Figure 7. PLK1-mediated phosphorylation of FOXO1 overrides FOXO1-induced delay in the late phases of the cell cycle. (A) FACS analysis of the effects of phosphorylation of FOXO1 on cell cycle progression. U2OS cell lines expressing Flag-tagged FOXO1 WT or a FOXO1 mutant (S75A, S75D, or S218AS329A) were synchronized at G1/S boundary by thymidine–aphidicolin double block, and released by culturing in aphidicolin-free medium. Cells were collected at different time points as indicated, fixed and stained with PI solution, and then analyzed by flow cytometry. (B) Results from 3 independent experiments are shown in a bar chart.