The Tumor Suppressor Kruppel-Like Factor 6 Is a Novel Aryl Hydrocarbon Receptor DNA Binding Partner

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 345; no. 3; pp. 419 - 429
• Main Authors: Wilson, Shelly R., Joshi, Aditya D., Elferink, Cornelis J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2013; The American Society for Pharmacology and Experimental Therapeutics
• Subjects: Animals; Blotting, Western; Cell Nucleus - drug effects; Cell Nucleus - metabolism; Cellular and Molecular; Chromatin Immunoprecipitation; DNA - metabolism; Electrophoretic Mobility Shift Assay; Environmental Pollutants; Female; Humans; Kruppel-Like Factor 6; Kruppel-Like Transcription Factors - metabolism; Mice; Mice, Inbred C57BL; Mice, Transgenic; Polychlorinated Dibenzodioxins - pharmacology; Promoter Regions, Genetic - drug effects; Protein Biosynthesis - drug effects; Proto-Oncogene Proteins - metabolism; Receptors, Aryl Hydrocarbon - metabolism; Response Elements - genetics; RNA-Binding Proteins - metabolism; Transcription, Genetic - drug effects; Xenobiotics - pharmacology; Zinc Fingers; PAS; KLF; hKLF6; Arnt; TCDD; AhR; XRE; ChIP; mAhR; NC-XRE; bHLH; hAhR; EMSA; PAI-1; TnT; mKLF6; PCR
• ISSN: 0022-3565; 1521-0103; 1521-0103
• DOI: 10.1124/jpet.113.203786

The aryl hydrocarbon receptor (AhR) is a ligand-mediated basic helix-loop-helix transcription factor of the Per/Arnt/Sim family that regulates adaptive and toxic responses to a variety of chemical pollutants, including polycyclic aromatic hydrocarbons and halogenated aromatic hydrocarbons, most notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Ligand activation leads to AhR nuclear translocation and binding to a xenobiotic response element (XRE) in association with the Arnt to regulate gene expression. Several recent genome-wide transcriptional studies identified numerous AhR target genes that lack the canonical XRE recognition site in the promoter regions. Characterization of one such target gene, the plasminogen activator inhibitor 1, identified a novel nonconsensus XRE (NC-XRE) that confers TCDD responsiveness independently of the Arnt protein. Studies reported here show that the NC-XRE is a recognition site for the AhR and a new binding partner, the Kruppel-like factor (KLF) family member KLF6. In vivo chromatin immunoprecipitations and in vitro DNA binding studies demonstrate that the AhR and KLF6 proteins form an obligatory heterodimer necessary for NC-XRE binding. Mutational analyses show that the protein-protein interactions involve the AhR C terminus and KLF6 N terminus, respectively. Moreover, NC-XRE binding depends on the 5′ basic region in KLF6 rather than the previously characterized zinc finger DNA binding domain. Collectively, the results unmask a novel AhR signaling mechanism distinct from the canonical XRE-driven process that will enrich our future understanding of AhR biology.