The Farnesoid X Receptor Controls Gene Expression in a Ligand- and Promoter-selective Fashion
Farnesoid X receptor (FXR) is a nuclear receptor for bile acids. Ligand activated-FXR regulates transcription of genes to allow feedback control of bile acid synthesis and secretion. There are five major bile acids in humans. We have previously demonstrated that lithocholate acts as an FXR antagonist, and here we show that the other four bile acids, chenodeoxycholate (CDCA), deoxycholate (DCA), cholate (CA), and ursodeoxycholate (UDCA), act as selective FXR agonists in a gene-specific fashion. In an in vitro coactivator association assay, CDCA fully activated FXR, whereas CA partially activated FXR and DCA and UDCA had negligible activities. Similar results were also obtained from a glutathione S-transferase pull-down assay in which only CDCA and the synthetic FXR agonist GW4064 significantly increased the interaction of SRC-1 with FXR. In FXR transactivation assays with a bile salt export pump (BSEP) promoter-driven luciferase construct, bile acids showed distinct abilities to activate the BSEP promoter: CDCA, DCA, CA, and UDCA increased luciferase activity by 25-, 20-, 18-, and 8-fold, respectively. Consistently, CDCA increased BSEP mRNA by 750-fold in HepG2 cells, whereas DCA, CA, and UDCA induced BSEP mRNA by 250-, 75-, and 15-fold, respectively. Despite the partial induction of BSEP mRNA, CA, DCA, and UDCA effectively repressed expression of cholesterol 7α-hydroxylase, another FXR target. We further showed that all four bile acids significantly increased FXR protein, suggesting the existence of an auto-regulatory loop in FXR signaling pathways. In conclusion, these results suggest that the binding of each bile acid results in a different FXR conformations, which in turn differentially regulates expression of individual FXR targets. Farnesoid X receptor (FXR) is a nuclear receptor for bile acids. Ligand activated-FXR regulates transcription of genes to allow feedback control of bile acid synthesis and secretion. There are five major bile acids in humans. We have previously demonstrated that lithocholate acts as an FXR antagonist, and here we show that the other four bile acids, chenodeoxycholate (CDCA), deoxycholate (DCA), cholate (CA), and ursodeoxycholate (UDCA), act as selective FXR agonists in a gene-specific fashion. In an in vitro coactivator association assay, CDCA fully activated FXR, whereas CA partially activated FXR and DCA and UDCA had negligible activities. Similar results were also obtained from a glutathione S-transferase pull-down assay in which only CDCA and the synthetic FXR agonist GW4064 significantly increased the interaction of SRC-1 with FXR. In FXR transactivation assays with a bile salt export pump (BSEP) promoter-driven luciferase construct, bile acids showed distinct abilities to activate the BSEP promoter: CDCA, DCA, CA, and UDCA increased luciferase activity by 25-, 20-, 18-, and 8-fold, respectively. Consistently, CDCA increased BSEP mRNA by 750-fold in HepG2 cells, whereas DCA, CA, and UDCA induced BSEP mRNA by 250-, 75-, and 15-fold, respectively. Despite the partial induction of BSEP mRNA, CA, DCA, and UDCA effectively repressed expression of cholesterol 7α-hydroxylase, another FXR target. We further showed that all four bile acids significantly increased FXR protein, suggesting the existence of an auto-regulatory loop in FXR signaling pathways. In conclusion, these results suggest that the binding of each bile acid results in a different FXR conformations, which in turn differentially regulates expression of individual FXR targets. Bile acids are the end products of cholesterol catabolism. The five major bile acids in humans are chenodeoxycholate (CDCA), 1The abbreviations used are: CDCA, chenodeoxycholate; FXR, farnesoid