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 early signaling mechanism of sphingosine 1-phosphate (S1P) on extracellular signal-regulated kinase (ERK) activation was investigated in C6 glioma cells. S1P activated the enzyme in association with a shift in the mobility on electrophoresis reflecting phosphorylation of both ERK1/ERK2 at as low as 10 nM. The lipid-induced ERK1/2 activation was partially inhibited by treatment of the cells with either phorbol 12-myristate 13-acetate (a long-term treatment to desensitize protein kinase C) or pertussis toxin (PTX) and was completely inhibited by a simultaneous treatment with both agents. Similarly, either calphostin C, an inhibitor of protein kinase C, or U73122, an inhibitor of phospholipase C, partially inhibited the S1Pinduced ERK1/2 activation in the nontreated cells with PTX and completely in the toxin-treated cells. On the other hand, the S1P-induced ERK activation was hardly affected by ethanol, which switched the product of phospholipase D from phosphatidic acid to metabolism-resistant phosphatidylethanol. S1P was able to activate ERK1/2 without a detectable increase in the intracellular content of the lipid, but sphingosine, a substrate of sphingosine kinase, which is an enzyme for S1P generation in the cells, hardly affected the ERK1/2 activation in spite of a marked elevation of intracellular S1P accumulation. This indicates that intracellular increase in S1P is not necessary for the S1P-induced ERK activation, and hence suggests the extracellular action mechanism of S1P. Supporting this idea, mRNAs of recently identified S1P specific receptors, Edg-1 and AGR16/H218, were expressed in C6 cells. Taken together, these results suggested that S1P acts on C6 cells extracellularly possibly through S1P receptors which are linked to at least two signaling pathways, i.e., the PTX-sensitive Gi/Go protein pathway and the toxin-insensitive Gq/G11-phospholipase C-PKC pathway, resulting in the activation of ERK.
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PMID:Possible involvement of cell surface receptors in sphingosine 1-phosphate-induced activation of extracellular signal-regulated kinase in C6 glioma cells. 988 6

Protein kinase C (PKC) designates a family of kinases that regulate many essential functions including cell growth and differentiation. The tight regulation of PKC activity is crucial for maintaining normal cellular proliferation and excessive activity leads to abnormal or uncontrolled cell growth. Recent reports indicate that malignant glioma cell lines express 100 to 1000-fold higher PKC activity when compared to non-neoplastic astrocytes. This high activity correlates well with the proliferation of tumor cells in vitro. We recently reported on the anti-proliferative properties of selective PKC inhibitors on the growth of U-373MG human astrocytoma cell line, and their ability to block mitogen-activated protein (MAP) kinase pathway activated by substance P (SP) neuropeptide receptor signaling via a PKC-dependent mechanism. Therefore, inhibiting PKC activity by selective PKC inhibitors may present a promising approach for improving astroglial brain tumor therapy. For this purpose, we constructed a high throughput model cell system to evaluate the efficacy of PKC inhibitors. This system is based on the measurement of light production in U-373MG cells stably transfected with the luciferase reporter gene whose expression depends on the transcriptional activation of GAL4-Elk1 fusion protein by enzyme components of the MAP kinase pathway and the upstream activation of PKC (PKC activation-->MAP kinases-->GAL4-Elk1 phosphorylation-->luciferase expression-->luciferase activity). In brief, we have demonstrated that the PKC activator 12-O-tetradecanoyl phorbol 13-acetate (TPA)-induced luciferase activity in this cell system is mediated via the MAP kinase pathway and can be blocked in the presence of MEK1 selective inhibitors (PD 098059 or U0126). We also demonstrated that TPA-induced luciferase activity in U-373MG stable clones can be blocked by PKC inhibitors (CGP 41251, Go 6976, and GF 109203X) in a concentration dependent manner. In contrast, epidermal growth factor (EGF)-induced luciferase activity, which is independent of PKC activation (Ras-->Raf-1-->MEK1-->MAP kinases-->GAL4-Elk1 phosphorylation-->luciferase expression-->luciferase activity) can only be blocked using a selective EGF receptor inhibitor (AG 1478). In conclusion, we have constructed a model cell system for the high throughput screening and identification of PKC inhibitors potentially active against astrocytoma cells in culture.
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PMID:A high throughput system for the evaluation of protein kinase C inhibitors based on Elk1 transcriptional activation in human astrocytoma cells. 991 10

C6-glioma cells endogenously express both 5-HT2A receptors and inducible nitric oxide synthase (iNOS). iNOS can be induced by transcriptional activation to produce nitric oxide (NO) in response to a challenge with the pro-inflammatory cytokines TNF-alpha and IFN-gamma. Experiments were conducted to determine whether 5-HT2A receptor activation could modify the production of NO in response to the inducing agents. 1 muM DOI produced a dose-dependent inhibition of the cytokine-inducted nitrite levels of 40% which was inhibited by spiperone and ritanserin. In addition, the DOI-mediated decrease was prevented by the PKC inhibitor chelerythrine (100 nM). The effectiveness of DOI was lost when added more than two hours after the addition of inducing agent, suggesting that DOI was regulating iNOS at the level of transcription rather than post-translationally. We suggest that there is a link between the serotonergic system and NO-mediated immune responses in the brain.
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PMID:Serotonin 5-HT2A receptor activation inhibits cytokine-stimulated inducible nitric oxide synthase in C6 glioma cells. 992 54

