A novel cis-acting element in a liver cytochrome P450 3A gene confers synergistic induction by glucocorticoids plus antiglucocorticoids.

摘要: The induction by dexamethasone of rat liver CYP3A1 differs from classical glucocorticoid gene regulation in part because both glucocorticoids and antiglucocorticoids such as pregnenolone 16 alpha-carbonitrile (PCN) induce through transcriptional activation. In the present study, we transiently expressed primary cultures hepatocytes plasmids consisting 5'-flanking sequences fused to a chloramphenicol acetyltransferase reporter plasmid. Deletional analysis identified 78-base pair (bp) element located approximately 135 bp upstream start site that was inducible treatment with or PCN induced synergistically plus PCN. Nuclear extract control protected two regions within 78-bp sequence against digestion DNase I. same were when nuclear extracts dexamethasone-treated animals used. Analysis "footprints" (FP1 FP2) failed reveal for glucocorticoid-responsive element. A 33-bp includes FP1 inserted into plasmid conferred profile similar However, an Escherichia coli receptor protein protect I footprinting experiments change its mobility gel shift assays. Moreover, judged assay, specific binding this fragment whether untreated rats We conclude activation transcription may involve proteins already bound controlling mechanism which GR presence hormone does not bind directly DNA.