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Molecular and Cellular Biology
Article . 2009 . Peer-reviewed
License: ASM Journals Non-Commercial TDM
Data sources: Crossref
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Functional Specificities of Brm and Brg-1 Swi/Snf ATPases in the Feedback Regulation of Hepatic Bile Acid Biosynthesis

Authors: Sungsoon Fang; Clay E.S. Comstock; Jongsook Kim Kemper; Ji Young Lee; Ji Miao; Karen E. Knudsen;

Functional Specificities of Brm and Brg-1 Swi/Snf ATPases in the Feedback Regulation of Hepatic Bile Acid Biosynthesis

Abstract

Bile acid homeostasis is critical in maintaining health and is primarily regulated by the nuclear receptors farnesoid X receptor (FXR) and small heterodimer partner (SHP). Bile acid-activated FXR indirectly inhibits expression of cholesterol 7alpha hydroxylase (CYP7A1), a key enzyme in conversion of cholesterol to bile acids, by induction of SHP. We recently demonstrated that SHP inhibits CYP7A1 transcription by recruiting chromatin-modifying cofactors, including Brm-Swi/Snf. Swi/Snf complexes contain either Brm or Brg-1 ATPases, and whether these subunits have distinct functions remains unclear. We have examined the role of these subunits in regulation of bile acid metabolism under physiological conditions by FXR and SHP. Brg-1 interacted with FXR and enhanced FXR-mediated transactivation of SHP, whereas Brm interacted with SHP and enhanced SHP-mediated repression of CYP7A1 and, interestingly, auto-repression of SHP. Chromatin immunoprecipitation and remodeling studies revealed that after treatment with FXR agonists, Brg-1 was recruited to the SHP promoter, resulting in transcriptionally active accessible chromatin, whereas Brm was recruited to both CYP7A1 and SHP promoters, resulting in inactive inaccessible chromatin. Our studies demonstrate that Brm and Brg-1 have distinct functions in the regulation of two key genes, CYP7A1 and SHP, within a single physiological pathway, feedback inhibition of bile acid biosynthesis, by differentially targeting SHP and FXR.

Keywords

Feedback, Physiological, Transcriptional Activation, DNA Helicases, Down-Regulation, Nuclear Proteins, Receptors, Cytoplasmic and Nuclear, Ligands, Cell Line, Substrate Specificity, Bile Acids and Salts, Mice, Liver, Animals, Humans, Cholesterol 7-alpha-Hydroxylase, Protein Binding, Transcription Factors

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citations
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
40
Top 10%
Top 10%
Top 10%
bronze