THE AH RECEPTOR IN MARINE ANIMALS - PHYLOGENETIC DISTRIBUTION AND RELATIONSHIP TO CYTOCHROME-P4501A INDUCIBILITY

In mammals, the induction of cytochrome P4501A forms by chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and halogenated biphenyls is under control of a soluble protein known as the Ah (aromatic hydrocarbon) receptor. Little is known about the presence and properties of the Ah receptor in other vertebrate and invertebrate species. In these studies, we sought evidence for an Ah receptor in the liver or liver-equivalent of 20 species of marine and freshwater animals, using the photoaffinity ligand 2-azido-3-[I-125]iodo-7,8-dibromodibenzo-p-dioxin (N3[I-125]Br2DD). Specific labeling of cytosolic proteins by N3[I-125]Br2DD was observed in seven species of teleost and elasmobranch fish, in PLHC-1 fish hepatoma cells, and in beluga whales. No specifically labeled proteins were found in cytosol from two species of agnathan fish nor in any of nine invertebrate species representing eight classes of four phyla. The presence or absence of specifically labeled polypeptides corresponds with the inducibility of cytochrome P4501A and sensitivity to the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related planar halogenated aromatic hydrocarbons in many of these groups. Thus, Ah receptor function may have arisen early in vertebrate evolution and has been conserved from elasmobranch and teleost fish to mammals.