FoxP3 interacts with linker histone H1.5 to modulate gene expression and program Treg cell activity

Area of Science:

• Immunology
• Epigenetics
• Molecular Biology

Background:

• The transcription factor FoxP3 is essential for regulatory T (Treg) cell development and function.
• Epigenetic mechanisms underlying FoxP3's role in gene modulation within Treg cells are not fully understood.

Purpose of the Study:

• To identify proteins interacting with FoxP3 in human T cells.
• To elucidate the functional consequences of FoxP3-interacting proteins on Treg cell activity and gene expression.

Main Methods:

• Co-immunoprecipitation followed by mass spectrometry (MS) to identify FoxP3-interacting proteins.
• Site-directed mutagenesis to investigate the role of specific FoxP3 domains in protein interactions.
• Gene silencing techniques (e.g., siRNA) to assess the impact of protein depletion on gene expression and Treg function.
• Chromatin immunoprecipitation (ChIP) to analyze histone association at target gene promoters.

Main Results:

• FoxP3 was found to interact with linker histone H1.5 through its leucine zipper (LZ) domain.
• Mutations in the FoxP3 LZ domain, observed in IPEX patients, disrupted H1.5 interaction.
• FoxP3 and H1.5 cooperatively repressed interleukin-2 (IL-2) expression; H1.5 depletion impaired FoxP3-mediated IL-2 suppression.
• FoxP3 enhanced H1.5 binding at the IL-2 promoter while reducing it at the CTLA4 promoter, correlating with altered histone acetylation.
• H1.5 depletion in human Treg cells compromised their suppressive function.

Conclusions:

• FoxP3 interacts with histone H1.5 to epigenetically regulate gene expression in T cells.
• This interaction is critical for programming the suppressive function of human Treg cells.
• The findings reveal a novel mechanism by which FoxP3 controls Treg cell activity through modulation of histone association.