University of ZurichZurich Open Repository and Archive

Winterthurerstr. 190

CH-8057 Zurich

http://www.zora.uzh.ch

Year: 2009

Nuclear receptor regulation of bile acid transporters

Kullak-Ublick, G A; Eloranta, J J

Kullak-Ublick, G A; Eloranta, J J (2009). Nuclear receptor regulation of bile acid transporters. In: Keppler, D;Beuers, U; Steihl, A; Trauner, M. Bile Acid Biology and Therapeutic Actions. Berlin, 111-114.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:Keppler, D; Beuers, U; Steihl, A; Trauner, M 2009. Bile Acid Biology and Therapeutic Actions. Berlin, 111-114.

Kullak-Ublick, G A; Eloranta, J J (2009). Nuclear receptor regulation of bile acid transporters. In: Keppler, D;Beuers, U; Steihl, A; Trauner, M. Bile Acid Biology and Therapeutic Actions. Berlin, 111-114.Postprint available at:http://www.zora.uzh.ch

Posted at the Zurich Open Repository and Archive, University of Zurich.http://www.zora.uzh.ch

Originally published at:Keppler, D; Beuers, U; Steihl, A; Trauner, M 2009. Bile Acid Biology and Therapeutic Actions. Berlin, 111-114.

Falk Symposium 165

XX International Bile Acid Meeting

Amsterdam, June 13-14, 2008

Nuclear receptor regulation of bile acid transporters

GERD A. KULLAK-UBLICK and JYRKI J. ELORANTA

Correspondence:

Gerd A. Kullak-Ublick, M.D.

Division of Clinical Pharmacology and Toxicology

Department of Internal Medicine

University Hospital Zurich

Rämistrasse 100

CH-8091 Zurich, Switzerland

(E-mail: gerd.kullak@usz.ch)

(Telephone: + 41 1 255 2068)

(Fax: + 41 1 255 4411)

1

The enterohepatic circulation of bile acids is maintained by the active transport of bile acids across

the apical and basolateral plasma membrane domains of intestinal enterocytes and hepatocytes.

Uptake of bile acids from sinusoidal blood into hepatocytes is mediated by the Na+-taurocholate

cotransporting polypeptide NTCP (SLC10A1), as well as by sodium-independent uptake transporters

from the family of organic anion transporting polypeptides (OATPs). OATP1B1 and OATP1B3 are

expressed almost exclusively in hepatocytes, whereas OATP2B1 and OATP1A2 exhibit a wide

tissue distribution (1). Uptake of bile acids from the intestinal lumen into enterocytes is mediated by

the apical sodium-dependent bile acid transporter ASBT (SLC10A2). At the basolateral membrane,

bile acids are effluxed into portal blood by the heterodimeric organic solute transporters alpha and

beta (OSTα / OSTβ).

The expression level of bile acid transporters is regulated in part by direct or indirect effects of

bile acids on the transcription of the corresponding genes. The transcriptional effects of bile acids

are mediated largely by the nuclear bile acid receptor FXR (NR1H4 gene in humans). The

endogenous ligands of FXR include bile acids, with CDCA being the more potent ligand than CA (2-

4), as well as the oxysterol 22(R)-hydroxycholesterol (5) and androsterone (6). Naturally occurring

exogenous ligands include stigmasterol, a soy lipid-derived phytosterol that appears to function as

an antagonist of FXR activity, thereby possibly contributing to the cholestasis associated with

neonatal parenteral nutrition (7), as well as cafestol, a diterpenic compound found in coffee beans

and in unfiltered coffee that functions as an FXR agonist (8). Synthetic FXR ligands include GW4064

and the semi-synthetic bile acid derivative 6-ethyl chenodeoxycholic acid (9). In accordance with its

function as the bile acid receptor, FXR is most abundantly expressed in the tissues commonly

exposed to bile acids: liver, intestine, and kidneys. The preferred DNA-binding sequence for FXR

within its target promoters is the so-called "inverted repeat-1" motif (IR-1, inverted hexameric repeat

separated by one base pair) (10), to which FXR binds as a heterodimer with another nuclear

receptor, namely the retinoid X receptor (RXR).

