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Reverse Yeast Two-hybrid System to Identify Mammalian Nuclear Receptor Residues that Interact with Ligands and/or Antagonists
Published on: November 15, 2013
Activation of testicular orphan receptor 4 by fatty acids
Nien-Pei Tsai1, Mostaqul Huq, Pawan Gupta
1Department of Pharmacology, University of Minnesota Medical School, 6-120 Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455-0217, USA.
Abstract:
Nuclear receptors can be activated by chemicals, metabolites, hormones or environmental compounds to regulate gene expression. Bioassay-guided screening of mouse tissue extracts found that natural fatty acids of a certain carbon length and level of unsaturation could activate the mouse orphan nuclear receptor, testicular orphan receptor 4 (TR4). Subsequent experiments focused on gamma-linoleic acid, a compound identified during screening of mouse tissues that exerts regulatory activity in TR4 transactivation assays. gamma-linoleic acid positively modulates TR4 activity to promote the expression of downstream genes such as apolipoprotein E (ApoE) and phosphoenolpyruvate carboxykinase, and to activate a reporter carrying direct repeat 1 from the ApoE promoter. It also induced the interaction of TR4 with transcription coregulators such as RIP140 and PCAF. Comparisons of transactivation by TR4 and the metabolism-related peroxisome proliferator-activated nuclear receptors indicate that gamma-linoleic acid regulation is specific to TR4. The data suggest that TR4 might exert its physiological function by sensing certain lipids. Identifying these compounds could be useful for examining the physiological pathways in which TR4 and its target genes are involved.
Insights
Natural fatty acids activate the testicular orphan receptor 4 (TR4), a nuclear receptor. Gamma-linoleic acid specifically enhances TR4
Area of Science:
- Endocrinology
- Molecular Biology
- Biochemistry
Background:
- Nuclear receptors regulate gene expression in response to various stimuli.
- Orphan nuclear receptors, like TR4, have poorly defined functions and ligands.
- Lipids and fatty acids are critical signaling molecules in cellular processes.
Purpose of the Study:
- To identify natural compounds that activate the mouse orphan nuclear receptor TR4.
- To investigate the specific effects of gamma-linoleic acid on TR4 activity and downstream gene expression.
- To explore the potential physiological role of TR4 in lipid sensing.
Main Methods:
- Bioassay-guided screening of mouse tissue extracts.
- In vitro transactivation assays using TR4.
- Analysis of downstream gene expression (ApoE, PEPCK) and coregulator interactions.
- Comparative analysis with other nuclear receptors (PPARs).
Main Results:
- Natural fatty acids, particularly gamma-linoleic acid, were identified as activators of mouse TR4.
- Gamma-linoleic acid specifically enhanced TR4-mediated transactivation, promoting ApoE and PEPCK expression.
- Gamma-linoleic acid induced TR4 interaction with coregulators RIP140 and PCAF.
- TR4 activation by gamma-linoleic acid was found to be specific and distinct from PPAR-mediated regulation.
Conclusions:
- The testicular orphan receptor 4 (TR4) can be activated by specific fatty acids, suggesting a role in lipid sensing.
- Gamma-linoleic acid is a TR4-specific modulator, influencing the expression of key metabolic genes.
- Understanding TR4-ligand interactions provides insights into its physiological functions and potential therapeutic targets.
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