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  • 1
    Electronic Resource
    Electronic Resource
    Adrenergic Regulation of ICER (Inducible Cyclic AMP Early Repressor) and β1-Adrenergic Receptor Gene Expression in C6 Glioma Cells (1996)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 67 (1996), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: ICER (inducible cyclic AMP early repressor), a member of the cyclic AMP response element (CRE) modulator (CREM) family of transcription factors, is a powerful repressor of cyclic AMP-mediated transactivation. Our studies characterize the regulation of ICER in C6 glioma cells and investigate its role in repressing transcription of the β1-adrenergic receptor (β1AR) gene. Incubation with isoproterenol (100 nM) results in a rapid induction in levels of mRNA for ICER and its splice variant ICERγ, with maximal induction occurring after 2 h of treatment. Incubation with isoproterenol also increased levels of CREM isoforms within 1 h; this was unexpected given previous reports that these isoforms are not rapidly induced. Increased expression of ICER and CREM was accompanied by induction of two CRE-binding complexes. The presence of ICER in these two CRE-binding complexes is demonstrated by their disruption with CREM antibody and by their comigration with recombinant ICER. Because the time course for isoproterenol induction of ICER mRNA and CRE binding corresponds to that for down-regulation of β1AR mRNA levels in C6 glioma cells, the influence of ICER on β1AR transcription was directly examined. Coexpression of ICER significantly decreased transcriptional activity of a rat β1AR promoter-luciferase reporter construct that contains a CRE. In contrast, coexpression of ICER did not influence two truncated rat β1AR promoter constructs that lack the CRE site. These data demonstrate that ICER can interact at the β1AR promoter to repress transcription.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1996.67020490.x
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  • 2
    Electronic Resource
    Electronic Resource
    Agonist and Cyclic AMP-Mediated Regulation of β1-Adrenergic Receptor mRNA and Gene Transcription in Rat C6 Glioma Cells (1994)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 63 (1994), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Exposure of rat C6 glioma cells to either agonists or agents that increase cyclic AMP levels leads to down-regulation of β1-adrenergic receptors (β1AR) as measured by loss of radioligand binding sites. The present study examines the influence of isoproterenol and forskolin treatment on levels of β1AR mRNA, mRNA stability, and gene transcription rate. Isoproterenol treatment of C6 cells altered β1AR mRNA levels in a biphasic manner; i.e., short-term exposure (30–60 min) increased by 50%, whereas longer exposure (2–6 h) decreased by 50% the levels of β1AR mRNA. The extent of both the up- and down-regulation was dependent on agonist concentration. Similar regulation of β1AR mRNA was observed in forskolin-treated cells. Pretreatment of the cells with Pseudomonas exotoxin A, a potent inhibitor of protein synthesis, completely blocked isoproterenol- and forskolin-mediated down-regulation of β1AR mRNA, and thereby potentiated the increase in receptor mRNA up to fourfold over the 6-h time course. The mechanisms underlying β1AR mRNA down-regulation were examined. The half-life of β1AR mRNA was slightly increased (from 61 to 77 min) after a 2-h exposure of the cells to either isoproterenol or forskolin. Nuclear run-on analysis demonstrated that the rate of β1AR gene transcription was increased after isoproterenol incubation for 60 min, but then decreased after 90–240 min, consistent with the time course for up- and down-regulation of β1AR mRNA. Isoproterenol treatment (120 min) also decreased the level of β1AR nascent transcripts, purified by affinity chromatography of RNA isolated from 4-thiouridine-pulsed cells. The results demonstrate that β1AR mRNA has a relatively short half-life and that agonist regulation of β1AR mRNA is mediated by activation of the cyclic AMP system. Moreover, the results indicate that agonist regulation of β1AR mRNA occurs at the level of β1AR gene transcription, not mRNA stability. Finally, the observed requirement for protein synthesis indicates that β1AR mRNA down-regulation may be mediated by the induction of a repressor of the β1AR gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1994.63051635.x
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  • 3
    Electronic Resource
    Electronic Resource
    Modulation of Adenylylcyclase by Protein Kinase C in Human Neurotumor SK-N-MC Cells: Evidence that the α Isozyme Mediates Both Potentiation and Desensitization (1994)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 63 (1994), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Exposure of human SK-N-MC neurotumor cells to 4β-phorbol 12-myristate 13-acetate (PMA) increased isoproterenol stimulation of cyclic AMP levels by severalfold. This potentiation was blocked by inhibitors of protein kinase C (PKC) and did not occur in cells in which PKC had been down-regulated. PMA treatment also enhanced the stimulation by dopamine, cholera toxin, and forskolin. Thus, the effect of PMA on the adenylylcyclase system was postreceptor and involved either the guanine nucleotide binding regulatory (G) proteins or the cyclase itself. As PMA treatment did not impair the inhibition of isoproterenol stimulation by neuropeptide Y, an involvement of the inhibitory G protein Gi was unlikely. Cholate extracts of membranes from control and PMA-treated cells were equally effective in the reconstitution