Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.4.3 (phospholipase C)
18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The rat neurotensin receptor cDNA sequence was transfected in Chinese hamster ovary cells and cellular clones which stably express the corresponding protein were isolated and characterized. The Scatchard analysis of the specific binding of [3H]neurotensin indicated a Kd value of 0.45 +/- 0.08 nM and a Bmax value of 3.27 +/- 0.29 pmol/mg of protein. Displacement experiments using peptidic analogs of neurotensin and levocabastine confirmed that the transfected receptor exhibits the binding properties of the neurotensin receptor characterized in the rat brain. Neurotensin stimulated the phosphoinositides hydrolysis in a time- and concentration-dependent manner and this effect was mimicked by neurotensin(8-13) and by neuromedin N. The stimulation of phosphoinositides hydrolysis was not inhibited by pertussis toxin. These results indicate that the transfected cells actively express the rat neurotensin receptor which is functionally coupled to phospholipase C through a pertussis toxin-insensitive GTP-binding protein, and that neuromedin N is able to induce the phosphoinositides turnover by interaction with the neurotensin receptor.
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PMID:Phospholipase C activation by neurotensin and neuromedin N in Chinese hamster ovary cells expressing the rat neurotensin receptor. 133 89

The influence of acute and chronic ethanol exposures on the coupling of neurotensin and bradykinin receptors to phospholipase C was determined in intact N1E-115 cells. Phospholipase C was monitored by the formation of total [3H]inositol phosphates in the presence of lithium in cells prelabeled with [3H]inositol. Acute exposure to ethanol over a range of 50 to 200 mM inhibited the stimulation of [3H]inositol phosphate formation elicited by neurotensin and bradykinin. In cells chronically exposed to 100 mM ethanol for 7 days, neither basal- nor neurotensin-stimulated [3H]inositol phosphate formation differed significantly from those of control (untreated) cells. In contrast, the [3H]inositol response to bradykinin was significantly inhibited in cells chronically exposed to ethanol. Because chronic ethanol exposure had no parallel effects on either the specific binding of [3H]bradykinin or the stimulation of [3H]inositol phosphate formation by the stable GTP analog, guanine 5'-(y-thiotriphosphate), it is suggested that chronic ethanol impairs the ability of bradykinin receptors to activate the guanine nucleotide binding protein associated with phospholipase C. In addition, because chronic ethanol had no effect on the inositol phosphate response to neurotensin, it is proposed that certain types of receptor-guanine nucleotide binding protein interactions are more vulnerable than are others to disruption by chronic ethanol treatment.
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PMID:Selective effects of acute and chronic ethanol exposure on neuropeptide and guanine nucleotide stimulated phospholipase C activity in intact N1E-115 neuroblastoma. 190 59

Both ethanol and neurotensin produce sedation and hypothermia. When administered in combination the behavioral effects of these two substances are potentiated. In order to better understand the biochemical nature of this interaction, the direct effects of ethanol on neurotensin receptors and an associated signal transduction process were determined in NIE-115 neuroblastoma cells. Ethanol in physiologically relevant concentrations (50mM) significantly reduced neurotensin stimulated [3H]inositol phosphate production while having no effect on the specific binding of [3H]neurotensin. In addition, ethanol up to 200 mM had no effect on GTPYS mediated [3H]inositol phosphate production. The results indicate that acute exposure to ethanol partially disrupts the normal coupling of activated neurotensin receptors to the guanine nucleotide binding protein associated with phospholipase C.
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PMID:The effects of acute exposure to ethanol on neurotensin and guanine nucleotide-stimulation of phospholipase C activity in intact NIE-115 neuroblastoma cells. 217 77

The heterologous desensitization of the bradykinin (BK)-induced increase in intracellular Ca2+ concentration ([Ca2+]i) by neurotensin was studied in neuroblastoma x glioma hybrid NG108-15 cells. The addition of neurotensin to the cells resulted in an increase in [Ca2+]i and an increase in the formation of inositol phosphates in Ca2+-free medium. Pretreatment of the cells with neurotensin resulted in 43% decrease in the BK-induced increase of [Ca2+]i. The increase in [Ca2+]i induced by ionomycin, which causes Ca2+ release from the intracellular pool, was not decreased by pretreatment with neurotensin. This indicates that the inhibitory effect of neurotensin on the BK-induced increase of [Ca2+]i was not due to depletion of the intracellular Ca2+ pool. Pretreatment with neurotensin also caused a 47% decrease in the BK-induced formation of inositol trisphosphates (IP3). This decrease was not due to depletion of phosphatidylinositol bisphosphates. Neurotensin did not inhibit [3H]BK binding to cell membranes. These results show that neurotensin desensitizes the BK responses of NG108-15 cells, heterologously, perhaps by changes in phospholipase C and/or guanine nucleotide-binding protein (G-protein).
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PMID:Heterologous desensitization of bradykinin-induced phosphatidylinositol response and Ca2+ mobilization by neurotensin in NG108-15 cells. 272 52

