HDAC9 and acute myeloid leukemia: To further investigate which HDAC isoforms, among HDAC1, HDAC2, and HDAC3, play important roles in regulating expression of BRCA1, CHK1, and RAD51 in AML cells, we individually knocked down HDAC1, HDAC2, and HDAC3 in THP-1 cells (Figure 4A, designated THP-1/HDAC1, THP-1/HDAC2, and THP-1/HDAC3, respectively; Western blot verification of knockdown was previously published [15]).