Stem C ells C R
®
oncise eview
HOX and Non-HOX Homeobox Genes in Leukemic Hematopoiesis BRONWYN M. OWENS,a,b ROBERT G. HAWLEYa,b,c a
Hematopoiesis Department, Holland Laboratory, American Red Cross, Rockville, Maryland, USA; Program in Molecular and Cellular Oncology, Institute for Biomedical Sciences, The George Washington University, Washington, D.C., USA; cDepartment of Anatomy and Cell Biology, The George Washington University Medical Center, Washington, D.C., USA
b
Key Words. Homeobox genes · Transcription factors · Hematopoiesis · Leukemia
A BSTRACT Dysregulation of homeobox (HB)-containing genes is becoming increasingly recognized as the underlying basis of many hematologic malignancies. Expression of clustered HB (HOX) genes within the hematopoietic system, and enforced overexpression and knockout studies have provided support for the concept that these homeodomaincontaining transcription factors play a significant role in the developmental biology of hematopoietic cells. Diverged
HB (non-HOX) genes have recently been identified as either cofactors and/or accelerators of leukemic disease mediated by HOX genes or as bona fide oncogenes. In this review, we examine the evidence that supports a central role for HB genes in normal and malignant hematopoiesis, paying particular attention to the non-HOX class and the possible mechanisms through which they contribute to leukemic transformation. Stem Cells 2002;20:364-379
INTRODUCTION The finding of specific chromosomal rearrangements in acute leukemia first suggested that genes at these loci were responsible for transformation [1, 2]. Transcription factors are frequent targets in these lesions, and rearrangements can result in the generation of fusion proteins, as in E2A-PBX1 associated with pre-B-cell acute lymphoblastic leukemia (ALL) or the juxtaposition of tightly regulated genes next to highly active promoter regions. Immunoglobulin (Ig) and T-cell-receptor (TCR) loci are often involved in the latter scenario, most likely due to the fact that these genes normally undergo rearrangement during B- and T-cell development. Evaluation of breakpoint regions within translocations in leukemia patients and retroviral insertion sites associated
with hematologic malignancies in murine models has implicated several members of the homeodomain-containing (HD) family of transcription factors in leukemogenesis. HD transcription factors contain a 61-amino-acid helix-turnhelix DNA-binding domain [3]. Sequences flanking the HD also influence specificity by coordinating interaction with cofactor proteins that influence DNA-binding properties. HD encoding (homeobox [HB]) genes are broadly divided into two classes. Class I includes clustered HB (HOX) genes, recognized for their role in anteroposterior patterning during embryogenesis, while the class II divergent HB (non-HOX) genes are dispersed throughout the genome. The HOX gene loci are believed to have arisen from gene duplication and consist of 13 paralogous groups
Correspondence: Robert G. Hawley, Ph.D., Cell Therapy Research and Development, Holland Laboratory, American Red Cross, 15601 Crabbs Branch Way, Rockville, Maryland 20855, USA. Telephone: 301-738-0420; Fax: 301-738-0444; e-mail:
[email protected] Received May 23, 2002; accepted for publication July 17, 2002. ©AlphaMed Press 1066-5099/2002/$5.00/0
STEM CELLS 2002;20:364-379
www.StemCells.com
365
organized into four clusters (A-D) on chromosomes 7, 17, 12, and 2, respectively. HOX genes exhibit high homology to the HOM genes of Drosophila, with groups 1-8 being most closely related to Drosophila antennapedia (Antp), and groups 9-13 more closely related to Drosophila abdominal-B (Abd-B) [3, 4]. During embryonic development, genes of paralogous groups 1-13 are sequentially expressed 3′ to 5′ along the anteroposterior axis and are regulated in a temporal and spatial manner. HOX gene expression has been identified in normal hematopoietic tissues, including primary human CD34+ stem/progenitor cells, and in leukemic samples [5, 6]. Only expression of HOX genes from paralogous groups A, B, and C has been detected in normal hematopoietic cells, while expression from all clusters has been demonstrated in leukemic cells. The function of HOX genes in hematopoiesis has been investigated through knockout mouse models and enforced overexpression from retroviral vectors in hematopoietic stem cells from murine fetal liver and bone marrow and in human cord blood progenitors. Overexpression of HOXA10 in murine hematopoietic stem cells leads to perturbations in myeloid and B-cell differentiation, expansion of megakaryocyte progenitors, and ultimately, myeloid leukemia [7]. Mice lacking Hoxa9 have disrupted hematopoiesis, including lower numbers of lymphocytes, granulocytes, and committed progenitors of several cell lineages, but retain normal levels of more primitive progenitors with long-term culture-initiating cell activity. Conversely, overexpression of Hoxa9 results in defective Tcell development as well as acute myeloid leukemia (AML) [8-10]. HOXA5 overexpression in human bone marrow and cord blood progenitors leads to a selective greater number of myeloid cells and lower BFU-E numbers and erythroid differentiation, while the use of antisense oligonucleotides targeting HOXA5 results in a higher number of erythroid progenitors and fewer myelomonocytic cells [11, 12]. There is a strong correlation between HOXB6 expression and erythroid development, since targeted disruption of Hoxb6 results in an expansion of erythroid progenitors, and inhibition by antisense methodology decreases erythroid differentiation [13, 14]. However, HOXB6 expression also has been detected in myelomonocytic cell lines [15]. HOXB4 overexpression in embryoid bodies confers engraftment potential and induces a greater number of repopulating cells in murine bone marrow, without evidence of leukemic transformation [16-19]. In contrast, ectopic expression of HOXB3 in murine bone marrow, which is normally expressed in the CD34+Lin– (lacking lineage differentiation markers) progenitor population, results in a disruption of lymphoid differentiation, greater granulopoiesis, and myeloproliferative disease (MPD) [20]. HOXC gene transcripts have been identified in a number of hematopoietic subpopulations but have not been directly
HOX and Non-HOX Genes in Leukemic Hematopoiesis implicated in leukemogenesis. However, a number of these genes are expressed in neoplastic cells of the lymphoid lineage [21, 22]. Expression of Hoxc6 has been detected in erythroleukemic cell lines and correlates with stage of differentiation of these cells, since the use of antisense oligonucleotides to Hoxc6 inhibits late-erythroid but not BFU-E-derived colony formation [23, 24]. Expression of HOXD genes has been demonstrated in a small number of leukemic cells, including HOXD3 in the HEL erythroleukemic cell line [25] and HOXD13, which is fused to NUP98 in AML [26, 27]. These and other studies imply that HOX proteins play a direct role in normal differentiation of hematopoietic cells, with some specificity in the lineages that they influence, and that leukemia may arise due to overexpression (or perhaps absence) of HD transcription factors. Several non-HOX HD proteins have been shown to function as cofactors for HOX proteins and are cosynthesized during embryonic development. These include the three-amino-acid-loop-extension (TALE) proteins, PBX, MEIS, and PREP1/KNOX1. PBX genes are widely expressed in fetal and adult tissues, although PBX1 transcripts are notably absent from lymphocytes [28]. PBX proteins interact preferentially with the 3′ HOX proteins homologous to Antp and have been shown to influence cooperative DNA binding in vitro. PBX1 is the most frequently activated non-HOX HB oncogene in human leukemia, being translocated in 20% of pre-B-cell ALL cases to create a fusion protein with the transcription factor E2A [29, 30]. The MEIS family of cofactor proteins was initially recognized during studies of the myeloid leukemias that frequently develop in BXH-2 mice. Meis1 was found to be routinely coactivated with Hoxa7 and Hoxa9, suggesting that it acts in a cooperative capacity in leukemia development [31, 32]. MEIS proteins have been shown to preferentially interact with 5′ HOX proteins homologous to ABD-B as well as to PBX proteins [33]. PREP1/KNOX1, which encodes a protein that is normally associated with PBX proteins and plays a regulatory role in PBX availability, is broadly expressed; to date, it has not been associated with leukemic transformation [34-36]. Other non-HOX HB genes are more restricted in their patterns of expression, and their encoded HD proteins are involved in organogenesis or differentiation of specific cell types. The HOX11 protein is required for spleen development and is not normally expressed in adult tissues. However, HOX11 is highly expressed in transformed T-cell precursors bearing the t(10;14) or t(7;10) translocation found in a subset of T-cell ALL (T-ALL), where it is translocated to TCR loci [37-41]. A number of other nonHOX HB genes are expressed in normal and malignant hematopoietic cells and are discussed below.