Bile acid transporters that are directly transactivated by FXR include OATP1B3 (SLCO1B3) at

the basolateral membrane of hepatocytes (11), and the bile salt efflux pump BSEP (ABCB11), the

2

multidrug resistance protein MRP2 (ABCC2) and the multidrug resistance gene product MDR3

(ABCB4) at the canalicular membrane (12). In the intestine, the heterodimeric transporter OSTα /

OSTβ is activated by FXR (13). FXR can also lead to inhibition of bile acid transporter gene

expression, usually this involves activation of the transcriptional repressor protein short heterodimer

partner (SHP). Target genes of FXR mediated repression include NTCP (SLC10A1) and OATP1B1

(SLCO1B1) in hepatocytes, and ASBT (SLC10A2) in the intestine.

In the case of NTCP and ASBT, the mechanism of bile acid / FXR mediated gene suppression have

been recently elucidated. Both genes, SLC10A1 and SLC10A2, are activated by the glucocorticoid

receptor, GR (14, 15). Bile acid activated FXR induces the transcriptional repressor SHP, which

negatively interacts with the GR, thereby reducing GR-mediated activation of gene transcription. The

negative interaction of SHP with nuclear receptors has also been found in the context of the

hepatocyte nuclear factor HNF-4α. HNF-4α directly binds to and activates the promoter regions of

the genes coding for the organic cation transporter OCT1 (SLC22A1) and the organic anion

transporter OAT2 (SLC22A7) (16). Bile acid-induced SHP inhibits the activation of the reporter-

linked hOCT1 and hOAT2 promoters by HNF-4α (17, 18) and thus decreases endogenous

expression of OCT1 and OAT2. Another gene that is regulated by HNF-4α is the hepatocyte nuclear

factor HNF-1α. HNF-1α binds to and activates the transcription of the SLCO1B1 gene, thereby

maintaining a high level of OATP1B1 expression in the liver (19). Bile acid activated SHP reduces

HNF-4α regulated HNF-1α expression, thereby indirectly also reducing OATP1B1 expression (20).

Since OATP1B1 transports not only bile acids, but also a variety of drugs, decreased OATP1B1

expression in conditions associated with elevated intracellular bile acid levels is bound to affect the

hepatic uptake and thus the pharmacokinetics of OATP1B1 substrates such as simvastatin (21).

In an analogous manner to the SLCO1B3 gene, expression of the OSTα / OSTβ heterodimeric bile

acid efflux system is induced by bile acids through direct binding of FXR-RXR heterodimers to the

two human OST promoters (13, 22). In addition to established cell lines, both OSTα and OSTβ gene

expression can be induced by bile acids in short-term tissue culture of human ileal biopsies. Further

physiological evidence in support of the induction of OST gene expression by bile acids is provided

3

by a study showing that both mRNA and protein levels of OSTα and OSTβ are increased in

cholestatic liver tissue of patients suffering from primary biliary cirrhosis (23). Furthermore, reduced

expression of FXR correlates with decreased expression of OSTα / OSTβ in the ileum of female

non-obese gallstone patients (24).

The Familial Intrahepatic Cholestasis-1 (FIC1) protein, encoded by the ATP8B1 gene, is expressed

at the liver canalicular membrane and at the apical membrane of enterocytes, in addition to many

other tissues (25). FIC1 acts as an aminophospholipid flippase, translocating phosphatidylserine

from the outer leaflet of the lipid bilayer of the plasma membranes. Genetic variants in the ATP8B1

gene have been associated with familial intrahepatic cholestasis, characterized by low γ-

glutamyltranspeptidase plasma levels. In PFIC1 patients, decreased hepatic and intestinal mRNA

levels of FXR and of genes transactivated by FXR have been found (26, 27). FIC1 may influence the

expression and/or function of FXR, perhaps contributing to the pathogenesis of the liver disease. In

a recent report, it was shown that whereas the wild-type FIC1 was capable of potent activation of the

BSEP promoter, the PFIC1-associated FIC1 variants were inactive, and the BRIC1-associated FIC1

variants activated the BSEP promoter to only a moderate degree (28). The authors hypothesized

that the wild-type FIC1 protein induces nuclear localization of FXR through stimulation of a

phosphorylation cascade targeting FXR, and that FIC1-related disease may be caused by the

compromised ability of the associated FIC1 variants to influence FXR localization and function.

