a complex pattern of endogenous Pc1 forms by GPS cleavage. GPS cleavage generates not only the heterodimeric cleaved full-length Pc1 (Pc1(cFL)) in which the N-terminal fragment (NTF) remains noncovalently associated with the C-terminal fragment (CTF) but also a novel (Pc1) form (Pc1(deN)) in which NTF becomes detached from CTF. Uncleaved Pc1 (Pc1(U)) resides primarily in the endoplasmic reticulum (ER), whereas both Pc1(cFL) and Pc1(deN) traffic through the secretory pathway in vivo. GPS cleavage is not a prerequisite, however, for Pc1 trafficking in vivo. Importantly, Pc1(deN) is predominantly found at the plasma membrane of renal epithelial cells. By functional genetic complementation with five Pkd1 mouse models, we discovered that CTF plays a crucial role in Pc1(deN) trafficking. Our studies support GPS cleavage as a critical regulatory mechanism of Pc1 biogenesis and trafficking for proper kidney development and homeostasis.

Adhesion G-protein-coupled receptors: elusive hybrids come of age

Adhesion G-protein-coupled receptors (GPCRs) are the most recently identified and least understood subfamily of GPCRs. Adhesion GPCRs are characterized by unusually long ectodomains with adhesion-related repeats that facilitate cell- cell and cell-cell matrix contact, as well as a proteolytic cleavage site-containing domain that is a structural hallmark of the family. Their unusual chimeric structure of adhesion-related ectodomain with a seven-pass transmembrane domain and cytoplasmic signaling makes these proteins highly versatile in mediating cellular signaling in response to extracellular adhesion or cell motility events. The ligand binding and cytoplasmic signaling modes for members of this family are beginning to be elucidated, and recent studies have demonstrated critical roles for Adhesion GPCRs in planar polarity and other important cell-cell and cell-matrix interactions during development and morphogenesis, as well as heritable diseases and cancer.

The orphan adhesion G protein-coupled receptor GPR97 regulates migration of lymphatic endothelial cells via the small GTPases RhoA and Cdc42

The important role of the lymphatic vascular system in pathological conditions such as inflammation and cancer has been increasingly recognized, but its potential as a pharmacological target is poorly exploited. Our study aimed at the identification and molecular characterization of lymphatic-specific G protein-coupled receptors (GPCRs) to assess new targets for pharmacological manipulation of the lymphatic vascular system. We used a TaqMan quantitative RT-PCR-based low density array to determine the GPCR expression profiles of ex vivo isolated intestinal mouse lymphatic (LECs) and blood vascular endothelial cells (BECs). GPR97, an orphan adhesion GPCR of unknown function, was the most highly and specifically expressed GPCR in mouse lymphatic endothelium. Using siRNA silencing, we found that GPR97-deficient primary human LECs displayed increased adhesion and collective cell migration, whereas single cell migration was decreased as compared with nontargeting siRNA-transfected control LECs. Loss of GPR97 shifted the ratio of active Cdc42 and RhoA and initiated cytoskeletal rearrangements, including F-actin redistribution, paxillin and PAK4 phosphorylation, and β1-integrin activation. Our data suggest a possible role of GPR97 in lymphatic remodeling and furthermore provide the first insights into the biological functions of GPR97.

Gpr97 is essential for the follicular versus marginal zone B-lymphocyte fate decision

Gpr97 is an orphan adhesion GPCR and is highly conserved among species. Up to now, its physiological function remains largely unknown. Here, we show that Gpr97 deficiency results in an extensive reduction in B220⁺ lymphocytes in mice. More intensive analyses reveal an expanded marginal zone but a decreased follicular B-cell population in Gpr97^−/−spleen, which displays disorganized architecture characterized by diffuse, irregular B-cell areas and the absence of discrete perifollicular marginal and mantle zones. In vivo functional studies reveal that the mutant mice could generate antibody responses to T cell-dependent and independent antigens, albeit enhanced response to the former and weakened response to the latter. By screening for the molecular events involved in the observed phenotypes, we found that lambda 5 expression is downregulated and its upstream inhibitor Aiolos is increased in the spleen of mutant mice, accompanied by significantly enhanced phosphorylation and nuclear translocation of cAMP response element-binding protein. Interestingly, increased constitutive Nf-κb p50/p65 expression and activity were observed in Gpr97^−/− spleen, implicating a crucial role of Gpr97 in regulating Nf-κb activity. These findings uncover a novel biological function of Gpr97 in regulating B-cell development, implying Gpr97 as a potential therapeutic target for treatment of immunological disorders.

