The Aryl Hydrocarbon Receptor (AhR) is a basic helix-loop-helix transcription factor activated by diverse polycyclic aromatic hydrocarbons, including the prototypical ligand and persistent environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin,TCDD). Canonically, the ligand activated AhR translocates to the nucleus, dissociates from chaperones, and heterodimerizes with the Aryl Hydrocarbon Receptor Nuclear Translocator (Arnt) to transcriptionally regulate target genes via the cis DNA motif GCGTG, termed the xenobiotic response element (XRE). Recent work has shown a number of dioxin responsive AhR target genes lack an XRE. We have recently discovered the AhR to form a novel protein complex through an interaction with Kruppel-like Factor 6 (KLF6), which binds DNA via a novel non-consensus XRE (NC-XRE). We have subsequently shown that the KLF6/AhR complex regulates expression of a novel set of AhR genes, in response to dioxin, via binding to the NC-XRE. In this light, I hypothesize the KLF6/AhR heterodimer represents a novel regulatory complex conferring transcriptional control on novel target genes via binding to the NC-XRE. To investigate this novel protein interaction I will use in vivo chromatin immunoprecipitation next generation sequencing (ChIP-seq) experiments to identify the gene targets of this complex in the mouse liver coupled with whole transcriptome shotgun sequencing to anchor DNA binding of the KLF6/AhR transcription factor complex to changes in gene expression. This method will allow us to delineate functional vs. non-functional NC-XREs in KLF6/AhR target genes. I will examine the KLF6/AhR protein-protein interaction and identify the protein elements necessary for the interaction and characterize the key NC-XRE DNA motif elements necessary for KLF6/AhR binding. It is widely accepted that the AhR is required for the development of toxicity following exposure to dioxin. However, little is known about the mechanisms of the AhR driving the development of this toxicity. As our data suggest the NC-XRE represents a novel signaling cascade for the AhR following dioxin exposure, this work will provide novel insight on the mechanisms of dioxin toxicity with respect to the AhR, while shedding light on novel prognostic and diagnostics tools for identifying and treating the deleterious health effects associated with TCDD exposure.

Public Health Relevance

Exposure to polycyclic aromatic hydrocarbons (in particular dioxin) is a common problem contributing to developmental abnormalities, cancer, immune complications, liver disease, and diabetes in humans. While it is well accepted the Aryl Hydrocarbon Receptor (AhR) is to blame for these maladies, little is known about how this process occurs. Our goal is to characterize a newly discovered function for the AhR to understand how this process may contribute to diseases associated with dioxin exposure and thus provide insight on the prevention and treatment of said diseases.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Predoctoral Individual National Research Service Award (F31)
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Special Emphasis Panel (ZRG1)
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Humble, Michael C
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University of Texas Medical Br Galveston
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United States
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Jackson, D P; Joshi, A D; Elferink, C J (2015) Ah Receptor Pathway Intricacies; Signaling Through Diverse Protein Partners and DNA-Motifs. Toxicol Res (Camb) 4:1143-1158