Response of [ Ah] battery genes to compounds that protect against menadione toxicity

Abstract

We have studied the response of genes in the dioxin-inducible [ Ah] battery to three compounds that protect mouse hepatoma cells (Hepa-1c7c7 wild-type, wt) against menadione toxicity. Pretreatment of wt cells with 25 μM 5,10-dihydroindeno[1,2- b]indole (DHII), 25 μM tert-butylhydroquinone (tBHQ), or 10 μM menadione itself, generated substantial protection against toxicity produced by subsequent menadione exposure. The gene response was examined in wt cells, and three mutant lines: CYP1A1 metabolism-deficient ( c37 or P − 1); nuclear translocation-impaired ( c4 or nt −); and AHR-deficient ( c2 or r −, containing < 10% of normal functional receptor levels). DHII treatment of wt cells for 12 hr markedly elevated the enzyme activities and mRNA levels of genes in the [ Ah] battery: aryl hydrocarbon hydroxylase ( Cyplal), NAD(P)H: menadione oxidoreductase ( Nmol), cytosolic aldehyde dehydrogenase class 3 (Ahd4), and UDP-glucuronosyltransferase form 1∗06 ( Ugtl∗ 06). Treatment of the c4 and c2 cells with DHII failed to induce mRNA levels of the genes, indicating that induction of the [ Ah] gene battery by DHII is aromatic hydrocarbon receptor (AHR)-mediated. On the other hand, neither tBHQ nor menadione caused increases in CYP1A1 mRNA, but tBHQ significantly enhanced the NMO1, AHD4, and UGT1∗06 mRNA levels in all three mutant cell lines. In conclusion, we expect one or more putative electrophile response elements (EpRE), previously found in the regulatory regions of the murine Nmol, Ahd4, and Ugtl∗ 06 genes, to be functional in responding to phenolic antioxidants.