Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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We describe the cloning and functional expression of a cDNA encoding a novel G protein-coupled receptor, which was isolated from the central nervous system of the pond snail Lymnaea stagnalis. The amino acid sequence predicted by this cDNA shows highest similarity with the sequence of the Locusta tyramine receptor, the Drosophila tyramine/octopamine receptor, and the mammalian alpha-adrenergic receptors. On expression in mammalian cells, [3H]rauwolscine, an alpha2-adrenergic receptor antagonist, binds with high affinity (K(D) = 2.9 x 10(-9) M) to the receptor. Of several tested neurotransmitters, octopamine (which is considered to be the invertebrate counterpart of norepinephrine) showed the highest affinity (1.9 x 10(-6) M) for the receptor. Therefore, we consider this receptor to be the first true octopamine receptor to be cloned. The ligand binding properties of the novel receptor, designated Lym oa1, seem to be distinct from any of the binding profiles described for octopamine receptors in tissue preparations. Although the pharmacological profile of Lym oa1 shows some similarity with that of Tyr/Oct-Dro and Tyr-Loc, there are also clear differences. In particular, phentolamine, chlorpromazine, and mianserine display markedly higher affinities for Lym oa1 than for the insect receptors. As far as the vertebrate adrenergic receptors are concerned, the ligand binding properties of Lym oa1 resemble alpha2-adrenergic receptors more than they do alpha- or beta-adrenergic receptors. Octopaminergic stimulation of Lym oa1 induces an increase in both inositol phosphates and cAMP (EC50 = 9.1 x 10(-7) M and 5.1 x 10(-6) M, respectively). This is in contrast to the signal transduction pathways described for the related tyramine- and alpha2-adrenergic receptors, which couple in an inhibitory way to adenylyl cyclase.
Mol Pharmacol 1997 Feb
PMID:Molecular cloning and pharmacological characterization of a molluscan octopamine receptor. 920 35

The GnRH receptor is an unusual member of the G protein-coupled receptor (GPCR) superfamily with several unique features. One of these is a variant of the conserved DRY motif that is located at the junction of the third transmembrane domain and the second intracellular (2i) loop of most GPCRs. In the GnRH receptor, the Tyr residue of the conserved triplet is replaced by Ser, giving a DRS sequence. The aspartate and arginine residues of the triplet are highly conserved in almost all GPCRs. The functional importance of these residues was evaluated in wild type and mutant GnRH receptors expressed in COS-7 cells. Mutants in which Asp138 was replaced by Asn or Glu were poorly expressed, but showed significantly increased internalization and exhibited augmented inositol phosphate generation to maximal agonist stimulation compared with the wild type receptor. In contrast, receptors in which Arg139 was substituted with Gln, Ala, or Ser showed reduced internalization, and the GnRH-induced inositol phosphate response for the Arg139Gln mutant was significantly impaired in proportion to its low expression level. Replacing Ser140 with Ala affected neither internalization nor signal transduction. The role of the polar amino acids at the C terminus of the 2i loop was evaluated in two additional mutants (Ser151Ala, Ser153Ala, and Ser151Ala, Ser153Ala, Lys154Gln, Glu156Gln). Both of these mutants exhibited agonist-induced inositol phosphate responses similar to that of the wild type receptor, but showed increased receptor internalization. This mutational analysis indicates that the conserved Asp and Arg residues in the DRY/S triplet make important contributions to the structural integrity of the receptor and influence receptor expression, agonist-induced activation, and internalization.
Mol Endocrinol 1997 Aug
PMID:Mutations of the conserved DRS motif in the second intracellular loop of the gonadotropin-releasing hormone receptor affect expression, activation, and internalization. 925 12