Whole-cell [(32)P]-protein phosphorylation assays and two-dimensional gel electrophoresis (2-DGE) were applied to the analysis of the beta-adrenoceptor (betaAR)-linked signal transduction pathway. Rat C6 glioma cells were stimulated with isoproterenol and the protein lysates were resolved by 2-DGE. Two dimensional [(32)P]-phosphoprotein 'maps' were generated depicting the modulation of intracellular proteins after isoproterenol stimulation versus unstimulated cells. A total of 274 distinct phosphoprotein spots were detected, of which 200 were up-regulated, 69 were down-regulated, and 5 remained unchanged. An evaluation of isoproterenol's activity across several kinase pathways was performed using a computer-generated 2-DGE template incorporating the location and identification of individual signaling phosphoprotein intermediaries. The template served as a 'reference map' for drug treatment comparisons. We observed a significant increase in the phosphorylation states of several nuclear transcription factors, notably CREB-1, ATF-1, NFkappaB/IkappaBalpha and ELK-1, but not c-Jun. A parallel series of radioimmunoprecipitation studies confirmed our 2-DGE findings. Moreover, isoproterenol increased the phosphorylation state of PKC and of several MAPK-dependent pathway kinases which correlated with a significant increase in their endogenous kinase activity. Isoproterenol's effects on PKA, PKC and ERK-dependent activities were blocked by propranolol, a betaAR antagonist. In conclusion, an acute isoproterenol stimulus induced multiplex pathway modulation via the betaAR in the C6 glioma cell indicating that signaling pathway cross-talk is an essential feature for the regulation of cellular function. Moreover, the immediate advantages of the 2-DGE analytical approach were apparent, and further development of the protein database will provide a valuable tool to screen for broad-based drug-mediated signaling activities.
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PMID:Probing for drug-induced multiplex signal transduction pathways using high resolution two-dimensional gel electrophoresis: application to beta-adrenoceptor stimulation in the rat C6 glioma cell. 1040 86

Although protein kinase C has been shown to be involved in a wide range of biological functions, the precise role of each isoform in a specific cell function remains to be clarified. Here we demonstrate that a ribozyme specific for the human protein kinase C alpha (PKC alpha), a classical PKC isoform, induces cell death in glioma cell lines. This cell death was identified as apoptosis by morphologic alterations and endonucleosomal DNA fragmentation. The inhibition of PKC alpha gene expression by the ribozyme resulted in a significant reduction in Bcl-xL gene expression, a protein that inhibits apoptosis and is overexpressed in glioma cells. Taken together, our data suggest that the PKC alpha ribozymes are a potent inducer of apoptosis in glioma cells, which may act through suppressing Bcl-xL gene expression and/or activity. PKC alpha ribozymes may prove useful in the management of malignant gliomas.
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PMID:Ribozyme inhibition of the protein kinase C alpha triggers apoptosis in glioma cells. 1040 97

Glial glutamate transporter GLT-1 mRNA was selectively induced in C6 glioma cells exposed to hypertonic stress (HS), while the expression of two other subtypes, GLAST and EAAC1, was suppressed. HS increased phosphorylation of the MAPK family, ERK, p38 MAPK, and JNK. Treatment with a PKC inhibitor showed that phosphorylation of both p38 MAPK and JNK is PKC-dependent but ERK phosphorylation is independent. Inhibition of either ERK or p38 MAPK did not abolish GLT-1 mRNA induction. Inhibition of PKC also had no effect. These findings indicate that the induction of GLT-1 mRNA by HS is independent of the MAPK pathways. This is the first report that the expression of glial glutamate transporters is osmotically regulated.
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PMID:Selective induction of glial glutamate transporter GLT-1 by hypertonic stress in C6 glioma cells. 1054 20

To investigate the hypothesis that protein kinase Calpha (PKCalpha) is functional glial tumor cell invasion, stable PKCalpha sense and antisense transfected U-87 cell lines were established and PKCalpha expression characterized by Western blot and PKC activity assays. Invasion assays including barrier migration (Koochekpour et al., Extracellular matrix proteins inhibit proliferation, upregulate migration and induce morphological changes in human glioma lines. Eur. J. Cancer, 1995, 31, 375-380; Merzak et al., CD44 mediates human glioma cell adhesion and invasion in vitro. Cancer Res., 1994, 54, 3988-3992; Merzak et al., Cell surface gangliosides are involved in the control of human glioma cell invasion in vitro. Neurosci. Lett., 1994, 177, 11-16), and spheroid confrontation were used to study the relationship between PKCalpha expression and invasiveness. PKCalpha overexpressing clones show increased barrier migration (1.5x) relative to the control transfected clones. PKCalpha inhibited clones exhibited reduced invasiveness, to < 50%. In coculture with PKCalpha overexpressing clones, the remaining normal fetal rat brain aggregate volume was significantly decreased (up to 200%) but 90% of the initial brain volume was left in PKCalpha inhibited clone in the rat brain aggregate tumor spheroid confrontation. This effect was not associated with significant growth inhibition. We conclude that expression of PKCalpha in glioma-derived cell lines appears to be central to glioma invasion in vitro.
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PMID:The role of protein kinase Calpha in U-87 glioma invasion. 1057 7

