Two nonpeptide tachykinin antagonists act through epitopes on corresponding segments of the NK1 and NK2 receptors

The molecular mechanism of action for two chemically distinct and highly selective, nonpeptide antagonists, CP-96,345 and SR-48,968, was studied by development of a series of chimeric constructs between their respective target receptors, the NK1 (substance P) and NK2 (neurokinin A) receptors. The binding affinities of the natural peptide ligands, substance P and neurokinin A, were not affected by exchanging almost the entire C-terminal half of the NK1 receptor with the corresponding segment of the NK2 receptor. In contrast, it was found that transfer from the NK2 to the NK1 receptor of a segment corresponding to transmembrane segment VI, the amino-terminal half of transmembrane segment VII, and the connecting extracellular loop 3 completely switched the susceptibility for the nonpeptide antagonists. This chimeric exchange, corresponding to 17 nonconserved residues, conveyed full susceptibility for the NK2-specific compound SR-48,968 to the previously unresponsive NK1 receptor--i.e., the Ki value for inhibition of binding of 125I-labeled substance P decreased from > 10,000 to 0.97 nM. At the same time the affinity for the NK1-selective compound CP-96,345 decreased > 30-fold. The actual binding site for SR-48,968 was localized to this region of the NK2 receptor by use of [3H]SR-48,968, which did not bind to the NK1 receptor but bound with similar high affinities to the wild-type NK2 receptor and to the chimeric NK1 receptor with the NK2 receptor segment incorporated around transmembrane segments VI and VII, Kd = 1.5 nM and 1.0 nM, respectively. Our data indicate that two chemically very different nonpeptide antagonists, CP-96,345 and SR-48,968, act through epitopes located around transmembrane segment VI on their respective target receptors and that at least the nonconserved residues in these epitopes are not important for the binding of the natural peptide ligands, substance P and neurokinin A.

Antagonist for atrial natriuretic peptide receptors ameliorates glomerular hyperfiltration in diabetic rats

To evaluate the possible contribution of atrial natriuretic peptide (ANP) to the development of glomerular hyperfiltration, we examined the effect of non-peptide competitive antagonist for biological receptors of ANP, HS-142-1, on glomerular filtration rate (GFR) and renal plasma flow (RPF) in diabetic rats. Increased GFR and RPF in diabetic rats were significantly ameliorated by the injection of HS-142-1, while blood pressure remained unchanged. Urinary cyclic GMP excretion was significantly higher in diabetic rats than in control rats and HS-142-1 decreased urinary cGMP excretion significantly. These results indicate that atrial natriuretic peptide contributes to the development of glomerular hyperfiltration and hyperperfusion in diabetes and HS-142-1 might be useful in the treatment of them.

Molecular characterization of a novel retinal metabotropic glutamate receptor mGluR6 with a high agonist selectivity for L-2-amino-4-phosphonobutyrate

A cDNA clone for a new metabotropic glutamate receptor, termed mGluR6, was isolated from a rat retinal cDNA library by cross-hybridization with the previously isolated cDNA clone for a metabotropic glutamate receptor. The cloned mGluR6 subtype consists of 871 amino acid residues and exhibits a structural architecture common to the metabotropic receptor family, possessing a large extracellular domain preceding the seven putative membrane-spanning domains. mGluR6 shows the highest sequence similarity to mGluR4 among the metabotropic receptor subtypes and inhibits the forskolin-stimulated cyclic AMP accumulation in Chinese hamster ovary cells transfected with the cloned cDNA. mGluR6 potently reacts with L-2-amino-4-phosphonobutyrate (L-AP4) and L-serine-O-phosphate, and the potencies of these compounds are one order of magnitude greater than that of L-glutamate. Blot and in situ hybridization analyses indicated that mGluR6 mRNA is restrictedly expressed in the inner nuclear layer of the retina where ON-bipolar cells are distributed. The metabotropic receptor that responds strongly to L-AP4 and L-serine-O-phosphate in ON-bipolar cells is known to mediate glutamate synaptic transmission between photoreceptor cells and ON-bipolar cells. On the basis of the agonist selectivity of mGluR6 and its specific expression in retinal cells, the physiological role of this receptor subtype in the visual system is discussed.

