Epidermal growth factor (EGF) stimulation of Jab1 nuclear translocation is dependent on pERK and is associated with pERK in the nucleus in MDA-MB-231 cells. (a) Enhanced colocalization of Jab1 and pERK in the nucleus following EGF treatment. (b) Quantitative image analysis of nuclear Jab1 expression in cells treated with EGF and in cells treated with EGF and the ERK inhibitor, PD98059. Bars represent mean ± standard deviation. Statistical analysis was by t test (*P < 0.01). (c) Increased pERK expression following EGF treatment. The addition of ERK inhibitor, PD98059, eliminated this effect. DAPI, 4'-6-diamidino-2-phenylindole; ERK, extracellular signal-regulated kinase; Jab1, c-Jun activation domain-binding protein-1; pERK, phosphorylated extracellular signal-regulated kinase.