Owens, Hawley HOX GENES IN LEUKEMOGENESIS HOX gene involvement in leukemic transformation was initially inferred by the identification of constitutive activation of the Hoxb8 (Hox2.4) gene in the WEHI-3B myeloid leukemic cell line [42]. Transcriptional activation of Hoxb8 was attributed to insertion of an endogenous intracisternal A particle (IAP) provirus into a region upstream of the Hoxb8 gene, presumably leading to a block in differentiation of myeloid lineage cells [43]. In addition, coactivation of the interleukin-3 (IL-3) gene by an IAP element was assumed to have provided autocrine stimulation for the myeloid leukemic cells and contributed to the transformed phenotype [44, 45]. Experimental overexpression of the IL3 gene alone in murine bone marrow cells results in overproduction of differentiated myeloid cells, while ectopic Hoxb8 expression results in the generation of IL-3-dependent myelomonocytic, megakaryocytic, and mast cell lines in vitro, and eventually, leukemia in vivo after a long latency period [44, 46]. Notably, enforced expression from retroviral vectors revealed that the combination of the two genes is potently transforming, with mice rapidly developing aggressive tumors [44]. Further evidence for the involvement of HOX genes in leukemia came from the identification of retroviral coactivation of Hoxa7 and/or Hoxa9 with the Meis1 gene in BXH-2 mice [32, 47]. BXH-2 mice have naturally high spontaneous activation of endogenous murine leukemia virus with a corresponding greater incidence of myeloid leukemia. Cloning of the integration sites led to the identification of the insertionally activated Hoxa7 and Hoxa9 genes in the leukemic cells as well as the discovery of the prototypic member of the Meis family of non-HOX HB genes (Meis1) [31]. These studies, involving the BXH-2 mouse strain, have provided a model for the concept of non-HOX HD cofactors as accelerators of leukemic transformation, which has been subsequently confirmed by experimental coexpression of HOX and non-HOX HB genes in primary hematopoietic precursors. Enforced expression of Hoxa9 in murine bone marrow results in AML, and coexpression of Hoxa9 and Meis1b results in accelerated development of leukemia in mice compared with expression of Hoxa9 alone [9]. Coexpression of HOXA9/HOXA7 and MEIS1 has been observed in human AML, suggesting that collaboration between HOXA9 and MEIS1 is relevant to human leukemogenesis [48, 49]. In a small subset of human AML, the HOXA9 gene is fused to the NUP98 gene, which encodes a component of the nuclear pore complex, as a result of the t(7;11)(p15;p15) chromosomal translocation [50, 51]. The chimeric protein retains the HD of HOXA9 and the phenylalanine-glycine (FG) repeats from NUP98 [51]. Enforced expression of NUP98-
366
HOXA9 in NIH3T3 cells results in transformation, assessed by colony growth in soft agar, and MPD followed by AML in mice transplanted with transduced bone marrow cells [52, 53]. The oncogenic potential of NUP98-HOXA9 has been attributed, at least in part, to the FG repeats, which are capable of interacting with the transcriptional coactivator, cAmp-response-element-binding (CREB)-binding protein (CBP/p300) [52]. NUP98 also forms a fusion protein with HOXD13 and the non-HOX HD protein PMX1, demonstrating that NUP98 is a frequent target of chromosomal translocations [26, 27, 54]. In all cases, the NUP98 FG repeats are preserved. HOXA9 can also be a potent repressor of transcription, a property that is associated with its N-terminal domain, but which is lost upon fusion with NUP98 [52]. Loss of repressor activity may contribute to its oncogenic potential. The HOXA9 HD and association with PBX via a tryptophan-containing PBX-interaction motif (PIM) are required for NUP98-HOXA9-mediated transformation of NIH3T3 cells. Since in vivo transformation due to coexpression of Hoxa9/Meis1 involves overexpression of full-length proteins, transformation due to NUP98-HOXA9 may occur through different mechanisms, specifically by cooperation with PBX proteins. A potential difference in mechanisms is further suggested by the observation that NUP98-HOXA9 induced MPD in advance of AML, a condition not seen when Hoxa9 was expressed alone or when Hoxa9 was coexpressed with Meis1 [53]. However, NUP98-HOXA9 was shown to cooperate with Meis1 in murine bone marrow transduction experiments to accelerate development of AML, although to a lesser extent than seen with Hoxa9/Meis1. Moreover, coexpression of NUP98-HOXA9/Meis1 was not acutely transforming [53]. The nature of the interaction between NUP98-HOXA9 and Meis1 is not clear, since the portion of HOXA9 responsible for interaction with Meis1 is deleted in the fusion protein. Therefore, parallel oncogenic pathways may be activated, a model that is supported by the observation that ectopic coexpression of Meis1 with HOXB3 in murine bone marrow precursors accelerated induction of AML-like disease [55]. Interestingly, while Hoxa9 does not cooperate with Pbx1 to influence the onset of leukemogenesis, it does appear to work synergistically with E2A-PBX1 and results in rapid development of AML in which primitive hematopoietic cells are the primary target [56]. Although they have not been directly implicated in human leukemia, murine bone marrow transduction experiments with retroviral vectors have demonstrated that ectopic expression of a number of other HOX genes can perturb hematopoiesis. As noted above, mice transplanted with bone marrow expressing high levels of HOXA10 ultimately developed AML after a long latency [7]. By comparison, Hoxb4 overexpression selectively induced
367
the expansion of hematopoietic stem cells but did not result in leukemic transformation [16, 18], whereas constitutive expression of Hoxb3 resulted in perturbation of lymphocyte development and MPD [20, 57]. Since experimental data suggest that HOX genes have the potential to contribute to leukemia more than initially appreciated, inappropriate activation through demethylation or disruption of transcriptional regulatory pathways may also activate HOX gene expression in leukemic cells. In Drosophila, the trithorax (Trx) gene is required for maintenance of HOM gene expression, while polycomb (PcG) genes negatively affect HOM gene expression [58, 59]. This is of particular relevance, since the human ortholog of Trx, MLL, which is located at chromosome 11q23, is frequently involved in translocations associated with biphenotypic or mixed-lineage leukemia [60]. MLL is required for normal hematopoiesis since Mll+/– mice are anemic and have lower B-cell populations and myeloid lineage cell numbers [61]. Furthermore, analysis of yolk sac cells revealed that early hematopoiesis was affected in heterozygous and homozygous null mutants [62]. Body patterning and Hox gene expression are altered in Mll+/– mice, as in Trx+/– Drosophila, and the changes are consistent with the hypothesis that Mll is involved in maintenance rather than initiation of Hox gene expression [63]. Interestingly, a correlation has been made between a specific translocation involving MLL, t(4;11), and the upregulation of HOXA9 and MEIS1 expression in ALL [64]. This observation provides support for the notion that aberrant HOXA9 and MEIS1 coexpression in some cases of human leukemia may be due to indirect mechanisms. TALE COFACTOR PROTEINS Many HD proteins bind to common or similar DNA targets in vitro. In order to increase the specificity of the target sequence, HOX proteins interact with non-HOX HD cofactor proteins, and it is believed that these complexes can activate or repress a specific array of genes (Fig. 1). Members of the TALE family of non-HOX HD cofactor proteins, which include PBX, MEIS, and PREP1/KNOX1 proteins, are distinguished from other HD proteins by the inclusion of an additional three amino acids between α-helices 1 and 2 within the HD. Evidence from mouse models and human leukemic cells has indicated that inappropriate expression of TALE cofactors with certain HD proteins may contribute to leukemic transformation, while overexpression of TALE cofactors alone does not lead to disease development. However, as noted above and discussed in detail below, one of these proteins, PBX1, has oncogenic potential in the form of a fusion protein with E2A. The PBX1 gene was originally identified at the breakpoint of the t(1;19) translocation found in childhood pre-B-cell
