Key Points• We demonstrate a critical role for histone deacetylase 1 and 2 (HDAC1/2) in T-cell development and the maintenance of genomic stability.
IntroductionHistone deacetylase (HDAC) 1 and 2 are sister proteins (ϳ 80% identical), functionally redundant in many cell types, 1-3 which are recruited together into 3 main transcriptional complexes: Sin3A, 4 NuRD 5,6 and CoREST. 7,8 Classically, HDAC1 and 2 (HDAC1/2) function has been viewed in the context of transcriptional repression, because deacetylation of histone tails results in the tightening of nucleosomal arrays. 9,10 However, genome-wide mapping of HDAC1 (or Rpd3) binding sites in human cells 11 and yeast, 12 reveals a positive correlation with gene activity, suggesting a role for HDACs in the cyclical acetylation of histones within the vicinity of active promoters. 13 HDAC1/2 may thus have roles in both gene activation and repression.In the clinic, the HDAC inhibitor SAHA is used to treat patients with cutaneous T-cell lymphoma. 14 Therefore a greater understanding of the key pathways regulated by HDAC1/2 activity in T-lymphocyte development will help inform their use as drug targets. Moreover, as a dispensable cell type in a standard pathogen free environment, it is an excellent model to study essential genes, such as HDAC1/2. T-cell development, from immature double negative (DN), to double positive (DP) intermediates and mature (but naive) CD4 single positive (CD4SP, helper) and CD8 single positive (CD8SP, cytotoxic) populations is regulated by a number of transcription factors and chromatin modifying complexes. 15,16 Runx1 and Runx3 have nonredundant roles in the regulation of CD4 expression. [17][18][19] The zinc-finger transcriptional regulator, Gata3, is crucial for the development of the earliest T-cell progenitors. 20 ThPOK expression is necessary to direct CD4 expression in MHC II restricted cells and is also sufficient to redirect class-I MHC T cells into the CD4 T-helper lineage. 21 Individual HDACs have also been implicated in T-lymphocyte function. HDAC7 regulates cell survival and TCR signaling in DP thymocytes, 22 HDAC6 and HDAC9 regulate the activity of T-regulatory cells, 23,24 while HDAC11 directly controls IL-10 expression levels in antigen presenting cells. 25 Deletion of either Sin3A 26 or Mi2, 27 central components of the HDAC1/2 containing Sin3A and NuRD complexes, respectively, perturbs thymopoiesis. Loss of Sin3A causes a deficiency in the DN to DP transition and a significant reduction in the number of CD8SP cells. Mi2 also plays a role in DN to DP transition, and in addition is required for transcriptional activation of the Cd4 gene. These 2 studies clearly implicate HDAC1/2 in T-cell development. However, deletion of Hdac1 alone at the double positive stage of development produced a relatively mild phenotype 28 ; suggesting that, as in many other tissue systems, deletion of both Hdac1 and For personal use only. on May 9, 2018. by guest www.bloodjournal.org From Hdac2 is required to observe a more substantial phenotypic...