Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C1260386 (GSH)
 38,102 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Amino acid transport in mouse peritoneal macrophages is mediated by several membrane carriers with different substrate specificity and sensitivity to environmental stimuli. We reported previously that transport activities of cystine and arginine in the macrophages were induced markedly by low concentrations of bacterial lipopolysaccharide (LPS). It is known that a variety of macrophage functions are affected by ambient oxygen tension. In this study, we have investigated the effects of oxygen on the induction of amino acid transport activity by LPS and found that the induction of cystine, but not arginine, transport activity was dependent on the ambient oxygen tension. When the macrophages were cultured with 2% O(2) in the presence of 1 ng/ml LPS, induction of cystine transport activity was reduced by approximately 70% compared with cells cultured under normoxic conditions. In macrophages, transport of cystine is mediated by a Na(+)-independent anionic amino acid transporter named system x(c)(-). System x(c)(-) is composed of two protein components, xCT and 4F2hc, and the expression of xCT was closely correlated with system x(c)(-) activity. A putative NF-kappaB binding site was found in the 5'-flanking region of the xCT gene, but the enhanced expression of xCT by LPS and oxygen was not mediated by NF-kappaB binding. An increase in intracellular GSH in macrophages paralleled induction of xCT, but not gamma-glutamylcysteine synthetase. These results suggest the importance of system x(c)(-) in antioxidant defense in macrophages exposed to LPS and oxidative stress.
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PMID:Effect of oxygen on induction of the cystine transporter by bacterial lipopolysaccharide in mouse peritoneal macrophages. 1113 24

In mammalian cultured cells, the cystine/glutamate exchange transport mediated by system x(c)- is important to maintain intracellular GSH levels. System x(c)- consists of two protein components, xCT and the heavy chain of 4F2 antigen. The activity of system x(c)- is induced by various stimuli, including electrophilic agents like diethyl maleate. In the present study, we have investigated the mechanism of the transcriptional regulation of xCT mRNA by diethyl maleate. The xCT gene consisted of twelve exons and sequence analysis identified four electrophile response element (EpRE)-like sequences between -230 and -1 in the 5'-flanking region, designated EpRE-1 to EpRE-4. To identify sequences mediating the constitutive and induced expression of xCT, a series of 5'-deletion mutants created from the 5'-flanking region were cloned into a luciferase reproter vector and transfected into BHK21 cells. The 5'-deletion analysis revealed that the sequence between -116 and -82 is essential for the basal expression and the sequence between -226 and -116 containing EpRE-1 is essential in response to diethyl maleate. Mutational analysis demonstrated that EpRE-1 is critically involved in the response to diethyl maleate. Other stress agents like arsenite, cadmium, and hydroquinone seemed to induce system x(c)- activity via the same sequence. Furthermore, the experiments using the mouse embryonic fibroblasts derived from the Nrf2-deficient mice revealed that the induction of xCT gene by electrophilic agents is mediated by Nrf2. EpRE occurs in a broad spectrum of genes for the proteins that are involved in the defense against xenobiotics and regulates their expression. The present results have demonstrated that xCT is a novel member of this protein family.
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PMID:Electrophile response element-mediated induction of the cystine/glutamate exchange transporter gene expression. 1223 64