HOX and Non-HOX Genes in Leukemic Hematopoiesis ALL [29, 30]. Subsequently, two other PBX genes were identified [28]. The Drosophila ortholog of PBX, extradenticle (exd), has been shown to interact with Drosophila HOM genes and influence segment identity [65-68]. PBX genes are widely expressed among different cell types, including hematopoietic cells, although PBX1 is somewhat restricted in its expression compared with PBX2 and PBX3. Knockout studies of Pbx1 revealed its critical role in myelopoiesis; a severe reduction in common myeloid progenitors was observed in Pbx1-deficient animals, which died in utero due to anemia [69]. PBX proteins have been demonstrated to interact with HOX proteins in vitro on DNA target sequences, each protein binding to a specific DNA half site [70, 71]. PBX modulates the DNA binding of HOX proteins, and this interaction is mediated through the PIM located N-terminal to the HD in HOX proteins and through sequences in the HD and the C-terminal portion of PBX [72-74]. PBX proteins do not directly interact with 5′ HOX proteins since the pentapeptide motif is absent in paralogous groups 11-13. Instead, HOX proteins of groups 11-13 interact with MEIS/PREP proteins via N-terminal sequences in HOX, while paralogous groups 9 and 10 can interact with both PBX and MEIS/PREP [75]. Given that HOX proteins of paralogous groups 9 and 10 can interact with both PBX and MEIS, target gene expression may be dependent on differential availability of these cofactors. While MEIS1 was discovered in the context of leukemia, a related factor, PREP1 (PBX-regulating protein), was identified as a constituent of urokinase enhancer factor 3 (UEF3), associated with the induction of urokinase plasminogen activator expression [34]. PREP1 bears high homology to MEIS1 in two N-terminal regions, HR1 and HR2, and interactions between MEIS/PREP1 and PBX are mediated by N-terminal sequences from both proteins. However, in contrast to MEIS1, PREP1 was incapable of accelerating leukemogenesis when coexpressed with HOXA9 [55]. MEIS/PREP1 proteins regulate PBX availability for HOX proteins by inducing a conformational change in PBX that uncovers nuclear localization signals in the PBX HD [7678]; PBX mutants with a deletion in the N-terminal domain of PBX accumulate in the nucleus since the nuclear localization sequences are no longer masked [78]. Furthermore, nuclear import of Drosophila Exd has been observed downstream of Wingless and Decapentaplegic signaling [79], suggesting that extracellular signaling can modulate the availability of PBX for HOX protein function through interaction with MEIS/PREP1 in mammalian systems. Higher order complexes of HOX/PBX/MEIS proteins have been isolated from several cells types and, depending on the target sequence, some or all of the HDs may physically interact with the DNA [80-82]. Trimer complexes of
Owens, Hawley
368
Transcriptional activation
A
B
HD protein complex
CoA Transcriptional machinery
Transcriptional repression
C
D CoA/CoR
Figure 1. HD protein-dependent transcriptional dysregulation. Transcriptional activation: (A) In normal settings, HD proteins (H) interact with transcriptional coactivators (CoA) and/or components of the basal transcriptional machinery, including RNA polymerase II, TATA-binding protein, TFIIB, and other general transcription factors, in the presence of non-HOX HD cofactors (Co) and DNA target sequences. In these situations, HB gene expression is tightly regulated. (B) HB genes are frequently activated by chromosomal translocations in human leukemias, which, in many instances, produce fusion genes that encode chimeric HD proteins with enhanced transactivation potential. Dysregulated HB gene expression, thus, leads to quantitative and/or qualitative changes in HD protein interactions with cofactors, resulting in inappropriate transcription of downstream target genes. Transcriptional repression: (C) Repression of downstream target gene expression by HD proteins may normally be mediated by competition for binding sites of other transcription factors or through specific interactions with transcriptional coactivators/corepressors (CoA/CoR; e.g., CBP/p300) in DNA-dependent or DNA-independent manners. (D) Aberrant synthesis of HD proteins may result in inhibition of downstream target gene expression via the mechanisms described in C. HD protein-mediated disruption of transcriptional regulatory networks may lead to greater proliferation of hematopoietic precursors concomitant with a block in differentiation as an initiating event in leukemogenesis. The key HD protein downstream target genes that are up- or downregulated according to the scenarios depicted in B and D, respectively, remain to be identified.
HOXA9/PBX/MEIS have been isolated from myeloid cells in the absence of DNA binding [82]. This observation is somewhat at odds with the demonstration that Hoxa9 can immortalize bone marrow progenitors in the absence of Meis1 [83], but may indicate that multiple pathways are concurrently activated. The contribution of intact TALE HD proteins to transformation seems to be primarily related to their function as cofactors leading to augmentation of the transcriptional signal. However, the E2A-PBX1 fusion protein is oncogenic in humans and in murine models. E2A-PBX1 arises as a result of the fusion of two N-terminal transactivation domains from
the basic helix-loop-helix transcription factor E2A with the majority of the PBX1 protein, including the HD. The E2A gene encodes two proteins, E12 and E47, required for initiation of B-cell lymphopoiesis, and thus, expression of the E2A-PBX1 fusion protein is directed to the pre-B-cell compartment [84]. In addition to its oncogenic role in B-cell neoplasia in humans, E2A-PBX1 has been shown to transform fibroblasts that give rise to tumors in nude mice and to induce myeloid malignancies preceded by MPD in mice transplanted with E2A-PBX1-transduced bone marrow [56, 85]. Ectopic E2A-PBX1 expression in murine hematopoietic precursors in vitro resulted in the generation of factor-dependent
369
myeloid progenitor cell lines, suggesting that E2A-PBX1 is primarily involved in blocking differentiation [86]. E2APBX1 transgenic animals have also been shown to develop premalignant disease involving the spleen and thymus [87]. Cells carrying the E2A-PBX1 transgene exhibit greater rates of cell death as well as proliferation, and the animals ultimately develop T-cell lymphomas. Mutational analysis has demonstrated that the transactivation domains of E2A are essential for transformation. Structure-function studies indicate that the HD is dispensable for transformation of fibroblasts in vitro or T lymphocytes in vivo, but the HOX cooperativity motif and other portions of PBX N-terminal to the HD are required [68, 8890]. In contrast, the HD is essential for immortalization of myeloid cells [89]. PBX1 repressor function has been localized to an N-terminal domain, which is retained in E2APBX1 and appears to be independent of specific DNA binding. This domain may mediate repression through as yet unidentified cellular factors and may account for the difference in transforming capabilities of E2A-PBX1 mutants in NIH3T3 cells and T lymphocytes relative to myeloid cells. Several possible mechanisms of transformation have been proposed. Addition of the activation domains from E2A confers dominant transactivating activity on PBX1 and, likely, leads to inappropriate downstream gene expression. Indeed, E2A-PBX1 is a strong activator of transcription from the PBX responsive sequence (PRS), whereas PBX alone can bind at this site but is incapable of initiating transcription [91-93]. Overexpression of E2A-PBX1 may compete for DNA target sites, resulting in displacement of PBX2 and PBX3, both of which are normally expressed in B cells. Constitutive activation at responsive sites, which would otherwise be tightly controlled, would lead to a loss of gene regulation. Transformation may, therefore, occur due to overexpression of the E2A-PBX1 fusion protein, which then cooperates with 3′ HOX proteins, amplifying their effects inappropriately in the pre-B-cell compartment. Evidence for such cooperation, albeit in myeloid cells, was provided by experimental data showing that combining E2A-PBX1 with HOXA9 resulted in acceleration of AML [56]. In addition, since PBX1 interacts with MEIS/PREP1 proteins via its N-terminal domain, including the region that is deleted in the chimeric E2A-PBX1 oncoprotein [94], E2A-PBX1 may be restricted from binding to PBX/MEIS target sites. Altered subcellular localization may also be a factor, since E2A-PBX1 is confined to the nucleus. As discussed above, HD cofactors can contribute to leukemia development in the case of HOXA7/9 and MEIS1 [48, 49]. HOXB3 and HOXB4 also have been shown to interact with PBX1, and coexpression of these genes resulted
