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Using a genomics-based reverse pharmacological approach for screening orphan G-protein coupled receptors, we have identified and cloned a novel high-affinity histamine receptor. This receptor, termed AXOR35, is most closely related to the H3 histamine receptor, sharing 37% protein sequence identity. A multiple responsive element/cyclic AMP-responsive element-luciferase reporter assay was used to identify histamine as a ligand for AXOR35. When transfected into human embryonic kidney 293 cells, the AXOR35 receptor showed a strong, dose-dependent calcium mobilization response to histamine and H3 receptor agonists including imetit and immepip. Radioligand binding confirmed that the AXOR35 receptor was a high-affinity histamine receptor. The pharmacology of the AXOR35 receptor was found to closely resemble that of the H3 receptor; the major difference was that (R)-α-methylhistamine was a low potency agonist of the AXOR35 receptor. Thioperamide is an antagonist at AXOR 35. Expression of AXOR35 mRNA in human tissues is highest in peripheral blood mononuclear cells and in tissues likely to contain high concentrations of blood cells, such as bone marrow and lung. In situ hybridization analysis of a wide survey of mouse tissues showed that mouse AXOR35 mRNA is selectively expressed in hippocampus. The identification and localization of this new histamine receptor will expand our understanding of the physiological and pathological roles of histamine and may provide additional opportunities for pharmacological modification of these actions.

Using a genomics-based reverse pharmacological approach for screening orphan G-protein coupled receptors, we have identified and cloned a novel high-affinity histamine receptor. This receptor, termed AXOR35, is most closely related to the H3 histamine receptor, sharing 37% protein sequence identity. A multiple responsive element/cyclic AMP-responsive element-luciferase reporter assay was used to identify histamine as a ligand for AXOR35. When transfected into human embryonic kidney 293 cells, the AXOR35 receptor showed a strong, dose-dependent calcium mobilization response to histamine and H3 receptor agonists including imetit and immepip. Radioligand binding confirmed that the AXOR35 receptor was a high-affinity histamine receptor. The pharmacology of the AXOR35 receptor was found to closely resemble that of the H3 receptor; the major difference was that (R)-alpha-methylhistamine was a low potency agonist of the AXOR35 receptor. Thioperamide is an antagonist at AXOR 35. Expression of AXOR35 mRNA in human tissues is highest in peripheral blood mononuclear cells and in tissues likely to contain high concentrations of blood cells, such as bone marrow and lung. In situ hybridization analysis of a wide survey of mouse tissues showed that mouse AXOR35 mRNA is selectively expressed in hippocampus. The identification and localization of this new histamine receptor will expand our understanding of the physiological and pathological roles of histamine and may provide additional opportunities for pharmacological modification of these actions.

Opiate tolerance and dependence are major clinical and social problems. The anti-opiate neuropeptides FF and AF (NPFF and NPAF) have been implicated in pain modulation as well as in opioid tolerance and may play a critical role in this process, although their mechanism of action has remained unknown. Here we describe a cDNA encoding a novel neuropeptide Y-like human orphan G protein-coupled receptor (GPCR), referred to as HLWAR77 for which NPAF and NPFF have high affinity. Cells transiently or stably expressing HLWAR77 bind and respond in a concentration-dependent manner to NPAF and NPFF and are also weakly activated by FMRF-amide (Phe-Met-Arg-Phe-amide) and a variety of related peptides. The high affinity and potency of human NPFF and human NPAF for HLWAR77 strongly suggest that these are the cognate ligands for this receptor. Expression of HLWAR77 was demonstrated in brain regions associated with opiate activity, consistent with the pain-modulating activity of these peptides, whereas the expression in adipose tissue suggests other physiological and pathophysiological activities for FMRF-amide neuropeptides. The discovery that the anti-opiate neuropeptides are the endogenous ligands for HLWAR77 will aid in defining the physiological role(s) of these ligands and facilitate the identification of receptor agonists and antagonists.

We have identified a cDNA, designated HOFNH30, which encodes a 354 amino acid G-protein-coupled receptor (GPCR). This receptor has 96% amino acid identity to the Jurkat-T cell-derived EDG7 and could be a splice variant. RT-PCR analysis demonstrated that HOFNH30 mRNA is expressed in placenta whereas EDG7 mRNA shows highest expression in prostate. The HOFNH30 gene is localized to human chromosome 1p22.3-1p31.1. When HOFNH30 was expressed in RBL-2H3 cells, LPA and phosphatidic acid (PA) induced a calcium mobilization response with EC50 values of 13 nM and 3 μM, respectively. LPA also induced phosphorylation of mitogen-activated protein kinase (p42MAPK and p44MAPK) in HOFNH30-transfected but not vector-transfected RBL-2H3 cells. In the present study, we have identified a novel variant from the EDG receptor family, a GPCR for which LPA is a high-affinity endogenous ligand.

