Human
arylamine N-acetyltransferase 1, (HUMAN)NAT1, is a phase II
xenobiotic-metabolizing
enzyme that plays an important role in
drug and
carcinogen biotransformation and
cancer development. Its gene expression has been shown to be regulated by environmental factors. The purpose of the current study is to determine the involvement of
nuclear receptors in transcriptional regulation of (HUMAN)NAT1 gene. We show that among the
nuclear receptors examined, including the
glucocorticoid receptor,
retinoid acid receptor-related orphan receptor alpha,
constitutive androstane receptor,
pregnane X receptor,
aryl hydrocarbon receptor, and
retinoic acid receptor, the
glucocorticoid receptor plays a dominant role in regulating (HUMAN)NAT1 gene expression through distal promoter (P3). The involvement of the
glucocorticoid receptor in transcription regulation of (HUMAN)NAT1 gene expression was demonstrated by
dexamethasone treatment, reporter assay using plasmid-containing 3 kbp of 5'-end region of promoter 3, and treatment of anti-
glucocorticoid RU486 in primary culture of human hepatocytes and transfected HepG2 cells. In addition, translation inhibition did not affect
dexamethasone-induced gene expression through P3, suggesting that
dexamethasone effect is directly mediated by
glucocorticoid receptor activation. Furthermore, deletion analysis revealed the presence of multiple responsive elements within the 3 kbp fragment of P3. Transfection assays in mice using hydrodynamics-based procedure and reporter gene assay in a mouse cell line revealed that
glucocorticoid-induced
NAT gene expression is species dependent.
Dexamethasone treatment of transfected mice and mouse cell line decreased (MOUSE)Nat2 gene expression, (HUMAN)NAT1 homologue. These results suggest that
glucocorticoids serve as a modulator for (HUMAN)NAT1 gene expression via the P3-containing 5'-flanking region.