The 8;21 translocation, which involves the gene encoding the RUNX family DNA binding transcription factor AML1 (RUNX1) on chromosome 21 and the ETO (MTG8) gene on chromosome 8, generates AML1−ETO fusion proteins. Previous analyses have demonstrated that full length AML1−ETO blocks AML1 function and requires additional mutagenic events to promote leukemia in mice. More recently, we have identified an alternatively spliced form of AML1−ETO, AML1−ETO9a, from t(8;21) AML patient samples (

Yan et al.
Nat. Med.
). AML1−ETO9a lacks the C−terminal NHR3 and NHR4 domains of AML1−ETO and is highly leukemogenic in mice. Here, we report that the AML1 DNA binding domain and the ETO NHR2 dimerization domain, but not the ETO NHR1 domain are critical for the induction of acute myeloid leukemia by AML1−ETO9a. Using retroviral mediated gene expression and hematopoietic cell transplantation in recipient mice, we examined AML1−ETO9a, AML1−ETO9a without the NHR1 domain [AML1−ETO9a (dNHR1)] or the NHR2 domain [AML1−ETO9a(dNHR2)], without a histone deacetylase/Sin3A interacting domain between NHR1 and NHR2 [AML1−ETO9a(d350–428)], and mutant AML1−ETO9a proteins that have lost the capacity to bind DNA [AML1−ETO9a(L148D)] and [AML1−ETO9a(R173Q)] in leukemogenesis. All of the mice transplanted with AML1−ETO9a (n =11) and AML1−ETO9a(dNHR1) (n = 12) expressing cells developed acute myeloid leukemia with a similar phenotype (Lin−/c−kit+) within 21 weeks. The median survival times of mice with AML1−ETO9a and AML1−ETO9a(dNHR1) are 9.4 weeks and 10.5 weeks, respectively. Furthermore, all of the mice expressing AML1−ETO9a(d350–428) (n = 11) also developed leukemia with a median survival time of 17.2 weeks. Significant numbers of AML1−ETO9a(d350–428) expressing cells are positive for myeloid markers CD11b and Gr1 in these leukemic mice. In contrast, none of the mice with AML1−ETO9a(dNHR2) (n = 14), AML1−ETO9a(L148D) (n = 8), and AML1−ETO9a(R173Q) (n = 8) expressing hematopoietic cells developed leukemia. Taken together, these data suggest that the AML1 DNA binding domain and the ETO NHR2 domain are required for AML1−ETO9a induced leukemia development and the region between amino acids 350 and 428 of AML1−ETO9a also affects the differentiation stage and latency of leukemogenesis.

Disclosure: No relevant conflicts of interest to declare.

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