RESPONSE OF [AH] BATTERY GENES TO COMPOUNDS THAT PROTECT AGAINST MENADIONE TOXICITY

We have studied the response of genes in the dioxin-inducible [Ah] bat tery to three compounds that protect mouse hepatoma cells (Hepa-1c7c7 wild-type, wt) against menadione toxicity. Pretreatment of wt cells wi th 25 mu M 5,10-dihydroindeno[1,2-b]indole (DHII), 25 mu M tert-butylh ydroquinone (tBHQ), or 10 mu M 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-imp aired (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 i n the [Ah] battery: aryl hydrocarbon hydroxylase (Cyplal), NAD(P)H:men adione oxidoreductase (Nmol), cytosolic aldehyde dehydrogenase class 3 (Ahd4), and UDP-glucuronosyltransferase form 106 (Ugt1*06). Treatmen t 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, neith er tBHQ nor menadione caused increases in CYP1A1 mRNA, but tBHQ signif icantly enhanced the NMO1, AHD4, and UGT106 mRNA levels in all three mutant cell lines. In conclusion, we expect one or more putative elect rophile response elements (EpRE), previously found in the regulatory r egions of the murine Nmol, Ahd4, and Ugt106 genes, to be functional i n responding to phenolic antioxidants.