A receptor subtype involved in neuropeptide-Y-induced food intake

Neuropeptide Y (NPY) is a powerful stimulant of food intake and is proposed to activate a hypothalamic 'feeding' receptor distinct from previously cloned Y-type receptors. This receptor was first suggested to explain a feeding response to NPY and related peptides, including NPY2-36, that differed from their activities at the Y1 receptor. Here we report the expression cloning of a novel Y-type receptor from rat hypothalamus, which we name Y5. The complementary DNA encodes a 456-amino-acid protein with less than 35% overall identity to known Y-type receptors. The messenger RNA is found primarily in the central nervous system, including the paraventricular nucleus of the hypothalamus. The extent to which selected peptides can inhibit adenylate cyclase through the Y5 receptor and stimulate food intake in rats correspond well. Our data support the idea that the Y5 receptor is the postulated 'feeding' receptor, and may provide a new method for the study and treatment of obesity and eating disorders.

The KiSS-1 receptor GPR54 is essential for the development of the murine reproductive system

GPR54 is a G-protein-coupled receptor that displays a high percentage of identity in the transmembrane domains with the galanin receptors. The ligand for GPR54 has been identified as a peptide derived from the KiSS-1 gene. KiSS-1 has been shown to have anti-metastatic effects, suggesting that KiSS-1 or its receptor represents a potential therapeutic target. To further our understanding of the physiological function of this receptor, we have generated a mutant mouse line with a targeted disruption of the GPR54 receptor (GPR54 -/-). The analysis of the GPR54 mutant mice revealed developmental abnormalities of both male and female genitalia and histopathological changes in tissues which normally contain sexually dimorphic features. These data suggest a role for GPR54/KiSS-1 in normal sexual development, and indicate that study of the GPR54 mutant mice may provide valuable insights into human reproductive syndromes.

Molecular identification and characterization of the platelet ADP receptor targeted by thienopyridine antithrombotic drugs

ADP plays a critical role in modulating thrombosis and hemostasis. ADP initiates platelet aggregation by simultaneous activation of two G protein-coupled receptors, P2Y1 and P2Y12. Activation of P2Y1 activates phospholipase C and triggers shape change, while P2Y12 couples to Gi to reduce adenylyl cyclase activity. P2Y12 has been shown to be the target of the thienopyridine drugs, ticlopidine and clopidogrel. Recently, we cloned a human orphan receptor, SP1999, highly expressed in brain and platelets, which responded to ADP and had a pharmacological profile similar to that of P2Y12. To determine whether SP1999 is P2Y12, we generated SP1999-null mice. These mice appear normal, but they exhibit highly prolonged bleeding times, and their platelets aggregate poorly in responses to ADP and display a reduced sensitivity to thrombin and collagen. These platelets retain normal shape change and calcium flux in response to ADP but fail to inhibit adenylyl cyclase. In addition, oral clopidogrel does not inhibit aggregation responses to ADP in these mice. These results demonstrate that SP1999 is indeed the elusive receptor, P2Y12. Identification of the target receptor of the thienopyridine drugs affords us a better understanding of platelet function and provides tools that may lead to the discovery of more effective antithrombotic therapies.

Short-chain fatty acids act as antiinflammatory mediators by regulating prostaglandin E2 and cytokines

AIM: To investigate the effect of short-chain fatty acids (SCFAs) on production of prostaglandin E₂ (PGE₂), cytokines and chemokines in human monocytes.

METHODS: Human neutrophils and monocytes were isolated from human whole blood by using 1-Step Polymorph and RosetteSep Human Monocyte Enrichment Cocktail, respectively. Human GPR41 and GPR43 mRNA expression was examined by quantitative real-time polymerase chain reaction. The calcium flux assay was used to examine the biological activities of SCFAs in human neutrophils and monocytes. The effect of SCFAs on human monocytes and peripheral blood mononuclear cells (PBMC) was studied by measuring PGE₂, cytokines and chemokines in the supernatant. The effect of SCFAs in vivo was examined by intraplantar injection into rat paws.

