DNMT3a mediates lineage-specific, de novo DNA methylation at the ifng promoter and contributes to ifng gene silencing in Th2, Th17 and Treg cells (88.15)

Abstract Naïve CD4+ T cells can differentiate into distinct subsets of effectors that express unique cytokine profiles upon activation. T helper 1 (Th1) cells robustly secrete IFNγ, a cytokine essential for clearance of intracellular pathogens and anti-tumor responses, while Th2, Th17, and regulatory T cells (Tregs) do not. The silencing of “off-pathway” cytokine genes during differentiation is incompletely understood, but may involve epigenetic mechanisms of gene repression. CpG dinucleotides in the ifng promoter, which are largely unmethylated in naïve CD4+ T cells and Th1 cells, are sites of substantial de novo methylation in non-IFNγ-producing lineages. To determine whether such de novo DNA methylation contributes to ifng gene silencing, we used mice with T cell-specific deletion of the de novo DNA methyltransferase, DNMT3a. While “on-pathway” cytokine expression polarized normally, DNMT3a-deficient CD4 T cells did not accumulate de novo ifng promoter methylation seen in wild-type cells during Th2, Th17 or Treg differentiation. Maintenance DNA methylation at the ifng intronic enhancer was not affected. Failed de novo methylation was associated with failed silencing, as DNMT3a-deficient Th2, Th17 and Treg cells produce significant levels of IFN-γ after secondary re-polarization toward the Th1 lineage. These results indicate that DNMT3a restricts the plasticity of CD4+ T helper cell fates via de novo DNA methylation of the ifng promoter in Th2, Th17 and Treg cells.