T-bet antagonizes mSin3a recruitment and transactivates a fully methylated IFN-γ promoter via a conserved T-box half-site

Abstract

Promoter DNA methylation is a major epigenetic mechanism for silencing genes and establishing commitment in cells differentiating from their precursors. The transcription factor T-bet is a key determinant of IFN-␥ gene expression in helper T cells, but the mechanisms by which it achieves this effect are not clear. It is shown here that T-bet binds to a highly conserved T-box half-site in the IFN-␥ promoter, is recruited to the endogenous IFN-␥ promoter in T lymphoid cells, and transactivates gene expression through this sequence in a manner dependent on consensus T-box residues. This conserved promoter site is methylated in a model T cell line, and enforced T-bet expression did not alter its complete methylation. T-bet transactivated the conserved core promoter in transfection assays and collaborated functionally with C͞EBP␤ despite methylation of the conserved element. Importantly, enforced T-bet expression led to dissociation of the mSin3a corepressor from the endogenous, chromatinized IFN-␥ promoter without decreasing loading of the methyl-CpG binding protein MeCP2. These data indicate that T-bet can override repressive epigenetic modification by a mechanism in which this master regulator acts through a T-box half-site to enforce the activation of IFN-␥ gene expression in part by decreased loading of a corepressor on methylated DNA.corepressor ͉ DNA methylation ͉ transcription

Temporal Dissection of T-bet Functions

“…T-bet has been implicated in the chromatin remodeling of the IFN-␥ locus during Th1 differentiation (12,16,26) and transactivated IFN-␥ reporter constructs in vitro (4,14,15). Our results suggest that T-bet activity is required acutely in order for IFN-␥ to be produced and for CD122 and CxCR3 to be expressed at high levels.…”

“…Exactly how and when T-bet is required for the regulation of its putative target genes is unknown. In previous studies, T-bet transactivated IFN-␥ reporter constructs in vitro (4,14,15), suggesting a possible direct and active role of T-bet in IFN-␥ transcription. In addition, T-bet was important for maintaining histone hyperacetylation at the IFN-␥ promoter (16,17).…”

De Novo DNA Methylation Is Required to Restrict T Helper Lineage Plasticity

“…Second, these data indicate that Th17 cells have the capacity to bypass the epigenetic silencing marks that are initiated by DNMT3a. For instance, Tbet, the major trans-activator of ifn␥, can bind to its promoter element even when the CpG dinucleotide is methylated, displace co-repressor complexes, and reverse silencing marks at the ifn␥ locus (32,33). Why this or other mechanisms appear to be operating in Th17 cells, but not Th2 or iTreg, is not clear.…”

Role of IFN-α/β signaling in the prevention of genital herpes virus type 2 infection

“…Upon induction of IFN-γ gene expression, T-bet binds monomeric brachyury consensus sites in the IFN-γ promoter (Cho et al, 2003) and initiates chromatin remodeling of the IFN-γ gene locus during the first cell division of the developing Th1 cells (Mullen et al, 2002). T-bet initiates the transcription of the IFN-γ gene by the establishment of long-range histone hyperacetylation across the IFN-γ gene region (Chang and Aune, 2005;Shnyreva et al, 2004) and by inhibiting the IFN-γ gene repressor, mSin3a (Tong et al, 2005). The binding of T-bet alone is sufficient for IFN-γ expression, although the effect can be enhanced by interactions with other transcription factors.…”