Influence of cAMP on reporter bioassays for dioxin and dioxin-like compounds.
In reporter assays for detection of dioxins, the dioxin-responsive element (DRE) is generally used as a sensor sequence. In several systems, the CYP1A1 promoter containing DREs (DRE(cyp)) is inserted into a part of the long terminal repeat of mouse mammary tumor virus (LTR(MMTV)) to improve sensitivity of assays. We found that DRE(cyp)-LTR(MMTV) responds not only to dioxins and dioxin-like compounds but also to forskolin, a cAMP-elevating agent. This effect was dose-dependent and reproduced by other cAMP-elevating agents including 8-bromo-cAMP and 3-isobutyl-methylxanthine. The cAMP response element (CRE) and CRE-like sequences were absent in DRE(cyp)-LTR(MMTV) and not involved in this process. In contrast to the effect of dioxin, the activation of DRE(cyp)-LTR(MMTV) by cAMP was independent of the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor for DRE. Furthermore, neither DRE(cyp), LTR(MMTV) nor the consensus sequence of DRE alone was activated in response to cAMP. These data elucidated for the first time that the combination of DRE(cyp) with LTR(MMTV) causes a peculiar response to cAMP and suggested that use of AhR antagonists is essential to exclude false-positive responses of DRE(cyp)-LTR(MMTV)-based bioassays for detection and quantification of dioxins and dioxin-like compounds.
Department of Biochemistry, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Shimokato1110, Tamaho, Yamanashi 409-3898, Japan.
Ayumi
A
Kasai
Jian
J
Yao
Kozue
K
Yamauchi
Nobuhiko
N
Hiramatsu
Kunihiro
K
Hayakawa
Yiman
Y
Meng
Shuichiro
S
Maeda
Masanori
M
Kitamura
D000818:Animals; D001483:Base Sequence; D001681:Biological Assay / Q000379:methods*; D045744:Cell Line, Tumor; D005576:Colforsin / Q000494:pharmacology; D016384:Consensus Sequence / Q000235:genetics; D000242:Cyclic AMP / Q000494:pharmacology*; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics; D004147:Dioxins / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000032:analysis; D020536:Enzyme Activators / Q000494:pharmacology; D005189:False Positive Reactions; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter / Q000187:drug effects*; D022781:Hepatocytes; D008324:Mammary Tumor Virus, Mouse / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D018336:Receptors, Aryl Hydrocarbon / Q000187:drug effects; D020218:Response Elements / Q000187:drug effects / Q000235:genetics; D020079:Terminal Repeat Sequences / Q000187:drug effects / Q000235:genetics; D014162:Transfection
D004147:Dioxins; D004785:Environmental Pollutants; D020536:Enzyme Activators; D018336:Receptors, Aryl Hydrocarbon; D005576:Colforsin; D000242:Cyclic AMP; D019363:Cytochrome P-450 CYP1A1