Adaptive increases in intracellular glutathione (GSH) in response to oxidative stress are mediated by induction of L-cystine uptake via the anionic amino acid transport system x(c)(-). The recently cloned transporter xCT forms a heteromultimeric complex with the heavy chain of 4F2 cell surface antigen (4F2hc/CD98). Depletion of GSH by the electrophile diethylmaleate (DEM) induces the activity and expression of xCT in peritoneal macrophages. We here examine the effects of vitamin C on induction of xCT by DEM in human umbilical artery smooth muscle cells. DEM caused time- (3-24 h) and concentration- (25-100 microM) dependent increases in L-cystine transport, with GSH depleted by 50% after 6 h and restored to basal values after 24 h. xCT mRNA levels increased after 4 h DEM treatment with negligible changes detected for 4F2hc mRNA. DEM caused a rapid (5-30 min) phosphorylation of p38(MAPK). Inhibition of p38(MAPK) by SB203580 (10 microM) enhanced DEM-induced increases in L-cystine transport and GSH, whereas inhibition of p42/p44(MAPK) (PD98059, 10 microM) had no effect. Pretreatment of cells with vitamin C (100 microM, 24 h) attenuated DEM-induced adaptive increases in L-cystine transport and GSH levels. Inhibition of p38(MAPK), but not p42/p44(MAPK), reduced the cytoprotective action of vitamin C. Our findings suggest that DEM induces activation of xCT via intracellular signaling pathways involving p38(MAPK), and that vitamin C, in addition to its antioxidant properties, may modulate this signaling pathway to protect smooth muscle cells from injury.
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PMID:Vitamin C inhibits diethylmaleate-induced L-cystine transport in human vascular smooth muscle cells. 1249 85

Time course relationship between inductions of iNOS and HO-1 was evaluated in RAW264.7 macrophages stimulated with LPS. Expression of HO-1 mRNA increased in a biphasic pattern, but that of xCT (cystine transporter) and iNOS mRNA increased in a monophasic manner. HO-1 protein level increased also in a biphasic manner, at 1-2 h and again between 8 and 24 h. However, iNOS protein began to increase at 4 h, quickly reaching a high level in a monophasic induction pattern. Production of NO* began to occur at 6 h and nitrite continued to accumulate in the culture medium. Total GSH level decreased markedly (50% of control) by 2 h, began to recover at 4 h, returned to control level by 6 h and increased above the control level during 10-24 h. Collectively, these results indicated that overproduced O2*- depletes GSH and triggers induction of xCT, HO-1, iNOS and HO-1 expression in sequence. Most notably, the second-phase induction of HO-1 was caused by overproduced NO*, resulting from LPS-derived iNOS induction. When this iNOS-derived delivery of NO* was combined with prior depletion of GSH using buthioninesulfoximine, an inhibitor of GSH biosynthesis, induction of HO-1 was potentiated. Furthermore, upon such super-induction of HO-1, NO* production was inhibited along with suppression of iNOS expression. Collectively, these results suggested that HO-1 is induced in a biphasic manner, sequentially by the overproduced O*2- and NO*, and the elevated HO-1 suppresses the production of these radicals in an auto-regulatory manner. This may allow the macrophages to survive from injuries that can be caused by concomitant oxidative and nitrosative stresses initiated by the LPS-driven oxidative burst.
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PMID:Biphasic induction of heme oxygenase-1 expression in macrophages stimulated with lipopolysaccharide. 1545 Sep 36

Cystine/glutamate transporter, designated as system x(-)(c), mediates cystine entry in exchange for intracellular glutamate in mammalian cells. This transporter consists of two protein components, xCT and 4F2 heavy chain, and the former is predicted to mediate the transport activity. This transporter plays a pivotal role for maintaining the intracellular GSH levels and extracellular cystine/cysteine redox balance in cultured cells. To clarify the physiological roles of this transporter in vivo, we generated and characterized mice lacking xCT. The xCT(-/-) mice were healthy in appearance and fertile. However, cystine concentration in plasma was significantly higher in these mice, compared with that in the littermate xCT(-/-) mice, while there was no significant difference in plasma cysteine concentration. Plasma GSH level in xCT(-/-) mice was lower than that in the xCT(-/-) mice. The embryonic fibroblasts derived from xCT(-/-) mice failed to survive in routine culture medium, and 2-mercaptoethanol was required for survival and growth. When 2-mercaptoethanol was removed from the culture medium, cysteine and GSH in these cells dramatically decreased, and cells started to die within 24 h. N-Acetyl cysteine also rescued xCT(-/-)-derived cells and permitted growth. These results demonstrate that system x(-)(c) contributes to maintaining the plasma redox balance in vivo but is dispensable in mammalian development, although it is vitally important to cells in vitro.
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PMID:Redox imbalance in cystine/glutamate transporter-deficient mice. 1614 37