GnRH binds to a specific G protein-coupled receptor in the pituitary to regulate synthesis and secretion of gonadotropins. Using RT-PCR and human pituitary poly(A)+ RNA as a template, the full-length GnRH receptor (wild type) and a second truncated cDNA characterized by a 128-bp deletion between nucleotide positions 522 and 651 were cloned. The deletion causes a frame shift in the open reading frame, thus generating new coding sequence for further 75 amino acids. The truncated cDNA arises from alternative splicing by accepting a cryptic splicing acceptor site in exon 2. Distinct translation products of approximately 45-50 and 42 kDa were immunoprecipitated from COS-7 cells transfected with cDNA coding for wild type GnRH receptor and the truncated splice variant, respectively. Immunocytochemical and enzyme-linked immunosorbent assay studies revealed a membranous expression pattern for both receptor isoforms. Expression of the splice variant, however, occurred at a significantly lower cell surface receptor density. In terms of ligand binding and phospholipase C activation, the wild type receptor showed characteristics of a typical GnRH receptor, whereas the splice variant was incapable of ligand binding and signal transduction. Coexpression of wild type and truncated proteins in transiently or stably transfected cells, however, resulted in impaired signaling via the wild type receptor by reducing maximal agonist-induced inositol phosphate accumulation. The inhibitory effect depended on the amount of splice variant cDNA cotransfected and was specific for the GnRH receptor because signaling via other G(q/11)-coupled receptors, such as the thromboxane A2, M5 muscarinic, and V1 vasopressin receptors, was not affected. Immunological studies revealed that coexpression of the wild type receptor and the truncated splice variant resulted in impaired insertion of the wild type receptor into the plasma membrane. Thus, expression of truncated receptor proteins may highlight a novel principle of specific functional inhibition of G protein-coupled receptors.
Mol Endocrinol 1997 Aug
PMID:Inhibition of gonadotropin-releasing hormone receptor signaling by expression of a splice variant of the human receptor. 925 21

The CRF receptors, CRFR1 and CRFR2, are members of the G protein-coupled receptor superfamily. Despite their considerable sequence similarity, CRFR1 and CRFR2 have quite different affinities for the peptide ligand rat/human CRF. Previous studies using chimeric receptors between human CRFR1 and CRFR2 have identified three potentially important regions in the second and third extracellular domains of CRF receptor for the binding of rat/human CRF. The present report further demonstrates that these same three regions also affect the binding of urocortin and sauvagine, two other members of the CRF peptide family, albeit to different extents. We also show that a fourth region in the third extracellular domain, Asp254, has been identified to be important for sauvagine but not CRF or urocortin binding. Thus, the three peptide ligands not only interact with a different set of regions on CRFR1 and CRFR2 but also differentially interact with some of the same regions. These data could, at least in part, account for the much higher affinity of CRFR2 for urocortin and sauvagine compared with rat/human CRF. We have also identified two amino acid residues, His199 in the third transmembrane domain and Met276 in the fifth transmembrane domain, that are important for binding the non-peptide high-affinity CRFR1 antagonist NBI 27914. Mutations of His199 and Met276 to the corresponding amino acids in CRFR2 each decreased the binding affinity of NBI 27914 for CRFR1 by 40- and 200-fold, respectively. This suggests that the transmembrane regions are critically important in forming the binding pocket for the nonpeptide antagonist.
Mol Endocrinol 1997 Dec
PMID:Localization of agonist- and antagonist-binding domains of human corticotropin-releasing factor receptors. 941 8

A family of G protein-coupled P2Y receptors that are activated by adenine and uridine nucleotides has been identified recently. Degenerate primers based on conserved sequences in these P2Y receptors were used to amplify turkey DNA, which was used to isolate the complete coding sequence of a cDNA that encodes a novel G protein-coupled receptor. Stable expression of this avian cDNA in 1321N1 human astrocytoma cells resulted in the conveyance of marked inositol phosphate responses to various nucleotides. Although this cloned avian receptor exhibited its highest homology to the previously cloned mammalian P2Y4 receptor, its pharmacological selectivity was not consistent with the avian receptor's being a species homologue of the P2Y4 receptor. That is, whereas the P2Y4 receptor is selectively activated by UTP and is not activated by ATP or Ap4A, the novel avian receptor was potently activated by ATP and Ap4A as well as by UTP. Taken together, these results describe the identification of an avian phospholipase C-coupled P2Y receptor that, like the mammalian P2Y2 receptor, is activated by both adenine and uridine nucleotides.
Mol Pharmacol 1997 Dec
PMID:Molecular cloning and expression of an avian G protein-coupled P2Y receptor. 941 2

