Activation of ERK-2 in myeloid leukemia cell lines.

Lysates of myeloid leukemia cell lines were subjected to immunoprecipitation with an antibody against ERK-2 (which also cross-reacts with ERK-1). After washing the immunoprecipitates, immunocomplex kinase assays were performed as described in “Materials and methods.” (A) Western blot of the immunoprecipitates with an antibody specific for ERK-2 and an antibody specific for activated PP-ERK-1/2. (B) Autoradiogram of kinase assay demonstrating MBP phosphorylation by immunoprecipitated ERK-1/2. N-RAS (L61)–transformed NIH 3T3 fibroblasts were used as a positive control for the RAS-induced activation of ERK-1/2. A nonspecific antibody was used as a negative control.