PLZF expression inhibits 1,25(OH)₂D₃-dependent activation but not ATRA-dependent activation of the p21 promoter in U937 cells.

(A) Schematic diagram of the 2.4-kb fragment of the p21 promoter illustrated in panels B and C. The p21 promoter contained VDREs and a RARE located approximately 800 bp and 1200 bp from the start site of transcription.7 45 (B) PLZF expression reduces VDR-mediated activation of the p21 promoter. The p21 promoter cloned upstream of the luciferase gene was cotransfected with VDR and PLZF in U937 cells. Results are graphed as fold activation. (B) PLZF does not appreciably affect RARα-mediated p21 transcription. U937 cells were cotransfected with RARα, retinoid X receptor (RXR), and the p21 promoter and reporter. Results are graphed as fold activation. RXR was used here because strong ATRA-dependent activation of this promoter required its coexpression.