of adenylylcyclase activity in S49 cyc− membranes, which lack the stimulatory G protein subunit Gsα; thus, Gs did not appear to be the target of PMA action. Membranes from PMA-treated cells exhibited increased adenylylcyclase activity to all stimulators including Mn2+ and Mn2+ plus forskolin. In addition, activity was increased when control membranes were incubated with ATP and purified PKC from rat brain. This is consistent with a direct effect of PKC on the adenylylcyclase catalyst in SK-N-MC cells. PMA treatment also resulted in a shift to less sensitivity in the Kact for isoproterenol but not for dopamine or CGP-12177 (a β3-adrenergic agonist) stimulation. Thus, the β1 but not the D1 or β3 receptors were being desensitized by PKC activation. Analysis of SK-N-MC cells by western blotting with antibodies against different PKC isozymes revealed that both the α and ζ isozymes were present in these cells. Whereas PKC-α was activated and translocated from cytosol to membrane by phorbol esters, the ζ isozyme was not. Thus, PKC-α, which has been implicated in desensitization in other cell lines, also appears to potentiate adenylylcyclase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1994.63041361.x
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization and Regulation of β1-Adrenergic Receptors in a Human Neuroepithelioma Cell Line (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 56 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Intact human neuroepithelioma SK-N-MC cells bound the β-adrenergic antagonist (–)-[3H]-CGP 12177 with a KD of 0.13 nM and a Bmax of 17,500 sites/cell. When the cells were exposed to β-adrenergic agonists, they accumulated cyclic AMP in the following order of potency: isoproterenol norepinephrine 〉 epinephrine, which is indicative of a β1-subtype receptor. Membranes prepared from the cells bound (–)-3-[125I]iodocyanopindolol with a KD of 11.5 pM. Inhibition of agonist-stimulated cyclic AMP production and competition binding experiments indicated that the β1-selective antagonists CGP 20712A and ICI 89,406 were much more potent than the β2-selective antagonist ICI 118,551. Analysis of the displacement curves indicated that the cells contained only β1-adrenergic receptors. Northern blot analysis of SK-N-MC mRNA using cDNA probes for the β1- and β2-adrenergic receptors revealed the presence of a very strong β1-adrenergic receptor mRNA signal, while under the same conditions no β2-adrenergic receptor mRNA was observed. Thus, SK-N-MC cells appear to express a pure population of β1-adrenergic receptors. When the cells were exposed to isoproterenol, there was no observable desensitization during the first hour. After longer exposure, desensitization slowly occurred and the receptors slowly down-regulated to 50% of control levels by 24 h. Other agents that elevate cyclic AMP levels, such as forskolin, cholera toxin, and cyclic AMP analogues, caused no or little substantial receptor loss.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb08191.x
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  • 5
    Electronic Resource
    Electronic Resource
    D1 Dopamine Receptors Can Interact with Both Stimulatory and Inhibitory Guanine Nucleotide Binding Proteins (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Pretreatment of striatal membranes with N-ethylmaleimide in the presence of a D1specific agonist inactivated endogenous guanine nucleotide binding proteins (G proteins), but not D, dopamine receptors, resulting in a loss of high-affinity agonist binding sites. Such D1 receptors were solubilized, mixed with exogenous G proteins from cells not containing D1receptors, and reconstituted into phospholipid vesicles. These reconstituted receptors were able to couple to the exogenous G proteins, and the proportion of agonist high-affinity sites of the receptor (40–57%) was similar to levels obtained with naive receptors coupling to endogenous G proteins (40%) upon solubilization and reconstitution. These hybrid high-affinity sites were fully modulated by guanine nucleotides. Pretreatment of cells with pertussis toxin prior to extraction of G proteins resulted in a 50% decrease in the proportion of high-affinity sites; these sites remained sensitive to guanine nucleotides. When D, receptors were reconstituted with extracts of cyc− cells, which lack stimulatory G proteins, the proportion of high-affinity sites was reduced to 31% of the total. Pertussis toxin treatment of the cyc− cells completely abolished the formation of high-affinity sites. These results demonstrate that D1-dopaminergic receptors are able to couple to not only stimulatory G proteins (Gs), but also to inhibitory G proteins (Gi).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb08312.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of the Tricyclic Antidepressant Desipramine on β-Adrenergic Receptors in Cultured Rat Glioma C6 Cells (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 49 (1987), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Rat glioma C6 cells, cultured in the presence of the tricyclic antidepressant desipramine, lost a significant number of β-adrenergic receptors in a time-and dose-dependent manner. A similar loss was observed whether binding was determined on intact cells with the hydrophilic β-adrenergic antagonist (±)-[3H]4-(3-tert-butylamino-2-hydroxypropoxyl)benzimidazole -2 - on HCl ([3H]CGP-12177) or on cell lysates with the more hydrophobic antagonists [125I]iodocyanopindolol or [3H]dihydroalprenolol. When stimulated with the agonist isoproterenol, desipramine-treated cells accumulated less cyclic AMP than control cells. The affinity of the β-adrenergic receptors for either