Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017638 (glioma)
 30,880 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The characteristics of 5'-nucleotidase in a clonal line (C6) of rat glioma cells has been examined in detail. The cells liberated 6.80 +/- 0.33 mumol of inorganic phosphate/mg of cell protein/hour, producing nearly equimolar amounts of adenosine and inorganic phosphate from AMP in the extracellular fluid. No 5'-nucleotidase was released by the cells into the medium. Most of the 5'-nucleotidase activity was found to be located in the outer surface of the plasma membrane of C6 cells and rapidly accessible to exogenous AMP, by experiments based upon differential labeling of extracellular and intracellular compartments with 32P and 33P. The ecto-enzyme was active in the absence of divalent cations. However, Mn2+ or Co2+ were somewhat stimulatory. Zn2+ suppressed activity very markedly. The relationship of enzymatic reaction velocity to pH was complex, with an optimum at pH 7.4 for all substrates tested. The ecto-5'-nucleotidase readily hydrolyzed 5'-AMP and 5'-UMP. Other 5'-nucleoside monophosphates, including 5'-deoxy-AMP, were also hydrolyzed, but more slowly; 2'- or 3'-nucleoside monophosphates were not attacked. The ecto-5'-nucleotidase in the intact cell obeyed Michaelis-Menten kinetics. Apparent Km for AMP was 0.22 mM; apparent Km values for other substrates were similar and ranged from 0.16 to 0.18 mM. ADP exerted a very powerful inhibitory effect, behaving as a competitive inhibitor, and 5'-UMP behaved as a strictly competitive substrate for 5'-AMP. ATP and ITP were inhibitory. Of these, ITP served to increase Km for AMP. ATP did likewise, but also greatly lowered Vmax. These findings indicate that the intact cell is capable of rapid hydrolysis of exogenous 5'-AMP, to produce adenosine at the cell surface at a rate which responds directly to extracellular AMP concentration but which can be suppressed by extracellular ADP or ATP.
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PMID:Ecto-5'-nucleotidase of intact cultured C6 rat glioma cells. 81 33

The effect of Rhein (RH) on the protein synthetic activity and adenylate energy charge in human glioma cells cultured in vitro has been investigated. The results demonstrate that in RH-treated cells, the protein synthesis is strongly decreased, but no modifications in the qualitative pattern occur. The extent of inhibition is a function of the drug concentration as well as of the time of exposure. Such an inhibition must be ascribed mainly to a reduction of adenylate energy charge brought about by RH because of its effect on respiration and glycolysis. The correlation between the adenylate energy charge and cell viability, as well as the possibility of using rhein as a biochemical modulator to reduce or to reverse multidrug resistance, are also discussed.
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PMID:Protein synthetic activity and adenylate energy charge in Rhein-treated cultured human glioma cells. 142 10

The influence of extracellular matrix on the proliferation and differentiation of glioma cells in vitro was investigated by culturing glioma cells in collagen gel and on collagen and laminin films. Rat C-6 glioma cells extended thin cytoplasmic processes, proliferated, and differentiated in collagen gel and on collagen film. The cells were stellate with multiple thin processes like the astrocyte in vivo. The intracellular content of cyclic adenosine-monophosphate in rat C-6 glioma cells on collagen film increased approximately four fold over the control level. In laminin film culture, rat C-6 glioma cells extended thin cytoplasmic processes with many knotty structures and proliferated. These findings confirm that extracellular matrix induces the differentiation of glioma cells.
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PMID:Influence of extracellular matrix on the proliferation and differentiation of glioma cells in culture. 172 67

