Negative regulation of Ifng expression by MLL4 through CNS-28

Abstract Interferon-g (IFN-g) is a key cytokine produced by type 1 T helper (Th1) cells in response to viral or intracellular bacterial infections in mammals. While a number of positive regulatory elements have been well studied, no negative regulatory elements at the Ifng locus for its expression have been identified. Here we report a negative regulatory mechanism of Ifng expression by MLL4, a histone methyltransferase responsible for H3K4me1. Deletion of Mll4 resulted in loss of H3K4me1 signals at the previously unrecognized CNS-28 site and led to enhanced IFN-g expression during Th1 differentiation. GATA3 bound to the CNS-28 site and deletion of Gata3 resulted in a similar upregulation of IFN-g with Mll4 deletion. Furthermore, deletion of Mll4 compromised GATA3 binding to CNS-28 and led to a substantial reorganization of the 3D chromatin structure at the Ifng genomic locus in both naïve CD4+ T cells and Th1 cells. Thus, we conclude that MLL4 negatively regulates Ifng expression by facilitating GATA3 binding to the CNS-28 site and maintaining a special local chromatin organization.