CYP6B4, a cytochrome P450 gene from the tiger swallowtail caterpillar, is transcriptionally induced in the midgut by dietary furanocoumarins that can crosslink DNA when UV-activated. The CYP6B4 promoter contains a putative response element to the linear furanocoumarin, xanthotoxin (XRE-Xan) that is required for both basal and xanthotoxin-inducible expression of the related CYP6B1 promoter. To determine whether XRE-Xan is necessary for induction of CYP6B4 by xanthotoxin, a promoter fragment containing XRE-Xan and two shorter fragments lacking XRE-Xan were fused to the CAT reporter gene and cotransfected into Sf9 lepidopteran cells with an actin:b-galactosidase control plasmid. These transfections indicate that while the XRE-Xan containing constructs are significantly induced by xanthotoxin (5-6 fold), removal of this element does not completely abolish induction by xanthotoxin as seen with CYP6B1 (Petersen et al. 2003). The CYP6B4 promoter also contains a xenobiotic response element to aryl hydrocarbon that was first identified in the mammalian CYP1A1 gene, suggesting that CYP6B4 gene may be regulated by the aryl hydrocarbons in addition to furanocoumarins. CYP6B4 promoter constructs containing XRE-Xan with XRE-AhR and XRE-AhR alone were tested for a response to benzo(a)pyrene, a polycyclic aromatic hydrocarbon that is a widespread environmental pollutant. Benzo(a)pyrene induced CYP6B4 promoter constructs that contain both the XRE-Xan and XRE-AhR elements but not constructs containing XRE-AhR alone. Thus, induction of the CYP6B4 promoter by different types of toxins, exemplified by xanthotoxin and benzo(a)pyrene, is mediated by a conserved set of response elements originally characterized as having distinct regulatory pathways.
Species 1: Lepidoptera Papilionidae Papilio glaucus (eastern tiger swallowtail)
Keywords: xenobiotics, environmental toxicology
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