The cysteinyl leukotrienes (CysLTs) have been implicated in the pathophysiology of inflammatory disorders, in particular asthma, for which the CysLT receptor antagonists pranlukast, zafirlukast, and montelukast, have been introduced recently as novel therapeutics. Here we report on the molecular cloning, expression, localization, and pharmacological characterization of a CysLT receptor (CysLTR), which was identified by ligand fishing of orphan seven-transmembrane-spanning, G protein-coupled receptors. This receptor, expressed in human embryonic kidney (HEK)-293 cells responded selectively to the individual CysLTs, LTC4, LTD4, or LTE4, with a calcium mobilization response; the rank order potency was LTD4(EC50= 2.5 nM) > LTC4(EC50= 24 nM) > LTE4(EC50= 240 nM). Evidence was provided that LTE4is a partial agonist at this receptor. [3H]LTD4binding and LTD4-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor were potently inhibited by the structurally distinct CysLTR antagonists pranlukast, montelukast, zafirlukast, and pobilukast; the rank order potency was pranlukast = zafirlukast > montelukast > pobilukast. LTD4-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor was not affected by pertussis toxin, and the signal appears to be the result of the release from intracellular stores. Localization studies indicate the expression of this receptor in several tissues, including human lung, human bronchus, and human peripheral blood leukocytes. The discovery of this receptor, which has characteristics of the purported CysLT1receptor subtype, should assist in the elucidation of the pathophysiological roles of the CysLTs and in the identification of additional receptor subtypes.

The cysteinyl leukotrienes (CysLTs) have been implicated in the pathophysiology of inflammatory disorders, in particular asthma, for which the CysLT receptor antagonists pranlukast, zafirlukast, and montelukast, have been introduced recently as novel therapeutics. Here we report on the molecular cloning, expression, localization, and pharmacological characterization of a CysLT receptor (CysLTR), which was identified by ligand fishing of orphan seven-transmembrane-spanning, G protein-coupled receptors. This receptor, expressed in human embryonic kidney (HEK)-293 cells responded selectively to the individual CysLTs, LTC(4), LTD(4), or LTE(4), with a calcium mobilization response; the rank order potency was LTD(4) (EC(50) = 2.5 nM) > LTC(4) (EC(50) = 24 nM) > LTE(4) (EC(50) = 240 nM). Evidence was provided that LTE(4) is a partial agonist at this receptor. [(3)H]LTD(4) binding and LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor were potently inhibited by the structurally distinct CysLTR antagonists pranlukast, montelukast, zafirlukast, and pobilukast; the rank order potency was pranlukast = zafirlukast > montelukast > pobilukast. LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor was not affected by pertussis toxin, and the signal appears to be the result of the release from intracellular stores. Localization studies indicate the expression of this receptor in several tissues, including human lung, human bronchus, and human peripheral blood leukocytes. The discovery of this receptor, which has characteristics of the purported CysLT(1) receptor subtype, should assist in the elucidation of the pathophysiological roles of the CysLTs and in the identification of additional receptor subtypes.

We have established a rapid, sensitive, high-throughput assay that requires one assay condition to detect agonist effects from Gi-, Gs-, and Gq-coupled receptors. We utilized a vector containing a promoter with three multiple response elements, the vasoactive intestinal peptide promoter and a cAMP response element controlling the transcription of the luciferase gene. An adrenergic agonist, para-aminoclonidine, inhibited forskolin-stimulated luciferase expression when cells were cotransfected with the Gi-coupled α2-C adrenergic receptor and the MRE/CRE reporter vector. Further, we demonstrate that gastrin-releasing peptide, which activates a Gq-coupled GRP receptor, isoproterenol, which activates a Gs-coupled β-adrenergic receptor, calcium ionophores, and phorbol 12-myristate 13-acetate, a stimulator of protein kinase C, can mediate increases in luciferase expression in the presence of forskolin but not in its absence. The effect at Gi-coupled receptor activation correlates with the phosphorylation of the CRE binding protein (CREB); however, the mechanisms mediating the responses to Gq- and Gs-coupled receptors are more complex. We demonstrate that this assay is useful for pharmacological analysis of both agonists and antagonists and has the potential to associate orphan G-protein-coupled receptors with their corresponding ligands.