RESULTS: Human GPR43 is highly expressed in human neutrophils and monocytes. SCFAs induce robust calcium flux in human neutrophils, but not in human monocytes. In this study, we show that SCFAs can induce human monocyte release of PGE₂ and that this effect can be enhanced in the presence of lipopolysaccharide (LPS). In addition, we demonstrate that PGE₂ production induced by SCFA was inhibited by pertussis toxin, suggesting the involvement of a receptor-mediated mechanism. Furthermore, SCFAs can specifically inhibit constitutive monocyte chemotactic protein-1 (MCP-1) production and LPS-induced interleukin-10 (IL-10) production in human monocytes without affecting the secretion of other cytokines and chemokines examined. Similar activities were observed in human PBMC for the release of PGE₂, MCP-1 and IL-10 after SCFA treatment. In addition, SCFAs inhibit LPS-induced production of tumor necrosis factor-α and interferon-γ in human PBMC. Finally, we show that SCFAs and LPS can induce PGE₂ production in vivo by intraplantar injection into rat paws (P < 0.01).

CONCLUSION: SCFAs can have distinct antiinflammatory activities due to their regulation of PGE₂, cytokine and chemokine release from human immune cells.

Localization of 5-HT1B, 5-HT1D alpha, 5-HT1E and 5-HT1F receptor messenger RNA in rodent and primate brain

In situ hybridization histochemistry (ISHH) was used to study the distribution of various 5-HT1 receptor messenger RNAs (mRNA) in the mammalian nervous system. Since the cDNAs encoding the different 5-HT1 receptors, have not been cloned in one single species, brains of the species appropriate for the 5-HT1 receptor messenger RNA (mRNA) have been used. Thus, 5-HT1B and 5-HT1D alpha mRNA were determined in rat and mouse brain, while 5-HT1E and 5-HT1F mRNA were studied in human (and monkey) and guinea-pig brain, respectively. 5-HT1B and 5-HT1D alpha hybridization signals were predominantly present in caudate-putamen and cortical areas; in addition, 5-HT1B mRNA was also detected in hippocampus, cerebellum and cerebral arteries. In general, the distribution of 5-HT1B mRNA was characterized by high densities, whereas 5-HT1D alpha mRNA was expressed at very low levels. Comparison of the localization of the mRNAs to the regional distributions of the 5-HT1B and 5-HT1D binding sites in rat brain (described in a previous study), revealed that both receptor subtypes could be putative presynaptic heteroreceptors, modulating the release of various neurotransmitters in the central nervous system. The mRNA encoding the recently cloned 5-HT1E receptor, which has low affinity for the 5-HT1 receptor ligand 5-carboxamidotryptamine (5-CT), was localized in human brain. It was found to be present in cortical areas, caudate, putamen and amygdala, areas known to contain 5-CT insensitive 5-HT1 binding sites. The regional distribution of the 5-HT1F mRNA was determined in guinea-pig brain: high densities were observed in various cortical areas, the hippocampal formation and claustrum, which are regions known to contain 5-CT insensitive 5-HT1 or non 5-HT1A/1B/IC/ID [3H]5-HT binding sites. Altogether, this ISHH study describes the distribution of mRNAs of recently cloned 5-HT1 receptors in rodent and primate brain and compares these results to the distribution of the heterogeneous population of 5-HT1 binding sites.

A receptor autoradiographic and in situ hybridization analysis of the distribution of the 5-ht7 receptor in rat brain

1. Receptor autoradiography and in situ hybridization histochemistry have been used to delineate the distribution of the 5-ht7 receptor and its mRNA in rat brain. Receptor autoradiographic studies were performed using [3H]-5-carboxamidotryptamine (5-CT) as the radioligand. The binding characteristics of the masking compounds were determined in Cos-7 cells transfected with a panel of 5-HT receptor subtype cDNAs, including the rat 5-ht7 cDNA. In situ hybridization studies were carried out with 35S-labelled oligonucleotide probes to the rat 5-ht7 mRNA. 2. Specific binding of [3H]-5-CT was observed in many areas of the rat brain. Following co-incubation with 1 microM ergotamine, this binding was completely eliminated. After addition of the masking ligands, [3H]-5-CT binding remained in layers 1-3 of cortex, septum, globus pallidus, thalamus, hypothalamus, centromedial amygdala, substantia nigra, periaquaductal gray, and superior colliculus. Addition of the antagonist, methiothepin, to the incubation regimen eliminated most of the remaining [3H]-5-CT binding in the brain, with the exception of the globus pallidus and substantia nigra. 3. The 5-ht7 mRNA was discretely localized in rat brain. The most intense hybridization signals were observed over the thalamus, the anterior hippocampal rudiment, and over the CA3 region of the hippocampus. Other regions containing hybridization signals included the septum, the hypothalamus, the centromedial amygdala and the periaquaductal gray. The regions exhibiting a modest receptor binding signal after methiothepin incubation, the globus pallidus and the substantia nigra, contained no 5-ht7 hybridization signals, suggesting a non-5-ht7 subtype in these two related structures. 4. The distribution of the 5-ht7 receptor and its mRNA is suggestive of multiple roles for this novel 5-HT receptor, within several brain systems. The limbic system (centromedial amygdala, anterior hippocampal rudiment, hypothalamus) is particularly well-represented, indicating a potential role for the 5-ht7 receptor in affective processes.

