Biochemical and Biophysical Research Communications
Inhibition of the MEK-1/p42 MAP kinase reduces aryl hydrocarbon receptor–DNA interactions
Section snippets
Materials and methods
Cell culture, plasmids, and treatments. Wild type mouse Hepa1c1c7 cells were cultured in α-MEM supplemented with 10% fetal bovine serum (Life Technologies Gibco-BRL) and gentamicin (5 μg/ml) (Life Technologies Gibco-BRL), fungizone (0.25 μg/ml) (Life Technologies Gibco-BRL) under humidified air containing 5% CO2 at 37 °C. Hepa1c1c7 cells were serum-starved in α-MEM containing 0.5% fetal bovine serum for 40–48 h before treatment with inhibitors or TCDD. Hepa1c1c7 cells were pretreated with 100 μM
Effect of a MEK-1 inhibitor on TCDD-induced expression of cyp1a1
To investigate the possibility that the MEK-1/p42/p44 MAP kinase pathway modulates TCDD-induced gene expression, we measured TCDD-induced expression of cyp1a1 in Hepa1c1c7 cells that had been pretreated with MEK-1 specific inhibitor, PD98059. Northern analysis showed that pretreatment with the MEK-1 inhibitor PD98059 reduced expression of TCDD-induced expression of cyp1a1 gene (see Fig. 1).
To test whether PD98059 affects the enhancer activity of cyp1a1, we transfected Hepa1c1c7 cells with the
Discussion
TCDD induces the expression of cyp1a1. We showed here that pretreatment of mouse Hepa1c1c7 cells with the MEK-1-specific inhibitor PD98059 reduces this TCDD-induced cyp1a1 expression. We also observed that TCDD treatment results in the phosphorylation and activation of p42/p44 MAPK, a substrate of MEK-1. Separate experiments indicated that p42 MAPK participates in TCDD-induced cyp1a1 expression, since blocking p42 MAPK with a dominant negative form of the enzyme inhibited TCDD-induced
Acknowledgments
We thank Dr. MS Denison (School of Veterinary Medicine, University of California, Davis, CA) for generously providing the dioxin-responsive reporter plasmid pGud-luc1.1, and Dr. James P Whitlock, Jr., for providing the AhR and Arnt cDNAs. We thank Jungho Suh for excellent technical assistance. This study was supported by a Grant (F00061) from the Korean Research Foundation to H. Park. The luminescent image analyzer (Model Las3000, Fuji, Japan) was prepared by an intramural grant from the
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2016, Toxicology LettersCitation Excerpt :It has been demonstrated that the MEK-ERK1-2 pathway is involved in the interaction between the AhR/Arnt heterodimer and its responsive elements, leading to the expression of Cyp1a1 and Cyp1b1. Indeed, the MEK inhibitor U0126 or the dominant negative mutant of MEK both repress the gene expression induced by AhR ligands (Yim et al., 2004); moreover, AhR and DNA interaction is abolished by phosphatase treatment of AhR in-vitro (Yim et al., 2004). These data indicate that phosphorylation by MAPKs could be essential in the expression of cytochromes, and suggest why in our C6 glioma cells the treatment with DEP25 in presence of the MEK inhibitor U0126 did not induce increases in Cyp1b1 levels.
Effects of aflatoxin B<inf>1</inf>, fumonisin B<inf>1</inf> and their mixture on the aryl hydrocarbon receptor and cytochrome P450 1A induction
2015, Food and Chemical ToxicologyCitation Excerpt :In spleen cells, a similar effect was observed on cyp1A transcription, with the results revealing that the maximum effects of individual and combined toxins on the ahr gene expression in spleen cells occurred before the largest increases observed in the cyp1A transcription, suggesting that the expression of the latter gene was, at least in part, a consequence of an increased ahr mRNA level (Tijet et al., 2006). The potential interaction between the mycotoxins to induce cyp1A up-regulation may have been the result of: the combination of the Ahr activation by AFB1, the increased expression of ahr by both toxins, and the possible activation of intracellular signal transduction systems that involved protein tyrosine kinases (TK), ERK or protein kinase C (PKC) by FB1 (Gopee and Sharma, 2004; Mary et al., 2012; Rumora et al., 2007), since these kinases facilitate and/or amplify the functionality of Ahr, thus favoring the binding of the receptor to its target genes (Fang et al., 2013; Tan et al., 2004; Yim et al., 2004). Our results suggest that the large increase in cyp1A mRNA levels induced by the mycotoxin mixture in H4IIE cells might have favored AFB1 biotransformation to the highly carcinogenic metabolite AFBO and the malignant transformation of hepatic cells.
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2010, Journal of Biological ChemistryThe aryl hydrocarbon receptor cross-talks with multiple signal transduction pathways
2009, Biochemical PharmacologyCitation Excerpt :Immunoprecipitation experiments were suggestive of a ligand-independent association of AHR and ERK, suggesting that ERK might be important in the regulation of AHR function perhaps by targeting receptor phosphorylation or blocking ubiquitinylation [53]. Consistent with the above studies, over-expression of a dominant-negative variant of MEK1 or treatment with a MEK1 inhibitor reduced TCDD-dependent transcription of a reporter gene and inhibited the binding of the AHR to its cognate DNA motif in the Cyp1a1 gene promoter [54]. In summary, a relatively strong body of evidence indicates that there is a two-way cross-talk between MAP kinase pathways and AHR signaling.
Aryl hydrocarbon receptor- and calcium-dependent induction of the chemokine CCL1 by the environmental contaminant benzo[a]pyrene
2006, Journal of Biological ChemistryCitation Excerpt :However, it is noteworthy that several studies demonstrated a closed relation between calcium changes and protein kinase activation (48–50). Among these kinases, protein kinase C and/or mitogen-activate protein kinases are known to be activated by AhR agonists (51–55). Interestingly, these kinases are implicated in AhR phosphorylation to form a functional transcriptional complex that leads to trans-activation (52, 56).
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These authors contributed equally to this work.