HOX and Non-HOX Genes in Leukemic Hematopoiesis in greater colony formation in soft agar, as well as higher rates of proliferation and transformation of Rat-1 cells [95]. Hoxb8 requires interaction with Pbx1 to arrest myeloid differentiation [96]. ANTP SUPERCLASS OF DIVERGENT HB GENES There are numerous other HD proteins, beside those cofactors for HOX proteins, that have specific functions in organogenesis and tissue differentiation. Several of the corresponding HB genes occur in clusters dispersed throughout the human genome that are conserved in other organisms. Phylogenetic analysis of the ANTP superclass of genes suggests that these dispersed HB genes also arose due to gene duplication, since a number of common clusters have been identified in amphioxus (Branchiostoma belcheri), Drosophila, mice, and humans. These clusters— extended HOX, NKL, paraHOX, and EHGbox—are believed to have diverged early during vertebrate evolution [97]. For example, the 93D/E cluster in Drosophila, related to the NK cluster in mammalian genomes, contains several genes, including 93Bal and ladybird late, that are homologous to the HOX11 and LBX genes, respectively, which map to 10q24 in the human genome [98, 99]. A few of these tissue- and organ-specific HB genes have been implicated in leukemogenesis and are discussed here. HOX11/TCL3 and HOX11L2 The diverged HB oncogene, Hox11, has been proposed to act as a survival factor for splenic precursors and is required for organogenesis of the spleen, since Hox11–/– mice are asplenic [100, 101]. HOX11 (TCL3) was originally identified at the breakpoint of the t(10;14) translocation found in 7%-10% of pediatric T-ALL cases, and subsequently, in the t(7;10) translocation [37, 38, 40]. Rearrangements involving HOX11 juxtapose the intact gene next to TCRδ or TCRβ regulatory regions. As a result, the fulllength protein is expressed at high levels in thymocytes, in which it is otherwise absent, suggesting that its deregulation is an early step in leukemogenesis [102]. In addition to participating in two known translocation events in T-ALL, HOX11 is also frequently activated in T-ALL in the absence of overt genetic rearrangement. Promoter demethylation was correlated with HOX11 activation in the T-ALL specimens examined, regardless of whether it was found to be translocated [103]. These data showed that HOX11 was expressed in up to one-third of T-ALL cases. HOX11 can behave as an oncogene in other contexts under experimental conditions. Constitutive expression of HOX11 from the murine stem cell virus retroviral vector in murine bone marrow results in immortalization of hematopoietic precursors and subsequent leukemia formation with long latency (7-12
Owens, Hawley months) [39, 104]. Enforced expression from IgHµ transcriptional regulatory sequences in transgenic animals induced mature B-cell lymphomas over a 20-month period [105]. These results suggest that HOX11 is specifically associated with T-cell malignancy in humans because of aberrant TCR rearrangement. In other studies, ectopic HOX11 expression during in vitro hematopoietic differentiation of murine embryonic stem cells efficiently led to the establishment of novel cell lines with primitive and definitive erythroid properties [106]. Collectively, these findings suggest that the transforming capacity of HOX11 derives from its ability to alter gene expression programs regulating hematopoietic differentiation pathways. HOX11 contains a partial Hep motif (named for its presence in H2.0, engrailed and paired HD proteins), which may be involved in transcriptional repression activity, and a pentapeptide motif (FPWME) for PBX interactions. Recent data suggest that TALE HD cofactor interactions may be important for transformation induced by HOX11 [107]. HOX11 can interact with all PBX proteins, and PBX2 is highly expressed in the ALL-SIL and K3P T-ALL cell lines, which contain the t(10;14) translocation. In addition, trimeric complexes of HOX11, PBX2, and MEIS1b were shown to exist in vitro, and coexpression of HOX11 and PBX2 from a retroviral vector induced focus formation in NIH3T3 cells [107]. HOX11-mediated transformation may be a result of de novo expression of downstream HOX11 target genes or competition with the DNA-binding sites of HOX genes, blocking or mimicking their effects. Several studies have suggested a number of possible models. HOX11 interacts with CCAAT-box-binding transcription factor 1 (CTF1) in a HOX11-immortalized hematopoietic progenitor cell line [108]. CTF1 is a ubiquitous transcription factor that interacts with TFIIB, a component of the basal transcriptional machinery, suggesting a mechanism by which HOX11 directly regulates transcriptional activation or repression. Representational difference analysis for investigation of HOX11 target genes in transduced NIH3T3 cells identified the aldehyde dehydrogenase 1 (Aldh1) gene [109]. The possible significance of ALDH1 in leukemogenesis is uncertain though, since it does not appear to be expressed in HOX11positive T-ALL cells [109]. Another potential downstream target of HOX11 is the Wilms’ tumor (WT) 1 tumor suppressor gene, a zinc finger-containing transcription factor, homozygous deletion of which is associated with pediatric nephroblastoma. Wt1 is required for spleen development [110] and appears to act downstream of Hox11 during spleen organogenesis [111], but whether expression of WT1 is regulated by HOX11 in T-ALL is not known. Our data show that HOX11 can act as a repressor of transcription,
370
possibly by interfering with a component of the basal transcriptional machinery, and repression occurs in the absence of PBX cofactor interactions or an obvious HD DNA-binding site (our unpublished observations). The consequences of HOX11 expression may, therefore, be dependent on cellular context and cofactor availability. HOX11 has also been shown to interact with the serine/threonine protein phosphatases, PP1 and PP2A, and to disrupt a G2/M cell-cycle checkpoint [112]. Interaction with PP1/PP2A occurs in the absence of DNA binding and indicates a possible DNAindependent mechanism of HOX11-transforming function. Recently, the HOX11 family member, HOX11L2, was found to be transcriptionally activated as a result of the t(5;14)(q35;q32) translocation in T-ALL [113]. Notably, HOX11L2 overexpression was also identified in a subset of HOX11-negative T-ALL samples that exhibited the gene expression signature associated with authentic HOX11expressing cases revealed by gene profiling experiments [114]. Highlighted in this study was a correlation between HOX11L2 expression and a less favorable disease outcome compared with HOX11-positive leukemia. While the basis for this remains to be determined, these new findings suggest that the HOX11 family of HB genes contributes to T-ALL more than previously appreciated. HLX/HB24 Human and mouse orthologs of HLX (HB24) were independently identified from an activated human B-cell library and a murine pre-B-cell library, respectively [115, 116]. The HLX protein contains a Hep motif but lacks a PBX interaction motif. HLX is normally expressed in a number of tissues, including the mesenchyme of developing animals, primarily in regions that give rise to the liver, gall bladder, and gut [117]. HLX is also expressed in hematopoietic cells, including bone marrow cells enriched for CD34+ precursors [115, 116, 118]. Hlx knockout animals died at E15 due to anemia and lack of development of liver and gut [119]. Failure in hematopoiesis was shown to be due to impaired liver development, since fetal liver cells from Hlx–/– mice were transplantable and could reconstitute irradiated animals. It has been proposed that Hlx is involved in regulating epithelial-mesenchymal interactions in these tissues as well as in the placenta [120]. Although not essential for hematopoiesis, transgenic mice with HLX placed under the control of the TCRβ promoter exhibit altered T-cell development [121]. Specifically, ectopic HLX expression inhibited the differentiation of double-positive thymocytes into CD4+ T cells. Similarly, transgenic mice expressing murine Hlx in the B- and T-cell compartments exhibited defects in both B- and T-cell development [122]. In addition to its potential to disrupt
371
