PLZF-RARα functionally antagonizes PLZF-mediated repression at the c-MYC promoter. (A). PLZF and PLZF-RARα bind to an overlapping region of the c-MYC promoter, highlighted by the dotted box. This region lies upstream of the P0 promoter, approximately 1.5-kB upstream of the major transcriptional start site initiated from promoter P1. PLZF endogenous ChIP-chip was performed in the KG1a cell line and compared with PLZF-RARα ChIP-chip target genes identified in the U937:PLZF-RARα–inducible cell line. The major c-MYC transcripts initiated from this promoter region are indicated by solid black lines. Sequence analysis of the enriched peak using PATCH Public 1.0 identified putative RXR and RAR binding sites (underline) that may bind PLZF-RARα, overlapping with a previously characterized PLZF binding site (bold, enlarged font). (B) The pXP2-MYC2.5-kB luciferase reporter vector contains a 2.5-kB region of the c-MYC promoter harboring the PLZF-RARα–enriched peak. The c-Myc reporter (200 ng) was cotransfected with the indicated PLZF, PLZF-RARα, or PLZF-RARα mutant plasmids (800 ng) in 293 cells and lysates were harvested at 48 hours for luciferase activity. Data are expressed as mean ± SEM of 3 independent experiments (**P < .05).