The AML1/ETO fusion protein activates transcription of BCL-2

The AML1/ETO fusion protein activates transcription of BCL-2

^*Laboratory of Molecular Aspects of Hematopoiesis and ^†Laboratory of Hemato-Oncology, Sloan–Kettering Institute, Memorial Sloan–Kettering Cancer Center, 1275 York Avenue, New York, NY 10021

Abstract

The AML1 gene, located on chromosome 21, is involved in several distinct chromosomal translocations in human leukemia. In t(8;21) acute myelogenous leukemia (AML), the AML1 gene is juxtaposed to the ETO gene located on chromosome 8, generating an AML1/ETO fusion protein. Both AML1/ETO and the AML1 proteins recognize the same consensus DNA-binding motif (TGT/CGGT), which is found in the promoters of several genes involved in hematopoiesis. We found that two myeloid leukemia cell lines with the t(8;21) translocation, Kasumi and SKNO-1, have elevated levels of BCL-2 protein compared with other myeloid cell lines. In addition, we identified a consensus AML1 binding site in the BCL-2 promoter. Thus far, AML1/ETO has been shown to dominantly repress its target genes; however, we found that AML1/ETO activates transcription of the BCL-2 gene in U937 cells. This activation requires the presence of both the runt homology domain (rhd) and the C-terminal portion of AML1/ETO. We demonstrated sequence specific binding of both AML1A and AML1/ETO to the TGTGGT sequence in the BCL-2 promoter and showed that the AML1 binding site is required for responsiveness to AML1/ETO. Interestingly, AML1A and AML1B do not modulate the activity of the BCL-2 promoter. The elevated levels of BCL-2 in cells that express AML1/ETO may prolong their life span and contribute to the development of t(8;21) leukemia.

Footnotes

↵ ¶ To whom reprint requests should be addressed.
Paul A. Marks, Memorial Sloan–Kettering Cancer Center, New York, NY
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Abbreviations: GM-CSF, granulocyte/macrophage colony-stimulating factor; EMSA, electrophoretic mobility-shift assay; IL, interleukin; AML, acute myelogenous leukemia; rhd, runt homology domain.