Fig. 9. Forskolin downregulates the E2F-promoter activity. Reh cells were transfected with the pGL3TATA-6xE2F-promoter luciferase construct or with the basic pGL3TATA vector. An SV40-ßGalactosidase construct was cotransfected with the luciferase constructs as an internal control. 20 hours after transfection, the cells were treated with and without forskolin (100 µM) for (A) 2 hours, (B) 24 hours and (C) 72 hours. After forskolin treatment the cells were harvested and lysed in reporter lysis buffer. The luciferase activity was determined and normalized for transfection efficiency, with the activity of ß-galactosidase being used as a reference. The values are presented as the mean from four experiments, and the vertical bars represent the s.e.m.