Figure 6.

RXR and LXR agonists activate mouse SREBP-1c promoter. (A) The sequence of the mouse SREBP-1c 5′-flanking region (∼1.3 kb) is shown with the DR4 LXRE motif denoted by arrows. The putative transcription start site at −63 is boxed. (B) RXR and LXR agonists (LG268 and T0901317) synergistically activate a luciferase reporter driven by the SREBP-1c promoter. A 6.5-kb fragment of the SREBP-1c promoter was linked to pGL3 basic luciferase reporter. The resulting plasmid pBP1c(6500)-Luc was cotransfected into HEK-293 cells with a control reporter plasmid pCMV-βGal as described in Materials and Methods. Twenty hours after transfection, cells were treated with vehicle (DMSO and/or ethanol), LG268 (1 μM), T0901317 (10 μM), or LG268 (1 μM) plus T0901317 (10 μM). Normalized luciferase activity of cells treated with vehicle is arbitrarily defined as 1, and relative luciferase activities from different treatments are shown as “fold increase”. Each value represents data from four independent transfection experiments (each in duplicate). (C) Deletions of the ∼6500 kb mouse SREBP-1c promoter were assayed as described in B. Data shown are the average of three independent transfection experiments (each in duplicate) in the upper panel and two independent experiments in the lower panel. The 100% value for basal activity corresponds to the normalized luciferase activity obtained with the pBP1c(6500)-Luc promoter construct in the absence of LG268 and T0901317. Individual values for fold-activations were: upper panel 8.1 (4.9, 7.4, 12), 4.5 (3.8, 4.8, 5.0), 5.0 (2.4, 5.5, 7.0), 0.73 (0.4, 0.8, 1.0); lower panel 7.8 (5.1, 10.5), 0.85 (0.6, 1.1), 4.4 (4, 4.8), 0.98 (0.95, 1.0).