Lung surfactant levels are regulated by Ig-Hepta/GPR116 by monitoring surfactant protein D

Lung surfactant is a complex mixture of lipids and proteins, which is secreted from the alveolar type II epithelial cell and coats the surface of alveoli as a thin layer. It plays a crucial role in the prevention of alveolar collapse through its ability to reduce surface tension. Under normal conditions, surfactant homeostasis is maintained by balancing its release and the uptake by the type II cell for recycling and the internalization by alveolar macrophages for degradation. Little is known about how the surfactant pool is monitored and regulated. Here we show, by an analysis of gene-targeted mice exhibiting massive accumulation of surfactant, that Ig-Hepta/GPR116, an orphan receptor, is expressed on the type II cell and sensing the amount of surfactant by monitoring one of its protein components, surfactant protein D, and its deletion results in a pulmonary alveolar proteinosis and emphysema-like pathology. By a coexpression experiment with Sp-D and the extracellular region of Ig-Hepta/GPR116 followed by immunoprecipitation, we identified Sp-D as the ligand of Ig-Hepta/GPR116. Analyses of surfactant metabolism in Ig-Hepta^+/+ and Ig-Hepta^−/− mice by using radioactive tracers indicated that the Ig-Hepta/GPR116 signaling system exerts attenuating effects on (i) balanced synthesis of surfactant lipids and proteins and (ii) surfactant secretion, and (iii) a stimulating effect on recycling (uptake) in response to elevated levels of Sp-D in alveolar space.

Matching structure with function: the GAIN domain of adhesion-GPCR and PKD1-like proteins

Elucidation of structural information can greatly facilitate the understanding of molecular function. A recent example is the description of the G-protein-coupled receptor (GPCR) autoproteolysis-inducing (GAIN) domain, an evolutionarily ancient fold present in Adhesion-GPCRs (aGPCRs) and polycystic kidney disease 1 (PKD1)-like proteins. In the past, the peculiar autoproteolytic capacity of both membrane protein families at the conserved GPCR proteolysis site (GPS) had not been described in detail. The physiological performance of aGPCRs and PKD1-like proteins is thought to be regulated through the GPS, but it is debated how. A recent report provides pivotal details by discovery and analysis of the GAIN domain structure that incorporates the GPS motif. Complementary studies have commenced to analyze physiological requirements of the GAIN domain for aGPCR function, indicating that it serves as the linchpin for multiple receptor signals. Structural analysis and functional assays now allow for the dissection of the biological duties conferred through the GAIN domain.

Systematic identification and characterization of novel human skin-associated genes encoding membrane and secreted proteins

Through bioinformatics analyses of a human gene expression database representing 105 different tissues and cell types, we identified 687 skin-associated genes that are selectively and highly expressed in human skin. Over 50 of these represent uncharacterized genes not previously associated with skin and include a subset that encode novel secreted and plasma membrane proteins. The high levels of skin-associated expression for eight of these novel therapeutic target genes were confirmed by semi-quantitative real time PCR, western blot and immunohistochemical analyses of normal skin and skin-derived cell lines. Four of these are expressed specifically by epidermal keratinocytes; two that encode G-protein-coupled receptors (GPR87 and GPR115), and two that encode secreted proteins (WFDC5 and SERPINB7). Further analyses using cytokine-activated and terminally differentiated human primary keratinocytes or a panel of common inflammatory, autoimmune or malignant skin diseases revealed distinct patterns of regulation as well as disease associations that point to important roles in cutaneous homeostasis and disease. Some of these novel uncharacterized skin genes may represent potential biomarkers or drug targets for the development of future diagnostics or therapeutics.

