Coordinated induction of the c-jun gene with genes encoding quinone oxidoreductases in response to xenobiotics and antioxidants

Xenobiotics and antioxidants induce expression of detoxifying enzymes inclu ding NAD(P)H:quinone oxidoreductase (NQO1), NRH:quinone oxidoreductase (NQO 2), and glutathione S-transferase Ya (GST Ya), presumably to provide protec tion to cells against electrophilic and oxidative stress. Antioxidant respo nse elements (AREs) have been found in the promoter regions of the various detoxifying enzyme genes. An ARE is required for basal expression and induc tion of the various detoxifying enzyme genes in response to xenobiotics and antioxidants. In this study, we demonstrated that exposure of cells to xen obiotics [e.g. beta-naphthoflavone (beta-NF)] and antioxidants [e.g. tert-b utyl hydroquinone (t-BHQ)] also induced the expression of the proto-oncogen e c-jun. The induction of c-jun gene expression followed kinetics similar t o the induction of NRO1 and NRO2 genes with respect to the level and time o f exposure. Sequence analysis of the c-jun gene promoter revealed the prese nce of an ARE between nucleotides -538 and -514. The c-jun ARE was highly h omologous to the AREs from genes encoding NQO1, NQO2, and GST Ya. Construct s containing the c-jtm ARE and 1.7 and 4.5 kb of the c-jun promoter ligated to the chloramphenicol acetyltransferase (CAT) gene, upon transfection in human hepatoblastoma(Hep G2) cells, expressed the CAT gene, which was induc ible with beta-NF and t-BHQ. Band shift assays indicated binding of two spe cific nuclear protein complexes with the c-jun gene ARE. The faster running c-jun gene ARE-nuclear protein complex was specifically competed out by un labeled NQO1 and GST Ya gene AREs. These results suggest that c-jun gene ex pression is coordinately induced and regulated with detoxifying enzyme gene s in response to xenobiotics and antioxidants. The results also suggest inv olvement of an ARE mediated mechanism of induction of c-jun gene expression . However, a comparison of fold induction of endogenous c-jun gene and tran sfected c-jun promoter/ARE-CAT constructs indicated involvement of another ARE upstream of the 4.5-kb promoter and/or additional mechanisms such as st abilization of c-Jun RNA in response to exposure to xenobiotics and antioxi dants. (C) 1999 Elsevier Science Inc.