Covalent binding of quinones activates the Ah receptor in Hepa1c1c7 cells

Abstract

-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 Cyp1a1 (cytochrome P450 1A1) induction and AhR activation by these quinones. We detected Cyp1a1 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 Cyp1a1. Cyp1a1 induction mediated by 1,2-naphthoquinone (1,2-NQ), 1,4-NQ, 1,4-benzoquinone (1,4-BQ) and tert-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 Cyp1a1 promoter region. While mono-and bi-aromatic hydrocarbons are generally believed to be poor ligands for AhR and hence unable to induce Cyp1a1, our study suggests that the quinones of these molecules are able to modify AhR and activate the AhR/XRE pathway, thereby inducing Cyp1a1. Since we previously reported that 1,2-NQ and tert-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.

Quinone-mediated induction of cytochrome P450 1A1 in HepG2 cells through increased interaction of aryl hydrocarbon receptor with aryl hydrocarbon receptor nuclear translocator

“…4 and 5). Similar results were described previously in Hepa1c1c7 cells (Abiko et al, 2015). We reported that activation of the Akt/CREB signaling pathway in response to MeHg, which is an environmental electrophile and easily bind to thiol groups on the cellular proteins, in SH-SY5Y cells followed a bell-shaped curve (Unoki et al, 2016).…”

“…4B). Our previous study demonstrated that 1,2-NQ enhanced the interaction of AhR with ARNT in Hepa1c1c7 cells (Abiko et al, 2015). 1,2-NQ was a stronger AhR activator than TBQ.…”

“…In addition, aromatic hydrocarbons with ring numbers of one or two, such as benzenes and naphthalenes, are thought to be poor AhR ligands, except for halogenated naphthalene, which showed ligand activity for AhR (Waller and McKinney, 1995). Surprisingly, our recent study showed that monoand bi-cyclic quinoid metabolites of benzenes and napthalenes could activate AhR, thereby upregulating Cyp1a1 mRNA expression in Hepa1c1c7 cells and in liver from C57BL6 mice (Abiko et al, 2015). However, the contributions of quinones to AhR activation in human hepatic cell lines is still unclear.…”

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ABSTRACT -While it has long been believed that benzenes and naphthalenes are unable to activate the aryl hydrocarbon receptor (AhR) because they are poor ligands, we recently reported that these quinoid metabolites upregulated cytochrome P450 1A1 (CYP1A1) in Hepa1c1c7 cells (Abiko et al, 2015). In the current study, AhR activation, measured with a bioluminescence-based cell free assay, was induced by 1,2-naphthoquinone (1,2-NQ), a metabolite of naphthalene.

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“…The cells were cultured in serum-free medium for 24 hr and then exposed to each of the compounds as described for individual experiments. The cells were exposed to lower concentrations of bi-cyclic compounds (1,2-NQ, 1,4-NQ, and naphthalene) than of mono-cyclic compounds (1,4-BQ, TBQ, benzene, and tert-buthyl-1,4-BQ) because bi-cyclic quinones showed stronger CYP1A1 induction than mono-cyclic compounds (Abiko et al, 2015).…”