Targeted deletion of Gpbar1 protects mice from cholesterol gallstone formation

The Gpbar1 [G-protein-coupled BA (bile acid) receptor 1] is a recently identified cell-surface receptor that can bind and is activated by BAs, but its physiological role is unclear. Using targeted deletion of the Gpbar1 gene in mice, we show that the gene plays a critical role in the maintenance of bile lipid homoeostasis. Mice lacking Gpbar1 expression were viable, developed normally and did not show significant difference in the levels of cholesterol, BAs or any other bile constituents. However, they did not form cholesterol gallstones when fed a cholic acid-containing high-fat diet, and liver-specific gene expression indicated that Gpbar1-deficient mice have altered feedback regulation of BA synthesis. These results suggest that Gpbar1 plays a critical role in the formation of gallstones, possibly via a regulatory mechanism involving the cholesterol 7alpha-hydroxylase pathway.

ADP is the cognate ligand for the orphan G protein-coupled receptor SP1999

P2Y receptors are a class of G protein-coupled receptors activated primarily by ATP, UTP, and UDP. Five mammalian P2Y receptors have been cloned so far including P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11. P2Y1, P2Y2, and P2Y6 couple to the activation of phospholipase C, whereas P2Y4 and P2Y11 couple to the activation of both phospholipase C and the adenylyl cyclase pathways. Additional ADP receptors linked to Galpha(i) have been described but have not yet been cloned. SP1999 is an orphan G protein-coupled receptor, which is highly expressed in brain, spinal cord, and blood platelets. In the present study, we demonstrate that SP1999 is a Galpha(i)-coupled receptor that is potently activated by ADP. In an effort to identify ligands for SP1999, fractionated rat spinal cord extracts were assayed for Ca(2+) mobilization activity against Chinese hamster ovary cells transiently transfected with SP1999 and chimeric Galpha subunits (Galpha(q/i)). A substance that selectively activated SP1999-transfected cells was identified and purified through a series of chromatographic steps. Mass spectral analysis of the purified material definitively identified it as ADP. ADP was subsequently shown to inhibit forskolin-stimulated adenylyl cyclase activity through selective activation of SP1999 with an EC(50) of 60 nM. Other nucleotides were able to activate SP1999 with a rank order of potency 2-MeS-ATP = 2-MeS-ADP > ADP = adenosine 5'-O-2-(thio)diphosphate > 2-Cl-ATP > adenosine 5'-O-(thiotriphosphate). Thus, SP1999 is a novel, Galpha(i)-linked receptor for ADP.

Localization of messenger RNAs encoding three GABA transporters in rat brain: an in situ hybridization study

Localization of the messenger RNAs encoding three gamma-aminobutyric acid (GABA) transporters, termed GAT-1, GAT-2, and GAT-3, has been carried out in rat brain using radiolabeled oligonucleotide probes and in situ hybridization histochemistry. Hybridization signals for GAT-1 mRNA were observed over many regions of the rat brain, including the retina, olfactory bulb, neocortex, ventral pallidum, hippocampus, and cerebellum. At the microscopic level, this signal appeared to be restricted to neuronal profiles, and the overall distribution of GAT-1 mRNA closely paralleled that seen in other studies with antibodies to GABA. Areas containing hybridization signals for GAT-3 mRNA included the retina, olfactory bulb, subfornical organ, hypothalamus, midline thalamus, and brainstem. In some regions, the hybridization signal for GAT-3 seemed to be preferentially distributed over glial cells, although hybridization signals were also observed over neurons, particularly in the retina and olfactory bulb. Notably, hybridization signal for GAT-3 mRNA was absent from the neocortex and cerebellar cortex, and was very weak in the hippocampus. In contrast to the parenchymal localization obtained for GAT-1 and GAT-3 mRNAs, hybridization signals for GAT-2 mRNA were found only over the leptomeninges (pia and arachnoid). The differential distribution of the three GABA transporters described here suggests that while each plays a role in GABA uptake, they do so via distinct cellular populations.

