Evolutionarily conserved sequence elements that positively regulate IFN-γ expression in T cells

Our understanding of mechanisms by which the expression of IFN-gamma is regulated is limited. Herein, we identify two evolutionarily conserved noncoding sequence elements (IFNgCNS1 and IFNg CNS2) located approximate to5 kb upstream and approximate to18 kb downstream of the initiation codon of the murine Ifng gene. When linked to the murine Ifng gene (-3.4 to +5.6 kb) and transiently transfected into EL-4 cells, these elements clearly enhanced IFN-gamma expression in response to ionomycin and phorbol 12-myristate 13-acetate and weakly enhanced expression in response to T-bet. A DNase I hypersensitive site and extragenic transcripts at IFNgCNS2 correlated positively with the capacity of primary T cell subsets to produce IFN-gamma. Transcriptionally favorable histone modifications in the Ifng promoter, intronic regions, IFNgCNS2, and, although less pronounced, IFNgCNS1 increased as naive T cells differentiated into IFN-gamma-producing effector CD8(+) and T helper (TH) 1 T cells, but not into TH2 T cells. Like IFN-gamma expression, these histone modifications were T-bet-dependent in CD4(+) cells, but not CD8(+) T cells. These findings define two distal regulatory elements associated with T cell subset-specific IFN-gamma expression.