The temporal relationships between P450E protein content, catalytic activity, and mRNA levels in the teleost Fundulus heteroclitus following treatment with beta-naphthoflavone.
P450 induction occurs in some marine organisms following chemical exposure. The mode of 3-methylcholanthrene (MC)-type induction was evaluated by examining hepatic isozyme P450E content, catalytic activity, and mRNA levels in the marine teleost Fundulus heteroclitus after exposure to a single dose of beta-naphthoflavone (BNF). P450E is the major teleost P450 induced by MC-type compounds and is the catalyst for aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) activities. In a 20-day experiment, EROD activity was elevated in BNF-treated animals from Day 4 through Day 20. Increases in immunodetectable P450E showed the same trend as EROD activity, with consistently low control values and at least a 19-fold increase in the BNF-treated fish. Precipitation of liver RNA in vitro translation products with anti-P450E antibody gave no detectable signal from control fish, while the BNF-treated animals showed incorporation of [3H]leucine in a single 6,000 Mr band. In a shorter term experiment, EROD activity and P450E levels were again coordinately increased in response to BNF treatment, and immunoprecipitation of translation products from these fish showed a clear trend of increased P450E mRNA levels for all time points 6 h or more post-treatment. Hybridization of RNA from BNF-treated Fundulus with a trout P450IA1 cDNA also showed increases in a single band with time. The increases in P450E mRNA preceded increases in P450E protein and enzyme activity by about 25 h. However, P450E mRNA declined rapidly, reaching control levels by 5 days, while protein levels remained elevated for at least 13 days. The results support a hypothesis that transcriptional enhancement is involved in induction of MC-inducible P450s in fish, but indicate that P450E induction is also under other forms of regulatory control.
Kloepper-Sams
P J
PJ
Department of Biology, Woods Hole Oceanographic Institution, Massachusetts 02543.
Stegeman
J J
JJ
D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology*; D015152:Blotting, Northern; D003532:Cyprinodontiformes / Q000502:physiology*; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004790:Enzyme Induction / Q000187:drug effects; D005419:Flavonoids / Q000494:pharmacology*; D007695:Killifishes / Q000502:physiology*; D010088:Oxidoreductases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D019324:beta-Naphthoflavone
D001571:Benzoflavones; D005419:Flavonoids; D012333:RNA, Messenger; D019324:beta-Naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1