Glutamate receptor agonists enhance the expression of BDNF mRNA in cultured cerebellar granule cells

The influence of glutamate and its analogues on the expression of BDNF mRNA was studied in cultured cerebellar granule cells. Four-hour exposure of the neurons to the glutamate receptor agonists, quisqualate, kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA), increased levels of BDNF mRNA. Glutamate in combination with antagonists of the ionotropic glutamate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), D-2-amino-5-phosphonovalerate (AP-5) and/or (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine hydrogen maleate (MK-801), also increased levels of BDNF mRNA. However, the addition of glutamate itself to the cultures produced severe neuronal death and failed to increase the mRNA level. The onset of the increase in BDNF mRNA by kainate and NMDA lagged behind that by quisqualate. These results indicate that the non-ionotropic glutamate receptor might be involved in the induction of BDNF mRNA. Quisqualate is known to be a potent agonist of both the AMPA/kainate receptor and the metabotropic glutamate receptor. The specific antagonists of the AMPA/kainate receptor, CNQX and 6,7-dinitroquinoxaline-2,3-dione (DNQX) failed to block the increase of BDNF mRNA by quisqualate. Moreover, the desensitization of the metabotropic glutamate receptor by phorbol ester abolished the increase of BDNF mRNA by quisqualate. These results suggest that stimulation of the metabotropic glutamate receptor may be the most predominant component to increase BDNF mRNA in cerebellar granule cell culture.

Immunocytochemical localization of rat substance P receptor in the striatum

A trp E fusion protein containing a C-terminal portion of the rat substance P receptor (SPR) was expressed in bacteria and used to produce an antibody. The antibody specifically reacted with SPR expressed in a mammalian cell line and rat striatum. Light and electron microscope analyses of the rat striatum revealed intense SPR-like immunoreactivity in neuronal somata and dendrites. These immunoreactive neurons constituted approximately 3% of the total population of striatal neurons; they were putative interneurons of large and medium-sized aspiny type.

Biological receptors mediate anti-proliferative action of atrial natriuretic peptide in cultured mesangial cells

The mechanism of anti-proliferative action of atrial natriuretic peptide (ANP) was examined in cultured mesangial cells. HS-142-1, a selective antagonist for ANP biological receptors, inhibited ANP-induced cellular cGMP accumulation and prevented ANP-induced inhibition of both serum-stimulated incorporation of 3H-thymidine and cell proliferation. Des-[Gln18, Ser19, Gly20, Leu21, Gly22]-ANP4-23-NH2 (C-ANP) failed to inhibit 3H-thymidine incorporation. These results indicate that anti-proliferative action of ANP is mediated by the biological receptors in cultured mesangial cells.

Signal transduction, pharmacological properties, and expression patterns of two rat metabotropic glutamate receptors, mGluR3 and mGluR4

The metabotropic glutamate receptors are coupled to intracellular signal transduction via G-proteins and consist of a family of at least five different subtypes, termed mGluR1-mGluR5. We studied the signal transduction mechanism and pharmacological characteristics of the rat mGluR3 and mGluR4 subtypes in Chinese hamster ovary cells permanently expressing the cloned receptors. Both mGluR3 and mGluR4 inhibit the forskolin-stimulated accumulation of intracellular cAMP formation in response to agonist interaction. Consistent with the high degree of sequence similarity to mGluR2, mGluR3 closely resembles mGluR2 in its agonist selectivity; the potency rank order of agonists is L-glutamate > trans-1-aminocyclopentane-1,3-dicarboxylate > ibotenate > quisqualate. mGluR4 is totally different in its agonist specificity from any other member of the metabotropic receptors. This receptor potently reacts with L-2-amino-4-phosphonobutyrate (L-AP4) in a stereo-selective manner and moderately responds to L-serine-O-phosphate. mGluR4 thus corresponds well to the putative L-AP4 receptor characterized from brain preparations. Blot and in situ hybridization analyses indicated that both mRNAs are widely distributed in the rat brain. mGluR3 mRNA is highly expressed in neuronal cells of the cerebral cortex and the caudate-putamen, and in granule cells of the hippocampal dentate gyrus. The expression pattern of mGluR4 mRNA is more restricted, and this expression is prominent in the cerebellum, olfactory bulb, and thalamus. Furthermore, the mGluR3 mRNA, unlike the other mRNAs for the metabotropic receptors, is highly expressed in glial cells throughout the brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of the messenger RNA for a metabotropic glutamate receptor, mGluR2, in the central nervous system of the rat

