Histone Deacetylase 7 Functions as a Key Regulator of Genes Involved in both Positive and Negative Selection of Thymocytes

Abstract

Histone deacetylase 7 (HDAC7) is highly expressed in CD4 ؉ /CD8؉ thymocytes and functions as a signaldependent repressor of gene transcription during T-cell development. In this study, we expressed HDAC7 mutant proteins in a T-cell line and use DNA microarrays to identify transcriptional targets of HDAC7 in T cells. The changes in gene expression levels were compared to differential gene expression profiles associated with positive and negative thymic selection. This analysis reveals that HDAC7 regulates an extensive set of genes that are differentially expressed during both positive and negative thymic selection. Many of these genes play important functional roles in thymic selection, primarily via modulating the coupling between antigen receptor engagement and downstream signaling events. Consistent with the model that HDAC7 may play an important role in both positive and negative thymic selection, the expression of distinct HDAC7 mutants or the abrogation of HDAC7 expression can either enhance or inhibit the signal-dependent differentiation of a CD4 ؉ /CD8؉ cell line.The thymic development of T cells is a highly regulated process involving multiple extracellular signals. A complex integration of these signals results in changes in gene expression that can lead to the adoption of different developmental fates. Thymocytes pass two main developmental checkpoints that involve antigen receptor signaling. The first, called ␤-selection, occurs after the first of the two chains of the T-cell receptor (TCR) has been productively rearranged and is required for further developmental progression of thymocytes (24,55,75). After ␤-selection, thymocytes proliferate extensively, rearrange their antigen receptor ␣-chains, and become CD4 ϩ , CD8 ϩ , or double-positive (DP) thymocytes. The subsequent developmental fate of DP thymocytes is determined by signaling interactions with antigen-presenting cells (APCs) in the thymic cortex and medulla, most critically between the TCRs of thymocytes and self peptides bound to the major histocompatibility complex (MHC) molecules of the APCs. Broadly, DP thymocytes can adopt three different developmental fates based on the character of this interaction. The large majority of the thymocytes have no functional interaction between their TCRs and the MHC-self peptide complexes on the APCs, and die of neglect within a few days. Thymocytes expressing TCRs that have an interaction of intermediate strength undergo positive selection, after which they downregulate either the CD4 or CD8 coreceptor and exit the thymus as mature CD4 ϩ or CD8 ϩ T cells. Potentially autoreactive thymocytes, with TCRs that interact strongly with MHC-self peptide complexes, are deleted by an apoptotic process termed negative selection. How this continuum of different antigen receptor signal strengths leads to a discrete set of developmental outcomes, in terms of both lineage determination and survival, is still poorly understood.Numerous extracellular signals not involving the TCR have been implicated in the positive and...

Histone Deacetylase 7 Regulates Cell Survival and TCR Signaling in CD4/CD8 Double-Positive Thymocytes

“…HDAC7 thus appears to a negative regulator of the coupling between TCR engagement and the downstream signaling events that mediate cell death and perhaps other developmental decisions, in a manner that is required to maintain the viability of thymocytes at the DP stage. Many but not all of the molecules we identified as particularly interesting targets of HDAC7 in this study were also identified as HDAC7 targets in a prior study done by our group, involving microarray analysis of T cell hybridomas with altered HDAC7 function (11). These include Camk2d, Cd5, Dap, Dusp2/4, Egr1 and Egr2, Hdac5, IFN-g receptor, Ndrg-1, Pd-1, Pik3kd, L-selectin, Socs1, and TGF-b receptor.…”

“…Unexpectedly, we did not find that expression of Nur77 or its functionally redundant homolog Nor-1 is increased in either HDAC7-deficient or HDAC7-VP16 transgenic thymocytes. We did, however, establish that Hdac5, another direct target of HDAC7 in thymocytes (11), is increased in expression when HDAC7 function is absent or reversed by expression of HDAC7-VP16 (Fig. 5C, Supplemental Table I).…”

“…HDAC7 regulates the expression of the proapoptotic orphan steroid receptor Nur77, and mutation or loss of HDAC7 affects TCRinduced apoptosis (9). Although this suggests a role in negative selection, putative HDAC7 targets identified in T cell hybridomas are mostly genes differentially expressed during positive selection, and mutating or silencing HDAC7 interferes with in vitro differentiation of a DP thymoma (11).…”

Histone deacetylase 7, a potential target for the antifibrotic treatment of systemic sclerosis

“…Nucleocytoplasmic shuttling has been observed for all class II HDACs and reflects a putatively important regulatory mechanism. However, it should be stressed that HDAC-7 is expressed in heart and lung tissues, placenta, pancreas, and skeletal muscle as well as in CD4/CD8 doublepositive thymocytes (34)(35)(36)(37). HDAC-7 -/-mouse embryos display defects in the development and integrity of blood vessels (38).…”

Nuclear receptor Nr4a1 modulates both regulatory T-cell (Treg) differentiation and clonal deletion

“…This is most obvious for Eno3, which Kasler et al identified as a Nr4a1-transcriptional target in D011.10 cells overexpressing Nr4a1 (45) and in analyses of hepatic glucose metabolism (38). Nr4a1 binds directly to a response element in the Eno3 promoter (38).…”