Microinjection of rat brain mRNA in Xenopus oocytes induced acetylcholine, neurotensin, serotonin, and glutamate receptors in the cells. These receptors stimulate an intracellular reaction pathway, including G-protein activation, inositol trisphosphate (IP3) formation, and Ca2+-dependent Cl- channels. In the present study, we examined the roles of several protein kinases in these responses by means of inhibitors and activators of these kinases. Isoquinolinesulfonamides, inhibitors of protein kinases, caused no current responses and affected no receptor-mediated responses when injected into the oocytes at low doses (30-50 pmol), which inhibit cyclic nucleotide-dependent kinases or kinase C specifically, but abolished the receptor-mediated responses at a higher dose (300 pmol), which inhibit most protein kinases nonspecifically. Calmodulin inhibitors blocked the receptor-mediated responses strongly. Activation of cyclic nucleotide-dependent kinases or kinase C by injection of cAMP (or cGMP) or perfusion with phorbol esters caused no direct current responses but suppressed receptor-mediated responses. Current responses triggered by IP3 injection were not suppressed by these treatments. These results suggest that cAMP- (or cGMP-)dependent kinases or kinase C may not be involved in the pathway directly but may modulate it by inhibiting the initial part of the pathway (receptors, G-proteins, and/or phospholipase C), and they suggest that calmodulin may most likely be involved in the activation of Ca2+-dependent Cl- channels.
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PMID:Roles of protein kinases in neurotransmitter responses in Xenopus oocytes injected with rat brain mRNA. 289 16

Receptors for regulatory peptides (hormones or neurotransmitters) play a pivotal role in the ability of cells to taste the rich neuroendocrine environment of the gut. Recognition of low concentration of peptides with a high specificity and translation of the peptide-receptor interaction into a biological response through different signalling pathways (adenylyl cyclase-cAMP or phospholipase C-phosphatidylinositol) are crucial properties of receptors. While many new receptors have been identified and thereafter characterized functionally during the 1980s, molecular biology now emerges as the privileged way for the structural characterization and discovery of receptors. Different strategies of receptor cloning have been developed which may or may not require prior receptor purification. Among cloning strategies that do not require receptor purification, homology screening of cDNA libraries, expression of receptor cDNA or mRNA in Xenopus laevis oocytes or in COS cells, and the polymerase chain reaction method achieved great success, e.g. cloning of receptors for cholecystokinin, gastrin, glucagon-like peptide 1, gastrin-releasing peptide/bombesin, neuromedin K, neuropeptide Y, neurotensin, opioids, secretin, somatostatin, substance K, substance P and vasoactive intestinal peptide. All these receptors belong to the superfamily of G-protein-coupled receptors which consist of a single polypeptide chain (350-450 amino acids) with seven transmembrane segments, an N-terminal extracellular domain and a C-terminal cytoplasmic domain. In this chapter, we have detailed the properties of three receptors which play an important role in digestive tract physiology and illustrate various signal transduction pathways: pancreatic beta-cell galanin receptors which mediate inhibition of insulin release and intestinal epithelial receptors for vasoactive intestinal peptide and peptide YY, which mediate the stimulation and inhibition of water and electrolyte secretion, respectively.
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PMID:Receptors for gut regulatory peptides. 751 Sep 49

The major signal transduction pathway for neurotensin (NT) receptors is the G-protein-dependent stimulation of phospholipase C, leading to the mobilization of intracellular free Ca2+ ([Ca2+]i) and the stimulation of cyclic GMP. We investigated the functional actions of an analog of NT(8-13), N alpha MeArg-Lys-Pro-Trp-tLeu-Leu (NT1), and other NT related analogs by quantitative measurement of the cytosolic free Ca2+ concentration in HT-29 (human colonic adenocarcinoma) cells using the Ca(2+)-sensitive dye fura-2/AM and by effects on cyclic GMP levels in rat cerebellar slices. The NT receptor binding affinities for these analogs to HT-29 cell membranes and newborn (10-day-old) mouse brain membranes were also investigated. Data obtained from HT-29 cell and mouse brain membrane preparations showed saturable single high-affinity sites and binding densities (Bmax) of 130.2 and 87.5 fmol/mg protein, respectively. The respective KD values were 0.47 and 0.39 nM, and the Hill coefficients were 0.99 and 0.92. The low-affinity levocabastine-sensitive site was not present (K1 > 10,000) in either membrane preparation. Although the correlation of binding between HT-29 cell membranes and mouse brain membranes was quite significant (r = 0.92), some of the reference agents had lower binding affinities in the HT-29 cell membranes. The metabolically stable compound NT1 plus other NT analogs and related peptides [NT, NT(8-13), xenopsin, neuromedin N, NT(9-13), kinetensin and (D-Trp11)-NT] increased intracellular Ca2+ levels in HT-29 cells, indicating NT receptor agonist properties. The effect of NT1 in mobilizing [Ca2+]i blocked by SR 48692, a non-peptide NT antagonist. Receptor binding affinities of NT analogs to HT-29 cell membranes were positively correlated with potencies for mobilizing intracellular calcium in the same cells. In addition, NT1 increased cyclic GMP levels in rat cerebellar slices, confirming the latter findings of its NT agonist action. These results substantiate the in vitro NT agonist properties of the hexapeptide NT analog NT1.
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PMID:Agonist properties of a stable hexapeptide analog of neurotensin, N alpha MeArg-Lys-Pro-Trp-tLeu-Leu (NT1). 774 96

