Fig. 7. NF1/X represses Sp1 induction of the PDGF-A promoter. (A) Sp1 transactivates the PDGF-A promoter. Cells were transiently transfected with 2 µg of –154luc and the indicated amounts Sp1–pcDNA3 or pcDNA3. (B) NF1/X inhibits Sp1 transactivation of the PDGF-A promoter. The cells were transiently transfected with 3 µg of Sp1–pcDNA3 and the indicated amount of NF1/X or pCDNA3. Twenty-four hours after transfection, the cells were lysed and luciferase activity determined. The cells were also transfected with 2 µg of pRL–TK to normalize for transfection efficiency. Firefly luciferase activity was normalized to Renilla.