摘要：SummaryRegulatory T cells are important regulators of the immune system and have versatile functions for the homeostasis and repair of tissues. They express the forkhead box transcription factor Foxp3 as a lineage-defining protein. Negative regulators of Foxp3 expression are not well understood. Here, we generated double-stranded DNA probes complementary to theFoxp3promoter sequence and performed a pull-down with nuclear proteinin vitro, followed by elution of bound proteins and quantitative mass spectrometry. Of theFoxp3-promoter-binding transcription factors identified with this approach, one was T cell factor 1 (TCF1). Using viral over-expression, we identified TCF1 as a repressor of Foxp3 expression. In TCF1-deficient animals, increased levels of Foxp3intermediateCD25negativeT cells were identified. CRISPR-Cas9 knockout studies in primary human and mouse conventional CD4 T (Tconv) cells revealed that TCF1 protects Tconvcells from inadvertent Foxp3 expression. Our data implicate a role of TCF1 in suppressing Foxp3 expression in activated T cells.Graphical AbstractDisplay OmittedHighlights•Quantitative proteomics identifies proteins bound to theFoxp3gene promoter•Promoter-binding proteins are suppressing Foxp3 expression•TCF1-deficient animals have more Foxp3-expressing CTLA4−CD25−CD4+T cells•TCF1 suppresses Foxp3 expression in activated non-TregcellsMolecular Biology; Molecular Mechanism of Gene Regulation; Immunology; Proteomics