The cellular mechanism of action of the cannabimimetic drugs is examined using cultured cells. In membranes from N18TG2 neuroblastoma cells and the neuroblastoma X glioma hybrid cells, NG108-15, the psychoactive cannabinoid drugs and their nantradol analogs could inhibit adenylate cyclase activity. This response was not observed in either the soluble adenylate cyclase from rat sperm or membrane-bound adenylate cyclases from C6 glioma or S49 lymphoma cells. This cellular selectivity provides further evidence for the existence of specific receptors for the cannabimimetic compounds. Receptor-mediated inhibition of adenylate cyclase requires the presence of a guanine nucleotide-binding protein complex, Gi. Gi can be functionally inactivated as a result of an ADP-ribosylation modification catalyzed by pertussis toxin. The present study demonstrates that pertussis toxin treatment of cells abolished the cannabimimetic response in intact cells and in membranes derived therefrom. The action of pertussis toxin required NAD+ as substrate for in vitro modification of neuroblastoma membranes. Furthermore, pertussis toxin was able to catalyze the labeling of a neuroblastoma membrane protein in vitro using [32P] NAD+ under conditions similar to those by which attenuation of the cannabimimetic inhibition of adenylate cyclase could be demonstrated. This evidence demonstrates the requirement for a functional Gi in the action of cannabimimetic drugs.
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PMID:Involvement of Gi in the inhibition of adenylate cyclase by cannabimimetic drugs. 286 5

Prolonged stimulation of Gi-coupled receptors often sensitizes adenylate cyclase to subsequent activation by forskolin or Gs-coupled receptors. To identify mechanisms of heterologous sensitization, we characterized sensitization of cAMP accumulation that was induced by activation of recombinant dopamine D2 receptors expressed in C6 glioma and human embryonic kidney (HEK)293 cells. Pretreatment with dopamine or other agonists for 2 hr induced heterologous sensitization that was blocked by the D2 antagonist spiperone but not by the beta-adrenergic receptor antagonist propranolol. Sensitization was evident after 15 min of treatment with dopamine and persisted for at least 2 hr after washout. The EC50 value for sensitization by dopamine in HEK-D2L cells was 100 nM(r) approximately 80-fold higher than the IC50 value for dopamine inhibition of cAMP accumulation. The D2 receptor agonists quinpirole, 7-hydroxy-dipropylamin-otetralin, and pergolide also induced sensitization, whereas the high affinity ergot agonists bromocriptine and lisuride did not. Stimulation of either D2L or D2S receptors sensitized cAMP accumulation to similar extents, but stimulation of D3 receptors did not. In C6-D21 cells, sensitization of isoproterenol-stimulated activity was manifested as a > 100% increase in maximal response, with no change in potency. In contrast, the potency for forskolin-stimulated activity was increased 4-fold, with no apparent change in maximal response. Overnight treatment with pertussis toxin (25 ng/ml) had little effect on isoproterenol or forskolin activation of adenylate cyclase per se but prevented D2 receptor-mediated sensitization in both C6-D2L and HEK-D2L cells, indicating an involvement of one or more of the pertussis toxin-sensitive G proteins, Gi/Gzero. D2 receptor stimulation also sensitized type I and type II adenylate cyclases, each expressed in HEK293 cells together with D2L dopamine receptors. Rapid D2 receptor-mediated heterologous sensitization may be the result of enhanced interaction of G6 with adenylate cyclase and may represent a novel mechanism for modulation of neural activity by D2 receptors.
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PMID:Sensitization of endogenous and recombinant adenylate cyclase by activation of D2 dopamine receptors. 886 43

