The fusion protein AML1-ETO is generated from the translocation t(8;21)(q22;q22) and is identified in over 12% of normal acute myeloid leukemia cases. While AML1-ETO does not induce acute myeloid leukemia in the murine retroviral transduction model, a spliced isoform, AML1- ETO9a, is able to induce acute myeloid leukemia. One difference between AML1-ETO and AML1-ETO9a is the ability of AML1-ETO to induce an interferon response to a greater degree than AML1-ETO9a. Here I verify that interferons and interferon stimulated genes are transcribed to a greater degree in the presence of AE than AE9a in the U937T cell lines. I also show that AE expression and universal interferon treatment inhibit proliferation in the U937T cell line. Next I verify in mouse bone marrow cells that AE induces interferon stimulated genes more effectively than AE9a. In addition, the induction of interferon stimulated genes is greater in bone marrow cells of C57BL/ 6 wild type mice than interferon receptor knockout mice. I also show that both global interferon treatment and loss of interferon receptor lead to decreases in proliferation and self-renewal ability. Finally I show that lethally irradiated mice treated with AE9a transduced fetal liver cells from mice without interferon receptor experience enhanced acute myeloid leukemia development compared to mice receiving AE9a transduced fetal liver cells from wild type mice. I also show that similar spleen and liver mass, and leukocyte composition is observed in leukemic mice regardless of the genotype of the donor fetal liver cells

The 8;21 translocation is the most common chromosomal aberration occurring in acute myeloid leukemia (AML). This translocation causes expression of the RUNX1-ETO (AML1-ETO) fusion protein, which cooperates with additional mutations in leukemia development. We report here that interferons (IFNs) and IFN-stimulated genes are a group of genes consistently up-regulated by RUNX1-ETO in both human and murine models. RUNX1-ETO-induced up-regulation of IFN-stimulated genes occurs primarily via type I IFN signaling with a requirement for the IFNAR complex. Addition of exogenous IFN in vitro significantly reduces the increase in self-renewal potential induced by both RUNX1-ETO and its leukemogenic splicing isoform RUNX1-ETO9a. Finally, loss of type I IFN signaling via knockout of Ifnar1 significantly accelerates leukemogenesis in a t(8;21) murine model. This demonstrates the role of increased IFN signaling as an important factor inhibiting t(8;21) fusion protein function and leukemia development and supports the use of type I IFNs in the treatment of AML.

Fusion protein RUNX1-ETO (AML1-ETO, RUNX1-RUNX1T1) is expressed as the result of the 8q22;21q22 translocation [t(8;21)], which is one of the most common chromosomal abnormalities found in acute myeloid leukemia. RUNX1-ETO is thought to promote leukemia development through the aberrant regulation of RUNX1 (AML1) target genes. Repression of these genes occurs via the recruitment of the corepressors N-COR and SMRT due to their interaction with ETO. Mechanisms of RUNX1-ETO target gene upregulation remain less well understood. Here we show that RUNX1-ETO9a, the leukemogenic alternatively spliced transcript expressed from t(8;21), upregulates target gene Alox5, which is a gene critically required for the promotion of chronic myeloid leukemia development by BCR-ABL. Loss of Alox5 expression reduces activity of RUNX1-ETO9a, MLL-AF9 and PML-RARα in vitro. However, Alox5 is not essential for the induction of leukemia by RUNX1-ETO9a in vivo. Finally, we demonstrate that the upregulation of Alox5 by RUNX1-ETO9a occurs via the C₂H₂ zinc finger transcription factor KLF6, a protein required for early hematopoiesis and yolk sac development. Furthermore, KLF6 is specifically upregulated by RUNX1-ETO in human leukemia cells. This identifies KLF6 as a novel mediator of t(8;21) target gene regulation, providing a new mechanism for RUNX1-ETO transcriptional control.