FIG. 5.

p38 MAPK is activated in response to growth factor stimulation. (A) (Left) Lysates of PC12 cells that either were untreated or had been treated for 10 min with NGF (30 ng/ml) or for 30 min with anisomycin (20 μg/ml) were separated by SDS-PAGE and immunoblotted with anti-phospho-p38 MAPK (top) or anti-phospho-ERK antibodies (bottom). (Right) Lysates of NIH 3T3 cells that were untreated or treated for 10 min with EGF (30 ng/ml), or for 15 min with sorbitol (0.3 M) were separated by SDS-PAGE and immunoblotted with anti-phospho-p38 MAPK (top) or anti-phospho-ERK (bottom) antibodies. (B) p38 MAPK was immunoprecipitated from lysates of PC12 cells that were untreated (lane 1), treated with UV irradiation (lane 2), or treated with NGF (30 ng/ml) for various periods (lanes 3 to 8). p38 MAPK activity in the immune complex was measured by an in vitro kinase assay with GST-ATF2 protein as a substrate. The reaction products were examined by SDS-PAGE and autoradiography.