Identical immunoreactivity of afferents to the rat suprachiasmatic nucleus with antisera against avian pancreatic polypeptide, molluscan cardioexcitatory peptide and neuropeptide Y

Avian pancreatic polypeptide (APP)-like, molluscan cardioexcitatory peptide (FMRF)-like and neuropeptide Y (NPY)-like immunoreactivities were studied in a secondary visual pathway in rat brain. The cell bodies of this pathway are located in the lateral geniculate nucleus and its terminal plexus is found in the suprachiasmatic hypothalamic nucleus (SCN). The neurons and terminal plexus demonstrated by antiserum to each peptide are identical, and immunoreactivity is blocked by preabsorption of each antiserum with a low concentration of the antigen against which it was raised. Immunoreactivity is also blocked by preabsorption of each antiserum with either NPY or APP. In contrast, APP- and NPY-like immunoreactivities are blocked only partially when these antisera are preabsorbed with concentrations of FMRF as high as 100 microM. Since NPY is the only one of these peptides that has been isolated from mammalian brain, we conclude that NPY is the endogenous CNS peptide produced by neurons of the lateral geniculate-SCN projection.

Identification of overexpression of orphan G protein-coupled receptor GPR49 in human colon and ovarian primary tumors

We used gene expression profiling to probe differences in transcriptional output between 15 panels of colon tumor and matched normal colon tissues. This analysis revealed that GPR49, an orphan G Protein-Coupled Receptor (GPCR) is overexpressed in 66% (10/15) colon tumors compared with normal colon tissues. Subsequent analysis of an additional 39 sets of matched normal and tumor colon tissues by real-time quantitative reverse transcriptase confirmed the upregulation of this receptor. The differential expression of GPR49 between normal and tumor tissue was significant (p > 0.001). GPR49 was upregulated in 25 of 39 (64%) colon primary tumor tissues. In addition to colon tumors, GPR49 was also found to be upregulated in 18 of 33 (53%) ovarian primary tumor tissues analyzed by RT-PCR. Moreover, the expression level of GPR49 in colon and ovarian tumors increased in more advanced tumors suggesting a role for the receptor in tumor progression. The selective overexpression of GPR49 in tumor tissues was further illustrated by specific immunohistochemical staining of colon and ovarian tumor tissues, a finding that correlates with the mRNA expression of the receptor. In addition, expression of GPR49 induced transformation in a ligand-dependent manner and Knockdown of GPR49 mRNA level induced apoptosis in colon tumor cells. These novel findings provide a foundation for further studies and suggest a potential role for GPR49 in tumorigenesis.

Identification and characterization of a novel RF-amide peptide ligand for orphan G-protein-coupled receptor SP9155

Orphan G-protein-coupled receptors are a large class of receptors whose cognate ligands are unknown. SP9155 (also referred to as AQ27 and GPR103) is an orphan G-protein-coupled receptor originally cloned from a human brain cDNA library. SP9155 was found to be predominantly expressed in brain, heart, kidney, retina, and testis. Phylogenetic analysis shows that SP9155 shares high homology with Orexin, NPFF, and cholecystokinin (CCK) receptors, but identification of the endogenous ligand for SP9155 has not been reported. In this study, we have used a novel method to predict peptides from genome data bases. From these predicted peptides, a novel RF-amide peptide, P52 was shown to selectively activate SP9155-transfected cells. We subsequently cloned the precursor gene of the P52 ligand and characterized the activity of other possible peptides encoded by the precursor. This revealed an extended peptide, P518, which exhibited high affinity for SP9155 (EC50 = 7 nm). mRNA expression analysis revealed that the peptide P518 precursor gene is predominantly expressed in various brain regions, coronary arteries, thyroid and parathyroid glands, large intestine, colon, bladder, testes, and prostate. These results indicate the existence of a novel RF-amide neuroendocrine peptide system, and suggest that SP9155 is likely the relevant G-protein-coupled receptor for this peptide.

