HALOGENATED AROMATIC HYDROCARBON-BINDING PROTEINS IDENTIFIED IN SEVERAL INVERTEBRATE MARINE SPECIES

The vertebrate aryl hydrocarbon receptor (AhR) is a cytosolic protein which binds halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachl orodibenzo-p-dioxin (TCDD), In vertebrates, the AhR-ligand complex, in association with other proteins, binds specific DNA sequences and mod ifies the expression of a number of genes. Most of the toxic effects o f halogenated aromatic hydrocarbon exposure are mediated through this receptor. A similar receptor system has not yet been identified in inv ertebrates. The current study investigated whether proteins which spec ifically bind halogenated aromatic hydrocarbons were present in marine invertebrates. We used the photoaffinity TCDD-analog, 2-azido-3-[I-12 5]iodo-7,8-dibromodibenzo-p-dioxin ([I-125]N(3)Br(2)DpD), to detect th e presence of cytosolic proteins which specifically bound this ligand. Specific binding was defined as labeling which could be competed off by an excess of unlabeled ligand. Eleven species of marine invertebrat es were examined which represented six different phyla: Cnidaria, Moll usca, Annelida, Arthropoda, Chordata, and Echinodermata. Cytosols prep ared from gill and gonad in the soft-shell clam (Mya arenaria), the ea stern oyster (Crassostrea virginica), and hard-shell clam (Mercenaria mercenaria), as well as the hepatopancreas of the blue crab (Callinect es sapidus), contained proteins in the same size range (28-39 kDa) whi ch were specifically labeled with the dioxin analog. No proteins of th e size expected for vertebrate Ah receptors (95-146 kDa) were seen in any of the invertebrates. The biological function of these dioxin-bind ing proteins is not yet known.