Transcription factor Foxp1 regulates Foxp3 chromatin binding and coordinates regulatory T cell function

Area of Science:

• Immunology
• Molecular Biology
• Cellular Biology

Background:

• Regulatory T cells (Treg cells) are crucial for immune homeostasis, with their function governed by the transcription factor Foxp3.
• Foxp1, a related transcription factor, is expressed in Treg cells, but its specific role has remained largely unexplored.

Purpose of the Study:

• To investigate the functional significance of Foxp1 within Treg cells.
• To elucidate the molecular mechanisms by which Foxp1 influences Treg cell activity and gene expression.

Main Methods:

• Analysis of Foxp1 and Foxp3 genomic occupancy in Treg and conventional T cells (Tconv cells).
• Assessment of Treg cell function, gene expression (CD25, CTLA-4, SATB1), and interleukin-2 (IL-2) responsiveness following Foxp1 manipulation.
• Evaluation of rescue effects of IL-2 signaling on Treg cell characteristics.

Main Results:

• Foxp1 co-occupies numerous Foxp3-bound genomic sites and enhances Foxp3 binding in Treg cells.
• Foxp1 deficiency in Treg cells leads to impaired function, reduced CD25 and CTLA-4 expression, diminished IL-2 responsiveness, and increased SATB1.
• Strong IL-2 signaling can rescue the characteristic expression patterns of CD25, Foxp3, and CTLA-4 in Foxp1-deficient Treg cells.

Conclusions:

• Foxp1 plays a critical, non-redundant role in Treg cells by reinforcing Foxp3-mediated gene regulation.
• Foxp1 is essential for efficient IL-2 signaling and maintaining Treg cell function and competitive fitness.
• These findings reveal a key mechanism by which Foxp1 contributes to immune tolerance.