FIG. 9.

cAMP inhibits expression of c-Jun but not SRE activity. (A) HeLa cells were transfected with cDNA encoding a luciferase gene driven by three tandem copies of the SRE. After 18 h, the culture medium was replaced with 0.5% FBS for an additional 24 h, and then the cells were stimulated with vehicle or 10 ng/ml EGF for 6 h. Relative activity refers to the increase in luciferase activity. Transfection efficiency was monitored with a Renilla firefly luciferase reporter driven by the thymidine kinase promoter (24). The averages of three independent experiments are shown, with error bars representing standard error of the mean. (B) NIH 3T3 cells were grown as described for Fig. 4 and treated with DMSO or 10 μM forskolin and 50 μM IBMX for 15 min and then with 25 ng/ml FGF for 15 min or 120 min. Lysates were immunoblotted with the anti-c-Jun antibody. Results are representative of at least three independent experiments.