Primary structure and inducibility by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) of aryl hydrocarbon receptor repressor in a TCDD-sensitive and a TCDD-resistant rat strain.
The aryl hydrocarbon receptor repressor (AHRR) is a negative regulator of AH receptor (AHR), which mediates most of the toxic and biochemical effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). AHR has been shown to be the major reason for the exceptionally wide (ca. 1000-fold) sensitivity difference in acute toxicity of TCDD between two rat strains, sensitive Long-Evans (Turku/AB) (L-E) and resistant Han/Wistar (Kuopio) (H/W), but there is another, currently unknown contributing factor involved. In the present study, we examined AHRR structure and expression in these rat strains to find out whether AHRR could be this auxiliary factor. Molecular cloning of AHRR coding region showed that consistent with AHRR proteins in other species, the N-terminal end of rat AHRR is highly conserved, but PAS B and Q-rich domains are severely truncated or lacking. Identical structures were recorded in both strains. Next, the time-, dose-, and tissue-dependent expression of AHRR was determined using quantitative real-time RT-PCR. In liver, AHRR expression was very low in untreated rats, but it increased rapidly after TCDD exposure (100microg/kg). Testis exhibited the highest constitutive expression of AHRR, whereas kidney, spleen, and heart showed the highest induction of AHRR in response to TCDD treatment. Again, no marked differences were found between H/W and L-E rats, implying that AHRR is not the auxiliary contributing factor to the strain difference in TCDD sensitivity. However, simultaneous measurement of CYP1A1 mRNA reinforced the view that AHRR is an important determinant of tissue-specific responsiveness to TCDD.
Korkalainen
Merja
M
National Public Health Institute, Department of Environmental Health, P.O. Box 95, FIN-70701 Kuopio, Finland. Merja.Korkalainen@ktl.fi
Tuomisto
Jouko
J
Pohjanvirta
Raimo
R
D000595:Amino Acid Sequence; D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis; D004268:DNA-Binding Proteins; D004351:Drug Resistance; D018257:Helix-Loop-Helix Motifs; D008099:Liver / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D020318:Rats, Long-Evans; D017208:Rats, Wistar; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics
D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D019363:Cytochrome P-450 CYP1A1; D004268:DNA-Binding Proteins; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D012097:Repressor Proteins; D014157:Transcription Factors; C497398:ARNT protein, rat; C492161:Ahrr protein, rat