normal T-cell development, HLX enhanced tumorigenicity of the Jurkat T-cell line in nude mice [123]. HLX-expressing Jurkat T cells exhibited a greater rate of cell-cycle progression and upregulation of cell-surface activation markers (human leukocyte antigen DR, IL-2Rα, leukocyte function-associated antigen-1) [124]. As elevated levels of HLX have been observed in acute leukemias, it is possible that this HB gene may contribute to the leukemic phenotype in some instances [125, 126]. HEX HEX (hematopoietically expressed HB; Hhex/Prh) was initially identified in human hematopoietic cells, where it is expressed in multipotential progenitors, myeloid cells, and B cells, but not T or erythroid cells [127]. HEX expression has also been detected in peripheral blood leukocytes from leukemia patients [127, 128]. HEX/Hex expression is downregulated upon progenitor cell differentiation to monocytes/macrophages and megakaryocytes, while maintained or upregulated in granulocytes. Outside of the hematopoietic system, HEX/Hex transcripts have been detected in adult liver, lung, and thyroid tissues [129-133]. During embryogenesis, Hex is expressed in the forebrain, fetal liver, and thyroid [131] and is an early marker of endothelial cell precursors [133]. HEX is highly conserved across species, and orthologs have been identified in chicken, where it is expressed in bone marrow, peripheral blood and bursa, lung, and liver cells [134], as well as zebrafish and Xenopus. The HEX gene is located on chromosome 10 at 10q23 near HOX11 with which it shares high sequence similarity [127, 130]. Interestingly, HEX lacks the PIM but does contain a Hep motif within its N-terminus. HEX can repress transcription in vitro and in vivo, and in the zebrafish, overexpression of Hex results in the downregulation of bmp2b and wnt8 [132, 135, 136]. Interestingly, the HD is not required for repression in vitro, suggesting that sequestration of transcription factors may be a possible mechanism of repression. Hex–/– mice died at day E10.5 due to lack of liver formation [137]. Examination of hematopoiesis revealed normal differentiation of erythroid colonies, but granulocyte-macrophage colony-forming cell differentiation was impaired and monocytes were fewer or absent [137]. The possibility that HEX may be involved in leukemic processes is suggested from its expression in a number of human leukemia samples and from experimental evidence of retroviral insertional activation in B-cell leukemias arising in AKXD mice [138]. Interestingly, an interaction between Hex and c-Jun, a component of the AP-1 transcription factor complex, has been identified in which Hex binds to the N-terminal portion of Jun via the third helix of its HD
HOX and Non-HOX Genes in Leukemic Hematopoiesis [139]. Hex preferentially binds to Jun/Fos dimers, repressing transcription from AP-1 target sequences. Since AP-1 complexes mediate the transcriptional response to extracellular signals from growth factors, disruption of these pathways could have significant effects on cell differentiation or apoptosis. PMX1 PMX1 (Mhox1/Prx1/Phox1) is a member of the paired HB family of genes, but it also bears considerable homology with members of the ANTP HB gene family. It is primarily associated with embryonic mesoderm development and is involved in skeletal, heart, and forebrain development [140]. Knockout mice have abnormal vasculature and surrounding matrix as well as impaired skeletogenesis [141]. PMX1 does not appear to have a primary role in hematopoiesis, but it was identified as part of a fusion protein involved in the t(1;11)(q23;p15) translocation, which places the activation domain of NUP98 upstream of PMX1, resulting in constitutive expression. PMX1 can also interact with Maf oncoproteins to inhibit their DNA binding and transforming potential [142]. The relationship is not well understood, but inappropriate interaction with Maf proteins could potentially disrupt myeloid or erythroid differentiation schemes regulated by c-Maf or MafB, respectively. A further potential mechanism of action for PMX1 is implied by the observation that it and other members of the paired HB family can interact with pRB proteins, a family of tumor suppressor proteins that are frequently targeted in transformation [143]. DLX The DLX genes are related to the Drosophila distal-less gene. To date, eight DLX-like genes have been identified in humans. DLX7, which maps to chromosome 17q23, is expressed in normal bone marrow cells and leukemic cell lines with erythroid characteristics, e.g., K562 and HEL [144]. DLX7 levels increase upon differentiation of HEL with hemin, and antisense oligonucleotides to DLX7 in K562 lead to apoptosis and decreases in c-MYC and GATA1 levels. Therefore, DLX7 may be involved in hematopoietic cell survival and/or proliferation. A related gene, BP1, is also overexpressed in a large number of acute leukemias, particularly those of the monocytic lineage [145]. BP1 was originally identified as a repressor of β-globin gene expression; K562 cells overexpressing BP1 had a greater ability to grow in soft agar, suggestive of greater oncogenic potential [145]. Sequencing analysis suggests that DLX4, DLX7, and BP1 may be splice variants of a common gene, since they exhibit high levels of sequence identity [146]. Downstream target genes may be differentially regulated by this set of proteins,
Owens, Hawley since DLX7 binds to silencer I DNA located upstream of the β-globin gene but does not repress transcription [147]. LHX2 LIM domains are zinc-finger-like domains that are associated with protein-protein interactions rather than direct DNA binding. LHX2 (LH2; LIM-HD protein 2) was independently cloned from a pre-B-cell library and as an activator of the glycoprotein hormone α subunit, and is expressed in the γδ subset of T cells and the developing nervous system [148, 149]. Knockout mouse models demonstrated the requirement for Lhx2 for efficient development of definitive erythropoiesis [150]. The defect in erythroid development is likely to be due to a compromised fetal liver microenvironment rather than an intrinsic hematopoietic cell defect, since transplant of fetal liver cells into lethally irradiated mice resulted in reconstitution of erythropoiesis [150]. LHX2 expression has also been found at high levels in chronic myelogenous leukemia (CML) patients [151]. The LHX2 gene is located proximal to the region of chromosome 9 involved in the Philadelphia translocation and has been proposed to be activated, in part, due to the expression of BCR-ABL [152]. The significance of LHX2 expression in CML cells is unclear though, since LHX2 mRNA is also found in leukocytes from normal individuals, patients with chronic myeloproliferative disorders, and in Epstein-Barr virus-derived lymphoblastoid cell lines from CML patients, regardless of the status of BCR-ABL [153]. However, Lhx2 can immortalize kit ligand-dependent hematopoietic cell lines derived from murine embryonic stem cells differentiated in vitro [154]. These cell lines have the surface phenotype of hematopoietic stem/progenitor cells (CD34+, c-kit+). Moreover, Lhx2 can also immortalize hematopoietic stem cells in murine bone marrow with long-term engrafting potential as measured by serial transplantation in W41/W41 (ckit-defective) recipients [155], arguing for a role of LHX2 in CML pathophysiology. GBX2 Gastrulation and brain specific-2 HB gene (GBX2) is highly conserved among humans, mice, and chickens [156]. It has been particularly associated with prostate cancer and may be a marker of metastatic disease [157]. GBX2 has also been identified as a downstream target of the Myb oncogene; therefore, while it has not been directly implicated in human leukemia, it appears to be an intermediate of signaling through a pathway involved in myeloid cell differentiation [116, 141, 153, 158]. In the avian system, the v-myb oncogene associated with avian myeloblastosis virus induces the expression of Gbx2, which leads to the production of chicken myelomonocytic growth factor, allowing
372
