scholarly journals Restoration of sterol-regulatory-element-binding protein-1c gene expression in HepG2 cells by peroxisome-proliferator-activated receptor-γ co-activator-1α

2004 ◽  
Vol 381 (2) ◽  
pp. 357-363 ◽  
Author(s):  
Hannes OBERKOFLER ◽  
Elisabeth SCHRAML ◽  
Franz KREMPLER ◽  
Wolfgang PATSCH
Keyword(s):  
Gene Expression ◽  
Cell Lines ◽  
Hepg2 Cells ◽  
Binding Protein ◽  
Regulatory Element ◽  
Brown Adipocyte ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Element Binding Protein ◽  
Sterol Regulatory Element

The expression of SREBP-1 (sterol-regulatory-element-binding protein-1) isoforms differs between tissues and cultured cell lines in that SREBP-1a is the major isoform in established cell lines, whereas SREBP-1c predominates in liver and most other human tissues. SREBP-1c is transcriptionally less active than SREBP-1a, but is a main mediator of hepatic insulin action and is selectively up-regulated by LXR (liver X receptor) agonists. LXR-mediated transactivation is co-activated by PGC-1α (peroxisome-proliferator-activated receptor-γ co-activator-1α), which displays deficient expression in skeletal-muscle-derived cell lines. In the present paper, we show that PGC-1α expression is also deficient in HepG2 cells and in a human brown adipocyte cell line (PAZ6). In transient transfection studies, PGC-1α selectively amplified the LXR-mediated transcription from the human SREBP-1c promoter in HepG2 and PAZ6 cells via two LXR-response elements with extensive similarity to the respective murine sequence. Mutational analysis showed that the human LXR-response element-1 (hLXRE-1) was essential for co-activation of LXR-mediated SREBP-1c gene transcription by PGC-1α. Ectopic overexpression of PGC-1α in HepG2 cells enhanced basal SREBP-1c and, to a lesser extent, -1a mRNA expression, but only SREBP-1c expression was augmented further in an LXR/RXR (retinoic X receptor)-dependent fashion, thereby inducing mRNA abundance levels of SREBP-1c target genes, fatty acid synthase and acetyl-CoA carboxylase. These results indicate that PGC-1α contributes to the regulation of SREBP-1 gene expression, and can restore the SREBP-1 isoform expression pattern of HepG2 cells to that of human liver.

scholarly journals Effects of fatty acids on gene expression: role of peroxisome proliferator-activated receptor α, liver X receptor α and sterol regulatory element-binding protein-1c

2002 ◽  
Vol 61 (3) ◽  
pp. 371-374 ◽  
Author(s):  
Sander Kersten
Keyword(s):  
Fatty Acids ◽  
Binding Protein ◽  
Regulatory Element ◽  
Liver X Receptor ◽  
Dietary Fatty Acids ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Liver X Receptor Α ◽  
Element Binding Protein ◽  
Sterol Regulatory Element

Dietary fatty acids have numerous effects on cellular function, many of which are achieved by altering the expression of genes. The present paper reviews recent data on the mechanisms by which fatty acids influence DNA transcription, and focus specifically on the importance of three transcription factors: peroxisome proliferator-activated receptor α; liver X receptor α; sterol regulatory element-binding protein 1c. These data indicate that fatty acids induce or inhibit the mRNA expression of a variety of different genes by acting both as agonists and as antagonists for nuclear hormone receptors.

scholarly journals Functional Interaction of Hepatic Nuclear Factor-4 and Peroxisome Proliferator-Activated Receptor-γ Coactivator 1α in CYP7A1 Regulation Is Inhibited by a Key Lipogenic Activator, Sterol Regulatory Element-Binding Protein-1c

2007 ◽  
Vol 21 (11) ◽  
pp. 2698-2712 ◽  
Author(s):  
Bhaskar Ponugoti ◽  
Sungsoon Fang ◽  
Jongsook Kim Kemper
Keyword(s):  
Binding Protein ◽  
Regulatory Element ◽  
Dominant Negative Mutant ◽  
Peroxisome Proliferator ◽  
Nuclear Factor ◽  
Functional Interaction ◽  
Peroxisome Proliferator Activated Receptor ◽  
Histone Deacetylase 2 ◽  
Element Binding Protein ◽  
Sterol Regulatory Element

Abstract Insulin inhibits transcription of cholesterol 7α-hydroxylase (Cyp7a1), a key gene in bile acid synthesis, and the hepatic nuclear factor-4 (HNF-4) site in the promoter was identified as a negative insulin response sequence. Using a fasting/feeding protocol in mice and insulin treatment in HepG2 cells, we explored the inhibition mechanisms. Expression of sterol regulatory element-binding protein-1c (SREBP-1c), an insulin-induced lipogenic factor, inversely correlated with Cyp7a1 expression in mouse liver. Interaction of HNF-4 with its coactivator, peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), was observed in livers of fasted mice and was reduced after feeding. Conversely, HNF-4 interaction with SREBP-1c was increased after feeding. In vitro studies suggested that SREBP-1c competed with PGC-1α for direct interaction with the AF2 domain of HNF-4. Reporter assays showed that SREBP-1c, but not of a SREBP-1c mutant lacking the HNF-4 interacting domain, inhibited HNF-4/PGC-1α transactivation of Cyp7a1. SREBP-1c also inhibited PGC-1α-coactivation of estrogen receptor, constitutive androstane receptor, pregnane X receptor, and farnesoid X receptor, implying inhibition of HNF-4 by SREBP-1c could extend to other nuclear receptors. In chromatin immunoprecipitation studies, HNF-4 binding to the promoter was not altered, but PGC-1α was dissociated, SREBP-1c and histone deacetylase-2 (HDAC2) were recruited, and acetylation of histone H3 was decreased upon feeding. Adenovirus-mediated expression of a SREBP-1c dominant-negative mutant, which blocks the interaction of SREBP-1c and HNF-4, partially but significantly reversed the inhibition of Cyp7a1 after feeding. Our data show that SREBP-1c functions as a non-DNA-binding inhibitor and mediates, in part, suppression of Cyp7a1 by blocking functional interaction of HNF-4 and PGC-1α. This mechanism may be relevant to known repression of many other HNF-4 target genes upon feeding.

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