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This version published online on March 6, 2008
Molecular Endocrinology, doi:10.1210/me.2007-0565
A more recent version of this article appeared on June 1, 2008
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Submitted on December 18, 2007
Accepted on February 25, 2008

Liver Receptor Homolog-1 Regulates Bile Acid Homeostasis But Is Not Essential for Feedback Regulation of Bile Acid Synthesis

Youn-Kyoung Lee, Daniel R. Schmidt, Carolyn L. Cummins, Mihwa Choi, Li Peng, Yuan Zhang, Bryan Goodwin, Robert E. Hammer, David J. Mangelsdorf, and Steven A. Kliewer*

Departments of Molecular Biology, Pharmacology, and Biochemistry, and the Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390; and GlaxoSmithKline Research and Development, Research Triangle Park, North Carolina 27709

* To whom correspondence should be addressed. E-mail: steven.kliewer{at}utsouthwestern.edu.

Liver receptor homolog 1 (LRH-1), an orphan nuclear receptor, is highly expressed in liver and intestine, where it is implicated in the regulation of cholesterol, bile acid, and steroid hormone homeostasis. Among the proposed LRH-1 target genes in liver are those encoding cholesterol 7{alpha}-hydroxylase (CYP7A1) and sterol 12{alpha}-hydroxylase (CYP8B1), which catalyze key steps in bile acid synthesis. In vitro studies suggest that LRH-1 may be involved both in stimulating basal CYP7A1 and CYP8B1 transcription and in repressing their expression as part of the nuclear bile acid receptor (FXR)-small heterodimer partner (SHP) signaling cascade, which culminates in SHP binding to LRH-1 to repress gene transcription. However, in vivo analysis of LRH-1 actions has been hampered by the embryonic lethality of Lrh-1 knockout mice. To overcome this obstacle, mice were generated in which Lrh-1 was selectively disrupted in either hepatocytes or intestinal epithelium. LRH-1 deficiency in either tissue changed mRNA levels of genes involved in cholesterol and bile acid homeostasis. Surprisingly, LRH-1 deficiency in hepatocytes had no significant effect on basal Cyp7a1 expression or its repression by FXR. While Cyp8b1 repression by FXR was also intact in mice deficient for LRH-1 in hepatocytes, basal CYP8B1 mRNA levels were significantly decreased, and there were corresponding changes in the composition of the bile acid pool. Taken together, these data reveal a broad role for LRH-1 in regulating bile acid homeostasis but demonstrate that LRH-1 is either not involved in the feedback regulation of bile acid synthesis or is compensated for by other factors.


Key words: nuclear receptor • bile acids • cholesterol 7{alpha}-hydroxylase • sterol 12{alpha}-hydroxylase • knockout mice

NURSA Molecule Pages Link:

Nuclear Receptors:   SHP  |  LRH-1
Ligands:   GW4064






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