Dexamethasone responsiveness of a major glucocorticoid-inducible CYP3A gene is mediated by elements unrelated to a glucocorticoid receptor binding motif.
Elements responsible for dexamethasone responsiveness of CYP3A23, a major glucocorticoid-inducible member of the CYP3A gene family, have been identified. DNase I footprint analysis of the proximal promoter region revealed three protected sites (sites A, B, and C) within the sequence defined by -167 to -60. Mutational analysis demonstrated that both sites B and C were necessary for maximum glucocorticoid responsiveness and functioned in a cooperative manner. Interestingly, neither site contained a glucocorticoid responsive element. Embedded in site C was an imperfect direct repeat (5'-AACTCAAAGGAGGTCA-3'), showing homology to an AGGTCA steroid receptor motif, typically recognized by the estrogen receptor family, while site B contained an ATGAACT direct repeat; these core sequences were designated dexamethasone response elements 1 and 2 (DexRE-1 and -2), respectively. Neither element has previously been associated with a glucocorticoid-activated transcriptional response. Conversion of the DexRE-1 to either a perfect thyroid hormone or vitamin D3 responsive element further enhanced induction by dexamethasone. Gel-shift analysis demonstrated that glucocorticoid receptor did not associate with either DexRE-1 or -2; hence, glucocorticoid receptor does not directly mediate glucocorticoid induction of CYP3A23. These unusual features suggest an alternate pathway through which glucocorticoids exert their effects.
Huss
J M
JM
Department of Oncology, McArdle Laboratory, University of Wisconsin, Madison, 53706, USA.
Wang
S I
SI
Astrom
A
A
McQuiddy
P
P
Kasper
C B
CB
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism
D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; C022657:steroid hormone 6-beta-hydroxylase