In summary, bile acids are capable of regulating the expression of transporters that mediate the

enterohepatic circulation of both bile acids and drugs via complex feedforward and feedback

mechanisms. A key signalling molecule in these transcriptional circuits is the nuclear bile acid

receptor FXR, which binds to defined response elements and thus activates transcription of target

genes in the presence of FXR ligands, or represses gene transcription through the action of the

repressor SHP, which negatively interacts with key transcriptional activators such as HNF-4α or the

glucocorticoid receptor.

4

References

1. Kullak-Ublick GA, Stieger B, Meier PJ. Enterohepatic bile salt transporters in normal physiology

and liver disease. Gastroenterology 2004; 126: 322-42.

2. Lew JL, Zhao A, Yu J, Huang L, De Pedro N, Pelaez F, Wright SD, Cui J. The farnesoid X

receptor controls gene expression in a ligand- and promoter-selective fashion. J Biol Chem 2004;

279: 8856-8861.

3. Makishima M, Okamoto AY, Repa JJ, Tu H, Learned RM, Luk A, Hull MV, Lustig KD,

Mangelsdorf DJ, Shan B. Identification of a nuclear receptor for bile acids. Science 1999; 284:

1362-1365.

4. Parks DJ, Blanchard SG, Bledsoe RK, Chandra G, Consler TG, Kliewer SA, Stimmel JB, Willson

TM, Zavacki AM, Moore DD, Lehmann JM. Bile acids: natural ligands for an orphan nuclear

receptor. Science 1999; 284: 1365-1368.

5. Deng R, Yang D, Yang J, Yan B. Oxysterol 22(R)-hydroxycholesterol induces the expression of

the bile salt export pump through nuclear receptor farsenoid X receptor but not liver X receptor. J

Pharmacol Exp Ther 2006; 317: 317-325.

6. Wang S, Lai K, Moy FJ, Bhat A, Hartman HB, Evans MJ. The nuclear hormone receptor

farnesoid X receptor (FXR) is activated by androsterone. Endocrinology 2006; 147: 4025-4033.

7. Carter BA, Taylor OA, Prendergast DR, Zimmerman TL, Von Furstenberg R, Moore DD, Karpen

SJ. Stigmasterol, a soy lipid-derived phytosterol, is an antagonist of the bile acid nuclear receptor

FXR. Pediatr Res 2007; 62: 301-306.

8. Ricketts ML, Boekschoten MV, Kreeft AJ, Hooiveld GJ, Moen CJ, Muller M, Frants RR,

Kasanmoentalib S, Post SM, Princen HM, Porter JG, Katan MB, Hofker MH, Moore DD. The

cholesterol-raising factor from coffee beans, cafestol, as an agonist ligand for the farnesoid and

pregnane X receptors. Mol Endocrinol 2007; 21: 1603-1616.

9. Fiorucci S, Antonelli E, Rizzo G, Renga B, Mencarelli A, Riccardi L, Orlandi S, Pellicciari R,

Morelli A. The nuclear receptor SHP mediates inhibition of hepatic stellate cells by FXR and

protects against liver fibrosis. Gastroenterology 2004; 127: 1497-1512.

10. Laffitte BA, Kast HR, Nguyen CM, Zavacki AM, Moore DD, Edwards PA. Identification of the

DNA binding specificity and potential target genes for the farnesoid X-activated receptor. J Biol

Chem 2000; 275: 10638-10647.

5

11. Jung D, Podvinec M, Meyer UA, Mangelsdorf DJ, Fried M, Meier PJ, Kullak-Ublick GA. Human

organic anion transporting polypeptide 8 promoter is transactivated by the farnesoid X

receptor/bile acid receptor. Gastroenterology 2002; 122: 1954-1966.

12. Eloranta JJ, Kullak-Ublick GA. Coordinate transcriptional regulation of bile acid homeostasis and

drug metabolism. Arch Biochem Biophys 2005; 433: 397-412.

13. Landrier JF, Eloranta JJ, Vavricka SR, Kullak-Ublick GA. The nuclear receptor for bile acids,

FXR, transactivates human organic solute transporter-alpha and -beta genes. Am J Physiol

Gastrointest Liver Physiol 2006; 290: G476-G485.

