Inhibition of Aurora B kinase decreases G₁/S phase transition in MK cells. (A) Western blot analysis with or without AZD1152-HQPA added at day 5. Western blot showed a time-dependent induction of p53 and p21 and the appearance of the hypophosphorylated form of Rb onAZD1152-HQPA treatment. (Bi) Flow cytometric analysis of BrdU incorporation in CD41⁺ cells of day 7 MK culture incubated with or without inhibitor during 48 hours. The plots show propidium iodide staining, used to show the DNA content of cells against the level of BrdU for each cell measured. (Bii) The BrdU-positive or -negative populations in 2N to 4N and 8N or greater MKs with or without inhibitor were compared. BrdU incorporation diminished in 2N to 4N population and changed slightly in 8N or greater onAZD1152 treatment. BrdU-negative accumulation in 8N or greater after AZD1152 treatment was more important than 2N to 4N. Dot plots are from a representative experiment (n = 3).