A critical role for MAP kinases in the control of Ah receptor complex activity

The heterodimeric complex of aromatic hydrocarbon receptor (AHR) and Ah receptor nuclear translocator (ARNT) plays a pivotal role in controlling the expression of drug metabolism genes, such as the cytochromes p450 (Cyp) 1a1 and 1b1, believed to be responsible for most toxic effects of the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In this study, we show that activation of Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) modulates ARNT transcription activity and potentiates the transcriptional activity of AHR/ARNT complexes. Inhibition of ERK by chemical compounds and ablation of JNK caused significant decreases in CYP1A1 induction by TCDD. Compared to wild type, JNK2 ablation significantly reduced TCDD-stimulated CYP1A1 expression in mouse thymus and testis, but not in liver. In contrast, CYP1B1 expression was unaffected in all three tissues of the knockout mice. These data suggest that JNK and ERK modulate ARNT activity and AHR/ARNT-dependent gene expression, contributing to the gene-specific and tissue-specific toxicity of environmental contaminants.