Systemic steroid exposure is associated with differential methylation in chronic obstructive pulmonary disease

RATIONALE

Systemic glucocorticoids are used therapeutically to treat a variety of medical conditions. Epigenetic processes such as DNA methylation may reflect exposure to glucocorticoids and may be involved in mediating the responses and side effects associated with these medications.

OBJECTIVES

To test the hypothesis that differences in DNA methylation are associated with current systemic steroid use.

METHODS

We obtained DNA methylation data at 27,578 CpG sites in 14,475 genes throughout the genome in two large, independent cohorts: the International COPD Genetics Network (n(discovery) = 1,085) and the Boston Early Onset COPD study (n(replication) = 369). Sites were tested for association with current systemic steroid use using generalized linear mixed models.

MEASUREMENTS AND MAIN RESULTS

A total of 511 sites demonstrated significant differential methylation by systemic corticosteroid use in all three of our primary models. Pyrosequencing validation confirmed robust differential methylation at CpG sites annotated to genes such as SLC22A18, LRP3, HIPK3, SCNN1A, FXYD1, IRF7, AZU1, SIT1, GPR97, ABHD16B, and RABGEF1. Functional annotation clustering demonstrated significant enrichment in intrinsic membrane components, hemostasis and coagulation, cellular ion homeostasis, leukocyte and lymphocyte activation and chemotaxis, protein transport, and responses to nutrients.

CONCLUSIONS

Our analyses suggest that systemic steroid use is associated with site-specific differential methylation throughout the genome. Differentially methylated CpG sites were found in biologically plausible and previously unsuspected pathways; these genes and pathways may be relevant in the development of novel targeted therapies.

GPR56 and the developing cerebral cortex: cells, matrix, and neuronal migration

GPR56, a member of the adhesion G protein-coupled receptor (GPCR) family, is integral to the development of the cortex, as mutations in GPR56 cause bilateral frontoparietal polymicrogyria (BFPP). BFPP is a cobblestone-like cortical malformation, characterized by overmigrating neurons and the formation of neuronal ectopias on the surface of the brain. Since its original cloning a decade ago, GPR56 has emerged from an orphaned and uncharacterized protein to an increasingly well-understood receptor, both in terms of its signaling and function. Collagen III is the ligand of GPR56 in the developing brain. Upon binding to collagen III, GPR56 activates RhoA via coupling to Gα(12/13). This pathway appears to be particularly critical in the preplate neurons, which are the earliest born neurons in the cortex, as the expression pattern of GPR56 in these neurons mimics the anterior to posterior gradient of malformation associated with loss of GPR56 in both humans and mice. Further characterizing the role of GPR56 in the preplate will shed light on the mechanism of cortical development and patterning.

Characterization and functional study of a cluster of four highly conserved orphan adhesion-GPCR in mouse

BACKGROUND

Adhesion G protein-coupled receptors (aGPCR) constitute a structurally and functionally diverse class of seven-transmembrane receptor proteins. Although for some of the members important roles in immunology, neurology, as well as developmental biology have been suggested, most receptors have been poorly characterized.

RESULTS

We have studied evolution, expression, and function of an entire receptor group containing four uncharacterized aGPCR: Gpr110, Gpr111, Gpr115, and Gpr116. We show that the genomic loci of these four receptors are clustered tightly together in mouse and human genomes and that this cluster likely derives from a single common ancestor gene. Using transcriptional profiling on wild-type and knockout/LacZ reporter knockin mice strains, we have obtained detailed expression maps that show ubiquitous expression of Gpr116, co-expression of Gpr111 and Gpr115 in developing skin, and expression of Gpr110 in adult kidney. Loss of Gpr110, Gpr111, or Gpr115 function did not result in detectable defects, indicating that genes of this aGPCR group might function redundantly.

CONCLUSIONS

The aGPCR cluster Gpr110, Gpr111, Gpr115, and Gpr116 developed from one common ancestor in vertebrates. Expression suggests a role in epithelia, and one can speculate about a possible redundant function of GPR111 and GPR115.

