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)

N6-O'2-dibutyryl cAMP (dbcAMP), N6-monobutyryl cAMP (N6-mbcAMP), 8-Chloro cAMP (ClcAMP), and O'2-monobutyryl cAMP (O'2-mbcAMP) were used to study glial fibrillary acidic protein (GFAP) induction in rat C6 glioma. With the exception of O'2-mbcAMP, these cAMP analogs induced GFAP after stimulation of cells with a concentration of 0.5-1 mM. Only dbcAMP and N6-mbcAMP increased the intracellular concentration of cAMP. Protein kinase A (PKA) activation is often proposed to be involved in GFAP expression in astrocytes. Ion-exchange chromatography indicated that protein kinase activity is associated with PKA type II in C6. dbcAMP, N6-mbcAMP, and ClcAMP upregulated the amount of cAMP-binding proteins approximately twofold. RI was upregulated in the cytosol and particulate fraction, whereas RII was not affected after stimulation with dbcAMP. Concomitant, the PKA activity decreased approximately 60% and 40% in the cytosol and particulate fraction, respectively. CREB is constitutively expressed in C6 and is downregulated after stimulation with dbcAMP. The membrane-permeable PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinoline sulfonamide (H89) did not suppress the induction of GFAP-mRNA and its translation into GFAP. On the contrary, depending on the time difference between H89 and dbcAMP addition to C6, GFAP synthesis could even be potentiated more than twofold. Experiments in the presence of cycloheximide showed that protein synthesis is necessary for GFAP transcription. Although all components of the PKA signal transduction pathway are present in C6, GFAP synthesis is not dependent on PKA activation but required the synthesis of an unidentified factor.
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PMID:Cyclic AMP-mediated induction of the glial fibrillary acidic protein is independent of protein kinase A activation in rat C6 glioma. 916 58

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

Analysis of constitutive heat shock protein 70 (HSC70) concentration in unstressed proliferating and differentiated rat C6 glioma cells revealed a striking reduction in the amount of HSC70 in differentiated cells. Proliferating cells showed a significantly higher HSC70 concentration, particularly observable during S phase in synchronous cultures. The activity of the cAMP/PKA signaling pathway was enhanced in differentiated cells. cAMP-elevating treatments both inhibited growth and reduced HSC70 concentration. Inactivation of PKA by H-89 upregulated the reduced HSC70 expression in differentiated cells and stimulated proliferation. Treatment with an inhibitor of MAP kinase activation (PD98059) reduced the HSC70 concentration. We assume that cAMP does not directly inhibit HSC70 expression by transcriptional repression, but by its inhibitory effect on the MAP kinase pathway.
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PMID:Different constitutive heat shock protein 70 expression during proliferation and differentiation of rat C6 glioma cells. 1049 25

To investigate the possible mechanisms involved in forskolin-induced c-jun mRNA decrease in rat C6 glioma cells, we examined effects of a PKA inhibitor (H-89), a L-type Ca2+ channel blocker (nimodipine), a calmodulin activation inhibitor (calmidazolium chloride) and a Ca2+/calmodulin-dependent protein kinase II inhibitor (KN-62) on forskolin-induced c-jun mRNA down-regulation. H-89 caused a reversal of forskolin-induced c-jun mRNA decrease. Furthermore, nimodipine, KN-62 and calmidazolium chloride partially blocked forskolin-induced c-jun mRNA down-regulation. Our results suggest that activation of adenylate cyclase appears to be involved in a down-regulation of c-jun mRNA expression through a PKA pathway. In addition, L-type calcium channels, calmodulin and Ca2+/calmodulin-dependent protein kinase II may be partially involved in c-jun mRNA down-regulation induced by forskolin.
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PMID:Activation of adenylate cyclase results in down-regulation of c-jun mRNA expression in rat C6 glioma cells. 1058 73