Tumor cells respond to hypoxic stress by upregulating a variety of genes involved in glucose uptake, glycolysis, and angiogenesis, all essential to maintaining nutrient availability and intracellular ATP levels. Adenosine monophosphate-dependent kinase (AMPK) is a key sensor for cellular homeostasis and is highly sensitive to changes in AMP:ATP ratios. The two catalytic AMPK alpha isoforms (AMPKalpha1, AMPKalpha2) were investigated with respect to their expression, cellular distribution, and contribution to VEGF expression under hypoxic stress in human U373 glioblastoma cells. Quantitative real-time PCR analysis showed AMPKalpha1 mRNA to be constitutively expressed in normoxia and hypoxia, whereas AMPKalpha2 mRNA levels were low in normoxia and significantly induced in hypoxia. Fluorescent immunohistochemistry showed that AMPKalpha2 protein redistributed to the nucleus under hypoxia, whereas AMPKalpha1 remained distributed throughout the cell. The AMPK chemical inhibitor, 5-iodotubericidin, effectively repressed the hypoxic induction of VEGF mRNA levels and hypoxia inducible factor-1 dependent transcription. AMPKalpha2 repression with RNA interference reduced hypoxia-induced VEGF mRNA and HIF-1 transcription, whereas AMPKalpha1 repression did not. Human glioblastoma cell lines U118 and U138 also showed hypoxia-induction of AMPKalpha2 as well as VEGF. Immunohistochemistry analysis of human astrocytoma/glioma samples revealed AMPKalpha2 present in high grade gliomas within hypoxic pseudopalisading microenvironments. These data suggest that prolonged hypoxia promotes the expression and functional activation of AMPKalpha2 and VEGF production in glioma cell lines and glioblastoma multiform tumors, thus contributing to tumor survival and angiogenesis in high grade human gliomas.
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PMID:AMP-dependent protein kinase alpha 2 isoform promotes hypoxia-induced VEGF expression in human glioblastoma. 1651 31

Malignant gliomas are the most common and devastating primary tumors in the brain and, despite treatment, patients with these tumors have a poor prognosis. The participation of ecto-5'-NT/CD73 per se as a proliferative factor, being involved in the control of cell growth, differentiation, invasion, migration and metastasis processes has been previously proposed. In the present study, we evaluated the activity and functions of ecto-5'-NT/CD73 during the proliferation process of rat C6 and human U138MG glioma cell lines. Increasing confluences and culture times led to an increase in ecto-5'-NT/CD73 activity in both C6 and U138MG glioma cells. RT-PCR analysis and flow cytometry analysis showed a significant increase in ecto-5'-NT/CD73 mRNA and protein levels, respectively, comparing confluent with sub-confluent cultures in human U138MG glioma cells. Ecto-5'-nucleotidase/CD73 may regulate the extracellular adenosine 5'-monophosphate (AMP) and adenosine levels. Treatment with 1 microM APCP, a competitive ecto-5'-NT/CD73 inhibitor, caused a significant reduction of 30% in glioma cell proliferation. In addition, 100 microM adenosine increases cell proliferation by 36%, and the treatment with adenosine plus NBTI and dipyridamole, produced an additional and significant increase of on cell proliferation. The inhibitory effect on cell proliferation caused by APCP was reverted by co-treatment with NBTI and dipyridamole. AMP (1 mM and 3 mM) decreased U138MG glioma cell proliferation by 29% and 42%, respectively. Taken together, these results suggest the participation of ecto-5'-NT/CD73 in cell proliferation and that this process is dependent upon the enzyme's production of adenosine, a proliferative factor, and removal of AMP, a toxic molecule for gliomas.
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PMID:The role of ecto-5'-nucleotidase/CD73 in glioma cell line proliferation. 1863 15

Elevated tissue levels of zinc (Zn) have been associated with neurodegenerative diseases such as global ischemia, seizure, and Alzheimer's. The mechanism of action of Zn in causing neuronal injury is not clear. One of the possible mechanisms is the ability of Zn to alter cellular energy metabolism. Using the C6 glioma cell as a model, the present study aimed to determined the effects of increasing concentrations of Zn on cellular energy states, as defined by the levels of adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP), and adenosine 5'-monophosphate (AMP), the total adenosine nucleotides (TAN) (TAN = ATP + ADP + AMP), and the energy charge potential (ECP = [ATP + 0.5 ADP]/TAN). Uptake of Zn was visualized by the appearance of N-(6-methoxy-8-quinolyl)-p-toluene sulfonamide (TSQ)-stained fluorescent granules after a 3-h exposure to Zn in the medium. At [Zn] = 1 mM, cells appeared apoptotic. Levels of ATP and TAN decreased as the level of Zn increased. The change mirrors the increase in cell death as determined by the trypan blue exclusion test. However, when the ratio of ATP:ADP:AMP within the TAN was calculated, the percentage of ATP in the TAN increased significantly, while that of AMP decreased. The change in the relative AMP level mirrored the change in cell viability as measured by the MTT assay, which indicated a decreased in mitochondrial activity. Cellular ECP increased significantly from 0.85 +/- 0.007 to 0.92 +/- 0.04. The elevated ECP and relative ATP level, together with a significant decrease in the relative AMP level, are all indicators of inhibition of cellular metabolism. These results support the notion that acute exposure of C6 glioma cells to a high concentration of Zn might initially result in a decrease in relative AMP and an inhibition of mitochondrial activity. However, the ultimate toxic action of Zn on the C6 glioma cells appears to be due to a gradual inhibition of energy utilization, leading to cell shrinkage and apoptosis.
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PMID:Modulation of energy metabolism in c6 glioma cells as possible mechanism contributing to zinc neurotoxicity. 2002 Nov 52