Distribution of the messenger RNA for a metabotropic glutamate receptor, mGluR2, which is coupled to the inhibitory cyclic AMP cascade, was investigated in the central nervous system of the adult rat by in situ hybridization. Transcripts of mGluR2 were specifically localized to neuronal cells of the brain. Although the hybridization signals were widely distributed in the brain, the most prominent expression of mGluR2 messenger RNA was seen in Golgi cells of the cerebellum. Marked expression of mGluR2 messenger RNA was further observed in the mitral cells of the accessory olfactory bulb, neurons in the external part of the anterior olfactory nucleus, and pyramidal neurons in the entorhinal and parasubicular cortical regions. The granule cells of the accessory olfactory bulb, and many pyramidal and non-pyramidal neurons in the neocortical, cingulate, retrosplenial and subicular cortices, were moderately labeled. All of the granule cells in the dentate gyrus were also labeled moderately, whereas no significant hybridization signals were detected in Ammon's horn. In the basal forebrain regions, moderately labeled neurons were distributed in the triangular septal nucleus, in the lateral, basolateral and basomedial amygdaloid nuclei, and in the medial mammillary nucleus. Weakly labeled neurons were sparsely scattered in the striatum, globus pallidus, ventral pallidum and claustrum. The subthalamic nucleus was also labeled weakly. No significant labeling was found in the entopeduncular nucleus and substantia nigra. In the thalamus, moderately labeled neurons were distributed in the anterodorsal, anteromedial, ventromedial, intralaminar and midline nuclei; the ventrolateral part of the anteroventral nucleus and the rostral pole of the ventrolateral nucleus also contained moderately labeled neurons. No significant labeling was found in the thalamic reticular, submedius, ventroposterior, lateral geniculate and medial geniculate nuclei. In the lower brainstem, labeling was generally weak. No significant hybridization signals were found in the spinal cord. Some neurons in the inner part of the inner nuclear layer of the retina and some retinal ganglion cells were labeled moderately. The pattern of distribution of mGluR2 messenger RNA revealed in the present study indicates specific roles of mGluR2 in the glutamatergic system in the brain.

Different binding epitopes on the NK1 receptor for substance P and non-peptide antagonist

Non-peptide ligands for peptide receptors have been discovered in several systems through file screening programs, but the mechanism of action for these candidate drugs is obscure as they do not chemically resemble the native peptides. The compound CP 96345 is a high-affinity, non-peptide antagonist of the substance P (NK1) receptor, which is important in pain perception and neurogenic inflammation. Here we identify epitopes on the NK1 receptor responsible for the specific binding of CP 96345 by systematic exchange of corresponding segments between the NK1 receptor and the homologous NK3 (neurokinin B) receptor, which does not bind the non-peptide ligand. Non-conserved residues, in two epitopes around the top of transmembrane segment V and in one epitope at the top of transmembrane segment VI, are essential for the specific action of CP 96345 on the NK1 receptor, but are surprisingly not important for the binding of the natural peptide ligand, substance P. Susceptibility to the non-peptide antagonists can be conveyed to the previously unresponsive NK3 receptor by mutational transfer of this discontinuous epitope from the NK1 receptor.

