Point Mutation in Intron Sequence Causes Altered Carboxyl-Terminal Structure in the Aryl Hydrocarbon Receptor of the Most 2,3,7,8-Tetrachlorodibenzo-p-dioxin-Resistant Rat Strain
- Raimo Pohjanvirta1,2,
- Judy M. Y. Wong2,
- Wei Li2,
- Patricia A. Harper2,3,
- Jouko Tuomisto1 and
- Allan B. Okey2
- 1National Public Health Institute, Department of Environmental Medicine, FIN-70701 Kuopio, Finland (R.P., J.T.), 2Department of Pharmacology, University of Toronto, Toronto M5S 1A8, Canada (R.P., J.M.Y.W., W.L., P.A.H., A.B.O.), 3Division of Clinical Pharmacology and Toxicology, Research Institute, Hospital for Sick Children, Toronto M5G 1X8, Canada (P.A.H.)
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent dioxin. There are exceptionally wide inter- and intraspecies differences in sensitivity to TCDD toxicity with Han/Wistar (H/W) (Kuopio) rats being the most resistant mammals tested. A peculiar feature of H/W rats is that despite their unresponsiveness to the acute lethality of TCDD, their sensitivity to other biological impacts of TCDD (e.g., CYP1A1 induction) is preserved. The biological effects of TCDD are mediated by the aryl hydrocarbon receptor (AhR). We recently found that the AhR of H/W rats (about 98 kDa) is smaller than the receptor in other rat strains (106 kDa). In the present study, molecular cloning and sequencing of the H/W rat AhR revealed that the reason for its smaller size is a deletion/insertion-type change at the 3′ end of exon 10 in the receptor cDNA. This change emanates from a single point mutation at the first nucleotide of intron 10, resulting in altered mRNA splicing. At the protein level, the mutation leads to a total loss of either 43 or 38 amino acids (with altered sequence for the last seven amino acids in the latter case) toward the carboxyl-terminal end in the trans-activation domain of the AhR. H/W rats also harbor a point mutation in exon 10 that will cause a Val-to-Ala substitution in codon 497, but this occurs in a variable region of the AhR. These findings suggest that there is a relatively small region in the AhR trans-activation domain that may be capable of providing selectivity to its function.
Footnotes
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Send reprint requests to: Dr. Raimo Pohjanvirta, National Public Health Institute, Department of Environmental Medicine, P.O. Box 95, FIN-70701 Kuopio, Finland. E-mail: raimo.pohjanvirta{at}ktl.fi
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This study was supported by grants from the Academy of Finland (no. 31363, R.P.; 5410/4011/89, J.T.), from the Finnish Veterinary Foundation (R.P.), and from the Medical Research Council of Canada (A.B.O.), and by a contract (ENV4-CT96–0336) from European Commission (J.T. and R.P.).
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Some preliminary results were reported at the Dioxin ’97 Symposium held in Indianapolis, IN, 1997 Aug 25–29 (Abstr. pp. 287–291).
- Abbreviations:
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- AhR
- aryl hydrocarbon receptor
- ARNT
- aryl hydrocarbon receptor nuclear translocator
- bHLH
- basic helix-loop-helix
- hsp90
- 90-kDa heat-shock protein
- H/W
- Han/Wistar
- H/Wdv
- H/W deletion variant cDNA
- H/Wliv
- H/W longer insertion variant cDNA
- H/Wsiv
- H/W shorter insertion variant cDNA
- kb
- kilobase pair(s)
- L-E
- Long-Evans
- NT
- nucleotide
- PAS
- PER/ARNT/SIM (periodicity/aryl hydrocarbon receptor nuclear translocator protein/simple-minded)
- PCR
- polymerase chain reaction
- RT
- reverse transcription
- SD
- Sprague-Dawley
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- Received January 6, 1998.
- Accepted April 7, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
