FIG. 5.

Sp1 can contribute to the bFGF response. NIH 3T3 fibroblasts were transfected with a luciferase reporter containing a Gal4 binding site centered 20 nt upstream of the −63 CArG box of the SRF gene promoter. Where indicated, a plasmid expressing a Gal4-Sp1 fusion protein was included. Cells were starved for 36 h and stimulated with bFGF for 2 h, and luciferase assays were performed. Fold induction was determined by comparing the serum-starved level of expression with the stimulated level of expression. The level of expression in unstimulated cells of the reporter in the absence of Gal4-Sp1 was set to a value of 1.0. For each point, assays were performed in triplicate and values were corrected for transfection efficiency. Results from at least three independent experiments are shown. Expression of the Gal4 DNA binding domain alone did not enhance bFGF-stimulated expression (not shown).