X receptor; BSEP, bile salt export pump; Cyp7a, cholesterol 7α-hydroxylase; DCA, deoxycholate; CA, cholate; UDCA, ursodeoxycholate; LCA, lithocholate; SRC-1, steroid receptor coactivator protein-1; FBS, fetal bovine serum; CS, charcoal-stripped; DMEM, Dulbecco’s modified Eagle’s medium. GST, glutathione S-transferase; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid; SHP, small heterodimer partner. deoxycholate (DCA), cholate (CA), ursodeoxycholate (UDCA), and lithocholate (LCA) (1Hofmann A.F. Arch. Intern. Med. 1999; 159: 2647-2658Crossref PubMed Scopus (679) Google Scholar). In addition to their critical roles in lipid and vitamin absorption, bile acids are ligands for the nuclear receptor FXR and regulate expression of genes whose products are critically important for bile acid and cholesterol homeostasis (2Makishima M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2164) Google Scholar, 3Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1843) Google Scholar, 4Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1298) Google Scholar). Agonist-bound FXR activates expression of the BSEP (5Ananthanarayanan M. Balasubramanian N. Makishima M. Mangelsdorf D.J. Suchy F.J. J. Biol. Chem. 2001; 276: 28857-28865Abstract Full Text Full Text PDF PubMed Scopus (656) Google Scholar, 6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar), intestinal bile acid-binding protein (7Grober J. Zaghini I. Fujii H. Jones S.A. Kliewer S.A. Willson T.M. Ono T. Besnard P. J. Biol. Chem. 1999; 274: 29749-29754Abstract Full Text Full Text PDF PubMed Scopus (289) Google Scholar), phospholipid transfer protein (8Urizar N.L. Dowhan D.H. Moore D.D. J. Biol. Chem. 2000; 275: 39313-39317Abstract Full Text Full Text PDF PubMed Scopus (208) Google Scholar), dehydroepiandrosterone sulfotransferase (9Song C.S. Echchgadda I. Baek B.S. Ahn S.C. Oh T. Roy A.K. Chatterjee B. J. Biol. Chem. 2001; 276: 42549-42556Abstract Full Text Full Text PDF PubMed Scopus (171) Google Scholar), apolipoprotein C-II (10Kast H.R. Nguyen C.M. Sinal C.J. Jones S.A. Laffitte B.A. Reue K. Gonzalez F.J. Willson T.M. Edwards P.A. Mol. Endocrinol. 2001; 15: 1720-1728Crossref PubMed Scopus (224) Google Scholar), apolipoprotein E (11Mak P.A. Kast-Woelbern H.R. Anisfeld A.M. Edwards P.A. J. Lipid Res. 2002; 43: 2037-2041Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar), and kininogen (12Zhao A. Lew J.L. Huang L. Yu J. Zhang T. Hrywna Y. Thompson J.R. Pedro Nd N. Blevins R.A. Pelaez F. Wright S.D. Cui J. J. Biol. Chem. 2003; 21: 21Google Scholar). FXR represses expression of cholesterol 7α-hydroxylase (Cyp7a) (11Mak P.A. Kast-Woelbern H.R. Anisfeld A.M. Edwards P.A. J. Lipid Res. 2002; 43: 2037-2041Abstract Full Text Full Text PDF PubMed Scopus (107) Google Scholar, 13Chiang J.Y. Kimmel R. Weinberger C. Stroup D. J. Biol. Chem. 2000; 275: 10918-10924Abstract Full Text Full Text PDF PubMed Scopus (258) Google Scholar, 14Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol. Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1514) Google Scholar, 15Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1228) Google Scholar), sterol 12 α-hydroxylase (16Zhang M. Chiang J.Y. J. Biol. Chem. 2001; 276: 41690-41699Abstract Full Text Full Text PDF PubMed Scopus (211) Google Scholar), the Na+/taurocholate co-transporting polypeptide (17Denson L.A. Sturm E. Echevarria W. Zimmerman T.L. Makishima M. Mangelsdorf D.J. Karpen S.J. Gastroenterology. 2001; 121: 140-147Abstract Full Text PDF PubMed Scopus (370) Google Scholar), and apolipoprotein A-I (18Claudel T. Sturm E. Duez H. Torra I.P. Sirvent A. Kosykh V. Fruchart J.C. Dallongeville J. Hum D.W. Kuipers F. Staels B. J. Clin. Invest. 