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 mitogenic activity of several growth factors is mediated by calcium-dependent signal transduction. Calmodulin (CaM) binding proteins such as CaM-dependent protein kinases are important components of this pathway and may be altered in diseases characterized by abnormal cell growth. CaM kinase II is believed to regulate the phosphorylation of microtubular-associated proteins and control the initiation of DNA synthesis. Furthermore, drugs that inhibit CaM-mediated signal transduction also inhibit cellular proliferation and are cytotoxic to numerous malignant cell lines, including those established from malignant gliomas. Yet, little is known about CaM-dependent protein kinases in these tumors. Therefore, we have investigated the activity and distribution of CaM-dependent protein kinase II in normal and malignant glial tissues, a kinase believed to play a critical role in cell cycle regulation. C6 and 9L cells contained kinase activities that were activated by Ca2+/CaM and inhibited by trifluoperazine. Tissue extracts from these cell lines and from rat brain white matter phosphorylated exogenous synapsin I in a pattern consistent with the presence of CaM kinase II activity as determined by phosphopeptide mapping. CaM kinase II activity was confirmed using a specific peptide substrate and inhibitor. An unexpected finding was that glioma lines, but not rat brain white matter, also contained a CaM-dependent protein kinase detected by the phosphorylation of a M(r) 100,000 protein, subsequently identified as elongation factor 2, the only known substrate for CaM kinase III.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Calmodulin-dependent protein kinases in rat glioblastoma. 764 41

Certain calmodulin (CaM)-dependent protein kinases phosphorylate substrates have been implicated in regulating cellular proliferation. In this study, CaM-dependent phosphorylation has been examined in normal and tumor tissue from rat brain to determine whether differences exist. Using in vitro phosphorylation reactions, we compared endogenous substrates for Ca2+/CaM-dependent protein kinases in rat brain white matter (RBWM), a tissue rich in normal glia, to those of C6 rat glioma cells. A major phosphoprotein having a M(r) of 100,000 was observed in proliferating C6 cells that was not present in RBWM or in nonproliferating cells. Phosphorylation was stimulated by Ca2+ and CaM and inhibited by trifluoperazine. An antibody to elongation factor 2 (EF-2) immunoprecipitated the M(r) 100,000 protein from C6 cells. EF-2 was present in RBWM but was not phosphorylated. Homogenates of RBWM did not phosphorylate exogenous EF-2, which suggested the absence of CaM kinase III activity in normal glial tissue. Furthermore, the addition of purified, exogenous CaM kinase III to homogenates of RBWM resulted in EF-2 phosphorylation. These data demonstrate that a basal level of EF-2 phosphorylation exists in proliferating glioma cells that is markedly diminished or absent in normal glial tissue and is due to the activity of CaM kinase III.
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PMID:Phosphorylation of elongation factor 2 in normal and malignant rat glial cells. 848 12

eEF-2 kinase is a ubiquitous Ca2+/calmodulin-dependent protein kinase that is specific for protein synthesis elongation factor-2 (eEF-2). This study describes an improved procedure for the purification of eEF-2 kinase from rabbit reticulocyte lysate. The eEF-2 kinase preparation was used to raise polyclonal antibodies, which immunoprecipitated eEF-2 kinase protein and activity from rabbit reticulocyte lysate. The antibodies recognized a single 103 kDa band in extracts from several cell lines including NIH 3T3, PC12, C6 glioma, HeLa, and MCF-7 breast carcinoma. However, there was no immunoreactivity in extracts of rabbit or bovine liver or rabbit kidney despite the presence of abundant eEF-2 kinase activity in these tissues. Exposure of PC12 cells to nerve growth factor (NGF) resulted in rapid down-regulation of eEF-2 kinase activity and a decrease in immunoreactivity. After 24 h of incubation with NGF, the activity of the kinase recovered to 80% of initial values. In contrast, the immunoreactivity of eEF-2 kinase continued to decrease. These data suggest that tissue-specific isoforms of eEF-2 kinase may exist and that these isoforms may be regulated by growth factors.
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PMID:Elongation factor-2 kinase: immunological evidence for the existence of tissue-specific isoforms. 894 13

