Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recent cloning studies confirm the presence of two subtypes of bombesin (Bn) receptors. In contrast to the gastrin-releasing peptide (GRP)-preferring subtype, which has been widely studied, nothing is known about the cellular mechanisms of the neuromedin B (NMB)-preferring subtype, which occurs widely in the central nervous system and gastrointestinal tissues, partially because of the lack of a cell line with functional receptors. In the present study we have investigated Bn receptors on the rat glioblastoma cell line C-6, reported to contain mRNA of the NMB receptor subtype. Binding of 125I-[D-Tyr0]NMB to these cells was time- and temperature-dependent, saturable, reversible, and only inhibited by Bn receptor agonists or antagonists. For Bn receptor agonists the relative potencies were: NMB (1.7 nM) approximately equal to litorin (3 nM) greater than ranatensin (8 nM) greater than Bn (19 nM) greater than neuromedin C (NMC) (210 nM) greater than GRP (500 nM). These relative affinities were almost identical to those for the NMB receptor subtype on rat oesophageal tissue and for Balb 3T3 cells stably transfected with the NMB receptor subtype. These potencies differed from those for the GRP receptor subtype on rat pancreatic acini [Bn approximately equal to litorin (4 nM) greater than ranatensin, NMC, GRP (15-20 nM) much greater than NMB (351 nM)]. The relative potencies of four different classes of Bn receptor antagonists were compared. Results from C-6 tumour cells agreed closely with those for binding to the NMB receptor subtype on rat oesophageal tissue and in Balb 3T3 cells stably transfected with this receptor, and differed markedly from those for binding to the GRP receptor subtype on rat pancreatic acini. Four Bn receptor antagonists had a higher affinity for the GRP subtype ([D-Phe6]Bn-(6-13)ethyl ester (500 x), [D-Phe6][psi 13-14,Cpa14]Bn- (6-14) (70 x) (where psi 13-14 refers to the replacement of the -CONH- peptide bond between Leu13 and Met14 by -CH2NH2) [psi 13-14,Leu14]Bn, [D-Phe6]Bn-(6-13) propylamide (30 x)] and two had a higher affinity for the NMB subtype on C-6 cells and transfected cells ([D-Pro4,D-Trp7,9,10] substance P-(4-11) (9 x) and [Tyr4,D-Phe12]Bn (18 x)]. In C-6 tumour cells, Bn receptor agonists caused an increase in cytosolic Ca2+ and the generation of inositol phosphates. For both responses, NMB was more than 50-fold more potent than GRP. Neither NMB nor GRP increased cyclic AMP. These results demonstrate that the rat glioblastoma cell line C-6 possesses functional NMB-preferring Bn receptors, and agonist occupation activates phospholipase C, thus increasing cytosolic Ca2+ and inositol phosphate formation. Because the interaction of Bn-related peptides with C-6 cell receptors is identical with that reported in other tissues containing the mRNA for the NMB subtype, this cell line should prove useful in exploring further the cellular basis of action of the peptides that interact with this receptor in the central nervous system and various other tissues.
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PMID:Activation of neuromedin B-preferring bombesin receptors on rat glioblastoma C-6 cells increases cellular Ca2+ and phosphoinositides. 132 46

