Eos Mediates Foxp3-Dependent Gene Silencing in CD4 ⁺ Regulatory T Cells

Abstract

Regulatory T cells (Treg) are critical to the maintenance of immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. Treg specifically express the transcription factor Foxp3, which mediates the coordinate activation of genes such as CTLA-4 and GITR along with repression of T effector cytokines such as interleukin-2 and interferon-γ. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. Herein we report the identification of Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Treg. Eos interacts directly with Foxp3 and is necessary for gene silencing without affecting expression of Foxp3 activated genes. We further demonstrate that Eos and its corepressor C-terminal binding protein 1 (CtBP1) are necessary for histone modifications and ultimately promoter methylation involved in selective gene silencing in Treg. Knockdown of Eos in Treg abrogates their ability to suppress immune responses in vitro and in vivo and endows them with partial effector function. This transcriptional control of Treg function through association between Foxp3 and Eos/co-repressor can potentially be exploited for immune-based therapies.

Human FOXP3 and cancer

“…Recently, Pardoll and colleagues (Pan et al, 2009) demonstrated that FOXP3-dependent gene silencing involved in downregulation of IL-2 and IFNg in mouse Treg is related to FOXP3 interaction with Eos, a zincfinger transcription factor of the Ikaros family. Direct interaction of Eos and FOXP3 induces epigenetic chromatin modifications that result in gene silencing in Treg.…”

Molecular mechanisms underlying the regulation and functional plasticity of FOXP3+ regulatory T cells

“…The mechanism by which Eos is involved in Foxp3-dependent gene silencing may be through its corepressors such as C-terminal binding protein 1, which affects histone modification and promoter methylation involved in selective gene silencing. 168 Finally, FOXP3 has also been found to directly interact with c-Rel through its N-terminal region to repress the NF-kB pathway in mature Treg cells. 169 It is highly likely that FOXP3 has many other binding partners.…”

“…The knockdown of Eos reverses Foxp3-mediated suppression of IL-2 expression, but has little effect on CD25, CTLA-4 and GITR expression. 168 Therefore, Eos is necessary for gene silencing but not for the expression of Foxp3-activated genes. The mechanism by which Eos is involved in Foxp3-dependent gene silencing may be through its corepressors such as C-terminal binding protein 1, which affects histone modification and promoter methylation involved in selective gene silencing.…”

“…Eos is a zinc-finger transcription factor that belongs to the Ikaros family, and a recently identified functional component of the Foxp3 complex that acts specifically to promote Foxp3-mediated target gene repression. 168 Eos is highly expressed in Treg cells, especially in activated Treg cells (CD4 þ CD25 hi CD62L lo ) and can bind to the proline-rich domain of Foxp3. The knockdown of Eos reverses Foxp3-mediated suppression of IL-2 expression, but has little effect on CD25, CTLA-4 and GITR expression.…”

One way to pathogenesis, many ways to homeostasis

“…It also revealed a number of other transcriptional regulators of the Treg signature, including Eos, Helios, Lef1 and GATA-1, some were shown previously to be associated with Treg cell function. 5,6 The actual contributions of four transcription factors, Eos, GATA-1, Xbp1 and Helios, were then verified by direct expression profiling of Treg cells from the knockout mice of these genes. Surprisingly, the Treg signatures in each of these mutated mice were not altered significantly compared to wild-type cells.…”