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Developmental extinction of liver lipoprotein lipase mRNA expression might be regulated by an NF-1-like site
K Schoonjans1, B Staels, P Devos
1Laboratoire de Biologie des Régulations chez les Eucaryotes, UMR 134, CNRS, Nice, France.
Abstract:
The molecular mechanism underlying the extinction of lipoprotein lipase (LPL) expression in rat liver during development was investigated. A mouse (BWTG3) and a rat (7777) hepatoma, both of which exhibit characteristics of fetal hepatocytes, were found to contain LPL mRNA, whereas the more differentiated human (Hep G2 and Hep 3B) or rat (Fa32) hepatoma cell lines did not. Somatic cell hybrids between LPL-producing hepatoma cells and non-LPL-producing cells, such as adult rat hepatocytes or fibroblasts, exhibited extinction of LPL gene expression. Assay of expression of nested deletions in the 5' regulatory sequences of the LPL gene in the Hep G2 cell line and in BWTG3 cells localized sequences involved in the suppression of LPL production to a region between -591 and -288 relative to the transcription initiation site. A site with sequence homology to a glucocorticoid responsive element (GRE) was shown not to play an important role in the extinction process. A novel transcription factor, termed RF-1-LPL, was shown to bind to an NF-1-like site in this region. In contrast to neonatal animals, in adult animals an additional protein complex (RF-2-LPL), was formed on the NF-1-like site, suggesting that this sequence might recruit a trans-acting factor involved in the extinction of LPL gene expression in adult rat liver.
Insights
Lipoprotein lipase (LPL) gene expression is silenced during rat liver development. This extinction is linked to a specific DNA region and involves a novel transcription factor, RF-1-LPL, and an additional protein complex in adults.
Area of Science:
- Molecular Biology
- Developmental Biology
- Gene Regulation
Background:
- Lipoprotein lipase (LPL) plays a crucial role in lipid metabolism.
- LPL expression is downregulated in the liver during rodent development.
- Understanding the mechanisms of LPL gene silencing is important for metabolic research.
Purpose of the Study:
- To investigate the molecular mechanisms behind LPL gene expression extinction in developing rat liver.
- To identify regulatory DNA sequences and protein factors involved in LPL gene silencing.
Main Methods:
- Analysis of LPL mRNA expression in various hepatoma cell lines and somatic cell hybrids.
- Deletion analysis of the 5' regulatory sequences of the LPL gene.
- Electrophoretic mobility shift assays (EMSAs) to identify protein-DNA interactions.
Main Results:
- Fetal hepatoma cells expressed LPL mRNA, while differentiated cell lines did not.
- Somatic cell hybridization led to extinction of LPL gene expression.
- A region between -591 and -288 in the LPL gene's 5' regulatory sequence was implicated in suppression.
- A novel transcription factor, RF-1-LPL, binds to an NF-1-like site.
- An additional protein complex, RF-2-LPL, forms on this site in adult animals.
Conclusions:
- The extinction of LPL gene expression during rat liver development is a regulated process.
- Specific DNA sequences and the differential binding of transcription factors (RF-1-LPL and RF-2-LPL) mediate LPL gene silencing.