Exp Mol Med.  2010 Nov;42(11):731-738. 10.3858/emm.2010.42.11.074.

Estrogen modulates transactivations of SXR-mediated liver X receptor response element and CAR-mediated phenobarbital response element in HepG2 cells

• Min G

• KMID: 994396
• DOI: http://doi.org/10.3858/emm.2010.42.11.074

Abstract

The nuclear receptors, steroid and xenobiotic receptor (SXR) and constitutive androstane receptor (CAR) play important functions in mediating lipid and drug metabolism in the liver. The present study demonstrates modulatory actions of estrogen in transactivations of SXR-mediated liver X receptor response element (LXRE) and CAR-mediated phenobarbital response element (PBRU). When human estrogen receptor (hERalpha) and SXR were exogenously expressed, treatment with either rifampicin or corticosterone promoted significantly the SXR-mediated transactivation of LXRE reporter gene in HepG2. However, combined treatment with estrogen plus either rifampicin or corticosterone resulted in less than 50% of the mean values of the transactivation by rifampicin or corticosterone alone. Thus, it is suggested that estrogen may repress the SXR-mediated transactivation of LXRE via functional cross-talk between ER and SXR. The CAR-mediated transactivation of PBRU was stimulated by hERalpha in the absence of estrogen. However, the potentiation by CAR agonist, TCPOBOP, was significantly repressed by moxestrol in the presence of ER. Thus, ER may play both stimulatory and inhibitory roles in modulating CAR-mediated transactivation of PBRU depending on the presence of their ligands. In summary, this study demonstrates that estrogen modulates transcriptional activity of SXR and CAR in mediating transactivation of LXRE and PBRU, respectively, of the nuclear receptor target genes through functional cross-talk between ER and the corresponding nuclear receptors.

Keyword

constitutive androstane receptor; estrogen; liver X receptor; phenobarbital; pregnane X receptor; transcriptional activation

MeSH Terms

Corticosterone/pharmacology
Estrogens/*metabolism
Ethinyl Estradiol/analogs & derivatives/pharmacology
Hep G2 Cells
Humans
Liver/*metabolism
Orphan Nuclear Receptors/metabolism
Phenobarbital/metabolism
Pyridines/pharmacology
Receptor Cross-Talk
Receptors, Cytoplasmic and Nuclear/agonists/*metabolism
Receptors, Steroid/*metabolism
Response Elements
Rifampin/pharmacology
Transcriptional Activation/*drug effects/physiology