Induction of the transactivation of endogenous RARs on an RAR-responsive element by TT or 9CTT in APL-derived NB4 (A) and non-APL U937 (B) cells. Cells were transfected with TK-βREx3-LUC reporter by an electroporation technique and treated with TT or 9CTT for 24 hours. Luciferase activities were adjusted for the efficiency of transfection by cotransfected β-galactosidase activities. ATRA and 9CTA at 1 × 10^-6 mol/L induced the luciferase activity to 7.7 and 16.6 U, respectively, in NB4 cells and 24.8 and 54.8 U, respectively, in U937 cells. Values represent the means of three separate experiments.