Superfund Research Program
Mechanisms and Impacts of PCB Resistant Fish
Project Leader: Mark E. Hahn (Woods Hole Oceanographic Institution)
Co-Investigators: Sibel I. Karchner (Woods Hole Oceanographic Institution), Neelakanteswar Aluru (Woods Hole Oceanographic Institution)
Grant Number: P42ES007381
Funding Period: 1995-2020
The overall objective of this project is to understand the impact of long-term, multi-generational exposure to high levels of dioxin-like chemicals, including certain polychlorinated biphenyls (PCBs). To address this problem, Dr. Hahn and his research team are studying a population of estuarine fish, Atlantic killifish (Fundulus heteroclitus), in the New Bedford Harbor (NBH), a marine Superfund site. Dioxin resistance is being evaluated by measuring induction of the biomarker enzyme, cytochrome P450 1A (CYP1A), which occurs through activation of a signal transduction pathway involving the aryl hydrocarbon (Ah) receptor.
The potent Ah receptor agonist - 2,3,7,8-tetrachlorodibenzofuran (TCDF) - induces CYP1A protein and catalytic activity in killifish obtained from a reference site, Scorton Creek (SC), but not in fish from the NBH Superfund site. This year, project scientists began to investigate the step at which the Ah receptor pathway is altered in NBH fish. Measurement of CYP1A mRNA in TCDF-treated fish from SC and NBH showed that the resistance to induction occurs at a pre-translational level, and probably at the transcriptional level. The expression of the Ah receptor was determined in livers of SC and NBH fish by measuring the specific binding of [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Receptor content was highly variable in killifish and much lower than that seen in mammals. Mean levels of specific binding were lower in livers of NBH fish (1.2 ± 1.8 fmol/mg protein) compared to SC fish (8.9 ± 12.0 fmol/mg protein).
Previously, the scientists identified partial sequences of two Ah receptor genes (designated AhR1 and AhR2) in Fundulus, in contrast to the single AhR identified in most other vertebrate species. This year, they obtained the full-length sequence of AhR2 and the nearly full-length sequence for AhR1. For each AhR, alternatively spliced forms were identified that varied in the C-terminal sequence, including stop codons, so that the forms encode proteins of different sizes. A full-length killifish ARNT (dimerization partner of the Ah receptor) was cloned and sequenced. Current experiments are examining the expression ARNT, the various forms of Ah receptor, and their interactions in SC and NBH fish.