FIG. 3.

UV activation of JNK1 but not ERK2 is blocked by the PI 3-kinase inhibitor wortmannin. (A) Logarithmically growing NIH 3T3 cells were pretreated or not (Control) with 200 nM wortmannin. After an incubation period of 30 min, cells were UV irradiated (40 J/m²) or treated with MMS (2 mM). After a further incubation period of 30 min (for UV irradiation) and 60 min (for MMS) in the presence of the corresponding concentration of wortmannin, cells were harvested for determination of JNK1 activity (upper panel). An aliquot of the immunoprecipitated JNK1 was subjected to Western blot analysis with a phosphospecific JNK antibody (pJNK1 [lower panel]). Shown are the autoradiograms. Autoradiograms were densitometrically analyzed, and relative JNK1 activity (and the amount of pJNK1, respectively) in the untreated control was set to 1.0. (B) Logarithmically growing NIH 3T3 cells were pretreated or not (Control) with 200 nM wortmannin. After an incubation period of 30 min, cells were UV irradiated (40 J/m²). Ten minutes after irradiation, cells were harvested for determination of ERK2 activation by Western blot analysis. Arrows indicate the positions of the nonphosphorylated (lower band) and phosphorylated (activated) (upper band) ERK2 protein.