The hypolipidemic agent guggulsterone regulates the expression of human bile salt export pump: dominance of transactivation over farsenoid X receptor-mediated antagonism.
Conversion of cholesterol to bile acids in the liver is initiated by the rate-limiting enzyme cholesterol 7alpha-hydroxylase (CYP7A1) and excretion of bile acids from the liver is mediated by the bile salt export pump (BSEP). The expression of CYP7A1 and BSEP is coordinately regulated by a negative feedback and positive feed-forward mechanism, respectively, through bile acid-mediated activation of farsenoid X receptor (FXR). It is well established that hypolipidemic agent guggulsterone is an FXR antagonist and down-regulates FXR target genes. In this study, however, we have demonstrated that guggulsterone synergistically induced the expression of BSEP in cells treated with FXR agonist bile acids. A dissection study located in the BSEP promoter an activating protein (AP)-1 site supporting the action of guggulsterone. Deletion or mutation of the AP-1 element was diminished, whereas insertion of the AP-1 element into a heterologous promoter enhanced activation of the promoter by guggulsterone. Selective c-Jun N-terminal kinase and extracellular signal-regulated kinase inhibitors markedly decreased the transactivation, suggesting an involvement of AP-1 activation pathway in the up-regulation of BSEP by guggulsterone. Consistent with its FXR antagonism, guggulsterone antagonized bile acid-mediated transactivation of BSEP promoter when the AP-1 element was disrupted. In conclusion, guggulsterone regulates BSEP expression through composite mechanisms, and the transactivation through the AP-1 element is dominant over the FXR-mediated antagonism. The up-regulation of BSEP expression by guggulsterone without activating FXR pathway as an FXR agonist to suppress CYP7A1 expression represents a possible mechanism for guggulsterone-mediated hypolipidemic effect.
Deng
Ruitang
R
Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Fogarty Hall, 41 Lower College Road, Kingston, RI 02881, USA. DengR@mail.uri.edu
Yang
Dongfang
D
Radke
Amy
A
Yang
Jian
J
Yan
Bingfang
B
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D015536:Down-Regulation; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D000960:Hypolipidemic Agents / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000235:genetics; D011282:Pregnenediones / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis* / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018808:Transcription Factor AP-1 / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D015533:Transcriptional Activation; D014162:Transfection; D015854:Up-Regulation; D000099150:Receptor, Farnesoid X-Activated
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; D000960:Hypolipidemic Agents; D016660:NAD(P)H Dehydrogenase (Quinone); D011282:Pregnenediones; D018160:Receptors, Cytoplasmic and Nuclear; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C093491:ABCB11 protein, human; C023617:pregna-4,17-diene-3,16-dione; C447479:NQO1 protein, human