Clinical significance of GPR56, transglutaminase 2, and NF-κB in esophageal squamous cell carcinoma

Proteins do not operate as individual units, and components of intracellular canonical pathways often cross talk in tumor genesis. We hypothesized that G-protein-coupled receptor 56 (GPR56), transglutaminase (TG2), and nuclear factor-κB (NF-κB) may collaborate in interconnected pathways and contribute to the aggressive behavior of esophageal squamous cell carcinoma (ESCC). Immunohistochemical analysis of GPR56, TG2, and NF-κB was carried out using ESCC tissue microarrays. Immunostaining of all the three proteins revealed a significant increase in their expression in ESCCs as compared with normal epithelia and correlated with their concomitant expression. A significant correlation between GPR56, TG2, and NF-κB was observed that correlated with nodal metastasis and tumor invasion in ESCCs.

Orphan receptor GPR110, an oncogene overexpressed in lung and prostate cancer

Background

GPR110 is an orphan G protein-coupled receptor--a receptor without a known ligand, a known signaling pathway, or a known function. Despite the lack of information, one can assume that orphan receptors have important biological roles. In a retroviral insertion mutagenesis screen in the mouse, we identified GPR110 as an oncogene. This prompted us to study the potential isoforms that can be gleaned from known GPR110 transcripts, and the expression of these isoforms in normal and transformed human tissues.

Methods

Various epitope-tagged isoforms of GPR110 were expressed in cell lines and assayed by western blotting to determine cleavage, surface localization, and secretion patterns. GPR110 transcript and protein levels were measured in lung and prostate cancer cell lines and clinical samples, respectively, by quantitative PCR and immunohistochemistry.

Results

We found four potential splice variants of GPR110. Of these variants, we confirmed three as being expressed as proteins on the cell surface. Isoform 1 is the canonical form, with a molecular mass of about 100 kD. Isoforms 2 and 3 are truncated products of isoform 1, and are 25 and 23 kD, respectively. These truncated isoforms lack the seven-span transmembrane domain characteristic of GPR proteins and thus are not likely to be membrane anchored; indeed, isoform 2 can be secreted. Compared with the median gene expression of ~200 selected genes, GPR110 expression was low in most tissues. However, it had higher than average gene expression in normal kidney tissue and in prostate tissues originating from older donors. Although identified as an oncogene in murine T lymphomas, GPR110 is greatly overexpressed in human lung and prostate cancers. As detected by immunohistochemistry, GPR110 was overexpressed in 20 of 27 (74%) lung adenocarcinoma tissue cores and in 17 of 29 (59%) prostate adenocarcinoma tissue cores. Additionally, staining with a GPR110 antibody enabled us to differentiate between benign prostate hyperplasia and potential incipient malignancy.

Conclusion

Our work suggests a role for GPR110 in tumor physiology and supports it as a potential therapeutic candidate and disease marker for both lung and prostate cancer.

The adhesion GPCRs; gene repertoire, phylogeny and evolution

The Adhesion family is unique among the GPCR (G protein-coupled receptor) families because of several features including long N-termini with multiple domains. The gene repertoire has recently been mined in great detail in several species including mouse, rat, dog, chicken and the early vertebrate Branchiostoma (Branchiostoma floridae) and one of the most primitive animals, the cniderian Nematostella (Nematostella vectensis). There is a one-to-one relationship of the rodent (mouse and rat) and human orthologues with the exception the EMR2 and EMR3 that do not seem to have orthologues in either rat or mouse. All 33 human Adhesion GPCR genes are present in the dog genome but the dog genome also contains 5 additional full-length Adhesion genes. The dog and human Adhesion orthologues have higher average protein sequence identity than the rodent (rat and mouse) and the human sequences. The Adhesion family is well-represented in chicken with 21 one-to-one orthologous with humans, while 12 human Adhesion GPCRs lack a chicken ortholog. Branchiostoma has rich repertoire of Adhesion GPCRs with at least 37 genes. Moreover, the Adhesion GPCRs in Branchiostoma have several novel domains their N-termini, like Somatomedin B, Kringle, Lectin C-type, SRCR, LDLa, Immunoglobulin I-set, CUB and TNFR. Nematostella has also Adhesion GPCRs that are show domain structure and sequence similarities in the transmembrane regions with different classes of mammalian GPCRs. The Nematostella genome has a unique set of Adhesion-like sequences lacking GPS domains. There is considerable evidence showing that the Adhesion family is ancestral to the peptide hormone binding Secretin family of GPCRs.