Cyclic AMP is a ubiquitous second messenger that coordinates diverse cellular functions. Current methods for measuring cAMP lack both temporal and spatial resolution, leading to the pervasive notion that, unlike Ca(2+), cAMP signals are simple and contain little information. Here we show the development of adenovirus-expressed cyclic nucleotide-gated channels as sensors for cAMP. Homomultimeric channels composed of the olfactory alpha subunit responded rapidly to jumps in cAMP concentration, and their cAMP sensitivity was measured to calibrate the sensor for intracellular measurements. We used these channels to detect cAMP, produced by either heterologously expressed or endogenous adenylyl cyclase, in both single cells and cell populations. After forskolin stimulation, the endogenous adenylyl cyclase in C6-2B glioma cells produced high concentrations of cAMP near the channels, yet the global cAMP concentration remained low. We found that rapid exchange of the bulk cytoplasm in whole-cell patch clamp experiments did not prevent the buildup of significant levels of cAMP near the channels in human embryonic kidney 293 (HEK-293) cells expressing an exogenous adenylyl cyclase. These results can be explained quantitatively by a cell compartment model in which cyclic nucleotide-gated channels colocalize with adenylyl cyclase in microdomains, and diffusion of cAMP between these domains and the bulk cytosol is significantly hindered. In agreement with the model, we measured a slow rate of cAMP diffusion from the whole-cell patch pipette to the channels (90% exchange in 194 s, compared with 22-56 s for substances that monitor exchange with the cytosol). Without a microdomain and restricted diffusional access to the cytosol, we are unable to account for all of the results. It is worth noting that in models of unrestricted diffusion, even in extreme proximity to adenylyl cyclase, cAMP does not reach high enough concentrations to substantially activate PKA or cyclic nucleotide-gated channels, unless the entire cell fills with cAMP. Thus, the microdomains should facilitate rapid and efficient activation of both PKA and cyclic nucleotide-gated channels, and allow for local feedback control of adenylyl cyclase. Localized cAMP signals should also facilitate the differential regulation of cellular targets.
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PMID:Cyclic nucleotide-gated channels colocalize with adenylyl cyclase in regions of restricted cAMP diffusion. 1091 62

The effects of forskolin (FSK) and phobol 12-myristate-13-acetate (PMA) on c-fos and c-jun mRNA expressions in rat C6 glioma cells were studied. Both FSK and PMA increased the c-fos mRNA level. The C-jun mRNA level was decreased by FSK, whereas it was increased by PMA. The elevated c-fos mRNA level, induced by FSK or PMA, was significantly inhibited by dexamethasone (DEX). In contrast, DEX did not affect the FSK- and PMA-induced response of the c-jun mRNA level. Cycloheximide (CHX) caused a superinduction of the FSK- or PMA-induced c-fos mRNA level. Furthermore, CHX also potentiated the PMA-induced c-jun mRNA level. However, CHX did not affect the FSK-induced down-regulation of the c-jun mRNA level. When C6 glioma cells were incubated with PMA and FSK, the PMA-induced c-jun mRNA level was inhibited by FSK, whereas FSK did not affect the PMA-induced c-fos mRNA level. Our results suggest that the activations of PKA and PKC pathways have different roles in the regulation of the c-jun mRNA expression in rat C6 glioma cells. PKA activation can inhibit induction of the c-jun mRNA expression by PMA. In addition, DEX appears to have a selective inhibitory action against c-fos, but not c-jun, -mRNA expression that is regulated by PKA and PKC. On-going protein synthesis inhibition is required for the superinduction of the c-fos expression that is induced by PMA, or FSK and the PMA-induced c-jun mRNA level.
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PMID:Differential effects of forskolin and phobol 12-myristate-13-acetate on the c-fos and c-jun mRNA expression in rat C6 glioma cells. 1156 18

Recent evidence indicates that second messengers and protein kinases regulate the activity and expression of glutamate transporters. The aim of the present study was to determine if direct activation of protein kinases C or A modulates the activity of the sodium-dependent glutamate transporter EAAC1. EAAC1 modulation was studied in cRNA-injected Xenopus oocytes by measuring [3H]L-glutamate uptake or glutamate-evoked uptake currents. We found that activation of PKA was ineffective, whereas treatment with the PKC agonist phorbol 12-myristate 13-acetate (PMA) caused a significant decrease in EAAC1 transport activity (IC(50)=44.7+/-12 nM). PMA-induced EAAC1 inhibition was PKC-mediated because the inhibition could be blocked by specific PKC inhibitors and incubation with the inactive 4alpha-phorbol-12,13-didecanoate (4alpha-PDD) did not affect EAAC1. Saturation studies of glutamate-evoked uptake currents showed that PMA-mediated inhibition was due to a decrease in I(max) with no change in K(m). PMA simultaneously decreased membrane capacitance (C(m)) and transport-associated current and increased cytosolic accumulation of EAAC1 protein, compared to control. These results suggest that PKC activation inhibits EAAC1 by promoting its retrieval from the plasma membrane. PMA also significantly decreased glutamate uptake in a Madin-Darby canine kidney (MDCK) cell line stably transfected with EAAC1 but enhanced EAAC1-mediated glutamate uptake in the rat C6 glioma cells, consistent with previous observations. Because activation of PKC by phorbol esters leads to opposite effects on EAAC1 activity in different culture models, we conclude that the PKC-mediated regulation of EAAC1 is cell-type specific.
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PMID:Inhibition of the glutamate transporter EAAC1 expressed in Xenopus oocytes by phorbol esters. 1157 12

