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Isoform-specific inhibition of ROR alpha-mediated transcriptional activation by human FOXP3

Jianguang Du1, Chunjian Huang, Baohua Zhou

  • 1Immunology Program, Benaroya Research Institute, Seattle, WA 98101, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|March 21, 2008
PubMed

Insights

Full-length FOXP3 protein interacts with RORalpha, inhibiting Th17 cell gene expression. This interaction, mediated by exon 2, highlights functional differences between FOXP3 isoforms and expands understanding of T cell regulation.

Area of Science:

  • Immunology
  • Molecular Biology
  • Transcriptional Regulation

Background:

  • FOXP3 is a key transcriptional repressor for regulatory T cell development and function.
  • Human FOXP3 exists in two isoforms: full-length and a shorter form lacking exon 2 (DeltaEx2).
  • Both FOXP3 isoforms are expressed at similar levels in regulatory T cells and upon activation.

Purpose of the Study:

  • To investigate the interaction between FOXP3 and RORalpha.
  • To determine the functional consequences of this interaction on transcriptional activity.
  • To elucidate isoform-specific functions of FOXP3 in T cell gene regulation.

Main Methods:

  • Co-immunoprecipitation assays to detect protein-protein interactions.
  • Reporter gene assays to measure transcriptional activity.
  • Site-directed mutagenesis to identify critical interaction domains within FOXP3.
  • Analysis of gene expression in T cells under various conditions.

Main Results:

  • Full-length FOXP3, but not DeltaEx2 FOXP3, directly interacts with RORalpha.
  • Interaction occurs via an LxxLL motif within exon 2 of FOXP3.
  • FOXP3 interaction inhibits RORalpha-mediated transcriptional activation, independent of FOXP3's DNA-binding domain.
  • FOXP3 represses RORalpha-induced expression of Th17 cell signature genes.

Conclusions:

  • FOXP3 isoforms exhibit distinct functional properties.
  • Exon 2 of FOXP3 is crucial for interaction with RORalpha and subsequent repression of Th17-related gene expression.
  • FOXP3 can regulate T cell differentiation through DNA-binding-independent mechanisms.

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