Calmodulin-dependent protein kinases phosphorylate certain substrates that have been implicated in regulating cellular proliferation. For example, upon mitogenic stimulation, there is a rapid activation of calmodulin-dependent protein kinase III (CaM kinase III), which leads to the phosphorylation of elongation factor 2. Recently, our laboratory demonstrated that the activity of CaM kinase III is increased in glioma cells following exposure to mitogens and is diminished or absent in nonproliferating glial tissue. Rottlerin, a 5,7-dihydroxy-2,2-dimethyl-6-(2,4,6-trihydroxy-3-methyl-5-acetylbenzy l)-8-cinnamoyl-1,2-chromene isolated from the pericarps of Mallotus phillippinensis, has been shown to be an effective CaM kinase III inhibitor. Therefore, we evaluated the effects of rottlerin on the growth and viability of glioblastoma cell lines. Rottlerin decreased growth and induced cytotoxicity in rat (C6) and two human gliomas (T98G and U138MG) at concentrations that inhibited the activity of CaM kinase III in vitro and in vivo. Far less demonstrable effects were observed on other Ca2++/CaM-sensitive kinases. Incubation of glial cells with rottlerin produced a block at the G1-S interface and the appearance of a population of cells with a <2N complement of DNA. In addition, rottlerin induced changes in cellular morphology such as cell shrinkage, accumulation of cytoplasmic vacuoles, and packaging of cellular components within membranes. These data suggest that CaM kinase III may be an important link between the activation of CaM-dependent signaling, proliferation, and viability in malignant cells, and that inhibition of CaM kinase III may represent an interesting pharmacological target in malignant gliomas.
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PMID:Effects of rottlerin, an inhibitor of calmodulin-dependent protein kinase III, on cellular proliferation, viability, and cell cycle distribution in malignant glioma cells. 905 75

Recent evidence suggests that the machinery of protein synthesis may provide novel targets for anticancer drugs. For example, aberrations in protein synthesis are commonly encountered in established cancers, and disruption by mutation or overexpression of translation factors can cause cellular transformation. We previously demonstrated that the activity of eukaryotic elongation factor 2 (eEF-2) kinase was markedly increased in several forms of malignancy and that nonspecific inhibitors of this enzyme promoted cell death. On the basis of the predicted amino acid sequence of eEF-2 kinase deduced from the cloned cDNA, we hypothesized that inhibitors of prokaryotic histidine kinases might also inhibit the activity of eEF-2 kinase. We describe herein the screening of a series of imidazolium histidine kinase inhibitors and the identification of an active lead compound, NH125. NH125 inhibited eEF-2 kinase activity (IC(50) = 60 nM) in vitro, blocked the phosphorylation of eEF-2 in intact cells, and showed relative selectivity over other protein kinases: protein kinase C (IC(50) = 7.5 microM), protein kinase A (IC(50) = 80 microM), and calmodulin-dependent kinase II (IC(50) > 100 microM). NH125 decreased the viability of 10 cancer cell lines with IC(50)s ranging from 0.7 to 4.7 microM. Forced overexpression of eEF-2 kinase in a glioma cell line produced 10-fold resistance to NH125. In conclusion, these results suggest that identification of potent inhibitors of eEF-2 kinase may lead to the development of new types of anticancer drugs.
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PMID:Identification and characterization of an inhibitor of eukaryotic elongation factor 2 kinase against human cancer cell lines. 1458 88

2-Deoxy-d-glucose (2-DG), a synthetic glucose analogue that acts as a glycolytic inhibitor, is currently being evaluated in the clinic as an anticancer agent. In this study, we observed that treatment of human glioma cells with 2-DG activated autophagy, a highly conserved cellular response to metabolic stress and a catabolic process of self-digestion of intracellular organelles for energy use and survival in stressed cells. The induction of autophagy by 2-DG was associated with activation of elongation factor-2 kinase (eEF-2 kinase), a structurally and functionally unique enzyme that phosphorylates eEF-2, leading to loss of affinity of this elongation factor for the ribosome and to termination of protein elongation. We also showed that inhibition of eEF-2 kinase by RNA interference blunted the 2-DG-induced autophagic response, resulted in a greater reduction of cellular ATP contents, and increased the sensitivity of tumor cells to the cytotoxic effect of 2-DG. Furthermore, the blunted autophagy and enhanced 2-DG cytotoxicity were accompanied by augmentation of apoptosis in cells in which eEF-2 kinase expression was knocked down. The results of this study indicate that the energy stress and cytotoxicity caused by 2-DG can be accelerated by inhibition of eEF-2 kinase, and suggest that targeting eEF-2 kinase-regulated autophagic survival pathway may represent a novel approach to sensitizing cancer cells to glycolytic inhibitors.
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PMID:Silencing of elongation factor-2 kinase potentiates the effect of 2-deoxy-D-glucose against human glioma cells through blunting of autophagy. 1924 19

Inhibition of the survival kinase Akt can trigger apoptosis, and also has been found to activate autophagy, which may confound tumor attack. In this study, we investigated regulatory mechanisms through which apoptosis and autophagy were modulated in tumor cells subjected to Akt inhibition by MK-2206, the first allosteric small molecule inhibitor of Akt to enter clinical development. In human glioma cells, Akt inhibition by MK-2206 or siRNA-mediated attenuation strongly activated autophagy, whereas silencing of eukaryotic elongation factor-2 (eEF-2) kinase, a protein synthesis regulator, blunted this autophagic response. Suppression of MK-2206-induced autophagy by eEF-2 silencing was accompanied by a promotion of apoptotic cell death. Similarly, siRNA-mediated inhibition of eEF-2 kinase potentiated the efficacy of MK-2206 against glioma cells. Together, these results showed that blunting autophagy and augmenting apoptosis by inhibition of eEF-2 kinase could modulate the sensitivity of glioma cells to Akt inhibition. Our findings suggest that targeting eEF-2 kinase may reinforce the antitumor efficacy of Akt inhibitors such as MK-2206.
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PMID:eEF-2 kinase dictates cross-talk between autophagy and apoptosis induced by Akt Inhibition, thereby modulating cytotoxicity of novel Akt inhibitor MK-2206. 2130 30