Multifocal tumor recurrence of glioblastomas occurs in up to 14% of patients. In a parallel phase-II-study investigating post-operative treatment with tamoxifen (TAM), carboplatin and radiation therapy for glioblastomas, 16 of 49 patients (33%) showed multifocal recurrence, which developed after a mean of 46 weeks, raising the question of an association with therapy. We studied the interrelation of proliferation and migration in the presence of different protein-kinase-C(PKC) inhibitors (TAM, staurosporine, hypericin) in 2 glioma cell lines. In addition, 3 cell lines were selected for TAM resistance by repeated cycles of treatment with sub-lethal concentrations of TAM. The proliferative capacity and the invasive potential of selected sub-populations were assessed using growth-curve experiments, monolayer migration, and cell-adhesion assays. Treatment with all PKC inhibitors tested resulted in a dose-dependent decrease of proliferation, while motility was altered only at significantly higher doses. Resistance to TAM occurred in all 3 selected cell lines. The TAM-resistant sub-populations showed significantly increased proliferation, migration and adhesion as compared with the parental (non-selected) cell line. The higher incidence of multifocal disease after TAM treatment was paralleled by increased migratory potential of TAM-treated cells in vitro.
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PMID:Tamoxifen-resistant glioma-cell sub-populations are characterized by increased migration and proliferation. 1079 57

Ammonia is a neurotoxin whose administration in large doses causes coma and death of the exposed animals, but whether and in what degree these whole body effects are related to the death of CNS cells is not known. Since the downstream effects of ammonia in cultured CNS cells appear to be partly mediated by overactivation of several putative signalling mechanisms characteristic for the apoptotic program, we speculated that ammonia neurotoxicity may be apoptogenic. In this study, C6 glioma cells grown in 2% serum were exposed to 5 mM or 10 mM NH(4)Cl (ammonia) for 96 h and tested for the appearance of apoptosis by (a) Hoechst staining, (b) TUNEL reaction and (c) DNA ladder, at different times of exposure. In cultures exposed to either 5 mM or 10 mM ammonia, about 10% of the cells were found to enter apoptosis at 48 h of exposure, and the number of apoptotic cells rose to 30% at 72 h, and to 50% at 96 h of exposure, respectively. The first transduction signal purportedly involved in apoptosis, activation of PKCalphabeta, was transient and appeared already after 3-6 h of treatment. Coincident with pronounced manifestation of apoptosis (at 72 h and even more at 96 h of exposure) was an increased transfer of the transcription factor NFkappaB from cytoplasmto nucleus as revealed by EMSA assay. The number of cells affected by ammonia-induced apoptosis was markedly reduced by incubation with a NOS inhibitor, L-NAME at 100 microM concentration. The results indicate that ammonia-induced apoptosis is a result of a complex interplay of at least three signalling molecules: NO, PKC and the transcription factor NFkappaB, with NFkappaB being possibly involved in the induction of iNOS and generation of toxic levels of NO in the cells.
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PMID:Delayed induction of apoptosis by ammonia in C6 glioma cells. 1081 14

Protein kinase C (PKC) plays an important role in the regulation of glioma growth; however, the identity of the specific isoform and mechanism by which PKC fulfills this function remain unknown. In this study, we demonstrate that PKC activation in glioma cells increased their progression through the cell cycle. Of the six PKC isoforms that were present in glioma cells, PKC alpha was both necessary and sufficient to promote cell cycle progression when stimulated with phorbol 12-myristate 13-acetate. Also, decreased PKC alpha expression resulted in a marked decrease in cell proliferation. The only cell cycle-regulatory molecule whose expression was rapidly altered and increased by PKC alpha activity was the cyclin-cyclin-dependent kinase (CDK) inhibitor p21(Waf1/Cip1). Coimmunoprecipitation studies revealed that p21(Waf1/Cip1) upregulation was accompanied by an incorporation of p21(Waf1/Cip1) into various cyclin-CDK complexes and that the kinase activity of these complexes was increased, thus resulting in cell cycle progression. Furthermore, depletion of p21(Waf1/Cip1) by antisense strategy attenuated the PKC-induced cell cycle progression. These results suggest that PKC alpha activity controls glioma cell cycle progression through the upregulation of p21(Waf1/Cip1), which facilitates active cyclin-CDK complex formation.
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PMID:Involvement of p21(Waf1/Cip1) in protein kinase C alpha-induced cell cycle progression. 1084 85


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