Transcriptional Activators of Helper T Cell Fate Are Required for Establishment but Not Maintenance of Signature Cytokine Expression

Abramson Family Cancer Research Institute and Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
The Journal of Immunology (Impact Factor: 4.92). 12/2005; 175(9):5981-5. DOI: 10.4049/jimmunol.175.9.5981
Source: PubMed


The stability of helper T cell fates is not well understood. Using conditional introduction of dominant-negative factors, we now show that T-bet and GATA-3 are far more critical in establishment than maintenance of IFN-gamma and IL-4 activity during Th1 and Th2 maturation, respectively. We also show that a genetic interaction between T-bet and its target Hlx seems to be required for Th1 maturation, but that Hlx may also be dispensable for maintenance of a transcriptionally permissive ifng gene. In parallel to progressive activator independence in the permissive lineage, the ifng gene becomes more recalcitrant to switching as the forbidden lineage matures. T-bet plus Hlx can disrupt ifng silencing when introduced into developing Th2 cells, but they fail to perturb ifng silencing in mature Th2 cells. In contrast, a hypermorphic allele of T-bet can reverse silencing of the ifng gene in mature Th2 cells. These results suggest that signature gene activity of helper T cells is initially plastic but later becomes epigenetically fixed and offer an initial strategy for inducing mature cells to switch their fate.

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    • "Which factors are necessary to maintain the cellular memory of differentiated Th lineages? Several studies showed that the maintenance of the Ifng and Il4 transcriptional patterns in Th cells is not mediated exclusively by the lineage-specifying transcription factors [13-17]. Therefore, the lineage-specifying transcription factors may induce the expression of downstream specific factors or alternatively, facilitate restricted binding of a generally expressed epigenetic machinery. "
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    ABSTRACT: Following antigen recognition, naive T helper (Th; CD4+) cells can differentiate toward one of several effector lineages such as Th1 and Th2; each expressing distinctive transcriptional profiles of cytokine genes. These cytokines eventually instruct the strategy of the immune response. In our search for factors that propagate the transcriptional programs of differentiated Th cells, we previously found that Polycomb group (PcG) proteins, which are known as epigenetic regulators that maintain repressive chromatin states, bind differentially the signature cytokine genes. Unexpectedly, their binding to the Ifng (Interferon-g) in Th1 cells and Il4 (Interleukin-4) in Th2 cells, was correlated with transcriptional activation. Therefore, in this study we aimed to determine the functional role of PcG proteins in the regulation of the expression of the signature cytokine genes. PcG proteins were knocked down in primary and established murine Th cells using transduction of lentiviruses encoding short hairpin RNAs (shRNAs) directed to Mel-18, Ezh2, Eed and Ring1A, representative of two different PcG complexes. The chromatin structure and the binding activity of PcG proteins and transcription factors at the Ifng promoter were assessed by chromatin immunoprecipitation (ChIP) assays. Downregulation of PcG proteins was consistent with their function as positive regulators of the signature cytokine genes in primary and established Th1 and Th2 cells. Moreover, the PcG protein Mel-18 was necessary to recruit the Th1-lineage specifying transcription factor T-bet, and the T cell receptor (TCR)-inducible transcription factor NFAT1 to the Ifng promoter in Th1 cells. Nevertheless, our results suggest that PcG proteins can function also as conventional transcriptional repressors in Th cells of their known target the Hoxa7 gene. Our data support a model whereby the non-differentially expressed PcG proteins are recruited in a Th-lineage specific manner to their target genes to enforce the maintenance of specific transcriptional programs as transcriptional repressors or activators. Although our results suggest a direct effect of PcG proteins in the regulation of cytokine gene expression, indirect functions cannot be excluded.
    Journal of Molecular Signaling 05/2011; 6:5. DOI:10.1186/1750-2187-6-5
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    • "Thus, T cells that can remain quiescent in the peripheral blood for months or years may maintain the epigenetic state of sets of genes that were previously induced. Additionally, genes involved in both Th 1 and Th 2 responses are thought to be available for induction and only become epigenetically fixed once Th 1 /Th 2 switching has occurred (Martins et al. 2005). For the subset of genes in T cells that are induced at the level of transcription and epigenetic modification, such as CDC20 and IRF4, we observed an increase in the levels of active histone marks at the TSS and sometimes throughout the body of the gene. "
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    ABSTRACT: We investigated functional epigenetic changes that occur in primary human T lymphocytes during entry into the cell cycle and mapped these at the single-nucleosome level by ChIP-chip on tiling arrays for chromosomes 1 and 6. We show that nucleosome loss and flanking active histone marks define active transcriptional start sites (TSSs). Moreover, these signatures are already set at many inducible genes in quiescent cells prior to cell stimulation. In contrast, there is a dearth of the inactive histone mark H3K9me3 at the TSS, and under-representation of H3K9me2 and H3K9me3 defines the body of active genes. At the DNA level, cytosine methylation (meC) is enriched for nucleosomes that remain at the TSS, whereas in general there is a dearth of meC at TSSs. Furthermore, a drop in meC also marks 3' transcription termination, and a peak of meC occurs at stop codons. This mimics the 3' nucleosomal distribution in yeast, which we show does not occur in human T cells.
    Genome Research 07/2009; 19(8):1325-37. DOI:10.1101/gr.085530.108 · 14.63 Impact Factor
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    • "All other transductions were carried out in cells from wild-type Balb/C mice. Cell culture and transductions were carried out as described (Martins et al., 2005). "
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    ABSTRACT: Notch signaling plays multiple roles to direct diverse decisions regarding cell fate during T cell development. During helper T (Th) cell differentiation, Notch is involved in generating optimal Th2 cell responses. Here, we present data investigating how Notch mediates Th2 cell differentiation. Notch showed a CD4(+) T cell intrinsic role in promoting IL-4 expression that required GATA-3. In the absence of Notch signals, Gata3 expression was markedly diminished. Introduction of an activated allele of Notch1 into CD4(+) T cells led to the specific and direct upregulation of a developmentally regulated Gata3 transcript that included the exon 1a sequences. Furthermore, Notch acted in parallel with GATA-3 to synergistically activate IL-4 expression. Together, these data implicate Gata3 as a direct transcriptional Notch target that acts in concert with Notch signaling to generate optimal Th2 cell responses.
    Immunity 08/2007; 27(1):100-10. DOI:10.1016/j.immuni.2007.04.018 · 21.56 Impact Factor
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