TAL1 regulates proliferation of Jurkat and HSB2 T-ALL cell lines. (a, top) TAL1 protein in Jurkat and HSB2 cells that stably expressed shRNAs directed against human TAL1 (shTAL1) or hepatitis B virus (shCTL) was measured by immunoblotting. Actin is shown as a loading control. The data shown correspond to a representative experiment out of two performed. (middle) Growth curves of Jurkat and HSB2 cells expressing shTAL1 or shCTL. Graphs show number of cells ± SEM (n = 4 experiments). (bottom) doubling times of Jurkat and HSB2 cells expressing shCTL or shTAL1 analyzed during the exponential phase of the growth curves (***, P < 0.001). (b) Percentages of Jurkat (left) and HSB2 (right) cells expressing shCTL or shTAL1 in G1, S, and G2/M phases were determined at days 1, 2, and 3 of culture. Graphs show percentages of cells ± SEM (n = 4 experiments; *, P < 0.05; **, P < 0.01). (c, left) Percentages of BrdU-negative Jurkat cells expressing shCTL or shTAL1 cycling from G2/M to G1 were determined at days 1, 2, and 3 of culture. (right) BrdU mean fluorescence of HSB2 cells expressing shCTL or shTAL1 labeled with BrdU at days 1, 2, and 3 of culture. Graphs show percentages of cells ± SEM (n = 4 experiments; **, P < 0.01). MFI, mean fluorescence intensity.