Regulation of T cell development by HDAC3

摘要 胸腺细胞的发育受到严格的调控，需要细胞成功地通过几个 胸腺排出前的发育阶段和检查点。胸腺细胞发育的每个检查点， 涉及对一组特定基因的诱导或抑制。基因调控的中断导致 发育停滞，不能产生T细胞和适应性免疫缺陷。基因表达 由转录激活因子、抑制因子和染色质修饰剂协调。一般来说，组蛋白 乙酰化促进基因表达，而组蛋白去乙酰化导致抑制。我们调查的 使用CD2-icre条件性敲除（HDAC3 - 3）研究组蛋白去乙酰化酶-3（HDAC3）在T细胞发育中的作用。 cKO）小鼠。虽然T细胞在发育过程中共表达几种HDAC家族成员，但这些其他的HDAC家族成员在发育过程中可能会表达。 HDAC家族成员不能补偿HDAC 3的损失，因为HDAC 3-cKO小鼠在T细胞中具有阻滞， 由于不能进行阳性选择，DP阶段的细胞发育。T细胞阻滞 OT-IITCR转基因或Bcl-2或Bcl-xl转基因不能挽救发育。 成功的阳性选择需要下调ROR γ t，因为组成型表达ROR γ t的小鼠， ROR γ t在阳性选择时对T细胞发育具有类似的阻断作用。在HDAC3-cKO小鼠中，ROR γ t是 在DP阶段TCR刺激后未下调，表明阳性选择中的阻断 可能是由于不能下调ROR γ t。与此一致，我们观察到增强的RORC 启动子乙酰化在HDAC3的情况下，表明HDAC3可以直接脱乙酰化组蛋白， RORC启动子抑制表达。ROR γ t还控制DP期Bcl-xl的表达， 调节DP存活。因此，为了确定ROR γ t的持续表达是否是 在阳性选择中阻断ROR γ t-KO Bcl-xlTg HDAC3-cKO（下文称为RB3）小鼠， 产生，其恢复了正选择，导致产生正常数量的CD8SP 胸腺细胞（TCR β +，Runx3+）数量。然而，CD4SP胸腺细胞没有产生，表明 HDAC3在T细胞发育过程中的谱系选择中的潜在作用，我们认为这是由于HDAC3在T细胞发育过程中的缺陷。 在阳性选择和谱系定型期间的CD4表达。为了确认血统的改变 我们产生了OT-II RB3小鼠，并发现OT-II TCR表达胸腺细胞是 偏向CD 8谱系，而不是CD 4SP T细胞，正如在OT-II转基因中观察到的那样（否则 WT）小鼠。该建议的重点是确定HDAC3在阳性选择和CD4谱系中的作用 发展

Abstract Thymocyte development is tightly regulated, requiring successful transit of cells through several developmental stages and checkpoints prior to thymic egress. Each checkpoint of thymocyte development, involves induction or repression of a particular set of genes. Disruptions in gene regulation leads to developmental arrest, a failure to generate T cells and deficits in adaptive immunity. Gene expression is coordinated by transcriptional activators, repressors, and chromatin modifiers. In general, histone acetylation promotes gene expression while histone deacetylation leads to repression. We investigated the role of histone deacetylase-3 (HDAC3) in T cell development using CD2-icre conditional knockout (HDAC3- cKO) mice. Although T cells co-express several HDAC family members during development, these other HDAC family members cannot compensate for the loss of HDAC3 as HDAC3-cKO mice have a block in T cell development at the DP stage due to an inability to undergo positive selection. The block in T cell development could not be rescued by an OT-II TCR transgene, or by a Bcl-2 or Bcl-xl transgene. Successful positive selection requires down-regulation of RORγt, as mice with constitutive expression of RORγt have a similar block in T cell development at positive selection. In HDAC3-cKO mice, RORγt was not down-regulated upon TCR stimulation at the DP stage, demonstrating that the block in positive selection may be due to an inability to down-regulate RORγt. Consistent with this, we observed enhanced RORC promoter acetylation in the absence of HDAC3, indicating that HDAC3 may directly deacetylate histones at the RORC promoter to inhibit expression. RORγt also controls expression of Bcl-xl at the DP stage to regulate DP survival. Therefore, to determine whether sustained expression of RORγt was responsible for the block in positive selection, RORγt-KO Bcl-xl Tg HDAC3-cKO (hereafter called RB3) mice were generated, which restored positive selection leading to the generation of normal numbers of CD8SP thymocyte (TCRβ+, Runx3+) numbers. However, CD4SP thymocytes were not generated, indicating a potential role for HDAC3 in lineage choice during T cell development, which we believe is due to a defect in CD4 expression during positive selection and lineage commitment. To confirm the altered lineage commitment, we generated OT-II RB3 mice and found that the OT-II TCR-expressing thymocytes are skewed towards the CD8 lineage rather than CD4SP T cells as is observed in OT-II transgenic (otherwise WT) mice. The focus of this proposal is to define the role of HDAC3 in positive selection and CD4 lineage development