PPARγ phase separates with RXRα at PPREs to regulate target gene expression

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Peroxisome proliferator-activated receptor gamma (PPARγ) is crucial for adipogenesis and lipid metabolism.
• PPARγ functions as a heterodimer with retinoid X receptor (RXR) α, binding to PPAR response elements (PPREs).
• The precise mechanism by which PPARγ regulates transcriptional responses remains unclear.

Purpose of the Study:

• To investigate the role of phase separation in PPARγ-mediated transcriptional activation.
• To elucidate how PPARγ forms nuclear structures and interacts with RXRα at target gene loci.
• To determine if enforced condensate formation enhances PPARγ target gene expression.

Main Methods:

• In vitro phase separation assays.
• Cellular imaging to observe nuclear condensate formation.
• Optogenetic approaches to control condensate formation.
• Gene expression analysis of PPARγ target genes.

Main Results:

• PPARγ forms phase-separated droplets in vitro and solid-like nuclear condensates in cells.
• Condensate formation is mediated by the DNA-binding domain of PPARγ, specifically its zinc finger motif.
• PPARγ forms nuclear condensates at PPREs, recruiting and compartmentalizing RXRα.
• Enforced PPARγ/RXRα condensate formation at PPREs significantly enhances target gene expression.

Conclusions:

• PPARγ utilizes phase separation to form nuclear condensates at target gene sites.
• This mechanism facilitates the specific recruitment of RXRα and enhances transcriptional activation.
• Phase separation represents a novel regulatory mechanism for PPARγ-driven gene expression.