Although we have previously demonstrated the functional significance of excitatory amino acid transporters as well as glutamate (Glu) receptors (GluRs) expressed by chondrocytes, little attention has been paid to the possible expression of the cystine/Glu antiporter responsible for the bi-directional transmembrane transport of Glu in chondrocytes to date. In organotypic cultured mouse embryonic metatarsals isolated before vascularization, the chondral mineralization was significantly decreased in the presence of Glu at a high concentration. Apoptotic cells were detected within the late proliferating and prehypertrophic chondrocytic layers in metatarsals cultured in the presence of Glu. A group III metabotropic GluR (mGluR) antagonist partially, but significantly, prevented the inhibition of mineralization by Glu in metatarsals without affecting the number of apoptotic cells. Both decreased mineralization and apoptosis by Glu were significantly prevented by the addition of the cystine/Glu antiporter inhibitor homocysteic acid, as well as reduced glutathione (GSH) and cystine. Expression of mRNA for xCT and 4F2hc subunits, which are components of the cystine/Glu antiporter, was seen in both cultured mouse metatarsals and rat costal chondrocytes. In chondrocytes cultured with Glu, a significant decrease was seen in intracellular GSH levels, together with increases in the number of apoptotic cells and the level of intracellular reactive oxygen species. These results suggest that Glu could regulate chondrogenic differentiation toward mineralization through a mechanism associated with apoptosis mediated by the depletion of intracellular GSH after the retrograde operation of the cystine/Glu antiporter, in addition to the activation of group III mGluR, in chondrocytes.
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PMID:Glutamate inhibits chondral mineralization through apoptotic cell death mediated by retrograde operation of the cystine/glutamate antiporter. 1679 Apr 44

Reactive oxygen species (ROS) produced by neutrophils are essential in the host defense against infections but may be harmful to neutrophils themselves. Glutathione (GSH) plays a pivotal role in protecting cells against ROS-mediated oxidant injury. Cystine/glutamate transporter, designated as system xc- and consisting of two proteins, xCT and 4F2hc, is important to maintain GSH levels in mammalian-cultured cells. In the present paper, we have investigated system xc- in neutrophils. In human peripheral blood neutrophils, neither the activity of system xc- nor xCT mRNA was detected. The activity was induced, and xCT mRNA was expressed when they were cultured in vitro. The mRNA expression was much enhanced in the presence of opsonized zymosan or PMA. In contrast, mouse peritoneal exudate neutrophils, immediately after preparation, exhibited system xc- activity and expressed xCT mRNA. The activity and the expression were heightened further when they were cultured. Peritoneal exudate cells (mostly neutrophils) from xCT-deficient (xCT-/-) mice had lower cysteine content than those from the wild-type mice. GSH levels in the xCT-/-cells decreased rapidly when they were cultured, whereas those in the wild-type cells were maintained during the culture. Apoptosis induced in culture was enhanced in the xCT-/-cells compared with the wild-type cells. These results suggest that system xc- plays an important role in neutrophils when they are activated, and their GSH consumption is accelerated.
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PMID:Expression and function of cystine/glutamate transporter in neutrophils. 1720 Jan 46

Although previous studies including ours have demonstrated the functional expression of different glutamate (Glu) signaling machineries such as Glu receptors (GluRs) and transporters in osteoblasts and chondrocytes, little attention has been paid to the role of Glu in their ancestral mesenchymal stem cells to date. In the present study, we have evaluated the possible functionality of Glu in cultured mouse mesenchymal stem cell line C3H10T1/2 cells endowed to proliferate for the self-renewal and to differentiate toward osteoblast, chondrocyte, adipocyte, and myocyte lineages. Expression of mRNA was for the first time shown with the cystine/Glu antiporter composed of xCT and 4F2hc subunits, in addition to particular excitatory amino acid transporter (EAAT) isoforms and ionotropic GluRs, in undifferentiated C3H10T1/2 cells. Glu significantly suppressed the proliferation activity at a concentration over 500 microM without inducing cell death or differentiation, while the suppression occurred in a manner sensitive to the prevention by cystine and reduced glutathione (GSH), but not by EAAT inhibitors. A significant decrease was seen in intracellular GSH levels in C3H10T1/2 cells cultured with Glu, whereas the cellular proliferation activity was drastically decreased by the addition of the GSH depleter cyclohexene-1-one and the GSH biosynthesis inhibitor L-buthionine-[S,R]-sulfoximine, respectively. Transient overexpression of both xCT and 4F2hc subunits led to an increased basal proliferative activity in C3H10T1/2 cells. These results suggest that Glu could suppress the cellular proliferation toward self-renewal through a mechanism associated with the depletion of intracellular GSH after promoting the retrograde operation of the cystine/Glu antiporter in C3H10T1/2 cells.
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PMID:Suppression by glutamate of proliferative activity through glutathione depletion mediated by the cystine/glutamate antiporter in mesenchymal C3H10T1/2 stem cells. 1752 Jun 96

