The effect of CTCF over-expression on apoptosis and proliferation in leukemic cells. (A) A schematic outline of the pEGFP-N2-CTCF expression vector. The full-length CTCF gene was cloned into the pEGFP-N2 vector. (B) Effect of over-expressing CTCF on caspase-3 activation in Nalm-6 cells. The expression levels of procaspase-3, cleaved caspase-3 and the transfected plasmids were assessed by Western blot. (C) Over-expression of CTCF resulted in decreased early cell apoptosis [Annexin V (+)/PI (-)] and late cell apoptosis [Annexin V (+)/PI (+)]. The percentages of cells in early and late apoptosis are indicated in the figure, respectively. pEGFP-N2 vector was used as a control. (D) The percentage of cell apoptosis (both early and late apoptosis) in each group is indicated in the diagram as mean ± SD from three independent experiments (p = 0.012). (E) Clones over-expressing CTCF were seeded in a 96-well plate at 1 × 104 cells per well, with 3 replicates per clone. Viable cells were counted using the CCK-8 assay for 5 days. (F) The percentage of cell viability normalized to the empty vector pEGFP-N2 is shown in the diagram.