P2Y(13): identification and characterization of a novel Galphai-coupled ADP receptor from human and mouse

We have identified an orphan G protein-coupled receptor, SP174, that shares a high degree of homology with the recently described ADP receptor P2Y(12). mRNA for SP174 is abundant in the brain and in cells of the immune system. In the present study, we demonstrate that SP174 is also a receptor for ADP, which is coupled to Galphai. ADP potently stimulates SP174 with an EC(50) of 60 nM, and other related nucleotides are active as well, with a rank order of potency 2-methylthio-ADP tetrasodium = adenosine 5'-O-2-(thio)diphosphate = 2-methylthio-ATP tetrasodium > ADP > AP3A >ATP > IDP. This pharmacological profile is similar to that for P2Y(12). We have also identified the murine homolog of SP174, which exhibits 75% homology to the human receptor. ADP is also a potent agonist at the murine receptor, and its pharmacological profile is similar to its human counterpart, but ADP and related nucleotides are more potent at the murine receptor than the human receptor. In keeping with the general nomenclature for the purinergic receptors, we propose designating this novel receptor P2Y(13).

Epstein-Barr virus encodes a novel homolog of the bcl-2 oncogene that inhibits apoptosis and associates with Bax and Bak

The sequenced gammaherpesviruses each contain a single viral bcl-2 homolog (v-bcl-2) which may encode a protein that functions in preventing the apoptotic death of virus-infected cells. Epstein-Barr virus (EBV), a gammaherpesvirus associated with several lymphoid and epithelial malignancies, encodes the v-Bcl-2 homolog BHRF1. In this report the previously uncharacterized BALF1 open reading frame in EBV is identified as having significant sequence similarity to other v-bcl-2 homologs and cellular bcl-2. Transfection of cells with a BALF1 cDNA conferred apoptosis resistance. Furthermore, a recombinant green fluorescent protein-BALF1 fusion protein suppressed apoptosis and associated with Bax and Bak. These results indicate that EBV encodes a second functional v-bcl-2.

GPR119 is required for physiological regulation of glucagon-like peptide-1 secretion but not for metabolic homeostasis

G protein-coupled receptor 119 (GPR119) is expressed in pancreatic islets and intestine, and is involved in insulin and incretin hormone release. GPR119-knockout (Gpr119(-/-)) mice were reported to have normal islet morphology and normal size, body weight (BW), and fed/fasted glucose levels. However, the physiological function of GPR119 and its role in maintaining glucose homeostasis under metabolic stress remain unknown. Here, we report the phenotypes of an independently generated line of Gpr119(-/-) mice under basal and high-fat diet (HFD)-induced obesity. Under low-fat diet feeding, Gpr119(-/-) mice show normal plasma glucose and lipids, but have lower BWs and lower post-prandial levels of active glucagon-like peptide 1 (GLP-1). Nutrient-stimulated GLP-1 release is attenuated in Gpr119(-/-) mice, suggesting that GPR119 plays a role in physiological regulation of GLP-1 secretion. Under HFD-feeding, both Gpr119(+)(/)(+) and Gpr119(-/-) mice gain weight similarly, develop hyperinsulinemia and hyperleptinemia, but not hyperglycemia or dyslipidemia. Glucose and insulin tolerance tests did not reveal a genotypic difference. These data show that GPR119 is not essential for the maintenance of glucose homeostasis. Moreover, we found that oleoylethanolamide (OEA), reported as a ligand for GPR119, was able to suppress food intake in both Gpr119(+)(/)(+) and Gpr119(-/-) mice, indicating that GPR119 is not required for the hypophagic effect of OEA. Our results demonstrate that GPR119 is important for incretin and insulin secretion, but not for appetite suppression.

Distribution of a rat galanin receptor mRNA in rat brain

In situ hybridization histochemistry has been employed to determine the distribution of the mRNA encoding a recently cloned rat galanin receptor (rGalR1). The galanin receptor mRNA has been found to be discretely localized in rat brain. The most intense hybridization signals were found over neurons in the nucleus of the lateral olfactory tract, in the ventral posterior hippocampus, and in the lateral external subdivision of the parabrachial nucleus. A number of other brain regions also contain significant hybridization signals, including the hypothalamus, brain stem and spinal cord. The localization of rGalR1 mRNA indicates that this receptor may play a role in the varied functions ascribed to GAL, among them feeding, cognition and modulation of sensory information.