antagonist or agonist was unchanged after desipramine treatment. Desipramine interacted only weakly with the receptors and competed for [125I]iodocyanopindolol binding with a Ki of 30 μM. The presence in the culture medium of alprenolol or propranolol, potent β-adrenergic antagonists, however, did not prevent the reduction in receptors by desipramine. Desipramine also caused a loss of β-adrenergic receptors from cells maintained in serum-free medium and the cells themselves did not contain or secrete endogenous catecholamines. Although desipramine is a potent inhibitor of catecholamine uptake, it appears unlikely that the observed loss of β-adrenergic receptors in rat glioma C6 cells exposed to the drug is due to an increase in extracellular catecholamine levels or to a direct interaction with the receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb03427.x
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of Functional Neuropeptide Y Receptors in a Human Neuroblastoma Cell Line (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: We identified receptors for neuropeptide Y (NPY) on an established human neuroblastoma cell line, SK-N-MC, which are functionally coupled to adenylate cyclase through the inhibitory guanine nucleotide-binding protein of adenylate cyclase, Gi Intact SK-N-MC cells bound radiolabeled NPY with a KD of 2 nM and contained ˜83,000 receptors/cell. Unlabeled porcine and human NPY and structurally related porcine peptide YY (PYY) competed with labeled NPY for binding to the receptors. NPY inhibited cyclic AMP accumulation in SK-N-MC cells stimulated by isoproterenol, dopamine, vasoactive intestinal peptide, cholera toxin, and forskolin. NPY inhibited isoproterenol-stimulated cyclic AMP production in a dose-dependent manner, with half-maximal inhibition at 0.5 nM NPY. Porcine and human NPY and porcine PYY gave similar dose-response curves. NPY also inhibited basal and isoproterenol-stimulated adenylate cyclase activity in disrupted cells. Pertussis toxin treatment of the cells completely blocked the ability of NPY to inhibit cyclic AMP production and adenylate cyclase activity. The toxin catalyzed the ADP-ribosylation of a 41-kDa protein in SK-N-MC cells that corresponds to Gi. The receptors on SK-N-MC cells appeared to be specific for NPY, as other neurotransmitter drugs, such as α-adrenergic, dopaminergic. muscarinic, and serotonergic antagonists, did not compete for either NPY binding or NPY inhibition of adenylate cyclase. Thus, SK-N-MC cells may be a useful model for investigating NPY receptors and NPY-mediated signal trans-duction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1990.tb04164.x
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  • 8
    Electronic Resource
    Electronic Resource
    Reevaluation of the Role of Gangliosides as Receptors for Tetanus Toxin (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Binding of tetanus toxin to rat brain membranes was of lower affinity and capacity when binding was determined in 150 mM NaCl, 50 mM Tris-HCl (pH 7.4) than in 25 mM Tris-acetate (pH 6.0). Binding under both conditions was reduced by treating the membranes with neuraminidase. Pronase treatment, however, reduced toxin binding only in the Tris-saline buffer (pH 7.4). In addition, the concentration of gangliosides required to inhibit toxin binding was 100-fold higher in Trissaline compared to Tris-acetate buffer. The toxin receptors in the membranes were analyzed by ligand blotting techniques. Membrane components were dissolved in sodium dodecyl sulfate, separated by polyacrylamide gel electrophoresis, and transferred to nitrocellulose sheets, which were overlaid with 125I-labeled toxin. Tetanus toxin bound only to material that migrated in the region of the dye front and was extracted with lipid solvents. Gangliosides isolated from the lipid extracts or other sources were separated by TLC on silica gel and the chromatograms were overlaid with labeled tetanus toxin. The toxin bound to areas where the major rat brain gangliosides migrated. When equimolar amounts of different purified gangliosides were applied to the chromatogram, binding of the toxin was in the order GDlb≅ GTlb≅ GQ1b 〉 GD2 〉 GD3≫ GD1a≅ GM1. Thus, the toxin appears to have the highest affinity for gangliosides with a disialyl group linked to the inner galactosyl residue. When binding of tetanus toxin to transfers and chromatograms was determined in the Tris-saline buffer (pH 7.4), the toxin bound to the same components but the extent of binding was markedly reduced compared with the low-salt and -pH conditions. Our results indicate that the interaction of tetanus toxin with rat brain membranes and gangliosides is greatly reduced under more physiological conditions of salt and pH and raise the possibility that other membrane components such as sialoglycoproteins may be receptors for the toxin under these conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb02852.x
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  • 9
    Electronic Resource
    Electronic Resource
    A comparison of membrane glycoconjugates from mouse cells transformed by murine and primate RNA sarcoma viruses (1976)
    s.l. : American Chemical Society
    Biochemistry 15 (1976), S. 201-208 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00646a031
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  • 10
    Electronic Resource
    Electronic Resource
    Biosynthesis and localization of gangliosides in cultured cells (1982)
    s.l. : American Chemical Society
    Biochemistry 21 (1982), S. 3260-3265 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00257a002
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