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The mutant leucine-zipper domain impairs both dimerization and suppressive function of Foxp3 in T cells

Wook-Jin Chae1, Octavian Henegariu, Sang-Kyou Lee

  • 1Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.

Proceedings of the National Academy of Sciences of the United States of America
|June 14, 2006
PubMed

Insights

A single glutamic acid deletion in the Foxp3 protein impairs regulatory T cell function, leading to loss of immune tolerance and potential autoimmune disease. This finding highlights the critical role of specific Foxp3 domains in immune regulation.

Area of Science:

  • Immunology
  • Molecular Biology
  • Autoimmunity

Background:

  • Regulatory T cells (Tregs) expressing the Foxp3 transcription factor are crucial for preventing autoimmune diseases.
  • While the DNA-binding domain of Foxp3 is known to be essential, other functional domains are less understood.

Purpose of the Study:

  • To investigate the functional significance of the leucine-zipper domain of Foxp3, specifically the role of a single glutamic acid residue.
  • To elucidate the impact of a specific Foxp3 mutation on Treg suppressor activity, cytokine regulation, cell adhesion, and transcriptional function.

Main Methods:

  • Generating a mutant form of Foxp3 with a deletion of glutamic acid at position 250 (DeltaE250) within the leucine-zipper domain.
  • Analyzing the suppressor activity of CD4 T cells ectopically expressing wild-type versus mutant Foxp3 in vitro and in vivo.
  • Assessing cytokine secretion (Th1 and Th2), expression of adhesion molecules (l-selectin and CD103), transcriptional repressor activity, and homodimerization of Foxp3.

Main Results:

  • Deletion of glutamic acid (DeltaE250) in Foxp3 resulted in a loss of hyporesponsiveness upon antigenic stimulation.
  • Ectopic expression of the DeltaE250 Foxp3 mutant led to significant reductions in CD4 T cell suppressor activity.
  • The mutation altered the regulation of Th1 and Th2 cytokine secretion and impaired the expression of adhesion molecules, affecting Treg migratory behavior.
  • The mutation reduced Foxp3's transcriptional repressor activity and impaired its homodimerization.

Conclusions:

  • A single glutamic acid residue within the leucine-zipper domain of Foxp3 is critical for maintaining immune tolerance and preventing autoimmunity.
  • This mutation disrupts Treg function by impairing suppressor activity, cytokine regulation, cell migration, and transcriptional repression.
  • Understanding the role of specific Foxp3 domains provides insights into the mechanisms controlling autoimmune diseases.

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