The receptor that interacts with the mammalian bombesin-related peptide neuromedin B (NMB) is ubiquitous in the gastrointestinal tract and central nervous system. However, little is known regarding its cellular mechanisms of action. This receptor has been recently cloned, sequenced, and stably transfected into BALB 3T3 fibroblasts, permitting detailed study of the pharmacology and coupled biological activities of this receptor. In the present study, we compare the ability of transfected receptors to alter cell function with that of receptors natively expressed in small numbers by the rat glioblastoma cell line C6. NMB inhibited binding of 125I-[D-Tyro]NMB with high affinity in transfected cells (Ki = 3.08 +/- 0.14 nM) and in C6 cells (Ki = 1.90 +/- 1.10 nM), whereas the bombesin-related agonists gastrin-releasing peptide (GRP) and [D-Phe6, D-Ala11, Leu14]bombesin(6-16) (GRP analogue) had 100- and 300-fold lower affinities, respectively, for NMB receptors in either cell type. For both cell systems, maximal binding was observed between 5 and 15 min at 22 degrees. Both cell types internalized NMB at similar rates, with > 70% of bound ligand being internalized by 60 min at 22 degrees. The nonhydrolyzable guanosine analogue guanosine 5'-(beta,gamma-imido)triphosphate was equipotent in causing a decrease in binding of 125I-[D-Tyro]NMB due to decreased receptor affinity in both cell types, without a change in receptor number, demonstrating that the NMB receptor remained coupled to a guanine nucleotide-binding protein in both native and transfected cells. In both cell systems, NMB increased inositol monophosphate, inositol bisphosphate, and inositol trisphosphate in a time-dependent fashion. Inositol phosphates were increased in a dose-dependent fashion, with similar half-maximal values being obtained for NMB in both cell types (transfected, 1.01 +/- 0.09 nM; C6, 2.09 +/- 0.15 nM) and for the GRP analogue (transfected, 1855 +/- 140 nM; C6, 2129 +/- 250 nM). NMB mobilized intracellular Ca2+ in both cell systems, and the dose-response curves were superimposible (EC50 for transfected, 0.10 +/- 0.08 nM; C6, 0.11 +/- 0.02 nM). These data demonstrate that activation of the receptor for NMB stimulates phospholipase C and increases intracellular Ca2+. These results also demonstrate that transfected and native NMB receptors behave similarly, suggesting that the transfected cell line will be useful in future studies investigating ligand-receptor interactions, as well as in molecular biological studies of the structure-function relationship of the receptor.
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PMID:Neuromedin B receptors retain functional expression when transfected into BALB 3T3 fibroblasts: analysis of binding, kinetics, stoichiometry, modulation by guanine nucleotide-binding proteins, and signal transduction and comparison with natively expressed receptors. 133 12

Electrophysiological techniques and Xenopus oocytes were used to study the expression of neurotransmitter receptors encoded by mRNAs isolated from three human glioma cell lines. Oocytes injected with mRNAs from two glioblastoma cell lines did not show electrical responses to the various neurotransmitters tested. In contrast, oocytes injected with mRNA from an astrocytoma cell line (R-111) acquired acetylcholine and glutamate receptors as well as a small number of N-methyl-D-aspartate (NMDA) receptors. Acetylcholine elicited oscillatory Cl- currents that were abolished by muscarinic antagonists. The muscarinic receptors are coupled to the inositol phosphate-Ca2+ receptor-channel coupling system. Glutamate and its analogs kainate, quisqualate, and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid induced smooth currents. The non-NMDA responses were potently blocked by 6,7-dinitroquinoxaline-2,3 dione. Our results show that human astrocytoma cells contain mRNAs coding for functional acetylcholine and glutamate receptors that have properties similar to those of neurons. In contrast, human glioblastoma cells lacked those mRNAs. These differences might be useful for the development of new diagnostic and therapeutic procedures.
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PMID:mRNA coding for neurotransmitter receptors in a human astrocytoma. 134 61

alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase, inhibits the growth of brain tumor cell lines and is undergoing clinical trials as a treatment for brain tumors. Platelet-derived growth factor (PDGF) is thought to regulate the growth and development of precursors of both normal and neoplastic astrocytic cells; calcium signaling is thought to play a role in the transduction of PDGF signals. Using laser fluorescence image cytometry, flow cytometry, and spectrofluorometry, we studied the effect of DFMO on the calcium signals induced by PDGF in A172 human glioblastoma cells. Four days of treatment with 5 mM DFMO substantially shortened PDGF-induced calcium signals. The effect was reversed more than 10 h but less than 24 h after putrescine treatment, even though polyamines were repleted 4 h after putrescine and spermidine were added. DFMO did not substantially affect intracellular calcium release or the timing of the opening and closing of plasma membrane calcium channels. These findings support the notion that calcium signaling may be a target for inhibitors of polyamine metabolism.
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PMID:alpha-Difluoromethylornithine alters calcium signaling in platelet-derived growth factor-stimulated A172 brain tumor cells in culture. 145 66

