Nrf1 and Nrf2 regulate ARE-mediated expression and coordinated induction of a battery of genes encoding proteins that protect cells against oxidativestress

Detoxifying enzymes including quinone oxidoreductases (NQO1 and NQO2) and g lutathione S-transferases (GSTs) catalyze metabolic detoxification of xenob iotics, drugs and carcinogens, and thus, protect cells against redox cyclin g, oxidative stress and neoplasia. Genes encoding the various detoxifying e nzymes are ubiquitously expressed at varying levels among all tissues. The expression of detoxifying enzyme genes are coordinately induced in response to antioxidants and xenobiotics, presumably to provide protection against oxidative damage. Deletion mutagenesis and transfection assays have identif ied antioxidant response element (ARE) in the promoters of the various deto xifying enzqme genes, which regulate the expression and coordinated inducti on of detoxifying enzyme genes. ARE is a unique cis-element that contains t wo TRE/TRE-like elements followed by a 'GC' box. Band and supershift assays were used to demonstrate that nuclear transcription factors Nrf1, Nrf2, Ju n, Fos, and Era bind to the ARE. Overexpression of Nm and Nrf2 individually in human hepatoblastoma (Hep-Ga) cells significantly increased the ARE-med iated expression of NQO1 and GST Ya genes and their induction by P-naphthof lavone (beta-NF) and tert-butyl hydroquinone (t-BHQ). Nrf2 containing one m utated leucine in its leucine zipper region was more efficient in upregulat ion of ARE-mediated gene expression, as compared to Nrf1 with two mutated l eucines. Nrf1 and Nrf2 do not heterodimerize with each other. Nrf1 and Nrf2 associate with c-Jun to regulate ARE-mediated expression and coordinated i nduction of NQO1, GST Ya and other detoxifying enzyme genes in response to antioxidants and xenobiotics.