T-box proteins differentially activate the expression of the endogenous interferon γ gene versus transfected reporter genes in non-immune cells

The T-box transcription factor T-bet is expressed in a number of hematopoetic cell types and plays an essential role in the lineage determination of Th1 T-helper cells. In the absence of T-bet, CD4+ T-cells fail to induce IFNγ, the cytokine whose expression characterizes Th1 cells. Here we show that, surprisingly, T-bet induces the expression of endogenous IFNγ in non-immune human cells, including 293 and other cell lines. Thus T-bet can induce IFNγ expression independently of its role in T-cell lineage determination. In addition, mutations in T-bet, and chimeras of T-bet with other transcription factors including the T-box transcription factor, TBX2, differentially affect the ability of T-bet to activate expression of endogenous IFNγ versus a T-site regulated reporter gene. A truncated T-betVp16 fusion protein strongly activates the T-site reporter but fails to activate endogenous IFNγ. Conversely, native T-bet strongly activates endogenous IFNγ expression but only weakly activates the reporter gene. Fusion of the Vp16 activation domain to full-length T-bet greatly increases its activation of both endogenous IFNγ and transfected T-site reporter gene expression. In contrast, TBX2Vp16 potently activates the T-site reporter but has a negligible effect on endogenous IFNγ expression. Butyrate treatment of T-bet expressing cells potentiates the expression of endogenous IFNγ but weakly represses expression of the T-site reporter gene. These data indicate that induction of endogenous IFNγ can be uncoupled from differentiation into the Th1 lineage and that the expression of endogenous IFNγ versus a T-site reporter gene is differentially regulated by T-bet and other T-box proteins.