Verification of PML-RARα targets in U937 cells and in primary patient blasts. (A) ChIPs of zinc-induced U937-PML-RARα cells and U937–empty vector cells were performed with the indicated antibodies. Changes in PML-RARα binding and histone modifications for selected targets previously identified by microarrays were verified by real-time PCR. The fold change of PML-RARα or HDAC1 binding and the histone modifications in U937-PML-RARα cells versus U937-control cells are indicated. (B) A total of 2 different antibodies were used to verify enrichment of H3K4 trimethylation at PML-RARα–bound promoters by real-time PCR. The increase in H3K4 trimethylation in PML-RARα–expressing U937 cells versus U937 control cells is indicated for selected target genes. (C) PML-RARα binding was verified for selected targets by real-time PCR in U937-PML-RARα cells. The ratio between U937-PML-RARα cells versus U937-control cells is indicated for the ChIP-Chip assays and the PCR confirmation. (D) Verification of PML-RARα binding in primary patient APL. The fold enrichment in PML-RARα binding was analyzed by ChIP with an α-PML antibody versus IgG isotype control antibody.