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Functional interactions between nuclear receptors recognizing a common sequence element, the direct repeat motif
1Department of Life Science, Faculty of Science, Himeji Institute of Technology, Kamigori, Hyogo, 678-1297, Japan.
Journal of Biochemistry
|May 30, 1998
Summary
Nuclear hormone receptors like PPARalpha and HNF-4 bind to direct repeat motifs (DR-1). Their interactions reveal complex gene regulation, with HNF-4 suppressing PPARalpha activity through binding site competition.
Area of Science:
- Molecular biology
- Genetics
- Endocrinology
Background:
- Direct repeat motifs (DR-1) are recognized by nuclear hormone receptors.
- Key liver receptors include peroxisome proliferator-activated receptor alpha (PPARalpha), hepatocyte nuclear factor-4 (HNF-4), and chicken ovalbumin upstream transcription factor I (COUP-TFI).
Purpose of the Study:
- To investigate the interplay between PPARalpha, HNF-4, and COUP-TFI in gene regulation.
- To understand how these receptors interact on specific gene elements.
Main Methods:
- Gene transfection assays were used to examine receptor binding and transactivation.
- Specific gene enhancer elements (acyl-CoA oxidase and apolipoprotein CIII) were analyzed.
Main Results:
- PPARalpha and HNF-4 bound to the acyl-CoA oxidase gene enhancer, with PPARalpha showing stronger transactivation.
- HNF-4 suppressed PPARalpha's activation of the acyl-CoA oxidase gene due to binding site competition.
- HNF-4 activated the apolipoprotein CIII gene, while PPARalpha did not.
- COUP-TFI bound to both elements and suppressed activation by PPARalpha and HNF-4.
Conclusions:
- PPARalpha, HNF-4, and COUP-TFI exhibit distinct gene regulatory functions.
- The co-existence of these nuclear receptors leads to complex, interactive effects on gene expression.