THE REDOX-SENSITIVE HUMAN ANTIOXIDANT RESPONSIVE ELEMENT INDUCES GENE-EXPRESSION UNDER LOW-OXYGEN CONDITIONS

Transient transfection studies of human HepG2 and mouse Hepa hepatocar cinoma cells with a reporter gene construct regulated by a human antio xidant responsive element (ARE) from the NQO(1) gene demonstrated that the element is responsive to low oxygen conditions. The antioxidant N -acetyl L-cysteine (NAC) strongly inhibited basal aerobic reporter gen e activity in HepG2 cells without obviously affecting the hypoxic indu ction, as is consistent with ARE sensitivity to oxidative stress in ae robic cultures. Electrophoretic mobility shift (EMS) assays of nuclear extracts of HepG2 and Hepa cells lysed under aerobic or hypoxic condi tions or after exposure to the phenolic compound 3-(2)-tert-butyl-4-hy droxyanisole (BHA), showed specific and constitutive protein binding t o the ARE under all of these conditions. Taken together, these finding s show that the ARE can mediate gene expression in response to low oxy gen conditions. Co-ordinately regulated expression of ARE-dependent ge nes, such as phase II detoxification enzymes, may be an important phen otype of solid tumors containing significant regions of pathophysiolog ical hypoxia.