Nrf2 and c-Jun regulation of antioxidant response element (ARE)-mediated expression and induction of gamma-glutamylcysteine synthetase heavy subunit gene

gamma-Glutamylcysteine synthetase (gamma-GCS) is a rate-limiting enzyme in the de novo synthesis of glutathione, a known scavenger of electrophiles an d reactive oxygen species (ROS). The gamma-GCS gene is expressed ubiquitous ly and induced coordinately with NAD(P)H:quinone oxidoreductase(1) (NQO1) a nd glutathione S-transferase Ya (GST Ya) in response to xenobiotics and ant ioxidants. The antioxidant response element (ARE) is required for expressio n and induction of these genes. In the current report, we demonstrated that ARE-mediated gamma-GCS gene expression and induction is regulated by simil ar Nrf and Jun factors as reported earlier for the NQO1 and GST Ya genes. T he gamma-GCS gene ARE competed with the binding of nuclear proteins (Nrf Jun) to the NQO1 gene ARE (hARE). In addition, the overexpression of Nrf2 a nd Nrf1 with c-Jun significantly up-regulated gamma-GCS ARE-mediated basal expression and beta-naphthoflavone induction of the chloramphenicol acetylt ransferase gene in transfected HepG2 cells. Interestingly, Nrf2 + c-Jun was more effective than Nrf1 + c-Jun in the regulation of ARE-mediated gamma-G CS gene expression. Further experiments demonstrated that the c-Jun level w ithin the cells is an important determinant of the lever of ARE-mediated ga mma-GCS gene expression. Therefore, at higher concentrations of c-Jun, gamm a-GCS gene expression is repressed, presumably due to generation of a suffi cient amount of c-Jun + c-Fos complex that interferes with the binding of N rf2 + c-Jun complex to the ARE. BIOCHEM PHARMACOL 59;11:1433-1439, 2000. (C ) 2000 Elsevier Science Inc.