ARE-MEDIATED AND TRE-MEDIATED REGULATION OF GENE-EXPRESSION - RESPONSE TO XENOBIOTICS AND ANTIOXIDANTS

Antioxidant response elements (AREs) containing 12-O- tetradecanoylpho rbol-13-acetate response element (TRE) (perfect AP1) and TRE-like (imp erfect AP1) elements mediate high basal transcription of the NAD-(P)H: quinone oxidoreductase(1) (NQO(1)) and glutathione S-transferase Ya ge nes in tumor cells and its induction in response to xenobiotics and an tioxidants. Mutations in the human NQO(1) gene ARE (hARE) revealed the requirement for two TRE or TRE-like elements arranged in inverse orie ntation at the interval of three base pairs and a GC box for optimal e xpression and beta-naphthoflavone induction of the NQO(1) gene. A sing le TRE element from the human collagenase gene failed to respond to be ta-naphthoflavone. These results demonstrate that ARE (2 x TRE or TRE- like elements)-containing detoxifying enzyme genes and not genes that contain 1 x TRE are responsive to xenobiotics and antioxidants. Bandsh ift assays showed shifting of a complex of more or less similar mobili ty with hARE and TRE that could be competed by each other. Mutations i n the 3'-TRE of the NQO(1) gene hARE eliminated binding of nuclear pro teins to the hARE and resulted in the loss of basal and induced expres sion, indicating that 3'-TRE is the most important element within the hARE. 5'-TRE-like element within the NQO(1) gene hARE is required for xenobiotic response but may not bind to the nuclear proteins by itself . The GC box located immmediately following the 3'-TRE is required for optimal expression and induction of the NQO(1) gene. The comparison o f AREs from several different genes indicated the requirement for spec ific arrangement and spacing of two TRE and TRE-like elements within t he AREs.