The dominant negative form of JNK reduces the transcriptional activation of the uPA-MP reporter construct by interfering with the constitutively active MEK/ERK (chimeric kinase). (A) The uPA-MP reporter construct was cotransfected with 50 ng of the constitutively active MEK/ERK chimeric kinase (see Figure 1B) in HeLa cells. Cells were further cotransfected with increasing amounts of the construct expressing JNK^DN, and luciferase activity was monitored as described in “Materials and methods.” In HeLa cells, JNK^DN strongly decreases the transcriptional activity of the uPA-MP construct, elicited by MEK/ERK^A. Error bars indicate SD. (B) Quantitation of the results in panel A is as for Figure 1.