14. Jung D, Fantin AC, Scheurer U, Fried M, Kullak-Ublick GA. Human ileal bile acid transporter

gene ASBT (SLC10A2) is transactivated by the glucocorticoid receptor. Gut 2004; 53: 78-84.

15. Eloranta JJ, Jung D, Kullak-Ublick GA. The human Na+-taurocholate cotransporting polypeptide

gene is activated by glucocorticoid receptor and peroxisome proliferator-activated receptor-

gamma coactivator-1alpha, and suppressed by bile acids via a small heterodimer partner-

dependent mechanism. Mol Endocrinol 2006; 20: 65-79.

16. Zaïr ZM, Eloranta JJ, Stieger B, Kullak-Ublick GA. Pharmacogenetics of OATP (SLC21/SLCO),

OAT and OCT (SLC22) and PEPT (SLC15) transporters in the intestine, liver and kidney.

Pharmacogenomics 2008; 9: 597-624.

17. Saborowski M, Kullak-Ublick GA, Eloranta JJ. The human organic cation transporter-1 gene is

transactivated by hepatocyte nuclear factor-4alpha. J Pharmacol Exp Ther 2006; 317: 778-85.

18. Popowski K, Eloranta JJ, Saborowski M, Fried M, Meier PJ, Kullak-Ublick GA. The human

organic anion transporter 2 gene is transactivated by hepatocyte nuclear factor-4 alpha and

suppressed by bile acids. Mol Pharmacol 2005; 67: 1629-1638.

19. Jung D, Hagenbuch B, Gresh L, Pontoglio M, Meier PJ, Kullak-Ublick GA. Characterization of the

human OATP-C (SLC21A6) gene promoter and regulation of liver-specific OATP genes by

hepatocyte nuclear factor 1 alpha. J Biol Chem 2001; 276: 37206-37214.

20. Jung D, Kullak-Ublick GA. Hepatocyte nuclear factor 1 alpha: a key mediator of the effect of bile

acids on gene expression. Hepatology 2003; 37: 622-631.

21. The SEARCH Collaborative Group. SLCO1B1 variants and statin-induced myopathy – a

genomewide study. N Engl J Med 2008; 359: 1-11.

6

7

22. Lee H, Zhang Y, Lee FY, Nelson SF, Gonzalez FJ, Edwards PA. FXR regulates organic solute

transporters alpha and beta in the adrenal gland, kidney, and intestine. J Lipid Res 2006; 47:

201-214.

23. Boyer JL, Trauner M, Mennone A, Soroka CJ, Cai SY, Moustafa T, et al. Upregulation of a

basolateral FXR-dependent bile acid efflux transporter OSTalpha-OSTbeta in cholestasis in

humans and rodents. Am J Physiol Gastrointest Liver Physiol 2006; 290: G1124-G1130.

24. Renner O, Harsch S, Strohmeyer A, Schimmel S, Stange EF. Reduced ileal expression of

organic solute transporter alpha and beta (OSTalpha -OSTbeta ) in non-obese gallstone disease.

J Lipid Res 2008;

25. Ujhazy P, Ortiz D, Misra S, Li S, Moseley J, Jones H, Arias IM. Familial intrahepatic cholestasis

1: studies of localization and function. Hepatology 2001; 34: 768-775.

26. Alvarez L, Jara P, Sanchez-Sabate E, Hierro L, Larrauri J, Diaz MC, Camarena C, De la Vega A,

Frauca E, Lopez-Collazo E, Lapunzina P. Reduced hepatic expression of farnesoid X receptor in

hereditary cholestasis associated to mutation in ATP8B1. Hum Mol Genet 2004; 13: 2451-2460.

27. Chen F, Ananthanarayanan M, Emre S, Neimark E, Bull LN, Knisely AS, Strautnieks SS,

Thompson RJ, Magid MS, Gordon R, Balasubramanian N, Suchy FJ, Shneider BL. Progressive

familial intrahepatic cholestasis, type 1, is associated with decreased farnesoid X receptor

activity. Gastroenterology 2004; 126: 756-764.

28. Frankenberg T, Miloh T, Chen FY, Ananthanarayanan M, Sun AQ, Balasubramaniyan N, Arias I,

Setchell KD, Suchy FJ, Shneider BL. The membrane protein ATPase class I type 8B member 1

signals through protein kinase C zeta to activate the farnesoid X receptor. Hepatology 2008;