We found that adenosine 5'-monophosphate-activated protein kinase (AMPK), which is considered the "fuel sensor" of mammalian cells because it directly responds to the depletion of the fuel molecule ATP, is strongly activated by tumor-like hypoxia and glucose deprivation. We also observed abundant AMPK activity in tumor cells in vivo, using subcutaneous tumor xenografts prepared from cells transformed with oncogenic H-Ras. Such rapidly growing transplants of tumor cells, however, represent fully developed tumors that naturally contain energetically stressed microenvironments that can activate AMPK. Therefore, to investigate the induction of AMPK activity during experimental tumorigenesis, we used an established model of brain tumor (glioma) development in the offspring of rats exposed prenatally to the mutagen N-ethyl-N-nitrosourea. We observed that immunostaining for a specific readout of AMPK activity (AMPK-dependent phosphorylation of acetyl-CoA carboxylase) was prominent during N-ethyl-N-nitrosourea-initiated neurocarcinogenesis, from the occurrence of early hyperplasia (microtumors) to the emergence of large gliomas. Moreover, we observed that immunostaining for activating phosphorylation of AMPK correlated with the same stages of glioma development, notably in mitotic tumor cells in which the signal showed punctate as well as cytoplasmic patterns associated with spindle formation. Based on these observations, we propose that neurocarcinogenesis requires AMPK-dependent regulation of cellular energy metabolism.
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PMID:5'-AMP-activated protein kinase activity is elevated early during primary brain tumor development in the rat. 2063 88

Regulation of mRNA decay is an important mechanism controlling gene expression. Steady state levels of mRNAs can be markedly altered by changes in the decay rate. The control of mRNA stability depends on sequences in the transcript itself and on RNA-binding proteins that dynamically bind to these sequences. A well characterized sequence motif, which has been shown to be present in many short-lived mRNAs, is the de-stabilizing adenylate/uridylate-rich element (ARE) located at the 3' untranslated region (3'UTR) of mRNAs. HuR is an RNA-binding protein, which binds to AREs and in doing so, increases the half-life and steady state levels of the corresponding mRNA. Using tissue microarray technology, we found that HuR is over-expressed in human gliomas. We also found that there is a change in HuR localization from being solely in the nucleus to being expressed at high levels in the cytosol. Moreover, a positive correlation was found between total HuR levels, cytosolic localization and tumor grade. We also studied the decay rate of several HuR target mRNAs and found that these mRNAs have a slower rate of decay in glioma cell lines than in astrocytes. Finally, we have been able to decrease both the stability and steady state level of these transcripts in glioma cells using an RNA decoy. More importantly, the decoy transfected cells and cells exposed to a HuR inhibitor have reduced cell growth. In addition, pharmacological inhibition of HuR also resulted in glioma cell growth inhibition. In conclusion, our data suggest that post-transcriptional control abnormalities mediated by HuR are necessary to sustain the rapid growth of this devastating type of cancer.
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PMID:mRNA stability alterations mediated by HuR are necessary to sustain the fast growth of glioma cells. 2193 89


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