DEF6 and p21 are targets of PML-RARα. (A) ChIPs of zinc-induced U937-PML-RARα and U937–empty vector cells were performed with an α-PML antibody. The localization of PML-RARα binding at the DEF6 and p21 promoters was analyzed in U937 cells using a series of real-time PCR amplicons that tiled a 5-kb region surrounding the transcriptional start site. The fold enrichment of signal in PML-RARα–expressing U937 cells is indicated compared with empty vector–expressing U937 cells. (B) ChIPs with an α-PML antibody and an IgG control antibody were performed with blasts from a patient with APL with the t(15;17) translocation. The fold enrichment of signal in the ChIPs with α-PML antibody is shown compared with ChIPs with an IgG control antibody. (C) Top panel: Immunoblot analysis was performed for p21 from whole-cell lysates of U937-PML-RARα cells before and after PML-RARα induction. Bottom panel: CDK2 and CDK4 were immunoprecipitated before and after induction of PML-RARα. Histone H1 and GST-Rb were used as substrates for in vitro kinase reaction to analyze the kinase activity of CDK2 and CDK4 in PML-RARα–expressing cells. PML-RARα induction was associated with an increase in CDK2 and CDK4 kinase activity.