Dataset Information
Human FXR regulates SHP expression through direct binding to an LRH-1 binding site, independent of an IR-1 and LRH-1.
Ontology highlight
ABSTRACT: Background
Farnesoid X receptor/retinoid X receptor-alpha (FXR/RXR?) is the master transcriptional regulator of bile salt synthesis and transport in liver and intestine. FXR is activated by bile acids, RXR? by the vitamin A-derivative 9-cis retinoic acid (9cRA). Remarkably, 9cRA inhibits binding of FXR/RXR? to its response element, an inverted repeat-1 (IR-1). Still, most FXR/RXR? target genes are maximally expressed in the presence of both ligands, including the small heterodimer partner (SHP). Here, we revisited the FXR/RXR?-mediated regulation of human SHP.Methods
A 579-bp hSHP promoter element was analyzed to locate FXR/chenodeoxycholic acid (CDCA)- and RXR?/9cRA-responsive elements. hSHP promoter constructs were analyzed in FXR/RXR?-transfected DLD-1, HEK293 and HepG2 cells exposed to CDCA, GW4064 (synthetic FXR ligand) and/or 9cRA. FXR-DNA interactions were analyzed by in vitro pull down assays.Results
hSHP promoter elements lacking the previously identified IR-1 (-291/-279) largely maintained their activation by FXR/CDCA, but were unresponsive to 9cRA. FXR-mediated activation of the hSHP promoter was primarily dependent on the -122/-69 region. Pull down assays revealed a direct binding of FXR to the -122/-69 sequence, which was abrogated by site-specific mutations in a binding site for the liver receptor homolog-1 (LRH-1) at -78/-70. These mutations strongly impaired the FXR/CDCA-mediated activation, even in the context of a hSHP promoter containing the IR-1. LRH-1 did not increase FXR/RXR?-mediated activation of hSHP promoter activity.Conclusion
FXR/CDCA-activated expression of SHP is primarily mediated through direct binding to an LRH-1 binding site, which is not modulated by LRH-1 and unresponsive to 9cRA. 9cRA-induced expression of SHP requires the IR-1 that overlaps with a direct repeat-2 (DR-2) and DR-4. This establishes for the first time a co-stimulatory, but independent, action of FXR and RXR? agonists.
SUBMITTER: Hoeke MO
PROVIDER: S-EPMC3912179 | biostudies-literature | 2014
REPOSITORIES: biostudies-literature
Publications
Human FXR regulates SHP expression through direct binding to an LRH-1 binding site, independent of an IR-1 and LRH-1.
PloS one 20140203 2
<h4>Background</h4>Farnesoid X receptor/retinoid X receptor-alpha (FXR/RXRα) is the master transcriptional regulator of bile salt synthesis and transport in liver and intestine. FXR is activated by bile acids, RXRα by the vitamin A-derivative 9-cis retinoic acid (9cRA). Remarkably, 9cRA inhibits binding of FXR/RXRα to its response element, an inverted repeat-1 (IR-1). Still, most FXR/RXRα target genes are maximally expressed in the presence of both ligands, including the small heterodimer partne ...[more]
