High Levels of Expression of the NAD(P)H:quinone Oxidoreductase (NQO1) Gene in Tumor Cells Compared to Normal Cells of the Same Origin

NAD(P)H:quinone oxidoreductase (NQO1) is a flavoprotein which catalyzes the two-electron reduction of quinones and azo-dyes and thus prevents the formation of free radicals and toxic oxygen metabolites that may be generated by the one-electron reductions catalyzed by cytochrome P450 reductase. Analysis of RNA indicated 20- to 50-fold higher levels of NQO1 gene expression in the liver tumors and in the tissue surrounding the tumors of patients with hepatocarcinoma than in normal individuals. An approximately 50-fold higher level of NQO1 mRNA was also observed in human hepatoblastoma (Hep-G2) cells than in normal liver. By deletion mutagenesis in the human NQO1 gene promoter and subsequent transfection into hepatic and nonhepatic cell lines, a 1.42 kb DNA segment has been identified to contain cis-acting elements responsible for high levels of expression of the NQO1 gene in tumor cells.