Subcellular localization of FOXP3 in human regulatory and nonregulatory T cells.
The transcriptional regulator FOXP3 is an important determinant of regulatory T (Treg) cell development and function and is frequently used to quantitate Treg cells. However, FOXP3 is also expressed in recently activated conventional human T cells. Here, we investigated the FOXP3 expression patterns in Treg and activated T cells at a cellular level. Upon activation, human CD4(+) CD25(-)  T cells expressed FOXP3 mainly in the cytoplasm, in sharp contrast to human CD4(+) CD25(+)  Treg cells, where we found FOXP3 to be predominantly expressed in the nucleus. A GFP-FOXP3-fusion protein shuttled from the nucleus to the cytoplasm in transfected primary human T cells. We identified two novel leucine-rich nuclear export signals in FOXP3. Site-directed mutagenesis of both sequences completely abolished nuclear export of FOXP3 in human T cells. Both export sequences localized to exons affected by alternative splicing. The three isoforms FOXP3Δ2, FOXP3Δ7, and FOXP3Δ2Δ7 localized preferentially to the nucleus. Additionally, forced expression of nucleus-directed FOXP3 induced a Treg-cell-associated gene expression pattern and induced regulatory capacity. These findings should aid in the interpretation of future studies utilizing FOXP3 expression as a Treg-cell marker and shed some light on the molecular mechanisms controlling subcellular FOXP3 localization in human T cells.
Department of Pediatric Hematology/Oncology, Dr. von Haunersches Kinderspital, Munich, Germany.
Thomas
T
Magg
Joachim
J
Mannert
Joachim W
JW
Ellwart
Irene
I
Schmid
Michael H
MH
Albert
D002467:Cell Nucleus / Q000737:chemistry; D002478:Cells, Cultured; D003593:Cytoplasm / Q000737:chemistry; D051858:Forkhead Transcription Factors / Q000032:analysis* / Q000502:physiology; D006801:Humans; D008213:Lymphocyte Activation; D049790:Nuclear Export Signals; D013601:T-Lymphocytes / Q000737:chemistry* / Q000648:ultrastructure; D050378:T-Lymphocytes, Regulatory / Q000737:chemistry* / Q000648:ultrastructure
C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors; D049790:Nuclear Export Signals