Adhesion-GPCRS in tumorigenesis

Tumor growth is a highly complex, multistep process that involves tumor cell detachment, migration, invasion and metastasis accompanied by angiogenesis and extracellular matrix turn-over. Each of the steps is influenced by tumor cell interaction and interaction of the tumor cell with its microenvironment that consists of different cell types as tumor-associated fibroblasts, endothelial cells and leukocytes as well as the extracellular matrix produced by the tumor cells themselves or by the fibroblasts. Cellular communication takes place by the regulated expression of adhesion receptors. Adhesion-GPCRs are characterized by very long extracellular N-termini that have multiple domains. When considering this complex structure it is only logical that adhesion-GPCRs are involved in tumor cell interactions. Moreover, these receptors function in cell guidance and/or trafficking, which, in addition to their structure, makes them interesting for tumorigenesis. The aberrant expression of several adhesion-GPCRs on tumor cells and their involvement in tumor growth have been shown for some of the family members. This overview summarizes expression database data as well as data from original research articles of adhesion-GPCRs in tumors.

GPR56 and its related diseases

GPR56, an orphan G protein-coupled receptor (GPCR), was identified one decade ago by two independent groups through a degenerate PCR-based approach for secretin-like GPCRs and by differential display of melanoma cell lines with different metastatic potentials. The finding that GPR56 was significantly downregulated in high metastatic melanoma cell lines suggests its possible role in cancer metastasis. However, the function of GPR56 remained unclear until 2004 when mutations in the human GPR56 gene were found to cause a specific brain malformation called bilateral frontoparietal polymicrogyria. Although GPR56 is expressed in a wide range of tissues, the consequences of loss-of-function mutations in the GPR56 gene have only been observed in the central nervous system. Studies from knockout mouse model indicate that GPR56 regulates brain development by affecting the integrity of the pial basement membrane in the developing brain.

Novel markers for enterochromaffin cells and gastrointestinal neuroendocrine carcinomas

The gene expression profile of metastasizing serotonin-producing neuroendocrine carcinomas, which arise from enterochromaffin cells in the jejunum and ileum, is still largely unknown. The aim of this study was to identify genes and proteins, which are preferentially expressed by neuroendocrine carcinoma and enterochromaffin cells and therefore potential novel biomarkers and/or therapeutic targets. Six carcinoma specimens and six normal ileal mucosas were profiled by Affymetrix microarrays. Advanced bioinformatics identified differentially and specifically expressed genes, which were validated by quantitative real-time-PCR on tumor cells extracted by laser capture microdissection and normal enterochromaffin cells extracted by immunolaser capture microdissection. We identified six novel marker genes for neuroendocrine carcinoma cells: paraneoplastic antigen Ma2 (PNMA2), testican-1 precursor (SPOCK1), serpin A10 (SERPINA10), glutamate receptor ionotropic AMPA 2 (GRIA2), G protein-coupled receptor 112 (GPR112) and olfactory receptor family 51 subfamily E member 1 (OR51E1). GRIA2 is specifically expressed by neuroendocrine carcinoma cells whereas the others are also expressed by normal enterochromaffin cells. GPR112 and OR51E1 encode proteins associated with the plasma membrane and may therefore become targets for antibody-based diagnosis and therapy. Hierarchical clustering shows high similarity between primary lesions and liver metastases. However, chemokine C-X-C motif ligand 14 (CXCL14) and NK2 transcription factor related locus 3 Drosophila (NKX2-3) are expressed to a lower level in liver metastases than in primary tumors and normal enterochromaffin cells, which implies a role in neuroendocrine carcinoma differentiation. In conclusion, this study provides a list of genes, which possess relatively specific expression to enterochromaffin and neuroendocrine carcinoma cells and genes with differential expression between primary tumors and metastases. We verified six novel marker genes that may be developed as biomarkers and/or therapeutic targets.

