JNK acts as an upstream mediator of c-Jun phosphorylation and AP-1 activation.

<p>(A) mESCs transfected with siJNK were incubated in the presence or absence of 50 ng/ml FGF4 and then processed for Western blot analysis 1 h after treatment. (B) Data were quantified from triplicate experiments by densitometry after normalizing bands to total c-Jun protein. mESCs were also treated with each MAPK-specific inhibitor (10 µM) 30 min before addition of 50 ng/ml FGF4, and cells were adjusted to analyze AP-1-DNA binding activity by EMSA (C) or AP-1 activity using a luciferase assay kit (D) after 2 h of incubation. *p<0.05 and ***p<0.001 vs. untreated controls. ^###p<0.001 vs. cells treated with 50 ng/ml FGF4 only.