The mechanism by which AML1-ETO accomplishes leukemic transformation is unknown.     ///    The upregulation of M-CSF receptor expression by AML1-ETO may contribute to the development of a leukemic state in these patients..     ///    "however, AML1-ETO interferes with AML1 transactivation of such AML1 targets as the T-cell receptor beta enhancer and the granulocyte-macrophage colony-stimulating factor promoter. "    ///    Truncation mutants within the ETO portion of AML1-ETO revealed the region of ETO necessary for the cooperativity between AML1 and AML1-ETO lies between amino acids 347 and 540.     ///    "Herein, we explored the effect of AML1-ETO on regulation of a myeloid-specific AML1 target, the macrophage colony-stimulating factor (M-CSF) receptor promoter. "    ///    "We found that AML1-ETO and AML1 work synergistically to transactivate the M-CSF receptor promoter, thus exhibiting a different activity than previously described. "    ///    " AML1 is involved in the (8;21) translocation, associated with acute myelogenous leukemia (AML)-type M2, which results in the production of the AML1-ETO fusion protein: the amino-terminal 177 amino acids of AML1 and the carboxyl-terminal 575 amino acids of ETO. "