Combined gene expression and DNA occupancy profiling identifies potential therapeutic targets of t(8;21) AML

Abstract

IntroductionAcute myeloid leukemia (AML) is a common hematologic malignancy characterized by an abnormal accumulation of myeloid precursors in the bone marrow and blood. Similar to many other types of cancer, genetic abnormalities are associated with the development of AML, particularly chromosomal translocations that result in novel fusion proteins. One of the common translocations implicated in AML is the 8q22;21q22 translocation [t(8;21)]. 1 Based on the French-American-British (FAB) classification of leukemic cells, t(8;21) is associated with nearly 40% of the AML cases with the FAB M2 phenotype. 2 t(8,21) involves the AML1 (RUNX1) gene on chromosome 21 and the ETO (MTG8, RUNX1T1) gene on chromosome 8. [3][4][5] AML1 is the DNA-binding subunit of the core binding factor (CBF) transcription factor complex. Its N-terminus contains a highly conserved DNA binding domain called the runt homology domain (RHD). t(8;21) fuses the N-terminus of AML1 including RHD in-frame with almost the entire ETO protein to form AML1-ETO. [3][4][5][6] This fusion protein acts as a dominant negative form of AML1 during embryogenesis. 7,8 It functions as a transcriptional repressor by interacting with NCoR/SMRT/HDAC. 9,10 AML1-ETO was shown to activate expression of BCL-2 and p21, possibly via interacting with p300. [11][12][13] AML1-ETO promotes stem cell renewal and blocks hematopoietic differentiation. [14][15][16] However, its role in blocking cell-cycle progression and promoting apoptosis contradicts its function in promoting leukemogenesis and therefore requires secondary mutagenic events for full transformation. 17,18 We previously identified a single nucleotide insertion that resulted in a truncated AML1-ETO protein (AML1-ETOtr or AEtr), which rapidly promoted leukemia. 19 Subsequently, we identified a C-terminally truncated variant of AML1-ETO named AML1-ETO9a (AE9a), resulting from alternative splicing and found to coexist with full-length AML1-ETO in most analyzed t(8;21) AML patients. 20 Similar to AEtr, AE9a causes a rapid onset of leukemia in mice, 20 which provides a useful mouse model to study the molecular biology of t(8;21) leukemia.To understand the molecular mechanism of AML1-ETOrelated leukemia development and to explore novel therapeutic targets to treat this type of leukemia, in this study we combined gene expression microarray and promoter occupancy (ChIP-chip) analyses to identify genes directly modulated by AE9a in primary murine leukemia cells. Among the common targets of microarray and ChIP-chip assays, approximately 30% show human t(8;21)-specific up or down-regulation compared with AML that have other chromosomal abnormalities. CD45, a protein tyrosine phosphatase and a negative regulator of cytokine/growth factor receptor and JAK/STAT signaling, 21-23 is among those targets. Its expression is down-regulated in AE9a leukemia cells. Consequently, JAK/STAT signaling is enhanced in these leukemia cells. We show that re-expression of CD45 suppresses JAK/STAT activation, delays leukemia development by AE9a an...

Regulation of AKT signaling by Id1 controls t(8;21) leukemia initiation and progression

“…For example, AML1-ETO and its alternatively spliced variant AML1-ETO9a have recently been shown to enhance JAK/STAT signaling via downregulation of CD45, a protein tyrosine phosphatase and a negative regulator of JAK/STAT signaling. [31][32][33] The constitutive activation of STAT transcription factors, particularly STAT5, is a common event in myeloid leukemia and is seen in Kasumi-1 cells. 28 The JAK2 inhibitor TG101209 inhibited the proliferation and promoted the apoptosis of t(8;21) leukemia cells, 29 significantly impaired the leukemia-initiating potential of AE9a leukemia cells, and prolonged the survival of AE9a leukemia-bearing mice.…”

Loss of TET2 in hematopoietic cells leads to DNA hypermethylation of active enhancers and induction of leukemogenesis

“…Further analysis of peripheral blood and bone marrow using flow cytometry revealed that the GFP-positive leukemic blasts had lost expression of CD45 (Fig. 1E), a hallmark of t(8:21) AML patients (Lo et al 2012), and displayed an immature GMP-like myeloid immunophenotype (Supplemental Fig. S1D,E).…”

Role of altered growth factor receptor-mediated JAK2 signaling in growth and maintenance of human acute myeloid leukemia stem cells

“…31 In addition to PP2A, alterations in other negative regulatory genes such as CD45, 33 lymphocyte-specific adapter protein (LNK), suppressor of cytokine signaling 1 (SOCS-1), SOCS-6, and Casitas B-lineage lymphoma (CBL) could also contribute to enhanced GF receptor signaling and warrant further evaluation in future. 27,34 JAK2 inhibitors and siRNA-mediated knockdown of JAK1/2 and STAT3/5 expression resulted in minimal inhibition of normal CD34 1 cells and did not inhibit normal HSCs engrafted in immunodeficient mice, indicating selectively targeting of AML LSCs.…”