Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10749715 | Biochemical and Biophysical Research Communications | 2016 | 7 Pages |
Abstract
Liver X Receptors (LXRs) are sterol-activated transcription factors that play major roles in cellular cholesterol homeostasis, HDL biogenesis and reverse cholesterol transport. The aim of the present study was to investigate the mechanisms that control the expression of the human LXRα gene in hepatic cells. A series of reporter plasmids containing consecutive 5â² deletions of the hLXRα promoter upstream of the luciferase gene were constructed and the activity of each construct was measured in HepG2 cells. This analysis showed that the activity of the human LXRα promoter was significantly reduced by deleting the â111 to â42 region suggesting the presence of positive regulatory elements in this short proximal fragment. Bioinformatics data including motif search and ChIP-Seq revealed the presence of a potential binding motif for Hepatocyte Nuclear Factor 4 α (HNF-4α) in this area. Overexpression of HNF-4α in HEK 293T cells increased the expression of all LXRα promoter constructs except â42/+384. In line, silencing the expression of endogenous HNF-4α in HepG2 cells was associated with reduced LXRα protein levels and reduced activity of the â111/+384 LXRα promoter but not of the â42/+384 promoter. Using ChiP assays in HepG2 cells combined with DNAP assays we mapped the novel HNF-4α specific binding motif (H4-SBM) in the â50 to â40 region of the human LXRα promoter. A triple mutation in this H4-SBM abolished HNF-4α binding and reduced the activity of the promoter to 65% relative to the wild type. Furthermore, the mutant promoter could not be transactivated by HNF-4α. In conclusion, our data indicate that HNF-4α may have a wider role in cell and plasma cholesterol homeostasis by controlling the expression of LXRα in hepatic cells.
Keywords
HDLHNF-4αHNF-4LXRRCTHRELXRsDNAPPPARABCA1SREBP-1cChIP-SeqshRNAshort interfering RNAshort hairpin RNAsiRNAOxysterolschromatin immunoprecipitationGene regulationHepatocyte nuclear factor 4Hormone response elementSterol regulatory element binding protein 1cCHiPreverse cholesterol transportperoxisome proliferator-activated receptorLiver X receptorsNuclear receptor
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Authors
Dimitris Theofilatos, Aristomenis Anestis, Koshi Hashimoto, Dimitris Kardassis,