Regulation of rat hepatic hydroxysteroid sulfotransferase (SULT2-40/41) gene expression by glucocorticoids: evidence for a dual mechanism of transcriptional control.

Abstract

Glucocorticoid-inducible hydroxysteroid sulfotransferase (SULT2-40/41) gene transcription was investigated in primary cultured rat hepatocytes transiently transfected with a series of SULT2-40/41 5'-flanking region-luciferase reporter constructs, with emphasis on examining the functional role of an inverted repeat-0 nuclear receptor motif (IR0). Treatment of transfected cultures with any of four glucocorticoids activated luciferase expression from a construct containing 1938 base pairs (bp) of the SULT2-40/41 gene 5'-flanking sequence, whereas deletion of bp -227 to -158 (containing the IR0 motif) largely abolished the effect. On closer analysis, treatment of hepatocyte cultures with either of the potent glucocorticoids dexamethasone [strong cytochrome P-450 3A (CYP3A) inducer] or triamcinolone acetonide (weak CYP3A inducer) produced dose-dependent increases in luciferase activity when hepatocytes were transiently transfected with a construct containing as little as 158 bp of 5'-flanking sequence or containing a mutated IR0 motif. The dexamethasone dose-dependent increase in luciferase activity continued through a dose of 10(-6) M when the transfected construct contained the IR0 motif, but was maximal at 10(-7) M when the transfected construct lacked the IR0 motif. In contrast, triamcinolone acetonide-induced luciferase activity was maximal at a dose of 10(-7) M, irrespective of the presence or absence of the IR0 motif. Coincubation of transfected hepatocytes with 10(-8) M dexamethasone and the antiglucocorticoid RU486 inhibited luciferase expression. Luciferase induction by the prototypical CYP3A inducer pregnenolone 16alpha-carbonitrile was restricted to constructs containing the IR0 motif. These data suggest that glucocorticoid-inducible SULT2-40/41 gene expression occurs through a dual mechanism, whose components possibly involve the glucocorticoid receptor and the pregnane X receptor.