Ra. Prough et al., CYTOCHROMES-P450 .8. HORMONAL-REGULATION OF HEPATIC-ENZYMES INVOLVED IN FOREIGN COMPOUND METABOLISM, The FASEB journal, 10(12), 1996, pp. 1369-1377
The regulation of hepatic P450s has been the focus of numerous studies
because of the importance of these proteins in endocrinology, oncolog
y, and toxicology, as well as drug development. Considerable evidence
exists demonstrating that many hepatic P450s are regulated by developm
ental, sex, or hormonal factors in addition to receptors that interact
with foreign chemicals. The focus of work in our laboratory has been
on the effects of steroid hormones, especially glucocorticoids, on exp
ression of genes regulated by the Ah receptor. We have shown that most
rat hepatic genes of the Ah receptor gene battery are regulated by gl
ucocorticoids. We have used glucocorticoid-deficient animal models to
demonstrate that these steroids do modulate the expression (basal and
inducible) of these genes in vivo. Using cultured rat hepatocytes, we
have demonstrated that polycyclic aromatic hydrocarbon (PAH) induction
of cytochrome P4501A1, glutathione S-transferase Ya(1), and UDP-glucu
ronosyl-transferase 16 are apparently potentiated two- to fourfold up
on inclusion of glucocorticoids in the media to activate the glucocort
icoid receptor and further, that the receptor antagonist RU 38486 reve
rses these phenomenon. NAD(P)H:quinone oxidoreductase and aldehyde deh
ydrogenase 3 gene expression were repressed 70-80% by glucocorticoids
in cultured hepatocytes through a glucocorticoid receptor-mediated pro
cess as well. The effect of glucocorticoid concentration on PAH induct
ion of glutathione S-transferase Ya(1) subunit for glucocorticoids was
biphasic, but at physiological concentrations gene expression was rep
ressed to similar to 20-40% of control. At supraphysiological concentr
ations, glucocorticoids alone induced expression two- to threefold and
potentiated the PAH-inducible expression of the Ya(1) subunit gene. S
ubsequent work in our laboratory has focused on defining the molecular
basis of this hormonal regulation, specifically elucidating responsiv
e elements responsible for the action of the glucocorticoid receptor a
nd the mechanisms by which some of these genes are positively regulate
d and others are negatively regulated.