The mu-opioid receptor is the principal site of action in the brain by which morphine, other opiate drugs of abuse, and endogenous opioid peptides effect analgesia and alter mood. A member of the seven-transmembrane domain (TM) G protein-coupled receptor (GPCR) superfamily, the mu-opioid receptor modulates ion channels and second messenger effectors in an opioid agonist-dependent fashion that is reversible by the classic opiate antagonist naloxone. Mutation of a histidine residue (His297) in TM 6 afforded agonist-like G protein-coupled signal transduction mediated by naloxone and other alkaloid antagonists and enhanced the intrinsic activity of documented alkaloid partial agonists, including buprenorphine. The intrinsic activities of all opioid peptide agonists and antagonists tested were not altered at the His297 mutant receptors. Consistent with a role for the TM 6 histidine in maintaining high affinity binding sites for opioid agonists and antagonists, opioid ligand-dependent protection of this residue from a histidine-specific alkylating agent indicated that the His297 side chain is positioned in or very near the binding cavity. The TM 6 His297 mutants identify a discrete region of the receptor critical for determining whether a specific drug pharmacophore triggers receptor activation. Because many GPCRs possess a similarly positioned TM histidine residue, our findings with the mu-opioid receptor may extend to these receptors and potentially serve as a model for rational design of therapeutic GPCR partial agonists and antagonists.
Mol Pharmacol 1997 Dec
PMID:Naloxone activation of mu-opioid receptors mutated at a histidine residue lining the opioid binding cavity. 941 8

The mammalian bombesin (Bn)-like neuropeptide receptors gastrin-releasing peptide receptor (GRP-R) and neuromedin B receptor (NMB-R) transduce a variety of physiological signals that regulate secretion, growth, muscle contraction, chemotaxis and neuromodulation. We have used reverse transcription-polymerase chain reaction (PCR) to isolate a cDNA from human brain mRNA, GPCR/CNS, that encodes a putative G protein-coupled receptor (GPCR) based upon the presence of the paradigmatic seven heptahelical transmembrane domains in its predicted amino acid sequence. Analysis of the deduced protein sequence of GPCR/CNS reveals this putative receptor to be 98% identical to the deduced amino acid sequence of a recently reported gene product and minimally identical (approximately 23%) to both murine GRP-R and human endothelin-B (ET-B) receptor. Our deduced protein sequence differs at 12 positions, scattered throughout the open reading frame, relative to the original sequence. A 3.7 kb GPCR/CNS mRNA species is expressed in vivo in a tissue-specific manner, with highest levels detected in brain and spinal cord, lower levels found in testis, placenta and liver, but no detectable expression observed in any other tissue. Analysis of GPCR/CNS genomic clones reveals that the human gene contains one intron that is about 21 kb in length that divides the coding region into two exons and maps to human chromosome 7q31. No specific binding is observed with either a newly identified ligand (DTyr6, beta Ala11, Phe13, Nle14]Bn-(6-14)) having high affinity for all Bn receptor subtypes or Bn after GPCR/CNS is stably expressed in fibroblasts. No elevation in inositol trisphosphate is observed after the application of micromolar levels of either DPhe6, beta Ala11, Phe13, Nle14]Bn-(6-14) or Bn, a concentration of agonist known to activate all four known Bn receptor subtypes. When GPCR/CNS is expressed in Xenopus oocytes, no activation of the calcium-dependent chloride channel is detected despite the addition of micromolar levels of Bn peptide agonists. We conclude that the natural ligand for this receptor is none of the known naturally occurring Bn-like peptides and the true agonist for GPCR/CNS remains to be elucidated.
Brain Res Mol Brain Res 1998 Feb
PMID:A human gene encodes a putative G protein-coupled receptor highly expressed in the central nervous system. 952 70

We report the characterization of two distinct binding sites with receptor characteristics for leukotriene (LT)D4 and LTC4 in membranes from human lung parenchyma. The use of S-decyl-glutathione allowed us to characterize a previously unidentified high affinity binding site for LTC4. Computerized analysis of binding data revealed that each leukotriene interacts with two distinct classes of binding sites (Kd = 0.015 and 105 nM for LTC4 and 0.023 and 230 nM for LTD4) and that despite cross-reactivity, the two high affinity sites are different entities. LTD4 binding sites displayed features of G protein-coupled receptors, whereas LTC4 binding sites did not show any significant modulation by guanosine-5'-(beta, gamma-imido)triphosphate or stimulation of GTPase activity. The antagonists ICI 198,615 and SKF 104353 were unselective for the high and low affinity states of LTD4 receptor, whereas only SKF 104353 was able to recognize the two [3H]LTC4 binding sites although with different affinities. These data indicate that in human lung parenchyma, LTD4 and LTC4 recognize two different binding sites; these binding sites are different entities; and for LTD4, the two binding sites represent the interconvertible affinity states of a G protein-coupled receptor, whereas for LTC4, the high affinity site is likely to be a specific LTC4 receptor.
Mol Pharmacol 1998 Apr
PMID:Identification and characterization of two cysteinyl-leukotriene high affinity binding sites with receptor characteristics in human lung parenchyma. 954 67

