THE EXTRACELLULAR SIGNAL-REGULATED KINASE PATHWAY PHOSPHORYLATES AML1, AN ACUTE MYELOID-LEUKEMIA GENE-PRODUCT, AND POTENTIALLY REGULATES ITS TRANSACTIVATION ABILITY

AML1 (also called PEBP2 alpha B, CBFA2, or CBF alpha 2) is one of the most frequently disrupted genes in chromosome abnormalities seen in hu man leukemias. It has been reported that AML1 plays several pivotal ro les in myeloid hematopoietic differentiation and other biological phen omena, probably through the transcriptional regulation of various rele vant genes. Here, we investigated the mechanism of regulation of AML1 functions through signal transduction pathways. The results showed tha t AML1 is phosphorylated in vivo on two serine residues within the pro line-, serine-, and threonine-rich region, with dependence on the acti vation of extra-cellular signal-regulated kinase (ERK) and with interl eukin-3 stimulation in a hematopoietic cell line. These in vivo phosph orylation sites of AML1 were phosphorylated directly in vitro by ERK. Although differences between wild-type AML1 and phosphorylation site m utants in DNA-binding affinity were not observed, we have shown that E RK-dependent phosphorylation potentiates the transactivation ability o f AML1. Furthermore the phosphorylation site mutations reduced the tra nsforming capacity of AML1 in fibroblast cells. These data indicate th at AML1 functions are potentially regulated by ERK, which is activated by cytokine and growth factor stimuli. This study provides some impor tant clues for clarifying unidentified facets of the regulatory mechan ism of AML1 function.