1: Toxicol Sci. 2004 Nov;82(1):80-7. Epub 2004 Jul 22. A critical role for MAP kinases in the control of Ah receptor complex activity. Tan Z, Huang M, Puga A, Xia Y. Center for Environmental Genetics and Department of Environmental Health, University of Cincinnati Medical Center, 123 E. Shields Street, Cincinnati, OH 45267-0056, USA. 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. PMID: 15272135 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 2: Exp Cell Res. 2003 Nov 1;290(2):391-401. Hepatocyte growth factor signaling regulates transactivation of genes belonging to the plasminogen activation system via hypoxia inducible factor-1. Tacchini L, Matteucci E, De Ponti C, Desiderio MA. Institute of General Pathology, University of Milano, via L. Mangiagalli, 31, 20133 Milano, Italy. Hepatocyte growth factor (HGF) plays an important role in tumor growth and progression also by regulating invasive/metastatic phenotype and angiogenesis. Here we report that a molecular mechanism possibly contributing to these functions of HGF may be hypoxia inducible factor-1 (HIF-1)-dependent expression of genes of the plasminogen activation system. The following findings support this conclusion: (1) HGF enhanced the activity of a luciferase reporter construct under the control of multiple HIF-1 responsive elements (HRE) in HepG2 cells, and the cotransfection of the dominant negative for the beta-subunit (ARNT) prevented this increase; (2) HGF activated uPA and PAI-1 promoters through HIF-1 activity regulated by PI3K/JNK1 transducers, as demonstrated by cotransfection with the reporter gene promoters and the dominant negative for ARNT, p85 subunit of PI3K or JNK1; (3) hypoxia was additive to HGF in increasing reporter vector activities, but probably through different transduction pathways; (4) JNK1 wild-type expression vector increased HIF-1alpha protein expression probably in a phosphorylated state and, thus, functional for transactivating activity; and (5) c-Jun did not seem to be involved in the activation of the luciferase construct containing multiple HREs because it was not prevented by expression of TAM-67, which is the dominant negative mutant form for c-Jun. PMID: 14567996 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: Toxicol Appl Pharmacol. 1996 Nov;141(1):238-47. Dioxin induces transcription of fos and jun genes by Ah receptor-dependent and -independent pathways. Hoffer A, Chang CY, Puga A. Center for Environmental Genetics, University of Cincinnati Medical Center, Ohio 45267-0056, USA. Halogenated aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), and polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, are environmental contaminants that cause many apparently unrelated toxic effects. In a previous study, we have shown that treatment of mouse hepatoma cells with TCDD or B(a)P results in an increase in mRNA levels of the immediate-early protooncogenes c-fos, c-jun, junB, and junD, and the concomitant increase of the DNA-binding activity of the transcription factor AP-1, a dimer of FOS and JUN proteins. To analyze the mechanism of fos/jun activation by TCDD we have used electrophoretic mobility shift and transient expression assays of reporter gene constructs containing response elements for 12-O-tetradecanoyl-phorbol-13-acetate (TRE), serum (SRE), cAMP (CRE), and aromatic hydrocarbons (AhRE) from the fos and jun genes fused to the firefly luciferase gene under the control of the SV40 minimal promoter. In mouse hepatoma Hepa-1 cells, which have Ah receptor (AHR) and Ah receptor nuclear translocator (ARNT) proteins, inclusion of TRE, SRE, and the AhRE motifs from c-jun and junD, but not CRE or the AhREs from c-fos, fosB, and junB, causes a large TCDD-dependent increase in luciferase expression. In agreement with these results, c-jun and junD, but not c-fos, fosB, and junB AhREs, competed with a canonical Cyp1A1 AhRE for binding to the AHR ARNT heterodimeric complex. In African Green Monkey CV-1 cells, which lack AHR, expression plasmids with AhRE motifs require coexpression of AHR and ARNT for TCDD to stimulate luciferase expression. In contrast, SRE-containing expression plasmids respond equally well to TCDD whether or not AHR and ARNT are coexpressed. These results suggest that TCDD induces expression of the immediate-early response genes fos and jun by activation of possibly three separate signal transduction pathways, at least one of which does not require a functional Ah receptor complex. PMID: 8917696 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Ann N Y Acad Sci. 1993 Jun 23;685:624-40. Role of the Ah receptor and the dioxin-inducible [Ah] gene battery in toxicity, cancer, and signal transduction. Nebert DW, Puga A, Vasiliou V. Department of Environmental Health, University of Cincinnati Medical Center, Ohio 45267-0056. 1. On the basis of our current knowledge about the evolution of drug-metabolizing enzymes, it appears to be extremely likely that these enzymes play a critical role in maintaining steady-state levels of the ligands involved in ligand-modulated transcription of genes effecting growth, differentiation, homeostasis, and neuroendocrine functions. 2. The original observations about genetic differences in CYP1A1 (cytochrome P1-450) induction by TCDD or benzo[a]pyrene in the mouse have led to an appreciation for a similar polymorphism in the human and the recent cloning of the murine Ah receptor (Ahr) and human Ah receptor nuclear translocator (ARNT) genes. It is most likely that the correlation between genetic differences in human or murine CYP1A1 inducibility by polycyclic hydrocarbons or TCDD and increased risk of cancer will be explained by differences in the AHR gene, leading to enhanced tumor promotion (rather than in the CYP1A1 structural gene). Perhaps the same will be found for birth defects, immunotoxicity, and other forms of toxic damage caused by these environmental chemicals. 3. In a manner similar to that of the phorbol ester tumor promoter, TCDD induces intracellular Ca2+ changes, accumulation of FOS and JUN mRNAs, and large increases in AP-1 transcription factor activity. Interestingly, these early effects of TCDD, and also of benzo[a]pyrene, appear not to require the Ah receptor. 4. Many genes are induced by TCDD, and many others are induced by electrophilic metabolites such as quinones and H2O2; using several mouse experimental systems, we have defined a subset of six of these genes as constituting the [Ah] battery by the sole criterion that a functional CYP1A1 or CYP1A2 enzyme is able to repress the expression of genes that are members of this gene battery. Publication Types: Review Review, Tutorial PMID: 8395783 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------