Histone Deacetylase 11 (HDAC11) Interaction with Ikaros Represent a Novel Mechanism of Regulation of Essential Transcriptional Factors in CD4+ T Cells

Histone deacetylase 11 (HDAC11), the most recently identified histone deacetylase, is the sole member of class IV HDACs [1]. Since its discovery, no biological function was assigned to this HDAC until we demonstrated its central role in negatively regulating IL-10 production in antigen presenting cells (APCs) [2]. More recently, we have found that disruption of HDAC11 in T cells is associated with an enhanced pro-inflammatory cytokine profile and effector molecule production. Furthermore, T-cells lacking HDAC11 were less susceptible to regulatory T-cell (Treg) suppression in vitro, were refractory to tolerance induction in vivo and displayed enhanced allo-reactivity and anti-tumor responses in murine models. Of note, T-cells lacking HDAC11 expressed higher levels of the transcription factors Eomes and Tbet. Conversely, overexpression of HDAC11 in T-cells decreased the expression of both transcription factors. The molecular mechanism(s) by which HDAC11 regulates the expression of these transcription factors have remained unknown.

By using chromatin immunoprecipitation (ChIP) assay we found that in resting T-cells HDAC11 is present at the Eomes and Tbet gene promoters where it maintains histone deacetylation, a compacted chromatin and gene repression. Following T-cell stimulation, HDAC11 was largely absent from both promoters, which resulted in increased histone 3 (H3) acetylation and gene transcriptional activity. These findings were confirmed in T-cells isolated from HDAC11 knock out (KO) mice which also displayed an increase in H3 acetylation at the Tbet and Eomes gene promoter regions. Conversely, H3 acetylation was decreased in both gene promoters in T-cells overexpressing HDAC11 as compared to empty-vector transfected cells. Given that HDACs do not bind to DNA, we asked next which transcription factor(s) HDAC11 might be associated with, in order to regulate Tbet and Eomes gene transcriptional activity.

In prior studies we have found that HDAC11 form a molecular complex with another member of the HDAC family, HDAC6, which physically interacts with the transcription factor, STAT3 in both the cytoplasmic and nuclear compartments. However, in T-cells no direct interaction of HDAC11 with STAT3 was detected in either compartment. In contrast, we found for the first time that HDAC11 physically associates with Ikaros (Ikzf1), a member of the Ikaros zinc finger transcription factor family that has been previously implicated in the regulation of T-bet gene expression and IFN-g production in T-cells [3-5]. The protein complex HDAC11-Ikaros was mainly detected in the nuclear compartment and both proteins were present at the T-bet gene promoter. Collectively, these results point to the HDAC11-Ikaros complex as a novel epigenetic mechanism of regulation of Tbet and Eomes, transcription factors that are essential for T cell development and function.