The Ca2+ receptor is a G protein-coupled receptor that enables parathyroid cells and certain other cells in the body to respond to changes in the concentration of extracellular Ca2+. In this study, two novel phenylalkylamine compounds, NPS 467 and NPS 568, were examined for effects on Xenopus laevis oocytes expressing the bovine or human parathyroid Ca2+ receptors. Increases in chloride current (ICl) were elicited in oocytes expressing the bovine Ca2+ receptor when the extracellular Ca2+ concentration was raised above 1.5 mM, whereas Ca2+ concentrations > 3 mM were generally necessary to elicit responses in oocytes expressing the human Ca2+ receptor. NPS 467 and NPS 568 potentiated the activation of ICl by extracellular Ca2+ in oocytes expressing either Ca2+ receptor homolog, and this resulted in a leftward shift of the Ca2+ concentration-response curve. Neither compound was active in the absence of extracellular Ca2+. Certain inorganic and organic cations known to activate the Ca2+ receptor were substituted for elevated levels of extracellular Ca2+ to increase ICl and the effects of these agonists were also potentiated by NPS 568 or NPS 467. The effects of NPS 568 were stereoselective and the R-enantiomer was about 10-fold more potent than the corresponding S-enantiomer. Neither NPS 467 nor 568 affected ICl in water-injected oocytes or in oocytes expressing the substance K receptor or the metabotropic glutamate receptor 1a. These results provide compelling evidence that NPS 467 and NPS 568 act directly upon the parathyroid Ca2+ receptor to increase its sensitivity to activation by extracellular Ca2+. This activity suggests that these compounds are positive allosteric modulators of the Ca2+ receptor. As such, these compounds define a new class of pharmacological agents with potent and selective actions on the Ca2+ receptor.
Mol Pharmacol 1998 Jun
PMID:Allosteric activation of the Ca2+ receptor expressed in Xenopus laevis oocytes by NPS 467 or NPS 568. 961 12

The signaling of ligands operating via heterotrimeric G proteins is mediated by a complex network that involves sequential phosphorylation events. Signaling by the G protein-coupled receptor GnRH was shown to include elevation of Ca2+ and activation of phospholipases, protein kinase C (PKC) and extra-cellular signal-regulated kinase (ERK). In this study, GnRH was shown to activate Jun N-Terminal Kinase (JNK)/SAPK in alpha T3-1 cells in a PKC- and tyrosine kinase-dependent manner. GnRH as well as tumor-promoting agent (TPA) also increased c-Src activity, which peaked at 2 min after GnRH stimulation and was sensitive both to PKC and to tyrosine kinase inhibitors. Coexpression of Csk, which serves as a Src-dominant interfering kinase, and constitutively active forms of Src, together with JNK, confirmed the involvement of c-Src downstream of PKC in the GnRH-JNK pathway. Coexpression of dominant negative and constitutively active forms of CDC42, Rac1, Ras, MEKK1, and MEK1 with JNK indicated that JNK activation by GnRH and TPA is mediated by CDC42 and MEKK1. Ras and MEK1, which are involved in a related mitogen-activated protein kinase (MAPK) pathway, did not affect JNK activation in alpha T3-1 cells. Taken together, our results suggest that GnRH stimulation of JNK activity is mediated by a unique pathway that includes sequential activation of PKC, c-Src, CDC42, and probably also MEKK1.
Mol Endocrinol 1998 Jun
PMID:Stimulation of Jun N-terminal kinase (JNK) by gonadotropin-releasing hormone in pituitary alpha T3-1 cell line is mediated by protein kinase C, c-Src, and CDC42. 962 57


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