A. Schematic representation of pBL-FFL-CAT5 (WT) and its mutants, MA, MB, MC, and MD. B. The stimulatory effect by TPA is decreased in MA. In the presence or absence of TPA (100 ng/ml), pBL-FFL-CAT5 (WT) or its mutants (MA-D) were transfected into CV1 cells. CAT activity was measured with normalization of the transfection efficiency by the β-galactosidase activity (left panel). Fold activation (right panel) was calculated from CAT activity with TPA divided by that without TPA. C. The sequence between nt. 626/640 in the FFL cDNA mediates both TPA-dependent activation and negative regulation by T3/TR. In the presence or absence of TPA (100 ng/ml) and/or T3 (1 µM), pBL-FFL-CAT5 (WT) or its mutant, MA, was transfected into CV1 cells with or without TRβ1 expression plasmid. CAT activity was measured with normalization of the transfection efficiency by the β-galactosidase activity. The results are the means +/− SD from three independent experiments. *, P<0.05.