Papilio polyxenes represents a lepidopteran insect continually exposed to toxic furanocoumarins present in its hostplants. Its tolerance to these compounds is attributed to the transcriptional induction by furanocoumarins of the CYP6B1v3 gene that encodes a P450 capable of metabolizing linear furanocoumarins, such as xanthotoxin, at high efficiency. Transient expression of the CYP6B1v3 promoter in lepidopteran Sf9 cells defines a positive element (XRE-xan) required for both basal and xanthotoxin-inducible transcription. Fusion of the CYP6B1v3 XRE-xan to the Drosophila melanogaster Eip28/29 core promoter indicates that the XRE-xan functions in conjunction with its own core promoter but not with heterologous core promoters. Sequence searches of the CYP6B1v3 proximal promoter region identify a number of elements (EcRE, ARE, XRE-AhR, OCT-1, C/EBP, Inr) found in other regulated vertebrate and insect promoters. Mutagenesis of these putative elements and those in the core promoter indicates that these sequences are essential for basal and regulated transcription of this gene. Parallel dietary exposure of P. polyxenes caterpillars to natural steroids, synthetic antioxidants, and synthetic aryl hydrocarbons does not induce metabolism of xanthotoxin to any extent, whereas treatment with caffeic acid, a natural antioxidant found in Papilio hostplants, induces xanthotoxin metabolism at a low dose and inhibits at a high dose. In contrast, parallel treatment of Sf9 cells transiently transfected with wildtype CYP6B1v3 promoter with an aryl hydrocarbon induces transcription from the CYP6B1v3 promoter while treatment with other chemicals does not. These findings are incorporated into a working model for regulation of this toxin-inducible promoter.
Species 1: Lepidoptera Papilionidae Papilio polyxenes (black swallowtail)
Keywords: furanocoumarin, mutagenesis
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