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Response of [Ah] battery genes to compounds that protect against menadione toxicity
V Vasiliou1, H G Shertzer, R M Liu
1Department of Environmental Health, University of Cincinnati Medical Center, Ohio 45267-0056, USA.
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 microM 5,10-dihydroindenol[1,2-b]indole (DHII), 25 microM tert-butylhydroquinone (tBHO) or 10 microM 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 P1-); 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 (Cyp1a1), NAD(P)H:menadione oxidoreductase (Nmol), cytosolic aldehyde dehydrogenase class 3 (Ahd4), and UDP-glucuronosyltransferase form 1*06 (Ugt1*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 tBHO nor menadione caused increases in CYPlAl 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 ugt1*06 genes, to be functional in responding to phenolic antioxidants.
Insights
This study shows that compounds like DHII, tBHO, and menadione protect cells from toxicity. DHII induces genes via the aromatic hydrocarbon receptor (AHR), while tBHO and menadione activate other protective genes through electrophile response elements (EpREs).
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- The dioxin-inducible [Ah] gene battery plays a crucial role in cellular defense mechanisms.
- Understanding the regulation of these genes is vital for developing protective strategies against toxic compounds.
- Menadione toxicity and cellular protection pathways are key areas of research in hepatoma cells.
Purpose of the Study:
- To investigate the gene response in mouse hepatoma cells (Hepa-1c7c7) to protective compounds against menadione toxicity.
- To elucidate the role of the aromatic hydrocarbon receptor (AHR) and electrophile response elements (EpREs) in mediating cellular protection.
- To differentiate the signaling pathways activated by 5,10-dihydroindenol[1,2-b]indole (DHII), tert-butylhydroquinone (tBHO), and menadione.
Main Methods:
- Utilized wild-type (wt) and mutant mouse hepatoma cell lines (CYP1A1 metabolism-deficient, nuclear translocation-impaired, and AHR-deficient).
- Assessed the induction of enzyme activities and mRNA levels for genes in the [Ah] battery, including aryl hydrocarbon hydroxylase (Cyp1a1), NAD(P)H:menadione oxidoreductase (Nmol), cytosolic aldehyde dehydrogenase class 3 (Ahd4), and UDP-glucuronosyltransferase form 1*06 (Ugt1*06).
- Examined the effects of DHII, tBHO, and menadione pretreatment on cellular response to menadione-induced toxicity.
Main Results:
- DHII treatment significantly elevated mRNA levels of [Ah] battery genes in wt cells, an effect dependent on the aromatic hydrocarbon receptor (AHR).
- DHII failed to induce these genes in AHR-deficient or nuclear translocation-impaired mutant cell lines.
- tBHO and menadione did not increase CYP1A1 mRNA but significantly enhanced NMO1, AHD4, and UGT1*06 mRNA levels in all cell lines, suggesting an AHR-independent pathway involving EpREs.
Conclusions:
- The induction of the [Ah] gene battery by DHII is mediated by the aromatic hydrocarbon receptor (AHR).
- Phenolic antioxidants like tBHO and menadione activate protective genes through AHR-independent pathways, likely involving electrophile response elements (EpREs).
- These findings highlight distinct mechanisms of cellular protection against oxidative stress and toxic insults.