title: Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice.
abstract: Endotoxemia correlates with the degree of liver failure and may participate in worsening of liver diseases. Lipopolysaccharide (LPS; synonymous with endotoxin) treatment in mice lowered the hepatic glutathione (GSH) level, which in turn is a variable that determines susceptibility to LPS-induced injury. We previously showed that LPS treatment in mice lowered hepatic expression of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase (GCL). The aim of our current work was to determine the molecular mechanism(s) responsible for these changes. Studies were done using RAW cells (murine macrophages), in vivo LPS-treated mice, and mouse hepatocytes. We found that LPS treatment lowered GCL catalytic and modifier (Gclc and Gclm) subunit expression at the transcriptional level, which was unrelated to alterations in nitric oxide production or induction of NF-κB/p65 subunit. The key mechanism was a decrease in sumoylation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and MafG, which is required for their heterodimerization and subsequent binding and trans-activation of the antioxidant-response element (ARE) present in the promoter region of these genes that is essential for their expression. LPS treatment lowered markedly the expression of ubiquitin-conjugating enzyme 9 (Ubc9), which is required for sumoylation. Similar findings also occurred in liver after in vivo LPS treatment and in LPS-treated mouse hepatocytes. Overexpression of Ubc9 protected against LPS-mediated inhibition of Gclc and Gclm expression in RAW cells and hepatocytes. In conclusion, LPS-mediated lowering of GCL expression in hepatocytes and macrophages is due to lowering of sumoylation of Nrf2 and MafG, leading to reduced heterodimerization, binding, and trans-activation of ARE.
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Maria Lauda
authors.initials: ML
authors.lastname: Tomasi
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Minjung
authors.initials: M
authors.lastname: Ryoo
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Heping
authors.initials: H
authors.lastname: Yang
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Department of Genetics, Faculty of Science and Technology, University of the Basque Country, Leioa, Bilbao, Spain.
authors.forename: Ainhoa
authors.initials: A
authors.lastname: Iglesias Ara
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Department of Nutritional Science and Food Management, College of Health Science, Ewha Women's University, Seoul, Korea.
authors.forename: Kwang Suk
authors.initials: KS
authors.lastname: Ko
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Los Angeles, CA 90033, USA; Southern California Research Center for Alcoholic Liver and Pancreatic Diseases and Cirrhosis, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA. Electronic address: shellylu@usc.edu.
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
mesh_terms: D000818:Animals; D015971:Gene Expression Regulation, Enzymologic; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis* / Q000235:genetics; D005978:Glutathione / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D008070:Lipopolysaccharides / Q000633:toxicity; D017093:Liver Failure / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D008264:Macrophages / Q000378:metabolism / Q000473:pathology; D051259:MafG Transcription Factor / Q000378:metabolism; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism; D058207:Sumoylation
chemical_list: D008070:Lipopolysaccharides; D051259:MafG Transcription Factor; C491247:Mafg protein, mouse; D051267:NF-E2-Related Factor 2; D016328:NF-kappa B; C495636:Nfe2l2 protein, mouse; D012097:Repressor Proteins; D009569:Nitric Oxide; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione
keywords: Antioxidant response element; Free radicals; Glutamate–cysteine ligase; MafG; Nrf2; Sumoylation