Cloning and expression of a betaine/GABA transporter from human brain

A cDNA clone encoding a human gamma-aminobutyric acid (GABA) transporter has been isolated from a brain cDNA library, and its functional properties have been examined in mammalian cells. The nucleotide sequence predicts a transporter with 614 amino acids and 12 putative transmembrane domains. The highest degree of amino acid identity is with a betaine/GABA transporter originally cloned from the dog termed BGT-1 (91%) and a related transporter from mouse brain (87%). These identities are similar to those for species homologues of other neurotransmitter transporters and suggest that the new clone represents the human homologue of BGT-1. The transporter displays high affinity for GABA (IC50 of 30 microM) and is also sensitive to phloretin, L-2,4-diaminobutyric acid, and hypotaurine (IC50 values of approximately 150-400 microM). The osmolyte betaine is approximately 25-fold weaker than GABA, displaying an IC50 of approximately 1 mM. The relative potencies of these inhibitors at human BGT-1 differ from those of mouse and dog BGT-1. Northern blot analysis reveals that BGT-1 mRNA is widely distributed throughout the human brain. The cloning of the human homologue of BGT-1 will further our understanding of the roles of GABA and betaine in neural function.

Distribution of the neuropeptide Y Y2 receptor mRNA in rat central nervous system

Our group has recently reported the expression cloning of the human neuropeptide Y Y2 receptor DNA and subsequently the cloning of the rat homologue. These studies have made it possible to localize the mRNA encoding this NPY receptor subtype in rat tissues. We have, thus, carried out in situ hybridization studies, using radiolabeled oligonucleotide probes to the rat Y2 receptor mRNA, to determine the distribution of Y2 mRNA in rat brain and limited peripheral ganglia. Probe specificity was confirmed by testing antisense and sense probes in transfected cells. In rat brain, hybridization signals obtained with the antisense probes were discrete and were restricted to neuronal profiles in specific subregions of the cortex, hippocampus, amygdala, thalamus, hypothalamus, mesencephalon and pons. Among the regions exhibiting the most intense labeling were the CA3 region of the hippocampus, the arcuate nucleus of the hypothalamus and layer 3 of the piriform cortex. Other regions containing labeled neurons included the medial amygdala, the centromedial thalamic nucleus, the dorsal raphe, the dorsal motor nucleus of the vagus and the trigeminal ganglion. The present results indicate that the mRNA encoding the Y2 receptor is discretely localized in the rat brain and that the distribution is generally consistent with previous radioligand-binding studies. This study should help clarify the relationship between the Y2 receptor distribution and functional studies of NPY receptor subtype classification and provides further evidence for the involvement of the Y2 receptor in multiple physiological processes.

Lack of FFAR1/GPR40 does not protect mice from high-fat diet-induced metabolic disease

OBJECTIVE

FFAR1/GPR40 is a G-protein-coupled receptor expressed predominantly in pancreatic islets mediating free fatty acid-induced insulin secretion. However, the physiological role of FFAR1 remains controversial. It was previously reported that FFAR1 knockout (Ffar1(-/-)) mice were resistant to high-fat diet-induced hyperinuslinemia, hyperglycemia, hypertriglyceridemia, and hepatic steatosis. A more recent report suggested that although FFAR1 was necessary for fatty acid-induced insulin secretion in vivo, deletion of FFAR1 did not protect pancreatic islets against fatty acid-induced islet dysfunction. This study is designed to investigate FFAR1 function in vivo using a third line of independently generated Ffar1(-/-) mice in the C57BL/6 background.

RESEARCH DESIGN AND METHODS

We used CL-316,243, a beta3 adrenergic receptor agonist, to acutely elevate blood free fatty acids and to study its effect on insulin secretion in vivo. Ffar1(+/+) (wild-type) and Ffar1(-/-) (knockout) mice were placed on two distinct high-fat diets to study their response to diet-induced obesity.

