Absence of leucine zipper in the natural FOXP3Delta2Delta7 isoform does not affect dimerization but abrogates suppressive capacity

TY - JOUR

T1 - Absence of leucine zipper in the natural FOXP3Delta2Delta7 isoform does not affect dimerization but abrogates suppressive capacity

AU - Mailer, Reiner K W

AU - Falk, Kirsten

AU - Rötzschke, Olaf

PY - 2009/7/1

Y1 - 2009/7/1

N2 - BACKGROUND: Phenotype and function of regulatory T cells (Treg) largely depend on the presence of the transcription factor FOXP3. In contrast to mice, human Treg cells express isoforms of this protein. Besides the full length version (FOXP3fl), an isoform lacking the exon 2 (FOXP3Delta2) is co-expressed in comparable amounts. Recently, a third splice variant has been described that in addition to exon 2 also misses exon 7 (FOXP3Delta2Delta7). Exon 7 encodes for a leucine zipper motif commonly used as structural dimerization element. Mutations in exon 7 have been linked to IPEX, a severe autoimmune disease suggested to be caused by impaired dimerization of the FOXP3 protein.PRINCIPAL FINDINGS: This study shows that the lack of exon 7 does not affect (homo-) dimerization. Moreover, the interaction of FOXP3Delta2Delta7 to RUNX1, NFAT and NF-kB appeared to be unchanged in co-immunoprecipitation experiments and reporter gene assays, when compared to FOXP3fl and FOXP3Delta2. Nevertheless, retroviral transduction with FOXP3Delta2Delta7 failed to induce the typical Treg-associated phenotype. The expression of FOXP3-induced surface molecules such as CD25 and CTLA-4 were not enhanced in FOXP3Delta2Delta7 transduced CD4+ T cells, which also failed to exhibit any suppressive capacity. Notably, however, co-expression of FOXP3fl with FOXP3Delta2Delta7 resulted in a reduction of CD25 expression by a dominant negative effect.CONCLUSIONS: The leucine zipper of FOXP3 does not mediate dimerization or interaction with NFAT, NF-kB and RUNX1, but is indispensable for the characteristic phenotype and function in Treg cells. FOXP3Delta2Delta7 could play a role in regulating the function of the other FOXP3 isoforms and may be involved in cancer pathogenesis, as it is overexpressed by certain malignant cells.

AB - BACKGROUND: Phenotype and function of regulatory T cells (Treg) largely depend on the presence of the transcription factor FOXP3. In contrast to mice, human Treg cells express isoforms of this protein. Besides the full length version (FOXP3fl), an isoform lacking the exon 2 (FOXP3Delta2) is co-expressed in comparable amounts. Recently, a third splice variant has been described that in addition to exon 2 also misses exon 7 (FOXP3Delta2Delta7). Exon 7 encodes for a leucine zipper motif commonly used as structural dimerization element. Mutations in exon 7 have been linked to IPEX, a severe autoimmune disease suggested to be caused by impaired dimerization of the FOXP3 protein.PRINCIPAL FINDINGS: This study shows that the lack of exon 7 does not affect (homo-) dimerization. Moreover, the interaction of FOXP3Delta2Delta7 to RUNX1, NFAT and NF-kB appeared to be unchanged in co-immunoprecipitation experiments and reporter gene assays, when compared to FOXP3fl and FOXP3Delta2. Nevertheless, retroviral transduction with FOXP3Delta2Delta7 failed to induce the typical Treg-associated phenotype. The expression of FOXP3-induced surface molecules such as CD25 and CTLA-4 were not enhanced in FOXP3Delta2Delta7 transduced CD4+ T cells, which also failed to exhibit any suppressive capacity. Notably, however, co-expression of FOXP3fl with FOXP3Delta2Delta7 resulted in a reduction of CD25 expression by a dominant negative effect.CONCLUSIONS: The leucine zipper of FOXP3 does not mediate dimerization or interaction with NFAT, NF-kB and RUNX1, but is indispensable for the characteristic phenotype and function in Treg cells. FOXP3Delta2Delta7 could play a role in regulating the function of the other FOXP3 isoforms and may be involved in cancer pathogenesis, as it is overexpressed by certain malignant cells.

KW - Animals

KW - Base Sequence

KW - Core Binding Factor Alpha 2 Subunit/metabolism

KW - DNA Primers

KW - Dimerization

KW - Exons

KW - Forkhead Transcription Factors/chemistry

KW - Humans

KW - Leucine Zippers

KW - Mice

KW - Mice, Inbred BALB C

KW - NF-kappa B/physiology

KW - NFATC Transcription Factors/physiology

KW - Protein Binding

KW - Protein Isoforms/chemistry

KW - Reverse Transcriptase Polymerase Chain Reaction

KW - Subcellular Fractions/metabolism

KW - T-Lymphocytes, Regulatory/immunology

KW - Transcription, Genetic/physiology

U2 - 10.1371/journal.pone.0006104

DO - 10.1371/journal.pone.0006104

M3 - SCORING: Journal article

C2 - 19568423

VL - 4

SP - e6104

JO - PLOS ONE

JF - PLOS ONE

SN - 1932-6203

IS - 7

ER -