Regulatory T (Treg) cells are involved in self tolerance, immune homeostasis, prevention of autoimmunity, and suppression of immunity to pathogens or tumours. The forkhead transcription factor FOXP3 is essential for Treg cell development and function as mutations in FOXP3 cause severe autoimmunity in mice and humans. However, the FOXP3-dependent molecular mechanisms leading to this severe phenotype are not well understood. Here we introduce the chromatin remodelling enzyme SATB1 (special AT-rich sequence-binding protein-1) as an important target gene of FOXP3. So far, SATB1 has been associated with normal thymic T-cell development, peripheral T-cell homeostasis, TH1/TH2 polarization, and reprogramming of gene expression. In natural and induced murine and human FOXP3+ Treg cells SATB1 expression is significantly reduced. While there is no differential epigenetic regulation of the SATB1 locus between Treg and Teffector cells, FOXP3 reduces SATB1 expression directly as a transcriptional repressor at the SATB1 locus and indirectly via miR-155 induction, which specifically binds to the 3’UTR of the SATB1 mRNA. Reduced SATB1 expression in FOXP3+ cells achieved either by overexpression or induction of FOXP3 is linked to significant reduction in TH1 and TH2 cytokines, while loss of FOXP3 function either by knock down or genetic mutation leads to significant upregulation of SATB1 and subsequent cytokine production. Alltogether, these findings demonstrate that reduced SATB1 expression in Treg cells is necessary for maintenance of a Treg-cell phenotype in vitro and in vivo and places SATB1-mediated T cell-specific modulation of global chromatin remodelling central during the decision process between effector and regulatory T-cell function. Last Updated (by provider): Nov 14 2011 Contributors: Marc Beyer S Classen J Schultze