RESULTS

Insulin secretion was reduced by approximately 50% in Ffar1(-/-) mice, confirming that FFAR1 contributes significantly to fatty acid stimulation of insulin secretion in vivo. However, Ffar1(+/+) and Ffar1(-/-) mice had similar weight, adiposity, and hyperinsulinemia on high-fat diets, and Ffar1(-/-) mice showed no improvement in glucose or insulin tolerance tests. In addition, high-fat diet induced comparable levels of lipid accumulation in livers of Ffar1(+/+) and Ffar1(-/-) mice.

CONCLUSIONS

FFAR1 is required for normal insulin secretion in response to fatty acids; however, Ffar1(-/-) mice are not protected from high-fat diet-induced insulin resistance or hepatic steatosis.

Vasa protein expression is restricted to the small micromeres of the sea urchin, but is inducible in other lineages early in development

Vasa is a DEAD-box RNA helicase that functions in translational regulation of specific mRNAs. In many animals it is essential for germ line development and may have a more general stem cell role. Here we identify vasa in two sea urchin species and analyze the regulation of its expression. We find that vasa protein accumulates in only a subset of cells containing vasa mRNA. In contrast to vasa mRNA, which is present uniformly throughout all cells of the early embryo, vasa protein accumulates selectively in the 16-cell stage micromeres, and then is restricted to the small micromeres through gastrulation to larval development. Manipulating early embryonic fate specification by blastomere separations, exposure to lithium, and dominant-negative cadherin each suggest that, although vasa protein accumulation in the small micromeres is fixed, accumulation in other cells of the embryo is inducible. Indeed, we find that embryos in which micromeres are removed respond by significant up-regulation of vasa protein translation, followed by spatial restriction of the protein late in gastrulation. Overall, these results support the contention that sea urchins do not have obligate primordial germ cells determined in early development, that vasa may function in an early stem cell population of the embryo, and that vasa expression in this embryo is restricted early by translational regulation to the small micromere lineage.

Analysis of respiratory syncytial virus F, G, and SH proteins in cell fusion

Recombinant expression of the human respiratory syncytial virus (RSV) fusion (F) glycoprotein, receptor-binding glycoprotein (G), and small hydrophobic (SH) protein was performed to determine the role(s) of these proteins in syncytia formation. These studies used a vaccinia virus expressing the bacteriophage (T7) RNA polymerase gene and plasmid vectors containing the RSV genes under the control of a T7 promoter. Within the context of this expression system, expression of any individual RSV gene, or coexpression of F+G genes, did not elicit the formation of syncytia. However, at plasmid input levels which were 10-fold higher than those normally used, coexpression of F+G induced low but detectable levels of cell fusion. In contrast, coexpression of F, G, and SH together elicited extensive cell fusion resembling that of an authentically infected cell monolayer. In addition, coexpression of F and SH elicited significant cell fusion, although to a lesser extent than was observed when G was included. Cell fusion induced by coexpression of F+SH was found to be specific to the RSV proteins, since coexpression of SH with the analogous F proteins from human parainfluenza virus type 3, human parainfluenza virus type 2, Sendai virus, or simian virus type 5 (SV5) did not elicit cell fusion. Finally, coexpression of the SV5 SH protein with the RSV or SV5 glycoproteins also failed to induce syncytia, suggesting type-specific restrictions between the two sets of viral proteins.

Identification and pharmacological characterization of a novel human melanin-concentrating hormone receptor, mch-r2

Melanin-concentrating hormone (MCH) is a neuropeptide highly expressed in the brain that regulates several physiological functions mediated by receptors in the G protein-coupled receptor family. Recently an orphan receptor, SLC-1, has been identified as an MCH receptor (MCH-R1). Herein we identify and characterize a novel receptor for human MCH (MCH-R2). The receptor is composed of 340 amino acids encoded by a 1023-base pair cDNA and is 35% homologous to SLC-1. (125)I-MCH specifically bound to Chinese hamster ovary cells stably expressing MCH-R2. MCH stimulated dose-dependent increases in intracellular free Ca(2+) and inositol phosphate production in these cells but did not affect cAMP production. The pharmacological profile for mammalian MCH, [Phe(13),Tyr(19)]MCH, and salmon MCH at MCH-R2 differed compared with MCH-R1 as assessed by intracellular signaling and radioligand binding assays. The EC(50) in signaling assays and the IC(50) in radioligand binding assays of salmon MCH was an order of magnitude higher than mammalian MCH at MCH-R2. By comparison, the EC(50) and IC(50) values of salmon MCH and mammalian MCH at MCH-R1 were relatively similar. Blot hybridization revealed exclusive expression of MCH-R2 mRNA in several distinct brain regions, particularly in the cortical area, suggesting the involvement of MCH-R2 in the central regulation of MCH-mediated functions.