Chronic exposure to elevated levels of free fatty acids (FFAs) has been shown to cause cell death (lipotoxicity), but the underlying mechanisms of lipotoxicity in hepatocytes remain unclear. We have previously shown that the saturated FFAs cause much greater toxicity to human hepatoma cells (HepG2) than the unsaturated ones (Srivastava and Chan, 2007). In this study, metabolic flux analysis (MFA) was applied to identify the metabolic changes associated with the cytotoxicity of saturated FFA. Measurements of the fluxes revealed that the saturated FFA, palmitate, was oxidized to a greater extent than the non-toxic oleate and had comparatively less triglyceride synthesis and reduced cystine uptake. Although fatty acid oxidation had a high positive correlation to the cytotoxicity, inhibitor experiments indicated that the cytotoxicity was not due to the higher fatty acid oxidation. Application of MFA revealed that cells exposed to palmitate also had a consistently reduced flux of glutathione (GSH) synthesis but greater de novo ceramide synthesis. These predictions were experimentally confirmed. In silico sensitivity analyses identified that the GSH synthesis was limited by the uptake of cysteine. Western blot analyses revealed that the levels of the cystine transporter xCT, but not that of the GSH-synthesis enzyme glutamyl-cysteine synthase (GCS), were reduced in the palmitate cultures, suggesting the limitation of cysteine import as the cause of the reduced GSH synthesis. Finally, supplementing with N-acetyl L-cysteine (NAC), a cysteine-provider whose uptake does not depend on xCT levels, reduced the FFA-toxicity significantly. Thus, the metabolic alterations that contributed to the toxicity and suggested treatments to reduce the toxicity were identified, which were experimentally validated.
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PMID:Application of metabolic flux analysis to identify the mechanisms of free fatty acid toxicity to human hepatoma cell line. 1761 59

The glutathione-dependent system is one of the key systems regulating cellular redox balance, and thus cell fate. Cysteine, typically present in its oxidized form cystine in the extracellular space, is regarded as the rate-limiting substrate for glutathione (GSH) synthesis. Cystine is transported into cells by the highly specific amino-acid antiporter system xc-. Since Burkitt's Lymphoma (BL) cells display limited uptake capacity for cystine, and are thus prone to oxidative stress-induced cell death, we stably expressed the substrate-specific subunit of system xc-, xCT, in HH514 BL cells. xCT-overexpressing cells became highly resistant to oxidative stress, particularly upon GSH depletion. Contrary to previous predictions, the increase of intracellular cysteine did not affect the cellular GSH pool, but concomitantly boosted extracellular cysteine concentrations. Even though cells were depleted of bulk GSH, xCT overexpression maintained cellular integrity by protecting against lipid peroxidation, a very early event in cell death progression. Our results show that system xc- protects against oxidative stress not by elevating intracellular GSH levels, but rather creates a reducing extracellular environment by driving a highly efficient cystine/cysteine redox cycle. Our findings show that the cystine/cysteine redox cycle by itself must be viewed as a discrete major regulator of cell survival.
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PMID:The cystine/cysteine cycle: a redox cycle regulating susceptibility versus resistance to cell death. 1782 97


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