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.

Identification of a core set of 58 gene transcripts with broad and specific expression in the microvasculature

OBJECTIVE

Pathological angiogenesis is an integral component of many diseases. Antiangiogenesis and vascular targeting are therefore promising new therapeutic principles. However, few endothelial-specific putative drug targets have been identified, and information is still limited about endothelial-specific molecular processes. Here we aimed at determining the endothelial cell-specific core transcriptome in vivo.

METHODS AND RESULTS

Analysis of publicly available microarray data identified a mixed vascular/lung cluster of 132 genes that correlated with known endothelial markers. Filtering against kidney glomerular/nonglomerular and brain vascular/nonvascular microarray profiles separated contaminating lung markers, leaving 58 genes with broad and specific microvascular expression. More than half of these have not previously been linked to endothelial functions or studied in detail before. The endothelial cell-specific expression of a selected subset of these, Eltd1, Gpr116, Ramp2, Slc9a3r2, Slc43a3, Rasip1, and NM_023516, was confirmed by real-time quantitative polymerase chain reaction and/or immunohistochemistry.

CONCLUSIONS

We have used a combination of publicly available and own microarray data to identify 58 gene transcripts with broad yet specific expression in microvascular endothelium. Most of these have unknown functions, but many of them are predicted to be cell surface expressed or implicated in cell signaling processes and should therefore be explored as putative microvascular drug targets.

Structural diversity of G protein-coupled receptors and significance for drug discovery

G protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and also the targets of many drugs. Understanding of the functional significance of the wide structural diversity of GPCRs has been aided considerably in recent years by the sequencing of the human genome and by structural studies, and has important implications for the future therapeutic potential of targeting this receptor family. This article aims to provide a comprehensive overview of the five main human GPCR families--Rhodopsin, Secretin, Adhesion, Glutamate and Frizzled/Taste2--with a focus on gene repertoire, general ligand preference, common and unique structural features, and the potential for future drug discovery.

Orphan G protein-coupled receptor GPR56 regulates neural progenitor cell migration via a G alpha 12/13 and Rho pathway

In the developing forebrain, the migration and positioning of neural progenitor cells (NPCs) are regulated coordinately by various molecules. Mutation of these molecules, therefore, causes cortical malformation. GPR56 has been reported as a cortical malformation-related gene that is mutated in patients with bilateral frontoparietal polymicrogyria. GPR56 encodes an orphan G protein-coupled receptor, and its mutations reduce the cell surface expression. It has also been reported that the expression level of GPR56 is involved in cancer cell adhesion and metastasis. However, it remains to be clarified how GPR56 functions in brain development and which signaling pathways are activated by GPR56. In this study, we showed that GPR56 is highly expressed in NPCs and has the ability to inhibit NPC migration. We found that GPR56 coupled with Galpha(12/13) and induced Rho-dependent activation of the transcription mediated through a serum-responsive element and NF-kappaB-responsive element and actin fiber reorganization. The transcriptional activation and actin reorganization were inhibited by an RGS domain of the p115 Rho-specific guanine nucleotide exchange factor (p115 RhoGEF RGS) and dominant negative form of Rho. Moreover, we have demonstrated that a functional anti-GPR56 antibody, which has an agonistic activity, inhibited NPC migration. This inhibition was attenuated by p115 RhoGEF RGS, C3 exoenzyme, and GPR56 knockdown. These results indicate that GPR56 participates in the regulation of NPC movement through the Galpha(12/13) and Rho signaling pathway, suggesting its important role in the development of the central nervous system.

Transposable element fragments in protein-coding regions and their contributions to human functional proteins

Transposable elements (TEs) and their contributions to protein-coding regions are of particular interest. Here we searched for TE fragments in Homo sapiens at both the transcript and protein levels. We found evidence in support of TE exonization and its association with alternative splicing. Despite recent findings that long evolutionary times are required to incorporate TE into proteins, we found many functional proteins with translated TE cassettes derived from young TEs. Analyses of two Bcl-family proteins and Alu-encoded segments suggest the coding and functional potential of TE sequences.