ETYA (5,8,11,14-eicosatetraynoic acid), an arachidonic acid analogue, inhibited DNA synthesis in human transformed U937 (monoblastoid), PC3 (prostate) and A172 (glioblastoma) cells, and partially differentiated the U937 and A172 lines. The agent is not primarily cytotoxic at the concentrations employed, based upon exclusion of trypan blue, continued attachment of PC3 and A172 cells, unchanged release of Cr51, and reversibility of inhibited thymidine incorporation after removal of ETYA. Leukotriene C4 partially reversed the suppression of U937 DNA synthesis, suggesting its modulation by leukotrienes. U937 and A172 cells partially differentiated, as judged by a number of criteria. ETYA increased whole cell and microsomal membrane fluidity, increased intracellular Ca2+ in PC3 and U937 cells, altered the distribution and activity of protein kinase C in U937 cells, and rapidly downregulated the transcription of U937 c-myc. Evidence from transmission electron microscopy consistent with oxidative stress including putative lipofuscin bodies, myelin figures and disordered mitochondrial cristae and matrices was especially evident in PC3 cells, less so in A172 and essentially absent in U937 cells. A specific 5'-lipoxygenase inhibitor, A63162 inhibited PC3 and U937 proliferation. Some of these events are believed to represent components of "signal" transduction pathways responsible for reversible inhibition of DNA synthesis and the induction of partial phenotypic differentiation in competent cells. Arachidonic acid analogues which exert selective effects on physical and functional properties of cell membranes may represent an additional class of membrane-active agents with potential anticancer activity. A subset of their activities can be duplicated by inhibitors of 5' lipoxygenase.
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PMID:ETYA, a pleotropic membrane-active arachidonic acid analogue affects multiple signal transduction pathways in cultured transformed mammalian cells. 155 Dec 35

Using laser image cytometry and Indo-1 fluorescence, we investigated the intracellular free Ca2+ concentration ([Ca2+]i) of confluent A172 human glioblastoma cells stimulated by the BB homodimer of platelet-derived growth factor (PDGF-BB). The shape of the calcium transients and the delay time between stimulation and the beginning of the transient varied considerably. The percentage of responsive cells, the peak [Ca2+]i and the duration of the response were directly related to PDGF-BB dose, while the delay time was inversely related; the maximal response occurred at a PDGF-BB concentration of 20 ng/ml. Studies with EGTA and inorganic calcium-channel blockers (Ni2+, La3+) showed that the increase of [Ca2+]i resulted from initial release of intracellular stores and subsequent calcium influx across the plasma membrane. Opening of calcium channels in the plasma membrane, monitored directly by studying Mn2+ quenching of Indo-1 fluorescence, was stimulated by PDGF-BB and blocked by La3+; the opening occurred 55 +/- 10 s after the initial increase in [Ca2+]i. Therefore, in these tumor cells, intracellular release always occurs before channel opening in the plasma membrane. Depolarization of cells with high extracellular [K+] did not generally induce calcium transients but did decrease calcium influx. L-type calcium-channel blockers (verapamil, nifedipine, and diltiazem) had little or no effect on the calcium influx induced by PDGF-BB. These results indicate that PDGF-BB induces calcium influx by a mechanism independent of voltage-sensitive calcium channels in A172 human glioblastoma cells.
Cell Calcium 1991 Jul
PMID:Calcium channels in PDGF-stimulated A172 cells open after intracellular calcium release and are not voltage-dependent. 165 94

The intracellular free calcium concentration ([Ca2+]i) of indo-1 loaded A172 human glioblastoma cells stimulated by platelet-derived growth factor (PDGF) was studied in cell suspensions by flow cytometry and spectrofluorometry and in confluent monolayers by laser image cytometry and spectrofluorometry. With all three techniques, the percentage of responsive cells, peak [Ca2+]i, and the duration of response were directly related, and the delay time was inversely related to PDGF dose. The maximum response occurred at a PDGF concentration of about 20 ng/ml. Basal and peak [Ca2+]i did not differ significantly from method to method even though different calibration procedures were used. Cells in suspension monitored by both spectrofluorometry and flow cytometry displayed significantly shorter calcium responses than attached cells. This did not appear to be a direct effect of trypsinization. Spectral analysis of indo-1 in cytoplasm, 40% glycerol, and aqueous solutions showed significant differences in the isosbestic point and quantum efficiency. Calibration of [Ca2+]i with spectrofluorometry is more accurate using the ratio of fluorescence intensities than the fluorescence intensities measured at either 405 or 485 nm.
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PMID:Attachment of A172 human glioblastoma cells affects calcium signalling: a comparison of image cytometry, flow cytometry, and spectrofluorometry. 179 52

