Characterization of an Aryl Hydrocarbon Receptor from a Cetacean: An Approach for Assessing Contaminant Susceptibility in Protected Species

Some cetaceans bioaccumulate substantial concentrations of halogenated aromatic hydrocarbons (HAH) in their tissues, but little is known about the effects of such burdens on cetacean health. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related HAH cause toxicity via activation of the aryl hydrocarbon receptor (AHR). Differences in AHR structure and function are known to contribute to species-specific differences in susceptibility to HAH toxicity. The goal of these studies was to ascertain the potential for HAH effects in cetaceans by characterizing the AHR from the beluga, Deiphinapterus leucas. The beluga AHR was characterized by its molecular structure, capacity for ligand binding, structure-binding relationships with various classes of HAH, as well as tissue-specific expression. These results show that: (1) in an in vitro system, the beluga AHR possesses binding affinities similar to AHRs of other mammals that are considered sensitive to toxic effects of HAH, (2) Structure-activity relationships are consistent with a common mechanism of coplanar HAH action among cetaceans and rodent species, and (3) the AHR protein is expressed in many tissues of the beluga, and is present at high levels in the lymphoid organs, liver and lung. Together, these data suggest that cetaceans can be considered sensitive to the action of coplanar HAH. Prepared in cooperation with Woods Hole Oceanographic Institution, MA.