The human endothelin-B receptor gene. Structural organization and chromosomal assignment

The gene encoding the human endothelin-B receptor (hET-BR) has been isolated, and its structural organization and chromosomal assignment have been determined. Southern blot analysis demonstrated a single copy of the hET-BR gene in the human genome. The hET-BR gene spans 24 kilobases and consists of seven exons and six introns. The size range for exons is 109-2855 base pairs, although that for introns is 0.2-14.5 kilobases. Every intron occurs near the border of the putative transmembrane domain in the coding region. The major transcription initiation sites were mapped to the positions 258 and 229 base pairs upstream of the ATG initiation codon by primer extension and nuclease S1 protection experiments. The 5'-flanking region of the hET-BR gene lacks conventional TATA and CCAAT boxes but contains a sequence of potential Sp1 binding sites upstream of the transcription initiation sites. There are some canonical consensus sequences of cis-elements including GATA motif, acute phase reactant regulatory element, and E box. Using human-rodent somatic hybrid cell lines, the hET-BR gene was assigned to human chromosome 13. The present study will lead to a better understanding of the mechanism for the transcriptional regulation of the hET-BR gene and will give a clue as to how to search for possible genetic disorders of hET-BR.

Molecular cloning and chromosomal localization of the key subunit of the human N-methyl-D-aspartate receptor

A complementary DNA encoding the key subunit of the human N-methyl-D-aspartate (NMDA) receptor (NMDAR1) has been cloned using a probe derived from the rat NMDAR1 cDNA. The cDNA encodes a 938-amino acid protein, which shows 99% amino acid homology with the rat counterpart. Of the 7 of 938 amino acids which are different, three occur in the region of the signal peptide and the others in the extracellular amino-terminal domain preceding the 4 putative transmembrane segments. Expression in Xenopus oocytes demonstrated that the single protein encoded by the cloned cDNA possesses the electrophysiological and pharmacological properties characteristic of the NMDA receptor, including Ca2+ permeability, voltage-dependent Mg2+ block, and inhibition by selective antagonists such as Zn2+ and channel blockers. The high evolutionary conservation in the structure and properties of NMDAR1 argues strongly for the importance of this receptor in functions of glutamate neurotransmission. RNA blot analysis showed abundant expression of mRNA whose size is about 4.5 and 4.8 kilonucleotides. The human gene encoding the NMDAR1 subunit has been mapped to chromosome 9q34.3 by the analyses of blot hybridization of a DNA panel of human/hamster somatic cell hybrids and fluorescence in situ hybridization of human chromosomes.

Subtype selectivity of a novel endothelin antagonist, FR139317, for the two endothelin receptors in transfected Chinese hamster ovary cells

We investigated the receptor-binding properties and the antagonist activities of FR139317, a novel endothelin (ET) antagonist, in transfected Chinese hamster ovary cells permanently expressing the two ET receptor subtypes (ETA and ETB). In displacement analysis using membrane preparations derived from the receptor-expressing cells, FR139317 showed a high affinity for ETA (Ki = 1 nM) and a lower affinity for ETB (Ki = 7.3 microM). FR139317 inhibited ETA-mediated phosphatidylinositol hydrolysis and arachidonic acid release and produced a parallel shift in the dose-response curve for ET-1, with respective pA2 values of 8.2 and 7.7. In contrast, FR139317 had no inhibitory effects on these ET-1-induced responses in ETB-expressing cells. FR139317 itself showed no stimulatory effects on phosphatidylinositol hydrolysis and arachidonic acid release in ETA- and ETB-expressing cells. Thus, FR139317 is a potent, competitive, and highly selective antagonist for ETA. This compound should be a powerful tool for investigation of the physiological properties of ETA and exploration of its role in diseases.

