Figure 7.

Down-regulation of Chk1 reduced the effects of AICAr and brequinar on the expression of differentiation markers and S-phase arrest. U937 cells were transfected with siRNA against Chk1 (mixture of four sequences), and respective nontargeting siRNA was used as a negative control. AICAr (0.2 or 0.5 mm) and brequinar (Breq) (0.5 μm) were added 24 h after transfection. A, total cell lysates were isolated 3 or 48 h after the addition of agents and analyzed by Western blotting for the level of Chk1. Representative immunoblots from three independent experiments are shown. B, representative histograms of propidium-labeled cells. C, the number of viable cells and the expression of differentiation markers were determined as described under “Experimental procedures.” Results are mean ± S.E. (error bars) of three independent experiments. *, p < 0.05 compared with control (ctrl).