Identification of a human gastrointestinal tract and immune system receptor for the peptide neuromedin U

Neuromedin U (NmU) is a 25 amino acid peptide prominently expressed in the upper gastrointestinal (GI) tract and central nervous system. It is highly conserved throughout evolution and induces smooth muscle contraction in a variety of species. Our understanding of NmU biology has been limited because the identity of its receptor was unknown. Here we demonstrate that GPR66/FM-3 is specifically stimulated by NmU, causing the mobilization of intracellular calcium. This response was dose-dependent (EC(50) = 10 nM) and specific in that none of over 1000 ligands tested, including other neuromedins (NmB, C, L, K, N), induced a calcium flux in GPR66/FM-3-transfected cells. The GPR66/FM-3 mRNA is prominently expressed in the upper GI tract of humans, as is the mRNA for NmU, consistent with role for this receptor-ligand pair in regulating the function of this organ system. In addition, we show that whereas neuromedin U is expressed by monocytes and dendritic cells, GPR66/FM-3 is expressed by T cells and NK cells. These data suggest a previously unrecognized role for NmU as an immunoregulatory molecule.

Identification of a novel neuromedin U receptor subtype expressed in the central nervous system

Neuromedin U is a neuropeptide prominently expressed in the upper gastrointestinal tract and central nervous system. Recently, GPR66/FM-3 (NmU-R1) was identified as a specific receptor for neuromedin U. A BLAST search of the GenBank(TM) genomic database using the NmU-R1 cDNA sequence revealed a human genomic fragment encoding a G protein-coupled receptor that we designated NmU-R2 based on its homology to NmU-R1. The full-length NmU-R2 cDNA was subsequently cloned, stably expressed in 293 cells, and shown to mobilize intracellular calcium in response to neuromedin U. This response was dose-dependent (EC(50) = 5 nm) and specific in that other neuromedins did not induce a calcium flux in receptor-transfected cells. Expression analysis of human NmU-R2 demonstrated its mRNA to be most highly expressed in central nervous system tissues. Based on these data, we conclude that NmU-R2 is a novel neuromedin U receptor subtype that is likely to mediate central nervous system-specific neuromedin U effects.

Human ADAM33 messenger RNA expression profile and post-transcriptional regulation

We examined transcript expression and post-transcriptional regulation of human ADAM33, a recently identified asthma gene. A detailed messenger RNA (mRNA) expression profile was obtained using Northern, reverse transcription polymerase chain reaction, and in situ hybridization analyses. ADAM33 mRNA was expressed significantly in smooth muscle-containing organs, minimally in immune organs and hematopoietic cells, and highly in repairing duodenal granulation tissue. Expression was seen in asthmatic subepithelial fibroblasts and smooth muscle but not in respiratory epithelium. In all tissues, transcripts of approximately 5 kb predominated over those of approximately 3.5 kb by 2- to 5-fold. The effect of the 3' untranslated region (UTR) on ADAM33 protein expression and maturation was examined. The presence of the 3'UTR in untagged full-length constructs promoted prodomain removal, detected as mature approximately 100 kD protein by ADAM33-reactive antibodies; in its absence, maturation was 2- to 3-fold less in HEK293 cells. His-tagged and untagged constructs lacking the 3'UTR demonstrated that lack of maturation was not a result of tag-mediated effects. Minimal maturation of ADAM33 occurred in primary lung and MRC5 fibroblasts following adenoviral-mediated expression of ADAM33 lacking the 3'UTR. In contrast, prodomain removal was observed with plasmids and adenovirus encoding only the pro- and catalytic domains. Thus, the 3'UTR of ADAM33 and domains downstream of the catalytic domain regulate potential ADAM33 activity. Mechanisms of regulation of ADAM33, distinct from closely related ADAMs, thus include mRNA localization and processing and protein maturation.