AML-2 IS A POTENTIAL TARGET FOR TRANSCRIPTIONAL REGULATION BY THE T(8-21) AND T(12-21) FUSION PROTEINS IN ACUTE-LEUKEMIA

AML-1B is targeted directly and indirectly in multiple chromosomal tra nslocations in myeloid and B-cells. The AML-1/ETO and TEL/AML-1 fusion proteins, created by the t(8;21) and t(12;21) respectively, disrupt A ML-1B-dependent transcription. Recently, two human members of the runt homology domain family of transcription factors have been identified, AML-2 and AML-3, which also regulate transcription through enhancer c ore motifs. If multiple factors regulate transcription through the sam e site, a dominant interfering protein may be required to promote leuk emogenesis, rather than the inactivation of both AML1 alleles. To dete rmine which AML family proteins are active in hematopoietic cells, we developed antisera specific to each family member for use in gel mobil ity shift assays. We have found that AML-1B is the major DNA binding a ctivity in T-cell lines, while both AML-1B and AML-2 are expressed in myeloid and B-cell lines. AML-1B represents most of the active protein in the mouse thymus, whereas AML-1 and AML-2 are equally expressed in the mouse spleen. AML-3 is expressed at very low levels in a single m yeloid cell line, 32D.3, and is the only core binding activity present in Buffalo rat liver cells. We demonstrate that AML-2-dependent trans activation mediated by enhancer core motifs is inhibited by the AML-1/ ETO and TEL/AML-1 fusion proteins. This indicates that the t(8;21) and t(12;21) fusion proteins inhibit transcriptional activation by the AM L-1 transcription factor family, and in so doing contributes to leukem ogenesis.