TitleThe role of liver X receptor-alpha in the fatty acid regulation of hepatic gene expression.
Publication TypeJournal Article
Year of Publication2003
AuthorsPawar, A, Botolin, D, Mangelsdorf, DJ, Jump, DB
JournalJ Biol Chem
Volume278
Issue42
Pagination40736-43
Date Published2003 Oct 17
ISSN0021-9258
KeywordsAnimals, Blotting, Northern, Blotting, Western, CCAAT-Enhancer-Binding Proteins, Cell Line, Cells, Cultured, Chloramphenicol O-Acetyltransferase, DNA-Binding Proteins, Dose-Response Relationship, Drug, Eicosapentaenoic Acid, Fatty Acid Synthases, Fatty Acids, Fish Oils, Gene Expression Regulation, Genes, Reporter, Hepatocytes, Liver, Liver X Receptors, Male, Orphan Nuclear Receptors, Plasmids, Pyruvate Kinase, Rats, Rats, Sprague-Dawley, Receptors, Cytoplasmic and Nuclear, RNA, RNA, Messenger, Sterol Regulatory Element Binding Protein 1, Transcription Factors, Transfection
Abstract
 

Liver X receptors (LXR) alpha and beta play an important role in regulating the expression of genes involved in hepatic bile and fatty acid synthesis, glucose metabolism, as well as sterol efflux. Studies with human embryonic kidney 293 cells indicate that unsaturated fatty acids interfere with oxysterols binding to LXR and antagonize oxysterol-induced LXRalpha activity. In this report, we evaluated the effects of unsaturated fatty acids on LXR-regulated hepatic gene expression. The LXR agonist, T1317, induced mRNAs encoding sterol regulatory element-binding protein 1c (SREBP-1c) and two SREBP-1c-regulated lipogenic genes, e.g. fatty-acid synthase and the S14 protein in primary hepatocytes. Treatment of hepatocytes with eicosapentaenoic acid (20:5n-3) suppressed these mRNAs in the absence and presence of T1317. The cis-regulatory elements targeted by T1317 were not required for fatty-acid suppression of FAS or S14 promoter activity. In contrast to SREBP-1-regulated lipogenic genes, 20:5n-3 had no effect on the T1317 induction of ABCG5 or ABCG8 in the rat hepatoma cell line, FTO-2B. These two genes require LXR but not SREBP-1c for their expression. Feeding rats a diet supplemented with fish oil suppressed hepatic SREBP-1c-regulated genes and induced PPARalpha-regulated genes but had no effect on the LXR-regulated transcripts, CYP7A1, ABCG5, or ABCG8. Transfection studies, using either full-length hLXRalpha or a chimera containing only the LXRalpha ligand binding domain, indicate that a wide array of unsaturated fatty acids had little effect on LXRalpha activity in primary hepatocytes or FTO-2B. These studies suggest that LXRalpha is not a target for unsaturated fatty acid regulation in primary rat hepatocytes or in liver. Thus, oxysterol/LXR-mediated regulation of transcripts involved in bile acid synthesis or sterol efflux appear insensitive to dietary unsaturated fatty acids. The unsaturated fatty acid suppression of SREBP-1 and its targeted lipogenic genes is independent of LXRalpha

DOI10.1074/jbc.M307973200
Alternate JournalJ. Biol. Chem.
PubMed ID12917410
Grant ListR01 DK043220 / DK / NIDDK NIH HHS / United States
DK43220 / DK / NIDDK NIH HHS / United States