DAX1 suppresses FXR transactivity as a novel co-repressor

Area of Science:

• Molecular Endocrinology
• Nuclear Receptor Signaling

Background:

• The farnesoid X receptor (FXR) is crucial for maintaining metabolic homeostasis, regulating bile acid, glucose, and lipid pathways.
• DAX1, an atypical nuclear receptor, functions as a co-repressor, lacking DNA-binding domains but interacting with other nuclear receptors.

Purpose of the Study:

• To investigate the interaction between DAX1 and FXR and elucidate DAX1's role in FXR-mediated gene regulation.
• To determine the mechanism by which DAX1 modulates FXR activity.

Main Methods:

• Co-localization studies to assess nuclear presence of DAX1 and FXR.
• Overexpression and knockdown experiments to evaluate the impact of DAX1 on FXR target gene expression.
• Analysis of LXXLL motifs in DAX1 for functional repression.
• Co-activator competition assays.

Main Results:

• DAX1 co-localizes with FXR in the nucleus and physically interacts with it.
• DAX1 acts as a negative regulator of FXR, down-regulating target gene expression upon overexpression and up-regulating upon knockdown.
• Specific LXXLL motifs in DAX1 are essential for repressing FXR transactivation.
• DAX1 competes with co-activators like SRC-1 and PGC-1α, thereby suppressing FXR activity.

Conclusions:

• DAX1 negatively modulates FXR transactivity by acting as a co-repressor.
• The interaction between DAX1 and FXR is critical for regulating hepatic metabolic pathways.