The development of acute myelogenous leukemia (AML), which is characterized by a block of myeloid di erentiation, is a multi-step process that involves several genetic abnormalities, but the molecular mechanisms by which these genetic alterations cooperate in leukemogenesis are poorly understood. The human chronic myelogenous leukemia (CML) is a model for multi-step leukemogenesis. BCR-ABL, a constitutively active tyrosine kinase, is a fusion protein generated by the t(9;22)(q34;q11) translocation found in the vast majority of CML patients. BCR-ABL e ciently induces a myeloproliferative disorder (MPD) in mice, but progression to CML blast phase requires additional mutations. The AML1/ MDS1/EVI1 (AME) transcription factor fusion protein, is a product of the human t(3;21)(q26;q22) translocation found as a secondary mutation in some cases of CML during the blast phase. We have previously shown that AME can induce an AML in mice but with a greatly extended latency, suggesting a requirement for additional mutations. Here we demonstrate that AME alone does not block myeloid di erentiation in vivo during the 4-month pre-leukemia stage, yet co-expression of BCR-ABL and AME in mice can block myeloid di erentiation and rapidly induce an AML. Our results suggest that block of myeloid di erentiation and induction of AML involves cooperation between mutations that dysregulate protein tyrosine kinase signaling and those that disrupt hematopoietic gene transcription. Oncogene (2001) 20, 8236 ± 8248.

The human t(3;21)(q26;q22) translocation is found as a secondary mutation in some cases of chronic myelogenous leukemia during the blast phase and in therapy-related myelodysplasia and acute myelogenous leukemia. One result of this translocation is a fusion between the AML1, MDS1, and EVI1 genes, which encodes a transcription factor of approximately 200 kDa. The role of the AML1͞MDS1͞EVI1 (AME) fusion gene in leukemogenesis is largely unknown. In this study, we analyzed the effect of the AME fusion gene in vivo by expressing it in mouse bone marrow cells via retroviral transduction. We found that mice transplanted with AME-transduced bone marrow cells suffered from an acute myelogenous leukemia (AML) 5-13 mo after transplantation. The disease could be readily transferred into secondary recipients with a much shorter latency. Morphological analysis of peripheral blood and bone marrow smears demonstrated the presence of myeloid blast cells and differentiated but immature cells of both myelocytic and monocytic lineages. Cytochemical and flow cytometric analysis confirmed that these mice had a disease similar to the human acute myelomonocytic leukemia. This murine model for AME-induced AML will help dissect the molecular mechanism of AML and the molecular biology of the AML1, MDS1, and EVI1 genes. C hromosomal abnormalities are common genetic bases of leukemias. Many of these cytogenetic changes result in the creation of fusion proteins that contain transcription factors. Studying the role of these fusion transcription factors in leukemogenesis is important for understanding the molecular mechanism of leukemias. A reciprocal translocation between chromosomes 3, band q26, and 21, band q22, has been found in certain patients with chronic myelogenous leukemia during blast phase (CML-BC), in patients with therapy-related myelodysplasia͞acute myelogenous leukemia (t-MDS͞t-AML), and on rare occasions in de novo acute myelogenous leukemia (AML) (1, 2). The t(3;21) translocation can result in fusion of the AML1 gene on chromosome 21 to several genes on chromosome 3, namely EAP, MDS1, and MDS1͞EVI1 (reviewed in refs. 3 and 4).The AML1 gene found on chromosome 21, band q22, encodes a transcription factor containing an N-terminal DNA-binding domain that is homologous to the Drosophila pair-rule gene runt. Normal AML1 protein (also known as CBFA2) is the DNAbinding subunit of the enhancer core-binding factor (CBF) and functions as a heterodimer with the non-DNA-binding subunit CBF␤ that enhances AML1's DNA-binding affinity. Both AML1 and CBF␤ play a crucial role in definitive hematopoiesis and blood vessel development (5, 6) and are targets of multiple chromosomal abnormalities in human leukemias and myelodysplasia. Besides the t(3;21) translocations mentioned above, the AML1 gene is also found fused to the ETO gene, a zinc-finger-containing transcription factor, in t(8;21)(q22;q22)-associated de novo AML (M2 subtype) (7,8), fused to the TEL gene, which encodes an ETS family transcription factor, in t(12;21)(p13;q22)-associated...

We have previously shown that BCR/ABL, a fusion protein generated by the t(9;22)(q34;q11) translocation found in the vast majority of chronic myelogenous leukemia (CML), cooperates with AML1/MDS1/EVI1 (AME), a fusion transcription factor generated by a t(3;21)(q26;q22) translocation identified as a secondary mutation in some cases of CML during the blast phase (CML-BC), in the rapid induction of an acute myelogenous leukemia (AML) in mice. In this study, we evaluated the leukemogenic potential of EVI1-, MDS1/EVI1-and AML1-related oncoproteins (AML1D, AML1/MDS1). We found that ectopic expression of either EVI1 or MDS1/EVI1 impaired hematopoiesis. However, neither EVI1 nor MDS1/EVI1 was sufficient for inducing AML in mice, although EVI1 did induce some hematologic neoplasia other than AML with a low efficiency. In addition, unlike AME, none of the EVI1-or AML1-related oncoproteins examined were capable of fully cooperating with BCR/ABL in the induction of AML. The results indicate that both the AML1 and EVI1 oncogenic components are required for the leukemogenic potential of AME and for the cooperation of AME and BCR/ABL in the induction of AML.