Transcriptional induction of uPA is stimulated through the p42/p44 MAP kinase pathway. CCL39-derivative cells were induced to express the Raf:ER chimera by estrogen treatment for the times indicated. (A) Estrogen-induced and noninduced cells were treated with UO126, as described, and total RNA was assayed by Northern blot using a murine urokinase probe. (B) The cells were also transfected with plasmids expressing wild-type Sp1 or mutant Sp1 upon tetracycline treatment, and total RNA was assayed as for panel A. The uPA mRNA increases after 4 hours of estrogen treatment in the presence of wild-type Sp1, whereas in the presence of mutant Sp1 uPA mRNA levels are barely above background and are absent from UO126-treated cells.