Fig 1: Effects of equal doses (IC20) of structurally-diverse HDACIs on acetylation of histones H3 and H4 and a-tubulin, and cytarabine-induced apoptosis in pediatric AML cells. Panel A: THP-1 cells were treated with equal doses (IC20s, determined by MTT assays) of MS-275, VPA or SAHA for 48 hrs. Acetylation of histones H3 and H4, and a-tubulin were determined by western blots probed by anti-ac-H3, -ac-H4, -ac-tubulin, or –H4 antibodies. Panel B: THP-1 cells were treated with cytarabine (900 nM, IC20) or equal doses of MS-275, VPA, or SAHA, alone or in combination for 48 hrs. Early and late apoptosis events were determined by annexin V/PI staining and flow cytometry analysis. **, p<0.005; *, p<0.05. Panels C&D: THP-1 cells were treated with equal doses (IC20s) of MS-275, VPA or SAHA for 48 hrs and protein extracts were subjected to immunoprecipitation with antibodies against class I HDACs, as described in the Materials and Methods. One half of the immunoprecipitated proteins was subjected to Western blots probed by anti-HDAC1, -HDAC2, -HDAC3, or -HDAC8 antibody (panel C), and the other half was used for measuring class I HDAC activities (panel D). The data are presented as means of three independent experiments normalized to the non-drug treatment controls.