autocrine growth stimulation of myeloid leukemic cells. Since Gbx2 induces an autocrine phenotype in cells that are dependent on exogenous cytokines for growth, a possible mechanism is suggested through which this HD protein could provide an early step during leukemic progression. CDX2 The normal expression of CDX2, a caudal-related HB gene, is tightly restricted to intestinal development. Lower expression of CDX2 has been associated with colorectal carcinoma, and mice heterozygous for Cdx2 have a propensity for developing adenomatous polyps and colon tumors [159-162]. CDX2 expression could be restored in a colorectal cancer cell line by introduction of a functional copy of the APC tumor suppressor gene, suggesting a critical relationship between these factors in colorectal carcinogenesis [160]. CDX2 is not normally expressed during hematopoietic differentiation, but it has been identified as one of the components in a fusion protein found in AML. This is, thus, another example (e.g., HOX11, PMX1) where a developmentally regulated HD protein not normally associated with hematopoiesis has been commandeered for leukemic outcome. CDX2 was identified as one of the genes involved in the t(12;13) translocation, fusing ETV6 (TEL) and CDX2 [163]. CDX2 expression was also observed in a case of leukemia lacking the translocation, indicating that CDX2 expression may be dysregulated through other means. CDX2 has been shown to interact with CBP in the Caco-2 intestinal cell line and to potentiate its transcriptional activity, suggesting that aberrant expression of downstream targets could represent a possible mechanism of CDX2-associated transformation in both colorectal carcinoma and leukemia [164]. MOLECULAR MODELS OF HB-GENE-MEDIATED TRANSFORMATION A number of models involving transcriptional activation or repression have been proposed to account for how HB genes may contribute to leukemogenesis (Fig. 1). HOX genes are preferentially expressed in primitive hematopoietic cells [5]. Therefore, inappropriate expression of HB genes or generation of a constitutively active HD-containing fusion protein could result in persistence of downstream target gene expression, perpetuating signals that prevent differentiation, and/or result in greater proliferation of hematopoietic precursor cells. Overexpression of non-HOX HD cofactor proteins, such as PBX or MEIS, or loss of regulation by MLL, can alter HOX protein function and levels. Experimentally, non-HOX HB gene cofactor activation, when coupled with HOX gene overexpression, has been shown to lead to a
373
rapidly developing acute leukemia [9, 32, 44, 47]. The probability of formation of HOX-containing complexes capable of DNA binding and transcriptional activation or repression increases in the presence of excess PBX or MEIS, since neither the cofactors nor the HOX proteins are limiting. Interestingly, although overexpression of HOXA10 in murine hematopoietic stem cells gives rise to myeloid leukemia [7], ectopic expression of HOXA10 has been shown to upregulate the cyclin-dependent kinase, p21, and induce differentiation of U937 myelomonocytic cells [165]. Differential HD cofactor availability may account for these contrasting outcomes. The HOXA5 gene has been shown to transactivate the p53 gene promoter and is preferentially methylated in breast cancer cells [166], concomitant with loss of expression of both genes. Although the p21 gene is a downstream effector of p53, no specific association between loss of HOXA5 expression (or loss of expression of other HOX genes) and leukemic hematopoiesis has been reported. Replacement of regulatory domains of HD proteins can also change the nature of the transcription factor. E2A-PBX1 is constitutively nuclear and acts as a transcriptional activator in contrast to wild-type PBX1, which has transcriptional repressor activity and requires association with MEIS/PREP1 for nuclear import. Similarly, a repressor domain of HOXA9 is deleted during the formation of the NUP98-HOXA9 oncoprotein [52]. Experimental data have indicated that certain HD proteins can interact with transcriptional coactivators or corepressors depending on availability, potentially providing an explanation for the differences in gene expression observed in different cellular milieu. One class of coactivators is exemplified by CBP and p300. Interaction of NUP98HOXA9 with CBP has already been discussed, and is hypothesized to be the means through which the fusion protein initiates aberrant gene expression. CBP and p300 are large, complex multidomain proteins that have inherent histone acetyltransferase activity and can participate in chromatin remodeling as well as acetylation of transcription factors [167, 168]. It is noteworthy that CBP/p300 can mediate both activation and repression of gene expression, and the proteins act as pro- or antidifferentiation factors depending on promoter context and associated factors. CBP/p300 interact with phosphorylated forms of CREB and other transcription factors, such as c-Jun, c-Fos, and p53, and can function as molecular scaffolds, bridging activators or repressors of transcription with the basal transcriptional machinery. Both are required for normal development, as the knockouts result in embryonic lethality. CBP is hypothesized to be a tumor suppressor gene, since it is targeted by various viral oncogenes including adenovirus E1A and simian virus 40 large T antigen, and heterozygosity in Rubenstein-Taybi
HOX and Non-HOX Genes in Leukemic Hematopoiesis syndrome (RTS) is characterized by a higher risk of malignancy in addition to multiple developmental abnormalities. CBP+/– mouse models of RTS exhibit extensive defects in normal hematopoietic differentiation with compensatory extramedullary hematopoiesis resulting in splenomegaly. Both humans and murine models exhibit a higher risk for hematologic malignancy. Interestingly, p300+/– mice do not have the same phenotype, suggesting a special role of CBP in hematopoietic regulatory mechanisms. Several HD proteins have been shown to interact directly with CBP. HOXB7 transactivation in transformed cells is induced by direct interaction with CBP, and this activity is augmented by the addition of trichostatin A, a histone deacetylase inhibitor [169]. The pancreatic factor, Pdx1, can act as both a transactivator and a repressor. Analysis of the heterodimeric Pdx-Pbx fusion protein showed that transactivation was mediated through association with CBP via the Pdx-1 N-terminal domain. Conversely, repression was brought about by association with a specific protein isoform of Pbx1, since interaction with Pbx1a but not Pbx1b recruited N-CoR/SMRT corepressors [170]. Interestingly, E2A-PBX1b possesses greater transforming potential than E2A-PBX1a [171], possibly reflecting differential interaction with corepressors. A similar observation was made with regard to the interaction of Hoxb1 on its autoregulatory element, in which HOX-PBX complexes recruit either corepressors (HDACs/N-CoR/SMRT) or CBP, a switch that was stimulated by extracellular signaling [172]. Hoxb1 does not efficiently activate or repress transcription in the absence of PBX, demonstrating that physical interaction with the HD cofactor protein is required. Shen and colleagues further demonstrated that a direct interaction between HOX proteins and CBP could result in a block of CBP histone acetyltransferase activity [173]. The region of the HD protein that interacted with CBP varied, but for some HOX proteins, it was localized to the HD. However, broad association with CBP does not account for the specificity of functions mediated by HD proteins. Other mechanisms of HD protein-mediated repression have been described, including direct repression by interfering with other components of the basal transcriptional machinery, competition with coactivators for DNA-binding sites, and quenching of transcriptional coactivators by blocking their transactivating ability [174-179]. CONCLUSIONS Studies of HB gene expression in primary human hematopoietic cells and leukemic samples, as well as knockout and retroviral transduction models, have provided evidence for the critical role of members belonging to both the HOX and non-HOX classes in hematopoietic regulatory
Owens, Hawley mechanisms and leukemic transformation. At present, only a limited number of HB genes are directly implicated in leukemogenesis in humans, but those identified contribute to a considerable proportion of the clinical cases. Moreover, given the high incidence of rearrangements involving MLL [60] and the recent appreciation of greater involvement of HOX11 family members in T-ALL [103, 113, 114], it is conceivable that HOX and non-HOX HB genes may be more widely involved in hematologic malignancies than heretofore appreciated. The DNA sequences targeted by HOX protein/non-HOX HD cofactor complexes in vivo are still incompletely defined, and future studies better characterizing these will assist in distinguishing the key downstream target
374
genes. Elucidation of the principal target genes regulated by HOX proteins during normal hematopoietic development will shed light on the manner in which the transcriptional networks they control are perturbed by aberrant expression of HOX and non-HOX HB genes, resulting in leukemia. ACKNOWLEDGMENTS This work was supported in part by National Institutes of Health grant HL66305 (to R.G.H.) and performed in partial fulfillment of the requirements for the Ph.D. degree in Molecular and Cellular Oncology from the Institute for Biomedical Sciences, The George Washington University, Washington, D.C. (B.M.O.).
