title: Mechanism and significance of changes in glutamate-cysteine ligase expression during hepatic fibrogenesis.
abstract: GSH is synthesized sequentially by glutamate-cysteine ligase (GCL) and GSH synthase and defends against oxidative stress, which promotes hepatic stellate cell (HSC) activation. Changes in GSH synthesis during HSC activation are poorly characterized. Here, we examined the expression of GSH synthetic enzymes in rat HSC activation and reversion to quiescence. Expression of the GCL catalytic subunit (GCLC) fell during HSC activation and increased when activated HSCs revert back to quiescence. Blocking the increase in GCLC expression kept HSCs in an activated state. Activated HSCs have higher nuclear levels and binding activity of MafG to the antioxidant response element (ARE) of GCLC but lower Nrf2/MafG heterodimer binding to the ARE. Quiescent HSCs have a lower nuclear MafG level but higher Nrf2/MafG heterodimer binding to ARE. This occurred because of enhanced sumoylation of Nrf2 and MafG by SUMO-1, which promoted Nrf2 binding to ARE and heterodimerization with MafG. In vivo, knockdown of GCLC exacerbated bile duct ligation-induced liver injury and fibrosis. Ursodeoxycholic acid and S-adenosylmethionine are anti-fibrotic in bile duct ligation, but this effect was nearly lost if GCLC induction was blocked. In conclusion, sumoylation of Nrf2 and MafG enhances heterodimerization and increases GCLC expression, which keeps HSCs in a quiescent state. Antifibrotic agents require activation of GCLC to fully exert their protective effect.
authors.affiliation: Division of Gastroenterology and Liver Diseases, USC Research Center for Liver Diseases, Keck School of Medicine of University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Komal
authors.initials: K
authors.lastname: Ramani
authors.forename: Maria Lauda
authors.initials: ML
authors.lastname: Tomasi
authors.forename: Heping
authors.initials: H
authors.lastname: Yang
authors.forename: Kwangsuk
authors.initials: K
authors.lastname: Ko
authors.forename: Shelly C
authors.initials: SC
authors.lastname: Lu
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic; D055785:Gene Knockdown Techniques; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis* / Q000235:genetics; D055166:Hepatic Stellate Cells / Q000201:enzymology* / Q000473:pathology; D008103:Liver Cirrhosis / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D051259:MafG Transcription Factor / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D012436:S-Adenosylmethionine / Q000235:genetics / Q000378:metabolism; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism; D058207:Sumoylation / Q000235:genetics; D014580:Ursodeoxycholic Acid / Q000235:genetics / Q000378:metabolism
chemical_list: D051259:MafG Transcription Factor; C491246:Mafg protein, rat; D051267:NF-E2-Related Factor 2; C495637:Nfe2l2 protein, rat; D012097:Repressor Proteins; D025842:SUMO-1 Protein; D014580:Ursodeoxycholic Acid; D012436:S-Adenosylmethionine; D005721:Glutamate-Cysteine Ligase; C544143:GCLC protein, rat