SP600125 inhibits c-jun phosphorylation but not phosphorylation of ERK or p38 MAPK. (A) WEHI-231 B-lymphoma cells were incubated with medium or treated with 10 μM SP600125 for 6 hours. In vitro kinase assays were performed on the cell lysates and subsequently analyzed by immunoblotting with an antibody to phospho-c-jun. (B) BJAB B-lymphoma cells were incubated with medium or treated with 10 μM SP600125 for 6 hours. Cell lysates were analyzed by immunoblotting with an antibody to phospho-c-jun. (C) BKS-2 B-lymphoma cells were incubated with medium or treated with 10 μM SP600125 for 6 hours. Cell lysates were analyzed by immunoblotting with an antibody to phospho-JNK, phospho-ERK, or phospho-p38. All the blots that were probed for phosphokinases were then stripped and reprobed with antibodies to total kinase or actin to correct for changes in protein loading in different lanes. Experiments were performed 2 times with similar results.