Downregulation of Uhrf1 activity by TGF-β signaling controls Foxp3 methylation and iTreg cell differentiation

Foxp3+ regulatory T cells (Treg cells) are essential for immune system homeostasis and suppression of excessive immune responses. Both TGF-β signaling and epigenetic modifications are important in the regulation of Foxp3 induction, but whether TGF-β signaling participates in the epigenetic regulation of Foxp3 has not been fully clarified. Here, we show that Uhrf1, which is induced by TCR stimulation and regulated by TGF-β signaling, controls Foxp3 methylation and iTreg cell differentiation. T cell-specific ablation of Uhrf1 led to Treg-biased differentiation in naïve T cells, with DNA hypomethylation upon TCR stimulation, and these Foxp3+ T cells had suppressive function. Uhrf1 maintained Foxp3 DNA methylation by recruiting Dnmt1 during cell division upon TCR stimulation. TGF-β treatment led to passive demethylation of the Foxp3 promoter to initiate its expression. Mechanistically, Uhrf1 was phosphorylated upon TGF-β stimulation and largely sequestered in the cytoplasm. Phosphorylated Uhrf1 underwent proteasomal degradation through inhibition of Usp7-mediated deubiquitination. Collectively, our study reveals a novel epigenetic mechanism of TGF-β-mediated iTreg cell differentiation regulated by Uhrf1 and reveals the differential role of active and passive demethylation in Foxp3 induction and stability. Wild-type (WT) and Uhrf1-/- mice T lymphocytes were analysed for: gene expression by RNA-seq, DNA methylation by whole-genome bisulfite sequencing (WGBS)