2002; 109: 961-971Crossref PubMed Scopus (287) Google Scholar). A few functional distinct classes of FXR ligands have been identified. We have previously shown that LCA is an FXR antagonist and that guggulsterones are SBARMs (selective bile acid receptor modulators) (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar, 19Cui J. Huang L. Zhao A. Lew J.L. Yu J. Sahoo S. Meinke P.T. Royo I. Pelaez F. Wright S.D. J. Biol. Chem. 2003; 278: 10214-10220Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar). GW4064 is a synthetic FXR agonist (20Maloney P.R. Parks D.J. Haffner C.D. Fivush A.M. Chandra G. Plunket K.D. Creech K.L. Moore L.B. Wilson J.G. Lewis M.C. Jones S.A. Willson T.M. J. Med. Chem. 2000; 43: 2971-2974Crossref PubMed Scopus (458) Google Scholar). Bile acids such as CDCA, DCA, and CA have been previously shown to be FXR agonists that regulate expression of FXR targets (2Makishima M. Okamoto A.Y. Repa J.J. Tu H. Learned R.M. Luk A. Hull M.V. Lustig K.D. Mangelsdorf D.J. Shan B. Science. 1999; 284: 1362-1365Crossref PubMed Scopus (2164) Google Scholar, 3Parks D.J. Blanchard S.G. Bledsoe R.K. Chandra G. Consler T.G. Kliewer S.A. Stimmel J.B. Willson T.M. Zavacki A.M. Moore D.D. Lehmann J.M. Science. 1999; 284: 1365-1368Crossref PubMed Scopus (1843) Google Scholar, 4Wang H. Chen J. Hollister K. Sowers L.C. Forman B.M. Mol. Cell. 1999; 3: 543-553Abstract Full Text Full Text PDF PubMed Scopus (1298) Google Scholar). In this study, we systematically characterized the FXR agonist activities of these bile acids using a series of cell-free and cell-based assays including coactivator recruitment, GST pull-down assay, FXR transactivation, and quantitative real-time PCR for examining the expression of FXR targets. Our results indicate that CDCA is a full FXR agonist that effectively regulates expression of FXR targets, whereas DCA, CA, and UDCA are partial agonists in FXR transactivation assays and regulate expression of FXR targets in a gene-selective fashion. These three bile acids partially induced BSEP mRNA but effectively repressed Cyp7a and strongly increased FXR protein expression. This study shows for the first time that distinct bile acids have unique properties as FXR agonists and reveals an auto-regulatory loop in FXR signaling pathways. Reagents—The following reagents were obtained from Invitrogen: DMEM and Opti-MEM I; regular fetal bovine serum (FBS) and charcoal-stripped FBS (CS-FBS); and TRIzol reagents. l-[35S]Methionine (1000 Ci/mmol) was obtained from Amersham Biosciences. The TnT T7 QuickCoupled transcription/translation kit and reagents for β-galactosidase and luciferase assays were from Promega (Madison, WI). Fu-GENE 6 transfection reagent was obtained from Roche Diagnostics. Bile acids were obtained from Steraloids, Inc. (Newport, RI). GW4064 was synthesized at Merck (Rahway, NJ). TaqMan reagents for cDNA synthesis and real-time PCR and TaqMan oligonucleotide primers and probes for human 18 S RNA were purchased from Applied Biosystems (Foster City, CA). FXR Coactivator Association Assays—Human GST-FXR-ligand binding domain fusion protein was prepared from Escherichia coli strain BL21. A homogeneous time-resolved fluorescence based FXR and coactivator SRC-1 interaction assay was used to examine the interaction of FXR-ligand binding domain with various ligands according to those described previously for other nuclear receptors (21Zhou G. Cummings R. Li Y. Mitra S. Wilkinson H.A. Elbrecht A. Hermes J.D. Schaeffer J.M. Smith R.G. Moller D.E. Mol. Endocrinol. 1998; 12: 1594-1604Crossref PubMed Scopus (160) Google Scholar) with minor modifications. 