Possible Involvement of Histone Acetylation in Differentiation of Erythroid Precursors and Proliferation of Granulocytic Precursors.

The commitment and differentiation of hematopoietic progenitors are thought to be associated with the restriction of transcriptional accessibility for genes of unselected cell-lineage. Histone acetylation-mediated remodeling of chromatin structures is known to regulate transcriptional activity of genes, and the acetylation level of histones is controlled by the balance between opposing activities of histone acetyltransferases and histone deacetylases (HDACs). In this study, we investigated the role of HDAC activity in the proliferation and differentiation of erythroid and granulocytic precursors, using a HDAC inhibitor FK228 [depsipeptide]. CD36⁺ erythroid precursors were generated from cord blood CD34⁺ cells with SCF, flt-3 ligand, TPO, IL-3, IL-6 [5GF], and EPO. These precursors expressed low or undetectable level of glycophorin A (GPA) but mostly expressed CD45. When these precursors were cultured with EPO alone in the presence of FK228 (0.4~0.5 ng/ml), the resulting cells expressed GPA at a low level in comparison with the cells cultured without FK228, and a large population of the GPA⁺ cells remained to be CD45⁺. On the other hand, most of cells in cultures without FK228 expressed a high level of GPA and a majority of the GPA⁺ cells were negative for CD45. These data suggest that FK228 represses the EPO-dependent differentiation of erythroid precursors.

The retardation of differentiation due to FK228 was, however, completely recovered when cells exposed to FK228 were incubated for additional 5 days without FK228. At these concentrations, FK228 did not affect the proliferation of erythroid precursors. Granulocytic precursors were also prepared from CD34⁺ cells with 5GF and G-CSF. In culture with G-CSF, FK228 did not affect the differentiation of granulocytic precursors but did inhibit their proliferation in a dose-dependent fashion. Histone acetylation induced by FK228 in precursors was confirmed using anti-acetylated histone antibodies. These data demonstrate a distinct and regulatory role for HDAC activity in the proliferation and differentiation of hematopoietic precursors.