Development of a Green Fluorescent Protein-Based Cell Bioassay for the Rapid and Inexpensive Detection and Characterization of Ah Receptor Agonists

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxic and biological effects of a variety of chemicals. Although halogenated and polycyclic aromatic hydrocarbons (HAHs and PAHs, respectively) represent the highest affinity and most toxic ligands, recent studies have demonstrated that the AhR can be activated by chemicals with structures distinctly different from HAHs/PAHs. In order to identify and characterize novel AhR ligands, we developed a rapid and inexpensive high-throughput screening bioassay based on the ability of AhR agonists to induce an HAH/PAH-responsive, enhanced green fluorescent protein (EGFP) reporter gene in a stably transfected mouse hepatoma (Hepa1c1c7) cell line. EGFP induction in the resulting recombinant cell line, H1G1.1c3, is sensitive (with a minimal 1-pM detection limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin, the most potent AhR ligand), and it responds to HAHs and PAHs in a time-, dose-, and chemical-specific manner. Application of this bioassay was demonstrated by the rapid characterization of the relative inducing potency of a series of previously uncharacterized dioxin surrogates. This bioassay system has numerous advantages over currently available AhR-based bioassays including increased rapidity and ease of use, low reagent cost, and application for high-throughput screening.