Eukaryotic elongation factor-2 (eEF-2) kinase, also known as calmodulin-dependent protein kinase III, is a unique calcium/calmodulin-dependent enzyme. eEF-2 kinase can act as a negative regulator of protein synthesis and a positive regulator of autophagy under environmental or metabolic stresses. Akt, a key downstream effector of the PI3K signaling pathway that regulates cell survival and proliferation, is an attractive therapeutic target for anticancer treatment. Akt inhibition leads to activation of both apoptosis, type I programmed cell death and autophagy, a cellular degradation process via lysosomal machinery (also termed type II programmed cell death). However, the underlying mechanisms that dictate functional relationship between autophagy and apoptosis in response to Akt inhibition remain to be delineated. Our recent study demonstrated that inhibition of eEF-2 kinase can suppress autophagy but promote apoptosis in tumor cells subjected to Akt inhibition, indicating a role of eEF-2 kinase as a controller in the crosstalk between autophagy and apoptosis. Furthermore, inhibition of eEF-2 kinase can reinforce the efficacy of a novel Akt inhibitor, MK-2206, against human glioma. These findings may help optimize the use of Akt inhibitors in the treatment of cancer and other diseases.
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PMID:eEF-2 kinase, another meddler in the "yin and yang" of Akt-mediated cell fate? 2146 Jun 16

Elongation factor-2 kinase (eEF-2 kinase, also known as calmodulin-dependent protein kinase III), is a unique calcium/calmodulin-dependent enzyme that inhibits protein synthesis by phosphorylating and inactivating elongation factor-2 (eEF-2). We previously reported that expression/activity of eEF-2 kinase was up-regulated in several types of malignancies including Gliomas, and was associated with response of tumor cells to certain therapeutic stress. In the current study, we sought to determine whether eEF-2 kinase expression affected sensitivity of glioma cells to treatment with tumor the necrosis factor-related apoptosis-inducing ligand (TRAIL), a targeted therapy able to induce apoptosis in cancer cells but causes no toxicity in most normal cells. We found that inhibition of eEF-2 kinase by RNA interference (RNAi) or by a pharmacological inhibitor (NH125) enhanced TRAIL-induced apoptosis in the human glioma cells, as evidenced by an increase in apoptosis in the tumor cells treated with eEF-2 kinase siRNA or the eEF-2 kinase inhibitor. We further demonstrated that sensitization of tumor cells to TRAIL was accompanied by a down-regulation of the anti-apoptotic protein, Bcl-xL, and that overexpression of Bcl-xL could abrogate the sensitizing effect of inhibiting eEF-2 kinase on TRAIL. The results of this study may help devise a new therapeutic strategy for enhancing the efficacy of TRAIL against malignant glioma by targeting eEF-2 kinase.
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PMID:Inhibition of eEF-2 kinase sensitizes human glioma cells to TRAIL and down-regulates Bcl-xL expression. 2194 17

Eukaryotic elongation factor-2 kinase (eEF-2K) is a Ca(2+)/calmodulin-dependent enzyme that negatively regulates protein synthesis. eEF-2K has been shown to be up-regulated in cancer, and to play an important role in cell survival through inhibition of protein synthesis. Post-translational modification of protein synthesis machinery is important for its regulation and could be critical for survival of cancer cells encountering stress. The purpose of our study was to examine the regulation of eEF-2K during stress with a focus on the roles of phosphorylation in determining the stability of eEF-2K. We found that stress conditions (nutrient deprivation and hypoxia) increase eEF-2K protein. mRNA levels are only transiently increased and shortly return to normal, while eEF-2K protein levels continue to increase after further exposure to stress. A seemingly paradoxical decrease in eEF-2K stability was found when glioma cells were subjected to stress despite increased protein expression. We further demonstrated that phosphorylation of eEF-2K differentially affects the enzyme's turnover under both normal and stress conditions, as evidenced by the different half-lives of phosphorylation-defective mutants of eEF-2K. We further found that the eEF-2K site (Ser398) phosphorylated by AMPK is pivotal to the protein's stability, as the half-life of S398A mutant increases to greater than 24h under both normal and stress conditions. These data indicate that eEF-2K is regulated at multiple levels with phosphorylation playing a critical role in the enzyme's turnover under stressful conditions. The complexity of eEF-2K phosphorylation highlights the intricacies of protein synthesis control during cellular stress.
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PMID:Phosphorylation of elongation factor-2 kinase differentially regulates the enzyme's stability under stress conditions. 2274 97


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