Covalent binding of quinones activates the Ah receptor in Hepa1c1c7 cells
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Highly reactive quinone species produced by photooxidation and/or metabolic activation of mono- or bi-aromatic hydrocarbons modulate cellular homeostasis and electrophilic signal transduction pathways through the covalent modification of proteins. Polycyclic aromatic hydrocarbons, but not mono- or bi-aromatic hydrocarbons, are well recognized as ligands for the aryl hydrocarbon receptor (AhR). However, quinone species produced from mono- and bi-aromatic hydrocarbons could potentially cause AhR activation. To clarify the AhR response to mono- and bi-aromatic hydrocarbon quinones, we studied <i>Cyp1a1</i> (cytochrome P450 1A1) induction and AhR activation by these quinones. We detected <i>Cyp1a1</i> induction during treatment with quinones in Hepa1c1c7 cells, but not their parent compounds. Nine of the twelve quinones with covalent binding capability for proteins induced <i>Cyp1a1</i>. <i>Cyp1a1</i> induction mediated by 1,2-naphthoquinone (1,2-NQ), 1,4-NQ, 1,4-benzoquinone (1,4-BQ) and <i>tert</i>-butyl-1,4-BQ was suppressed by a specific AhR inhibitor and was not observed in c35 cells, which do not have a functional AhR. These quinones stimulated AhR nuclear translocation and interaction with the AhR nuclear translocator. Interestingly, 1,2-NQ covalently modified AhR, which was detected by an immunoprecipitation assay using a specific antibody against 1,2-NQ, resulting in enhancement of xenobiotic responsive element (XRE)-derived luciferase activity and binding of AhR to the <i>Cyp1a1</i> promoter region. While mono- and bi-aromatic hydrocarbons are generally believed to be poor ligands for AhR and hence unable to induce <i>Cyp1a1</i>, our study suggests that the quinones of these molecules are able to modify AhR and activate the AhR/XRE pathway, thereby inducing <i>Cyp1a1</i>. Since we previously reported that 1,2-NQ and <i>tert</i>-butyl-1,4-BQ also activate NF-E2-related factor 2, it seems likely that some of quinones are bi-functional inducers for phase-I and phase-II reaction of xenobiotics.
- The Journal of Toxicological Sciences
The Journal of Toxicological Sciences 40(6), 873-886, 2015
The Japanese Society of Toxicology