R EFERENCES 1 Look AT. Oncogenic transcription factors in the human acute leukemias. Science 1997;278:1059-1064. 2 Rabbitts TH. Chromosomal translocations in human cancer. Nature 1994;372:143-149. 3 Gehring WJ, Affolter M, Burglin T. Homeodomain proteins. Annu Rev Biochem 1994;63:487-526. 4 Gehring WJ, Qian YQ, Billeter M et al. HomeodomainDNA recognition. Cell 1994;78:211-223. 5 Magli MC, Largman C, Lawrence HJ. Effects of HOX homeobox genes in blood cell differentiation. J Cell Physiol 1997;173:168-177. 6 Sauvageau G, Lansdorp PM, Eaves CJ et al. Differential expression of homeobox genes in functionally distinct CD34+ subpopulations of human bone marrow cells. Proc Natl Acad Sci USA 1994;91:12223-12227. 7 Thorsteinsdottir U, Sauvageau G, Hough MR et al. Overexpression of HOXA10 in murine hematopoietic cells perturbs both myeloid and lymphoid differentiation and leads to acute myeloid leukemia. Mol Cell Biol 1997;17:495-505. 8 Izon DJ, Rozenfeld S, Fong ST et al. Loss of function of the homeobox gene Hoxa-9 perturbs early T-cell development and induces apoptosis in primitive thymocytes. Blood 1998;92:383-393. 9 Kroon E, Krosl J, Thorsteinsdottir U et al. Hoxa9 transforms primary bone marrow cells through specific collaboration with Meis1a but not Pbx1b. EMBO J 1998;17:3714-3725. 10 Lawrence HJ, Helgason CD, Sauvageau G et al. Mice bearing a targeted interruption of the homeobox gene HOXA9 have defects in myeloid, erythroid, and lymphoid hematopoiesis. Blood 1997;89:1922-1930. 11 Crooks GM, Fuller J, Petersen D et al. Constitutive HOXA5 expression inhibits erythropoiesis and increases myelopoiesis from human hematopoietic progenitors. Blood 1999;94:519-528. 12 Fuller JF, McAdara J, Yaron Y et al. Characterization of HOX gene expression during myelopoiesis: role of HOX A5 in lineage commitment and maturation. Blood 1999;93:3391-3400.
13 Kappen C. Disruption of the homeobox gene Hoxb-6 in mice results in increased numbers of early erythrocyte progenitors. Am J Hematol 2000;65:111-118. 14 Shen WF, Largman C, Lowney P et al. Expression of homeobox genes in human erythroleukemia cells. Adv Exp Med Biol 1989;271:211-219. 15 Ohnishi K, Tobita T, Sinjo K et al. Modulation of homeobox B6 and B9 genes expression in human leukemia cell lines during myelomonocytic differentiation. Leuk Lymphoma 1998;31:599-608. 16 Thorsteinsdottir U, Sauvageau G, Humphries RK. Enhanced in vivo regenerative potential of HOXB4-transduced hematopoietic stem cells with regulation of their pool size. Blood 1999;94:2605-2612. 17 Helgason CD, Sauvageau G, Lawrence HJ et al. Overexpression of HOXB4 enhances the hematopoietic potential of embryonic stem cells differentiated in vitro. Blood 1996;87:2740-2749. 18 Antonchuk J, Sauvageau G, Humphries RK. HOXB4induced expansion of adult hematopoietic stem cells ex vivo. Cell 2002;109:39-45. 19 Kyba M, Perlingeiro RC, Daley GQ. HoxB4 confers definitive lymphoid-myeloid engraftment potential on embryonic stem cell and yolk sac hematopoietic progenitors. Cell 2002;109:29-37. 20 Sauvageau G, Thorsteinsdottir U, Hough MR et al. Overexpression of HOXB3 in hematopoietic cells causes defective lymphoid development and progressive myeloproliferation. Immunity 1997;6:13-22. 21 Bijl J, van Oostveen JW, Kreike M et al. Expression of HOXC4, HOXC5, and HOXC6 in human lymphoid cell lines, leukemias, and benign and malignant lymphoid tissue. Blood 1996;87:1737-1745. 22 Lawrence HJ, Stage KM, Mathews CH et al. Expression of HOX C homeobox genes in lymphoid cells. Cell Growth Differ 1993;4:665-669. 23 Kongsuwan K, Webb E, Housiaux P et al. Expression of multiple homeobox genes within diverse mammalian haemopoietic lineages. EMBO J 1988;7:2131-2138.
375
24 Takeshita K, Bollekens JA, Hijiya N et al. A homeobox gene of the Antennapedia class is required for human adult erythropoiesis. Proc Natl Acad Sci USA 1993;90:3535-3538. 25 Taniguchi Y, Komatsu N, Moriuchi T. Overexpression of the HOX4A (HOXD3) homeobox gene in human erythroleukemia HEL cells results in altered adhesive properties. Blood 1995;85:2786-2794. 26 Shimada H, Arai Y, Sekiguchi S et al. Generation of the NUP98-HOXD13 fusion transcript by a rare translocation, t(2;11)(q31;p15), in a case of infant leukaemia. Br J Haematol 2000;110:210-213.
HOX and Non-HOX Genes in Leukemic Hematopoiesis 41 Lu M, Zhang N, Ho AD. Genomic organization of the putative human homeobox proto-oncogene HOX-11 (TCL-3) and its endogenous expression in T cells. Oncogene 1992;7:13251330. 42 Kongsuwan K, Allen J, Adams JM. Expression of Hox-2.4 homeobox gene directed by proviral insertion in a myeloid leukemia. Nucleic Acids Res 1989;17:1881-1892. 43 Blatt C, Aberdam D, Schwartz R et al. DNA rearrangement of a homeobox gene in myeloid leukaemic cells. EMBO J 1988;7:4283-4290.
27 Raza-Egilmez SZ, Jani-Sait SN, Grossi M et al. NUP98HOXD13 gene fusion in therapy-related acute myelogenous leukemia. Cancer Res 1998;58:4269-4273.
44 Perkins A, Kongsuwan K, Visvader J et al. Homeobox gene expression plus autocrine growth factor production elicits myeloid leukemia. Proc Natl Acad Sci USA 1990;87:83988402.
28 Monica K, Galili N, Nourse J et al. PBX2 and PBX3, new homeobox genes with extensive homology to the human proto-oncogene PBX1. Mol Cell Biol 1991;11:6149-6157.