Thrombin-mediated down-regulation of endothelin (ET) receptors was studied in rat glomerular mesangial cells. Overnight incubation of mesangial cells with thrombin (10 nM) resulted in a significant decrease (67%) in the number of ET receptors, with no change in affinity. Northern analysis of the mRNA from these cells showed a corresponding decrease in the ETA receptor message. Such a decrease in ET receptors could result from an increase in ET levels caused by an increase in synthesis and/or a decrease in degradation. It has been previously reported that thrombin stimulates ET production in endothelial and mesangial cells. Because ET is known to be degraded by neutral endopeptidase (NEP), which is present at high levels in the kidney, the potential effects of thrombin on NEP activity were evaluated. There was a decrease of NEP activity in mesangial cells at 16 and 24 hr after treatment with 10 nM thrombin. This effect was specific for thrombin, because NEP activity was not altered after treatment with thrombin in the presence of hirudin, an inhibitor of thrombin activity. The thrombin-mediated decrease in NEP activity correlated with a decrease in NEP protein and mRNA levels, as determined by Western and Northern analyses, respectively. To determine whether the thrombin-mediated decrease in ET receptors had a functional corollary, ET-1-stimulated intracellular calcium mobilization was measured. Overnight incubation with 10 nM thrombin resulted in a significant inhibition of ET-stimulated intracellular calcium mobilization. This effect was specific for ET, because thrombin pretreatment did not affect vasopressin-stimulated intracellular calcium mobilization in mesangial cells. These results indicate that the thrombin-mediated down-regulation of ET receptors is due, in part, to a thrombin-stimulated increase in ET resulting from the down-regulation of NEP and the reported increase in ET synthesis. In addition, pretreatment of mesangial cells with ET-1 caused a significant decrease (85%) in ET receptor number and ET-1-mediated intracellular calcium release (84%), without affecting vasopressin- or thrombin-mediated responses.

Urea is transported from mucosa to serosa across the skin of the stenohaline toad, Bufo marinus, studied under short circuit current (SCC) conditions. Mucosal to serosal transepithelial urea transport (Jm-->s(urea)) was markedly and asymmetrically enhanced in toads adapted to hypertonic (150 mM) NaCl and showed saturation kinetics with an estimated Kd for urea in the bathing solution of approximately 1 mM and a maximal rate of Jm-->s(urea) = 9.4 nmol.cm-2 x hr-1, consistent with a carrier-mediated transport mechanism. Jm-->s(urea) in the skin of 150 mM NaCl-adapted toads was characterized with drugs known to affect transepithelial urea transport (J(urea)) in the urinary bladder of this species. Amiloride (10(-8)-10(-3) M) inhibited Jm-->s(urea) in a dose-dependent fashion, but with a potency only 1/1000th of that for inhibition of SCC in the same skins. Phloretin (< or = 5 x 10(-4) M) had no effect on Jm-->s(urea) or SCC; ouabain (5 x 10(-4) M) and NaCN (10(-3) M) had no effect on Jm-->s(urea) but inhibited SCC (indicating inhibition of active sodium transport) by 70 and 67%, respectively and vasopressin (10(-8) M) had no effect on Jm-->s(urea), but stimulated SCC 179% above base line. The pyrazinoyl amiloride analog, 2-pyrazinoylguanidine (10(-4) M), reported to inhibit urea transport in mammals, also had no effect on Jm-->s(urea), but inhibited SCC approximately 30%. A 1.5 unit pH gradient (m-->s or s-->m) had no effect on Jm-->s(urea).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of thrombin on mesangial cell function was investigated. Thrombin caused a dose-dependent increase in [3H] thymidine incorporation (EC50 = 0.36 +/- 0.09 U/ml), intracellular calcium [(Ca++)i] mobilization (EC50 = 1.9 +/- 0.5 U/ml) and prostaglandin E2 (PGE2) production (EC50 = 0.25 +/- 0.02 U/ml) in rat glomerular mesangial cells. These effects were blocked by the thrombin inhibitor, hirudin (KB = 10.4 +/- 0.2 nM). The role of (Ca++)i mobilization and arachidonate metabolism in thrombin-stimulated proliferation was tested by the addition of the calcium channel blocker, nifedipine, and the cyclooxygenase inhibitor, indomethacin, to mesangial cell cultures. Indomethacin, at doses that completely inhibited the thrombin-mediated production of PGE2, had no significant effect on proliferation. The Ca++ channel blocker, nifedipine, inhibited both PGE2 production and [3H] thymidine incorporation in a dose-dependent fashion, but only at concentrations considered nonspecific. In addition to its effects on PGE2, thymidine incorporation and Ca++ mobilization, thrombin caused mesangial cell contraction as determined by a substrate distortion technique. This effect was not inhibited by indomethacin. These results indicate that thrombin can alter mesangial cell function in vitro.