Functional characterization and role of INrf2 in antioxidant response element-mediated expression and antioxidant induction of NAD(P)H : quinone oxidoreductase 1 gene

Antioxidant response element (ARE) and nuclear transcription factor Nrf2 ar e known to regulate expression and coordinated induction of NQO1 and other detoxifying enzyme genes in response to antioxidants and xenobiotics, A cyt osolic inhibitor of Nrf2, INrf2, that retains Nrf2 in the cytoplasm, was cl oned and sequenced, Treatment of cells with antioxidants and xenobiotics re sults in the release of Nrf2 from INrf2, Nrf2 then moves in the nucleus, Th is leads to the induction of ARE-mediated NQO1 and other detoxifying enzyme genes expression, INrf2 after dissociation from Nrf2 remains in the cytoso l, Overexpression of INrf2 repressed ARE-mediated NQO1 gene expression, Del etion mapping of INrf2 revealed the requirement of KELCH domain (amino acid residues 361-597) and C-terminal region (amino acid residues 598-624) in r etention of Nrf2 in the cytosol, Both these regions of INrf2 independently retained Nrf2 in the cytosol leading to the repression of ARE-mediated NQO1 gene expression, These results may indicate that two different regions of INrf2 interact with a single molecule of Nrf2 or two or more molecules of N rf2 interact with a single molecule of INrf2, The transcription of Nrf2 and INrf2 did not change in response to antioxidants and xenobiotics, This ind icated that INrf2 and/or Nrf2 might be post-transcriptionally modified in r esponse to antioxidants and xenobiotics leading to the release of Nrf2 from INrf2 and induction of ARE-mediated NQO1 and other detoxifying enzyme gene s expression.