Localization and characterization of endothelin receptors in surgical specimens of human gliomas (6 benign astrocytomas and 7 glioblastomas multiforme) and in normal human cortices were studied using quantitative receptor autoradiographic methods. Low numbers of [125I]endothelin-1 [( 125I]ET-1) binding sites were detected in the gray matter of the human frontal cortex, with little binding in the white matter. Conversely, relatively high numbers of [125I]ET-1 binding sites were homogeneously present in tissue sections derived from astrocytomas, whereas higher numbers of [125I]ET-1 binding sites were heterogeneously located on groups of cells with a pseudopalisading appearance and pleomorphic astrocytes in glioblastoma multiforme. Necrotic areas within the tissue sections derived from glioblastoma were devoid of binding. Binding of [125I]ET-1 to gliomas and normal gray matter was specific. Unlabeled ET-1 and its natural analogs (ET-2 and ET-3) inhibited the binding of [125I]ET-1 to these lesions in a concentration-dependent manner and with similar high potencies. Possibly related substances, such as ion channel regulators (omega-conotoxin, apamin, and tetrodotoxin), a Ca2+ channel blocker (nicardipine), and growth factors (epidermal growth factor and insulin-like growth factor I), did not affect the binding to tissue sections derived from gliomas or from normal frontal cortices. Scatchard analysis revealed the presence of a single class and high-affinity binding sites for endothelin in normal cortex and in gliomas. There was no significant difference in the binding affinities: dissociation constants (Kd) were 2.1 +/- 0.5 nM in 6 astrocytomas, 2.5 +/- 0.4 nM in 7 glioblastomas, and 1.4 and 1.5 nM in two normal cortices.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Localization and characterization of endothelin receptors in human gliomas: a growth factor? 216 28

We examined the signal transduction mechanism responsible for the IFN-gamma-induced HLA class II molecule expressions on glioblastoma cell lines, T98G and A172. A series of experiments demonstrated that the activation of protein kinase C (PKC) is involved in the DR and DP molecule expressions on T98G cells. In addition to the activation of PKC, calcium influx appeared to be involved in the DR and DP molecule expressions on T98G. Northern blot analyses with actinomycin D or cycloheximide revealed that these second messengers induce the transcription of DRA and B and DPA and B genes without de novo protein synthesis. Furthermore, we examined the region of the DPB gene that is responsible for IFN-gamma-induced gene transcription by gene transfer of a series of 5' and 3' deletion mutants in which the upstream region of the DPB was linked to a reporter gene, chloramphenicol acetyltransferase. By using these deletion mutants, it appeared that the region between -152 and -126 bp contains a critical IFN-gamma-responsive element. Taken together, these results suggest that IFN-gamma activates PKC and stimulates calcium influx, resulting in the induction of transcription of DRA and B and DPA and B genes without de novo protein synthesis. In DPB gene, we speculate that preexiting protein(s) phosphorylated by PKC in the presence of Ca2+ might directly bind or indirectly interact with the region between -152 and -126 bp of the upstream sequence, leading to the induction of the transcription (possibly in concert with other nuclear protein(s) bound to the promoter sequences).
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PMID:Regulation of HLA class II molecule expressions by IFN-gamma. The signal transduction mechanism in glioblastoma cell lines. 221 76

Calcineurin is one of the calmodulin binding proteins and a Ca2+-dependent and calmodulin-stimulated phosphoprotein phosphatase. We used antisera to the calcineurin as a cell-type-specific marker in order to identify neuronal cells in the rat brain and human neoplasms. In normal rat brain slices, basal ganglia were stained macroscopically, and other areas such as cerebral cortex, corpus callosum, cerebellar cortex, granular layer and pyramidal tract of the spinal cord were lightly identified as well. Under the light microscope, it was found that only the neuronal cells were stained, and astrocytes, oligodendrocytes, ependymal cells and vessels were not. Intracellular distribution of the staining showed various patterns and staining intensity of varying degree. Using the PAP method, localization of the calcineurin in formalin-fixed, paraffin-embedded tissues were studied in 65 human intracranial neoplasms, and in 11 human extracranial neoplasms. The neuronal elements of neuroblastoma, ganglioglioma, ganglioneuroma and retinoblastoma were clearly stained. In contrast, glioblastoma, astrocytoma, oligodendroglioma, ependymoma, meningioma, neurinoma, pituitary adenoma, craniopharyngioma, hemangioblastoma, hamartoma, lymphoma and mesenchymal tumor were all negative. Two cases out of 5 medulloblastomas were stained, but others were not. Although positive tumors disclosed various staining patterns and intensities, these results indicated that calcineurin could be a new neuronal marker in human brain tumors.
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PMID:Calcineurin as a neuronal marker of human brain tumors. 242 51


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