DNMT1 cooperates with MBD4 to inhibit the expression of Glucocorticoid-induced TNFR-related protein in human T cells.

Glucocorticoid-induced TNFR-related protein (GITR) is constitutively expressed in T regulatory (Treg) cells and regulates their suppressive function. We identified two methylated CpG islands in the Gitr locus. Using a ChIP assay, we demonstrate that both DNMT1 and methyl-CpG-binding domain Protein 4 (MBD4) bind to the Gitr promoter. Moreover, knockdown of DNMT1 decreases the binding activity of MBD4. We observed much higher levels of both DNMT1 and MBD4 in human CD4+ CD25- conventional T (Tconv) cells. Moreover, co-overexpression of DNMT1 and MBD4 in Treg cells significantly inhibits GITR expression and impairs their suppressive activity. Our results reveal a novel molecular mechanism by which MBD4 inhibits GITR expression in a DNMT1-dependent manner.