FoxP3 forms a head-to-head dimer in vivo and stabilizes its multimerization on adjacent microsatellites

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• FoxP3 is the master regulator of regulatory T cells (Tregs).
• FoxP3 utilizes distinct DNA-binding modes for sequence recognition.
• In vivo evidence for FoxP3's head-to-head (H-H) dimerization was previously lacking.

Purpose of the Study:

• To investigate the in vivo DNA-binding modes of FoxP3 in Tregs.
• To identify genomic motifs driving FoxP3 H-H dimerization.
• To analyze the genome-wide binding patterns of FoxP3 dimers and multimers.

Main Methods:

• Unbiased pull-down sequencing to identify FoxP3 binding sites.
• Systematic genome-wide analysis of FoxP3 binding motifs.
• Comparative analysis of FoxP3 multimerization and H-H dimerization.

Main Results:

• FoxP3 binds genomic DNA as both H-H dimers and multimers in Tregs.
• Relaxed DNA motifs were identified that drive FoxP3 H-H dimerization.
• H-H dimerization can initiate and stabilize multimerization on adjacent TnG repeats, particularly shorter ones.
• H-H dimerization is unique to FoxP3 orthologs, mediated by its accessory loop.

Conclusions:

• FoxP3 employs a dual-mode DNA-binding strategy (H-H dimerization and multimerization).
• This dual-mode binding expands FoxP3's sequence recognition and architectural function in chromatin.
• H-H dimerization is a FoxP3-specific mechanism enhancing its regulatory capacity in Tregs.