Reduction of intracellular ROS following IL-3 withdrawal or treatment with antioxidant PDTC or expression of phosphomimetic Bcl2 mutants results in inhibition of G1 → S transition. (A) Cells expressing nonphosphorylatable Bcl2 mutant (AAA) were deprived of IL-3 or treated with PDTC (500 μM) as indicated. The levels of intracellular ROS levels and cell cycle status were assessed as in Figure 1. (B) Cells were deprived of IL-3 for various times up to 48 hours, then IL-3 was added to cells for various times as indicated. Expression levels of p27 were determined by Western blotting using p27 antibody. (C) Cells were treated with various concentrations of PDTC for 24 hours. Expression levels of p27 were determined as in (B). (D) Cells expressing WT, A-, or E-Bcl2 mutants were lysed in detergent buffer. Expression levels of p27 were determined as described above.