198 μl of reaction mixture (100 mm HEPES, 125 mm KF, 0.125% (w/v) CHAPS, 0.05% dry milk, 4 nm human GST-FXR-ligand binding domain, 2 nm anti-GST-Eu3+-cryptate 10 nm biotin-SRC-1 fragment (human SRC-1, amino acids NSPSRLNIQP to VKVKVEKKEQ), and 20 nm SA/XL665 (streptavidin-labeled allophycocyanin)) was added to each by the addition of 2 μl of various of bile acids were at 4 by of a were as the of the at nm to that at nm by a of FXR assay was in a in a of The assay mixture the FXR fusion protein at Amersham protein binding assay Amersham and a FXR V. and Y. S. at 2 nm in an assay of 10 mm mm 10 mm mm 2 mm and 0.05% dry were at 4 for with was in a GST fusion protein was in E. coli strain and using as described previously (21Zhou G. Cummings R. Li Y. Mitra S. Wilkinson H.A. Elbrecht A. Hermes J.D. Schaeffer J.M. Smith R.G. Moller D.E. Mol. Endocrinol. 1998; 12: 1594-1604Crossref PubMed Scopus (160) Google Scholar). human FXR was synthesized using the TnT T7 QuickCoupled transcription/translation kit according to the 2 of protein was with 2 μl of human FXR J. Huang L. Zhao A. Lew J.L. Yu J. Sahoo S. Meinke P.T. Royo I. Pelaez F. Wright S.D. J. Biol. Chem. 2003; 278: 10214-10220Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar) in the of various FXR The mixture was at 4 with in a of CHAPS, 4 mm and bovine serum the end of the the were four with mm mm and 2 mm to a and by for of FXR of HepG2 with various FXR agonists and of nuclear from were as described previously J. Huang L. Zhao A. Lew J.L. Yu J. Sahoo S. Meinke P.T. Royo I. Pelaez F. Wright S.D. J. Biol. Chem. 2003; 278: 10214-10220Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar). 20 of nuclear was by was following the using FXR to and the kit used for were purchased from Amersham Biosciences. FXR were in using the 6 transfection reagent as described previously J. Yu J. Lo J.L. Huang L. Li Y. Schaeffer J.M. Wright S.D. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). FXR transactivation assay using was as described previously J. Huang L. Zhao A. Lew J.L. Yu J. Sahoo S. Meinke P.T. Royo I. Pelaez F. Wright S.D. J. Biol. Chem. 2003; 278: 10214-10220Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar). of with various FXR assays for and β-galactosidase activities were also as described previously J. Yu J. Lo J.L. Huang L. Li Y. Schaeffer J.M. Wright S.D. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). This assay was at Merck and in of HepG2 for were in at a of in DMEM FBS, and mm were with various of for in DMEM and mm RNA and RNA was from HepG2 using the TRIzol reagent according to the transcription and were according to the was with an increased of the of human 18 S RNA was used in the reaction of all of the as an mRNA was to 18 S of human BSEP and Cyp7a mRNA were as of primers and probes for human BSEP and Cyp7a were described previously (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar). and for human 18 S RNA were purchased from Applied Bile in FXR Coactivator Association homogeneous time-resolved FXR coactivator association assay was used to activities of bile acids FXR in a cell-free This assay association of FXR with the coactivator We have previously shown that CDCA is an FXR whereas LCA is an antagonist in this assay (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar). we the activities of other bile acids including CA, DCA, and UDCA FXR. with CDCA activated FXR with a at CA showed partial with a that was of that induced by CDCA, and DCA and UDCA were to in this assay CDCA CA was to their but with Similar to the DCA UDCA had activity in these assays These results indicate that each bile acid results in a different of SRC-1 by FXR. The binding of the of bile acids was by a FXR binding shown in LCA had the binding FXR with an of CDCA to FXR with an of whereas DCA and UDCA had an of and respectively. CA was the the five bile acids with an of The CA and CDCA had a to the bile These suggest that of the agonist activity for DCA and UDCA in the FXR coactivator association assay was to of the binding of FXR CA, a was to activate of bile acids human in a CDCA, but Bile