Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tumor necrosis factor (TNF) is an inflammatory cytokine that causes cell injury by generation of oxidative stress. Since glutathione (GSH) is a key cellular antioxidant that detoxifies reactive oxygen species, the purpose of our work was to examine the regulation of cellular GSH, the expression of heavy subunit chain of gamma-glutamylcysteine synthetase (gamma-GCS-HS), and control of intracellular generation of reactive oxygen species in cultured rat hepatocytes treated with TNF. Exposure of cells to TNF (10,000 units/ml) resulted in depletion of cellular GSH levels (50-70%) and overproduction of hydrogen peroxide (2-3-fold) and lipid peroxidation. However, cells treated with lower doses of TNF (250-500 units/ml) exhibited increased levels of GSH (60-80% over control). TNF treatment increased (70-100%) the levels of gamma-GCS-HS mRNA, the catalytic subunit of the regulating enzyme in GSH biosynthesis. Furthermore, intact nuclei isolated from hepatocytes treated with TNF transcribed the gamma-GCS-HS gene to a greater extent than control cells, indicating that TNF regulates gamma-GCS-HS at the transcriptional level. The capacity to synthesize GSH de novo determined in cell-free extracts incubated with GSH precursors was greater (50-70%) in hepatocytes that were treated with TNF; however, the activity of GSH synthetase remained unaltered by TNF treatment indicating that TNF selectively increased the activity of gamma-GCS. Despite activation of nuclear factor-kappaB (NF-kappaB) by TNF, this transcription factor was not required for TNF-induced transcription of gamma-GCS-HS as revealed by deletion constructs of the gamma-GCS-HS promoter subcloned in a chloramphenicol acetyltransferase reporter vector and transfected into HepG2 cells. In contrast, a construct containing AP-1 like/metal response regulatory elements increased chloramphenicol acetyltransferase activity upon exposure to TNF. Thus, TNF increases hepatocellular GSH levels by transcriptional regulation of gamma-GCS-HS gene, probably through AP-1/metal response element-like binding site(s) in its promoter, which may constitute a protective mechanism in the control of oxidative stress induced by inflammatory cytokines.
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PMID:Tumor necrosis factor increases hepatocellular glutathione by transcriptional regulation of the heavy subunit chain of gamma-glutamylcysteine synthetase. 937 27