FIGURE 4.

CDK·cyclin-dependent FOXK2 phosphorylation. A, U2OS cells were grown asynchronously (Asy) or in the presence of nocodazole (Noc) for 16 h and either left untreated or treated with 10 μm purvalanol A (PuA) or alsterpaullone (Alst) for 30 min before harvesting. Cell lysates were subjected to immunoprecipitation (IP) using anti-FOXK2 antibody followed by immunoblot (IB) with FOXK2 antibody. B, U2OS cells were transfected with siRNA duplexes against GAPDH, CDK2, cyclin A, or cyclin B where indicated. 30 h after transfection, cells were grown in the presence (Noc) or absence (Asy) of nocodazole for 16 h before harvesting. The expression of FOXK2, cyclin B, cyclin A, CDK2, and GAPDH was detected by Western analysis. C, cell cycle profiles of U2OS cells following treatment with the indicated siRNA constructs for 30 h prior to a further 16-h incubation in the presence or absence of nocodazole.