Regulation of sulfotransferase gene expression by glucocorticoid hormones and xenobiotics in primary rat hepatocyte culture.
In the rat liver, hydroxysteroid sulfotransferase-a (HST-a) and aryl sulfotransferase IV (ASTIV) represent two major rat hepatic sulfotransferases that are important to xenobiotic metabolism. Prototypic CYP1A1 and CYP2B/3A inducers regulate rat hepatic sulfotransferase gene expression although not necessarily in a coordinate direction. It has been previously reported that in vivo treatment with CYP1A1 inducer 3-methylcholanthrene (3-MC) suppresses rat hepatic HST-a mRNA expression in a dose-dependent manner. Similarly, HST-a and ASTIV mRNA levels become suppressed or induced, respectively, following in vivo treatment with phenobarbital (PB)-like CYP2B/3A inducers or prototypic CYP3A inducers such as glucocorticoid hormones. In the whole animal, sulfotransferase gene expression is modulated by members of the hypothalamic/pituitary-adrenal gonadal hormone axis. However, studies in primary rat hepatocyte culture suggest that prototypic P450 inducers regulate HST-a and ASTIV gene expression directly at the level of the hepatocyte. Glucocorticoid-mediated sulfotransferase expression was compared with the regulation of tyrosine amino transferase (TAT), a gene that is transcriptionally regulated by ligand bound glucocorticoid receptor. It was found that lower doses of dexamethasone (DEX, 10(-7) M) produced concomitant increases in ASTIV and TAT mRNA expression, whereas HST-a mRNA expression continued to rise as the DEX dose was increased through 10(-5) M. When hepatocytes were co-incubated with DEX and antiglucocorticoid/antiprogestin RU-486, DEX-stimulated HST-a mRNA expression was not significantly inhibited by RU-486, but ASTIV and TAT mRNA expression were inhibited to a similar extent. The results suggested that ASTIV, like TAT, is likely regulated by a classical glucocorticoid receptor mediated mechanism, whereas HST-a is probably regulated by glucocorticoids via an alternative mechanism. In contrast to the positive effects of glucocorticoid hormones, HST-a and ASTIV mRNA expression was negatively regulated by xenobiotics such as PB-like CYP2B/3A inducers or aryl hydrocarbon receptor (AhR) agonist CYP1A1 inducers. Incubation of primary cultured rat hepatocytes with PB or structurally dissimilar PB-like inducers clotrimazole, diphenylhydantoin, heptachlor, gamma-hexachlorocyclohexane or 2,2',4,4',5,5'-hexachlorobiphenyl suppressed HST-a and ASTIV mRNA levels. Also, incubation of primary cultured rat hepatocytes with CYP1A1 inducer beta-naphthoflavone or with archetypic AhR agonist, 2,3,7,8-tetrachloro-p-dioxin (TCDD) markedly suppressed HST-a and ASTIV mRNA expression. These data suggest that the rat HST-a and ASTIV genes are positively regulated by glucocorticoid hormones and negatively regulated by xenobiotics as a result of molecular and cellular mechanisms that act directly on the hepatocyte.
Runge-Morris
M
M
Institute of Chemical Toxicology, Wayne State University, Detroit, MI 48201, USA. m.runge-morris@wayne.edu
D000818:Animals; D002478:Cells, Cultured; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects* / Q000502:physiology*; D005938:Glucocorticoids / Q000494:pharmacology / Q000502:physiology*; D008099:Liver / Q000201:enzymology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015238:Sulfotransferases / Q000096:biosynthesis* / Q000235:genetics; D015262:Xenobiotics / Q000494:pharmacology*
D005938:Glucocorticoids; D015262:Xenobiotics; D015238:Sulfotransferases; C028152:alcohol sulfotransferase; C077557:tyrosine-ester sulfotransferase