the of FXR and SRC-1 in a GST the results that unique bile acids in different of of SRC-1 by FXR, these bile acids were also in a GST pull-down Similar to the FXR coactivator association assay, the GST pull-down assay interaction of SRC-1 with the FXR in a cell-free with the results in FXR coactivator association assay, CDCA the interaction of SRC-1 with FXR in a with an of and a and by DCA, CA, UDCA, LCA at were in this assay a synthetic FXR also the interaction of SRC-1 with FXR. GW4064 showed a of activity with that of CDCA These results that distinct FXR ligands differentially Bile in FXR with the BSEP the major bile acid in the is activated by FXR an in the BSEP (5Ananthanarayanan M. Balasubramanian N. Makishima M. Mangelsdorf D.J. Suchy F.J. J. Biol. Chem. 2001; 276: 28857-28865Abstract Full Text Full Text PDF PubMed Scopus (656) Google Scholar). The activity of each bile acid was also in FXR transactivation assays using a BSEP promoter-driven luciferase CDCA increased luciferase activity in a with a induction of In the DCA, CA, and UDCA increased luciferase activity by 20-, and 8-fold, and of the CDCA activity DCA, CA, and UDCA also had a that of CDCA DCA, CA, and UDCA act as partial agonists of FXR with Bile in of was previously that FXR agonists strongly induced BSEP expression in HepG2 (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar). In this study, these bile acids were also for their to regulate BSEP expression to their agonist activities FXR to CDCA, which we as a full HepG2 were with each of CDCA, CA, DCA, UDCA, and BSEP mRNA was by real-time PCR with (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar), CDCA strongly induced BSEP expression to 750-fold with an of whereas DCA showed a partial induction to with an of CA in a induction to at and UDCA had the induction of only These indicate that various bile acids different abilities in induction of BSEP expression. Bile in of Cyp7a been that FXR agonists Cyp7a This is to be by the nuclear receptors and Cyp7a binding B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol. Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1514) Google Scholar, 15Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1228) Google Scholar). we the of bile acids for of Cyp7a mRNA to further activities another FXR target. with the in BSEP CDCA was the bile acid in Cyp7a expression with an of 10 DCA, CA, and UDCA also effectively repressed Cyp7a expression but with In UDCA, which was a FXR agonist in other Cyp7a mRNA by at Bile FXR Bile acids increased FXR expression in G. Li H. Forman B.M. S. J. A.K. J. J. S. R. L. K. G. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). We these bile acids and the FXR synthetic agonist GW4064 FXR protein expression in HepG2 Our results indicate that CDCA induced FXR protein expression in a and this induction at In addition to CDCA, the other three bile acids, DCA, CA, and UDCA, also significantly increased FXR protein CDCA was the of FXR protein expression Similar to the results in of Cyp7a mRNA, DCA and UDCA showed a induction of FXR protein expression The synthetic FXR agonist GW4064 also effectively increased FXR protein These indicate that and synthetic FXR agonists effectively FXR protein expression and that the of induction was for and partial agonists of FXR. The induction of FXR by various FXR agonists that this auto-regulatory loop an important in We previously demonstrated that LCA was an FXR antagonist that the FXR BSEP transcription (6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar). In this study, we systematically characterized the other four bile acids in FXR using a series of cell-free and cell-based We showed here that CDCA was the FXR agonist in cell-free assays and effectively expression of BSEP and Cyp7a and also strongly increased