Regulation of neuropeptide expression in cultured cerebral cortical neurons by brain-derived neurotrophic factor

The neuropeptide-inducing activity of neurotrophic factors was tested in cultured cerebral cortical neurons. Brain-derived neurotrophic factor (BDNF) specifically increased contents of the neuropeptides somatostatin (SOM) and neuropeptide Y (NPY), but its effect on contents of cholecystokinin octapeptide and GABA was much less significant. The maximal induction of NPY content (15-fold increase) was achieved by 20 ng/ml of BDNF. These changes were also reproduced at the mRNA level. In contrast, neurotrophin-3 was much less potent at increasing NPY and SOM contents, and nerve growth factor had no effect on them. The expression of mRNA for NPY and SOM was fully dependent on the presence of BDNF in culture but irrelevant to the survival-promoting activity of BDNF, which has been reported previously. Most of the NPY immunoreactivity induced by BDNF was colocalized with glutamate decarboxylase immunoreactivity in cultured cortical neurons. These results suggest that BDNF regulates the peptidergic expression of GABAergic neurons in the cerebral cortex.

Alteration of Ca2+ permeability and sensitivity to Mg2+ and channel blockers by a single amino acid substitution in the N-methyl-D-aspartate receptor

The N-methyl-D-aspartate (NMDA) receptor plays an important role in glutamate-mediated neuronal plasticity and neurotoxicity in the central nervous system. This receptor is composed of a fundamental subunit (NMDAR1) and its potentiating subunits (NMDAR2A-NMDAR2D). The NMDA receptor is distinct from other glutamate receptor channels because of its high Ca2+ permeability and inhibition by selective cationic channel blockers such as Mg2+, Zn2+, and MK-801. In this study, we investigated the structural features that control Ca2+ permeation and channel blockade of the NMDA receptor by in vitro mutagenesis and expression in Xenopus oocytes. We constructed a series of mutations with single amino acid substitutions in the second transmembrane segment of NMDAR1 and examined channel properties of the resultant mutants in combined expression with the NMDAR2A subunit. Substitution of the asparagine with either glutamine or arginine altered both the Ca2+ permeability and the sensitivity to blockades by Mg2+ and MK-801. These mutations also reduced the inhibitory effects of Zn2+ and an antidepressant, desipramine. Based on these results, we concluded that an asparagine ring formed in the central part of the channel-forming second transmembrane segments plays a critical role in determining the Ca2+ permeability and the inhibition of open channel blockers.

Glutamate and quisqualate regulate expression of metabotropic glutamate receptor mRNA in cultured cerebellar granule cells

Metabotropic glutamate receptor (type 1; mGluR1) is expressed predominantly in the hippocampus and the cerebellum. Using cultured cerebellar granule cells, we investigated the regulation of the mGluR1 mRNA expression. Levels of mGluR1 mRNA were decreased to less than half by high potassium stimulation and by glutamate and quisqualate. Although these glutamate receptor agonists tested are also known to cause neuronal cell death in culture, the effect of cell death cannot explain the observed reduction in mGluR1 mRNA because of the following reasons: (a) antagonists of N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors inhibited cell death, but not the reduction of the level of mGluR1 mRNA; (b) mGluR1 mRNA returned to its initial level 48 h after the agonist application; and (c) the mRNA level of one of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptors (GluR1) was not altered by these conditions. Therefore, we conclude that the glutamate or quisqualate stimulation can specifically inhibit the expression of mGluR1 mRNA. The dose response of quisqualate for the reduction in mGluR1 mRNA is consistent with that for inositol phosphate formation stimulated through the cloned mGluR1. The mRNA reduction did not require extracellular calcium. Desensitization of mGluR1 with phorbol ester abolished the mRNA reduction. These results suggest that the reduction in mGluR1 mRNA is mediated by the activation of the metabotropic receptor itself.

Phase II study of recombinant human granulocyte-macrophage colony-stimulating factor in myelodysplastic syndrome and aplastic anemia

As phase II study, we treated 18 patients with myelodysplastic syndrome (MDS) and 37 patients with aplastic anemia (AA) with recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) for 14-28 days. Administration of rhGM-CSF resulted in a dose-dependent increase in circulating granulocyte counts, which was statistically significant in patients with AA. There were no consistent changes in monocyte and lymphocyte counts. Although no increase in both thrombocyte and erythrocyte counts was detected in the majority of the patients, a response of both lineages to rhGM-CSF, in addition to granulocyte lineage, was observed in 3 patients. Drug-associated adverse events developed in 28 patients (51%). The most frequent adverse event was fever. In general, the treatment with rhGM-CSF was well tolerated. The results suggest that rhGM-CSF is effective for patients with MDS and AA.

