CHARACTERIZATION OF THE ETO AND AML1-ETO PROTEINS INVOLVED IN THE 8-21-TRANSLOCATION IN ACUTE MYELOGENOUS LEUKEMIA

The AML1 and ETO genes are disrupted by the nonrandom chromosomal tran slocation t(8;21) in acute myelogenous leukemia (AML). While the AML1 gene encodes a transcription factor indispensable for definitive hemat opoiesis, the biological function of ETO is unknown. To understand the role of ETO and AML1-ETO in the pathogenesis of AML, the full length cDNAs of ETO and AML1-ETO were cloned and antibodies against AML1 and ETO proteins have been developed in our laboratory. Western blot analy sis showed that ETO and AML1-ETO were identified as 70 kDa and 94 kDa proteins, respectively, and that both proteins, like AML1, were associ ated with the nuclear matrix. To examine whether the t(8;21)-positive AMLs expressed a 94-kDa AML1-ETO, protein fractions isolated from leuk emia blasts of 10 patients with t(8;21)-positive AML and the Kasumi-1 cells were analyzed by Western blotting. The 94 kDa AML1-ETO fusion pr otein was detected in all samples. However, this fusion protein was no t detectable in all 40 patients with t(8;21)-negative AMLs. The biolog ical significance of AML1-ETO was examined in K562 cells, which stably overexpress AML1-ETO. We found that AML1-ETO blocked the erythroid di fferentiation of K562 cells induced by low doses of Ara-C. Thus, t(8;2 1)-positive AMLs appear to overexpress the AML1-ETO fusion protein, wh ich may be responsible for differentiation block and leukemogenesis in AML.