Since activated ERK1/2 phosphorylates CCAAT/enhancer-binding protein α (C/EBPα) on serine 21 and inhibits activity of this myeloid differentiation transcription factor23, we hypothesized that the aberrant activation of the MEK/ERK1/2 pathway through SYK might contribute to the differentiation blockade in AML cells. This evidence concerns the gene MAPK3 and acute myeloid leukemia.