Endopeptidase 24.16 was purified from rat kidney homogenate on the basis of its ability to generate the biologically inactive degradation products neurotensin (1-10) and neurotensin (11-13). On SDS gels of the proteins pooled after the last purification step, the enzyme appeared homogeneous and behaved as a 70-kDa monomer. The peptidase was not sensitive to specific inhibitors of aminopeptidases, pyroglutamyl aminopeptidase I, endopeptidase 24.11, endopeptidase 24.15, proline endopeptidase and angiotensin-converting enzyme but was potently inhibited by several metal chelators such as o-phenanthroline and EDTA and was blocked by divalent cations. The specificity of endopeptidase 24.16 towards peptides of the tachykinin, opioid and neurotensin families was examined by competition experiments of tritiated neurotensin hydrolysis as well as HPLC analysis. These results indicated that endopeptidase 24.16 could discriminate between peptides belonging to the same family. Neurotensin, Lys8-Asn9-neurotensin(8-13) and xenopsin were efficiently hydrolysed while neuromedin N and kinetensin underwent little if any proteolysis by the peptidase. Analogously, substance P and dynorphins (1-7) and (1-8) were readily proteolysed by endopeptidase 24.16 while neurokinin A, amphibian tachykinins and leucine or methionine enkephalins totally resisted degradation. By Triton X-114 phase separation, 15-20% of endopeptidase 24.16 partitioned in the detergent phase, indicating that renal endopeptidase 24.16 might exist in a genuine membrane-bound form. The equipotent solubilization of the enzyme by seven detergents of various critical miscellar concentrations confirmed the occurrence of a membrane-bound counterpart of endopeptidase 24.16. Furthermore, the absence of release elicited by phosphatidylinositol-specific phospholipase C suggested that the enzyme was not attached by a glycosyl-phosphatidylinositol anchor in the membrane of renal microvilli. Finally, endopeptidase 24.16 could not be released from these membranes upon trypsinolysis.
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PMID:Rat kidney endopeptidase 24.16. Purification, physico-chemical characteristics and differential specificity towards opiates, tachykinins and neurotensin-related peptides. 842 55

The agonist-induced internalization of the neurotensin receptor was studied in transfected Chinese hamster ovary cells expressing either the wild-type or a truncated rat neurotensin receptor, lacking the complete intracellular COOH-terminal end. Incubation of cells expressing the wild-type neurotensin receptor in the presence of the peptide resulted in a dramatic decrease in the [3H]neurotensin binding at the cell surface. This disappearance of cell surface binding sites resulted from the internalization of the receptor after the binding of the peptide. The receptor/peptide complexes were internalized in an intracellular compartment resistant to acid washes. The truncated receptor displayed high affinity binding properties for neurotensin in cell homogenates and activated phospholipase C as did the wild-type receptor. However, in cells expressing the truncated receptor, incubation with neurotensin only induced a partial decrease in cell surface binding, and internalization of the bound peptide was also impaired. On cell homogenates, the GTP analogue Gpp(NH)p was found to decrease the affinity of [3H]neurotensin for the wild-type receptor, whereas no similar effect was observed with the truncated receptor. These results show that the intracellular COOH-terminal region of the rat neurotensin receptor is not required for its functional coupling with intracellular G protein but is involved in the shift of the affinity of the receptor for the agonist, which occurs as a consequence of receptor activation and coupling. Because the truncated receptor was shown to internalize poorly, it may be proposed that internalization is not directly related to the activation of G protein but rather is a consequence of modification of receptor affinity, after activation by the agonist.
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PMID:Interaction of the COOH-terminal domain of the neurotensin receptor with a G protein does not control the phospholipase C activation but is involved in the agonist-induced internalization. 863 71

The regulation of neurotensin-induced phosphoinositide turnover was studied in transfected CHO cells expressing the rat neurotensin receptor. Stimulation of these cells with neurotensin resulted in an important, but transient, increase in inositol phosphate cell content. Preincubation of the cells with neurotensin dramatically decreased their response to further stimulation. This diminution, which was time-dependent and not related to the availability of phospholipase C substrate, is though to reflect a progressive homologous desensitization of the recombinant neurotensin receptor.
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PMID:Desensitization of neurotensin-induced phosphoinositide hydrolysis in transfected CHO cells. 868 90


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