The blood-brain barrier (BBB) is formed by the presence of tight junction complexes between brain endothelial cells that restrict paracellular permeability. As a consequence, a number of transport proteins are expressed on cerebral endothelial cells to facilitate the transport of nutrients into the brain. Although the modulation of barrier tight junction properties by glial-conditioned medium and by second messengers is well established, little is known about the effects of these factors on carrier-mediated BBB transport processes. The ECV304 cell line shows an endothelial phenotype and can be induced to upregulate certain BBB features in the presence of glial factors. In the present study, we have examined the effect of conditioned medium derived from rat C6-glioma cells (C6CM) on the function of the L-system amino acid transporter in ECV304 cells, using L-leucine as the model substrate, and have determined whether the changes observed can be mimicked by modulating intracellular cAMP levels. ECV304 cells exposed to C6CM exhibited a significant increase in both the affinity of leucine transport and the diffusional constant (Michaelis-Menten), while the maximal transport capacity remained unchanged. Conversely, acute exposure to modulators of the PKA and PKC second messenger pathways was found to reduce significantly the maximal transport capacity and diffusion constants, while transport affinity remained unchanged. In both cases, the maximal flux of leucine was increased, indicating transport of greater efficiency. This study indicates that exposure of ECV304 cells to C6CM provides an influence inducing L-system transport properties characteristic of brain endothelial cells. Furthermore, it appears that L-system-mediated transport of amino acids can be modulated by several distinct pathways.
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PMID:Glial induction of blood-brain barrier-like L-system amino acid transport in the ECV304 cell line. 1211 61

Hepatocyte growth factor (HGF) and its receptor c-Met are expressed in inappropriately high abundance in gliomas and are further upregulated during the transition from low- to high-grade malignancy. In these cells HGF induces expression of c-Met via PKC, Ras and mitogen activated protein kinase (MAPK) pathway. Here we report that secretion and expression of HGF in U87 astrocytoma is increased by a PKC activator, PMA, an effect which is abolished by a PKC inhibitor, Go6976, specific for PKCalpha and PKCbeta1. Activating PKA by forskolin, on the other hand, had no effect. Furthermore, messenger molecule downstream of PKC, i.e. MEK mediates such effect of PKC as specific MEK inhibitors (PD98059 and U0126) abolished PMA induced HGF secretion by U87 cells. Accordingly, PMA induced rapid phosphorylation of MEK substrate, i.e. Erk1/2 (p42/44 MAPK). In addition, such effect of PKC is Ras-dependent as specific Ras inhibitor L-744,832 attenuated both PMA mediated induction of Erk 1/2 phosphorylation as well as HGF secretion. Moreover, a specific p38 MAPK inhibitor (SB203580) almost completely inhibited basal HGF secretion to an undetectable level. Increased secretion of HGF is most likely exerted at the transcriptional level since inhibitor of transcription, actinomycin D abolished such increase. Furthermore, when assessed by Northern blot analysis, PMA increased HGF transcripts while U0127 and SB203580 inhibited. Therefore, our data reveal that HGF secretion in U87 cells is regulated by Ras-dependent PKC, MEK cascade and in parallel by p38 MAPK pathway. Since the Raf-PKC-MEK cascade is used for HGF's signaling via its receptor in astrocytoma cells, our data revealing similar regulatory mechanism for HGF secretion in these cells would help to explain the feed forward nature of HGF action in glioma cells that would further accentuate its basal secretion, exacerbating its effects on the progression of gliomas in an autocrine fashion.
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PMID:PKC, p42/44 MAPK and p38 MAPK regulate hepatocyte growth factor secretion from human astrocytoma cells. 1219 96

We investigated the signal pathway related to induction of Nurr1, transcription factor, by cAMP in neuroblastoma N2A and C6 glioma cell lines. Nurr1 expression was induced by forskolin, an adenylate cyclase activator, via activation of CREB in both N2A and C6 cells. The effect of forskolin on ERK, however, was cell specific. ERK phosphorylation was stimulated by forskolin in N2A cells whereas it was inhibited in C6 cells. Pretreatment with H89, a PKA inhibitor, blocked the forskolin-induced Nurr1 expression in both N2A and C6 cells. Interestingly, pretreatment with PD98059, an MEK inhibitor, showed differential effects. Pretreatment with PD98059 inhibited the forskolin-induced Nurr1 expression in N2A cells, however, in C6 cells, Nurr1 expression was further increased. Our results suggest that ERK pathway plays a differential role in cAMP-induced Nurr1 expression in N2A and C6 cells.
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PMID:Differential role of ERK in cAMP-induced Nurr1 expression in N2A and C6 cells. 1510 39


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