[A case of pulmonary tuberculosis complicated with drug toxicosis--value of shosaikoto and hochuekito as anti-allergic agents]

A clinical course of pulmonary tuberculosis was reported about adverse reaction of anti-tuberculous chemotherapy. A fifty-eight-year-old male patient was complicated with agranulocytosis induced by RFP, hepatic dysfunction and systemic eruption induced by INH, and high fever induced by SM. Adjuvant therapy with Shosaikoto and Hocheukito suppressed INH induced hepato-dermatological toxicosis moderately and suppressed SM induced high fever completely. By these anti-allergic therapy, combined chemotherapy with SM, EB, PAS and PZA became possible during more than six months, and chemotherapeutic effect was marked. This case report suggested possibility and significance of those Kampo agents against serious allergic reaction complicated with the chemotherapy for pulmonary tuberculosis.

Effect of granulocyte-macrophage colony-stimulating factor on chemotherapy-induced granulocytopenia in patients with malignancies

To investigate the effect of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on cytotoxic chemotherapy-induced granulocytopenia, we performed an open nonrandomized clinical trial in 46 patients with malignancies receiving cytotoxic chemotherapy regimen. Twenty-six patients who received two cycles of the identical chemotherapy regimen and had granulocytopenia less than 1 x 10(9) cells/l after the first cycle of chemotherapy were eligible for this study. They received 60, 125 or 250 micrograms/m2/day of rhGM-CSF randomly. The nadirs of peripheral granulocytes demonstrated significantly much higher levels in all dosages studied than those of control cycles. The duration of granulocytopenia was shortened with rhGM-CSF support. Such granulocyte recovery appeared in parallel with increasing dosages of GM-CSF, thus, infections with febrile episodes were reduced. Toxicity of rhGM-CSF was generally well tolerated.

Two types of ryanodine receptors in mouse brain: skeletal muscle type exclusively in Purkinje cells and cardiac muscle type in various neurons

Two types of ryanodine receptors, channels for Ca2+ release from intracellular stores, are known. We detected the skeletal muscle type only in cerebellum by immunoblot analysis of microsomes and partially purified proteins. The cardiac muscle type was found in all parts of the mouse brain. Immunohistochemical study showed that the cardiac muscle type was localized mainly at the somata of most neurons. Analysis of mutant cerebella suggested that the skeletal muscle type was present exclusively in Purkinje cells. These results suggest that Ca(2+)-induced Ca2+ release, probably mediated by the cardiac muscle receptor, functions generally in various neurons, whereas depolarization-induced Ca2+ release, probably mediated by the skeletal muscle receptor, functions specifically in Purkinje cells.

Two mammalian helix-loop-helix factors structurally related to Drosophila hairy and Enhancer of split

We report the molecular characterization of two novel rat helix-loop-helix (HLH) proteins, designated HES-1 and HES-3, that show structural homology to the Drosophila hairy and Enhancer of split [E(spl)] proteins, both of which are required for normal neurogenesis. HES-1 mRNA, expressed in various tissues of both embryos and adults, is present at a high level in the epithelial cells, including the embryonal neuroepithelial cells, as well as in the mesoderm-derived tissues such as the embryonal muscle. In contrast, HES-3 mRNA is produced exclusively in cerebellar Purkinje cells. HES-1 represses transcription by binding to the N box, which is a recognition sequence of E(spl) proteins. Interestingly, neither HES-1 nor HES-3 alone interacts efficiently with the E box, but each protein decreases the transcription induced by E-box-binding HLH activators such as E47. Furthermore, HES-1 also inhibits the functions of MyoD and MASH1 and effectively diminishes the myogenic conversion of C3H10T1/2 cells induced by MyoD. These results suggest that HES-1 may play an important role in mammalian development by negatively acting on the two different sequences while HES-3 acts as a repressor in a specific type of neurons.