Retinoic acid response element (RARE) is sufficient for synergistic activation of endogenous RAR activity by ATRA and GFs. (A) Schematic representation of luciferase reporters used to transfect U-937 cells. Numbers indicate sequences present in each construct and correspond to sequence with GenBank accession AF283809. (B) Induction of different luciferase reporter activities was measured 18 hours after treatment with indicated agents compared with uninduced luciferase activity. The activity of the control reporter lacking RARE and the β-galactosidase levels were not affected by any of the mediators (not shown). The results show the mean (number above bars) ± SD of one experiment done in duplicates, which has been repeated twice with similar results.