The transcriptome of the leukemogenic homeoprotein HOXA9 in human hematopoietic cells

Abstract

Hematopoietic defects in HOXA9 ؊/؊ mice demonstrate a key role for this homeoprotein in blood cell development. Conversely, enforced HOXA9 expression is leukemogenic in mice, and HOXA9 is frequently activated in human acute myeloid leukemia (AML). Although HOXA9 is thought to function as a transcription factor, few downstream targets have been identified. We searched for early HOXA9 target genes by using a transient overexpression strategy in 3 hematopoietic cell lines (2 myeloid, 1 lymphoid). cDNA microarray analyses identified 220 genes whose expression was modulated at least 2-fold. Expression IntroductionHOX homeodomain proteins exert important effects during embryogenesis and blood cell development. [1][2][3] As a member of this large family, HOXA9 is expressed in normal human CD34 ϩ blood cells and is down-regulated during differentiation. HOXA9-deficient mice display a variety of myeloid and lymphoid defects. 4,5 HOXA9 overexpression in bone marrow cells induces marked stem cell expansion, and HOXA9 Ϫ/Ϫ hematopoietic stem cells appear to have a major proliferative defect 6 (H.J. L. et al, in preparation).Several studies have established a role for HOXA9 overexpression in myeloid leukemogenesis. Acute myeloid leukemia (AML) arising in leukemia-prone BXH2 mice shows frequent retroviral activation of HOXA9. 7 Retroviral overexpression of HOXA9 immortalizes murine marrow cells in vitro and readily leads to leukemic transformation in vivo. 8,9 HOXA9 is also important in human AML because this gene is activated in most patients with acute AML, and a t(7;11) chromosomal translocation resulting in a NUP98-HOXA9 gene fusion is found in some patients. 7,10 In a previous gene expression study in human leukemia, HOXA9 emerged as one of the top 20 genes that distinguished AML from acute lymphoid leukemia (ALL), and high levels of HOXA9 expression correlated with poor prognosis. 11,12 Thus, HOXA9 expression is part of the gene expression signature for AML and may also be a prognostic factor.Several HOX genes, including HOXA9, are direct targets of the mixed lineage leukemia gene (MLL), and leukemias associated with MLL translocations show uniform activation of HOXA9. [13][14][15][16] The ability of an MLL fusion gene to induce myeloid leukemia in murine marrow cells requires the presence of HOXA9, suggesting that HOXA9 is a mediator of the transforming effects of MLL fusion proteins. 17 Thus, altered HOXA9 gene expression may be a common pathway that unifies diverse initiating events in many myeloid leukemias. 18 Because HOXA9 exerts major biologic effects on normal and leukemic hematopoiesis, and because very little is known about the molecular pathways regulated by this homeoprotein, we completed a comprehensive gene expression profile of hematopoietic cells in which HOXA9 was transiently overexpressed. This study reveals that HOXA9 rapidly modulates the expression of a large number of genes that are implicated in normal hematopoiesis and in oncogenesis. Materials and methods Cell linesTetracycline (tet)-inducibl...

Tumor Suppressor p16INK4A Regulates Polycomb-mediated DNA Hypermethylation in Human Mammary Epithelial Cells

“…Many HOXA9 target genes are expressed in CD34ϩ stem cells or are members of gene families involved in proliferation or myeloid differentiation. These data suggest that HOXA9 may mediate important biologic effects in normal and leukemic hematopoiesis (53). In striking contrast, the HOXA9 region is often silenced, either through deletion or hypermeth- …”

Correlation between differentiation plasticity and mRNA expression profiling of CD34+-derived CD14− and CD14+ human normal myeloid precursors

“…7,8 This property, referred to as 'lineage switching' or 'intrahematopoietic plasticity', was initially based on the observation that a number of leukemic cell lines undergo phenotypic changes 'in vitro' as a result of specific manipulations such as pharmacological treatments 9,10 or transcription factor overexpression. 11,12 Further reports have subsequently indicated that trans-differentiation processes can be reproduced by using normal CD34 þ -derived myeloid precursors. The capacity of primary myeloblasts/promyelocytes to undergo mono-macrophage differentiation upon treatment with VD represents a typical example of this plasticity.…”

“…7,8 This biological property of hematopoietic cells, referred to as 'lineage switching' or 'intrahematopoietic plasticity', is essentially based on the observation that a number of leukemic cell lines undergo phenotypic changes 'in vitro' as a result of specific manipulations, such as pharmacological treatments 9,10 and transcription factors overexpression. 11,12 By using this approach, lineage switches between erythroid and myeloid, megakaryocytic and erythroid, or even lymphoid and myeloid cell compartments have been reported. 7 The first demonstration of an intrahematopoietic lineage switching is probably represented by the observation that HL60 leukemic myeloblasts (M2-M3 type granulocytic precursors), normally differentiating toward granulocytes upon treatment with alltrans retinoic acid (ATRA), undergo monocyte-macrophage maturation when stimulated with 1a, 25 di-hydroxy-vitamin D3 (VD).…”

Reverse recruitment: The Nup84 nuclear pore subcomplex mediates Rap1/Gcr1/Gcr2 transcriptional activation

“…We also report here that the nucleoporin Nup84 and all but one of its subcomplex components activate transcription when fused to a DNA-binding domain, a result that recapitulates oncogenic nucleoporin-HoxA9 gene fusions in acute leukemias in humans (22,23). Transcriptional activation by most nucleoporins is severely impaired by removing either the Rap1 coactivator Gcr1 or the nuclear pore complex (NPC) component Nup84.…”

“…Despite the well established connection between repression and distal location in the nucleus of S. cerevisiae and other eukaryotes, an increasing body of evidence has indicated that transcriptional activation is far from an unusual occurrence at the nuclear rim (22)(23)(24)(25)(26)(32)(33)(34)(35)(36). Most interestingly, peripheral activation may be oncogenic in acute myeloid leukemia and related syndromes in humans (23,34) (Fig.…”