FXR protein expression in HepG2 we that DCA, CA, and UDCA were partial FXR agonists in FXR transactivation assays FXR targets in a gene-selective fashion. The three bile acids partially increased BSEP expression but repressed Cyp7a mRNA and increased FXR protein expression with as BSEP is a major bile acid whose in humans results in a that bile and S.A. N. H. E. K. S. V. A.F. A. J. A. G. R.M. Thompson 1998; PubMed Scopus Google Scholar). BSEP is a FXR and FXR agonists strongly BSEP mRNA in human and HepG2 (5Ananthanarayanan M. Balasubramanian N. Makishima M. Mangelsdorf D.J. Suchy F.J. J. Biol. Chem. 2001; 276: 28857-28865Abstract Full Text Full Text PDF PubMed Scopus (656) Google Scholar, 6Yu J. Lo J.L. Huang L. Zhao A. Metzger E. Adams A. Meinke P.T. Wright S.D. Cui J. J. Biol. Chem. 2002; 277: 31441-31447Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar). The and of bile acids in FXR transactivation assays with that in BSEP expression and Cyp7a the first and in the of cholesterol to bile acids. is that bile acid feedback Cyp7a have been to be for this feedback The first the FXR of that in turn the activity of Cyp7a binding a critical of Cyp7a J.Y. Kimmel R. Weinberger C. Stroup D. J. Biol. Chem. 2000; 275: 10918-10924Abstract Full Text Full Text PDF PubMed Scopus (258) Google Scholar, 14Goodwin B. Jones S.A. Price R.R. Watson M.A. McKee D.D. Moore L.B. Galardi C. Wilson J.G. Lewis M.C. Roth M.E. Maloney P.R. Willson T.M. Kliewer S.A. Mol. Cell. 2000; 6: 517-526Abstract Full Text Full Text PDF PubMed Scopus (1514) Google Scholar, 15Lu T.T. Makishima M. Repa J.J. Schoonjans K. Kerr T.A. Auwerx J. Mangelsdorf D.J. Mol. Cell. 2000; 6: 507-515Abstract Full Text Full Text PDF PubMed Scopus (1228) Google Scholar, S. Mol. 2000; PubMed Scopus Google Scholar, M. S. C. Okamoto A.Y. Shan B. S. A. 1999; PubMed Scopus Google Scholar). The of this is by the that Cyp7a expression was in L. D. Y. S. C.S. P. R.A. M. Moore D.D. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, T.A. S. M. K. S. T. Shan B. D.W. M. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). the bile Cyp7a was in L. D. Y. S. C.S. P. R.A. M. Moore D.D. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, T.A. S. M. K. S. T. Shan B. D.W. M. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar), suggesting the existence of other pathways. The other are the receptor X as the bile acid receptor that Cyp7a expression J.L. B. Jones S.A. D. A. Y. C.D. J. Willson T.M. Kliewer S.A. S. A. 2001; PubMed Scopus Google Scholar) and Cyp7a S. P. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). is that the bile acid activities in FXR transactivation and in Cyp7a expression is the of by FXR, is that the bile Cyp7a have been for nuclear receptors such as receptor 1999; PubMed Scopus Google Scholar), acid receptor and acid receptor K. R. R. T. H. S. S. Res. PubMed Scopus Google Scholar), X receptor Y. C. J. Li S. C. Mol. Endocrinol. 2002; PubMed Scopus Google Scholar), and In this study, we demonstrated that all of the bile acids as as the synthetic FXR agonist GW4064 strongly increased FXR protein, the that DCA, CA, and UDCA are partial agonists of FXR. with G. Li H. Forman B.M. S. J. A.K. J. J. S. R. L. K. G. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar) that DCA, CA, increased FXR mRNA in G. Li H. Forman B.M. S. J. A.K. J. J. S. R. L. K. G. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar), that this auto-regulatory loop is at in and is The existence of an FXR loop to of bile acid In conclusion, we have shown that different bile acids have unique properties as FXR from antagonist to partial agonist to full Our here suggest that each of the bile acids with FXR in a unique that to a and for These selective properties of bile acid of FXR FXR in and We and M. for critically the