45 Ymer S, Tucker WQ, Sanderson CJ et al. Constitutive synthesis of interleukin-3 by leukaemia cell line WEHI-3B is due to retroviral insertion near the gene. Nature 1985;317:255-258.
29 Kamps MP, Murre C, Sun XH et al. A new homeobox gene contributes the DNA binding domain of the t(1;19) translocation protein in pre-B ALL. Cell 1990;60:547-555.
46 Perkins AC, Cory S. Conditional immortalization of mouse myelomonocytic, megakaryocytic and mast cell progenitors by the Hox-2.4 homeobox gene. EMBO J 1993;12:3835-3846.
30 Nourse J, Mellentin JD, Galili N et al. Chromosomal translocation t(1;19) results in synthesis of a homeobox fusion mRNA that codes for a potential chimeric transcription factor. Cell 1990;60:535-545.
47 Moskow JJ, Bullrich F, Huebner K et al. Meis1, a PBX1related homeobox gene involved in myeloid leukemia in BXH-2 mice. Mol Cell Biol 1995;15:5434-5443.
31 Nakamura T, Jenkins NA, Copeland NG. Identification of a new family of Pbx-related homeobox genes. Oncogene 1996;13:2235-2242. 32 Nakamura T, Largaespada DA, Shaughnessy Jr JD et al. Cooperative activation of Hoxa and Pbx1-related genes in murine myeloid leukaemias. Nat Genet 1996;12:149-153. 33 Shen WF, Montgomery JC, Rozenfeld S et al. AbdB-like Hox proteins stabilize DNA binding by the Meis1 homeodomain proteins. Mol Cell Biol 1997;17:6448-6458. 34 Berthelsen J, Zappavigna V, Ferretti E et al. The novel homeoprotein Prep1 modulates Pbx-Hox protein cooperativity. EMBO J 1998;17:1434-1445. 35 Berthelsen J, Zappavigna V, Mavilio F et al. Prep1, a novel functional partner of Pbx proteins. EMBO J 1998;17:1423-1433. 36 Ferretti E, Schulz H, Talarico D et al. The PBX-regulating protein PREP1 is present in different PBX-complexed forms in mouse. Mech Dev 1999;83:53-64. 37 Dube ID, Kamel-Reid S, Yuan CC et al. A novel human homeobox gene lies at the chromosome 10 breakpoint in lymphoid neoplasias with chromosomal translocation t(10;14). Blood 1991;78:2996-3003.
48 Afonja O, Smith Jr JE, Cheng DM et al. MEIS1 and HOXA7 genes in human acute myeloid leukemia. Leuk Res 2000;24:849-855. 49 Lawrence HJ, Rozenfeld S, Cruz C et al. Frequent co-expression of the HOXA9 and MEIS1 homeobox genes in human myeloid leukemias. Leukemia 1999;13:1993-1999. 50 Borrow J, Shearman AM, Stanton Jr VP et al. The t(7;11)(p15;p15) translocation in acute myeloid leukaemia fuses the genes for nucleoporin NUP98 and class I homeoprotein HOXA9. Nat Genet 1996;12:159-167. 51 Nakamura T, Largaespada DA, Lee MP et al. Fusion of the nucleoporin gene NUP98 to HOXA9 by the chromosome translocation t(7;11)(p15;p15) in human myeloid leukaemia. Nat Genet 1996;12:154-158. 52 Kasper LH, Brindle PK, Schnabel CA et al. CREB binding protein interacts with nucleoporin-specific FG repeats that activate transcription and mediate NUP98-HOXA9 oncogenicity. Mol Cell Biol 1999;19:764-776. 53 Kroon E, Thorsteinsdottir U, Mayotte N et al. NUP98-HOXA9 expression in hemopoietic stem cells induces chronic and acute myeloid leukemias in mice. EMBO J 2001;20:350-361.
38 Hatano M, Roberts CW, Minden M et al. Deregulation of a homeobox gene, HOX11, by the t(10;14) in T cell leukemia. Science 1991;253:79-82.
54 Nakamura T, Yamazaki Y, Hatano Y et al. NUP98 is fused to PMX1 homeobox gene in human acute myelogenous leukemia with chromosome translocation t(1;11)(q23;p15). Blood 1999;94:741-747.
39 Hawley RG, Fong AZ, Reis MD et al. Transforming function of the HOX11/TCL3 homeobox gene. Cancer Res 1997;57:337-345.
55 Thorsteinsdottir U, Kroon E, Jerome L et al. Defining roles for HOX and MEIS1 genes in induction of acute myeloid leukemia. Mol Cell Biol 2001;21:224-234.
40 Kennedy MA, Gonzalez-Sarmiento R, Kees UR et al. HOX11, a homeobox-containing T-cell oncogene on human chromosome 10q24. Proc Natl Acad Sci USA 1991;88:8900-8904.
56 Thorsteinsdottir U, Krosl J, Kroon E et al. The oncoprotein E2A-Pbx1a collaborates with Hoxa9 to acutely transform primary bone marrow cells. Mol Cell Biol 1999;19:6355-6366.
Owens, Hawley
376
57 Sauvageau G, Thorsteinsdottir U, Eaves CJ et al. Overexpression of HOXB4 in hematopoietic cells causes the selective expansion of more primitive populations in vitro and in vivo. Genes Dev 1995;9:1753-1765.
74 Knoepfler PS, Kamps MP. The pentapeptide motif of Hox proteins is required for cooperative DNA binding with Pbx1, physically contacts Pbx1, and enhances DNA binding by Pbx1. Mol Cell Biol 1995;15:5811-5819.
58 Kennison JA. The Polycomb and trithorax group proteins of Drosophila: trans-regulators of homeotic gene function. Annu Rev Genet 1995;29:289-303.
75 Shen WF, Rozenfeld S, Lawrence HJ et al. The Abd-B-like Hox homeodomain proteins can be subdivided by the ability to form complexes with Pbx1a on a novel DNA target. J Biol Chem 1997;272:8198-8206.
59 Mazo AM, Huang DH, Mozer BA et al. The trithorax gene, a trans-acting regulator of the bithorax complex in Drosophila, encodes a protein with zinc-binding domains. Proc Natl Acad Sci USA 1990;87:2112-2116. 60 Ziemin-van der Poel S, McCabe NR, Gill HJ et al. Identification of a gene, MLL, that spans the breakpoint in 11q23 translocations associated with human leukemias. Proc Natl Acad Sci USA 1991;88:10735-10739. 61 Yagi H, Deguchi K, Aono A et al. Growth disturbance in fetal liver hematopoiesis of Mll-mutant mice. Blood 1998;92:108-117. 62 Hess JL, Yu BD, Li B et al. Defects in yolk sac hematopoiesis in Mll-null embryos. Blood 1997;90:1799-1806. 63 Yu BD, Hess JL, Horning SE et al. Altered Hox expression and segmental identity in Mll-mutant mice. Nature 1995;378:505-508. 64 Rozovskaia T, Feinstein E, Mor O et al. Upregulation of Meis1 and HoxA9 in acute lymphocytic leukemias with the t(4:11) abnormality. Oncogene 2001;20:874-878. 65 Peifer M, Wieschaus E. Mutations in the Drosophila gene extradenticle affect the way specific homeo domain proteins regulate segmental identity. Genes Dev 1990;4:1209-1223. 66 Rauskolb C, Peifer M, Wieschaus E. Extradenticle, a regulator of homeotic gene activity, is a homolog of the homeobox-containing human proto-oncogene pbx1. Cell 1993;74:1101-1112. 67 Rauskolb C, Wieschaus E. Coordinate regulation of downstream genes by extradenticle and the homeotic selector proteins. EMBO J 1994;13:3561-3569. 68 van Dijk MA, Murre C. Extradenticle raises the DNA binding specificity of homeotic selector gene products. Cell 1994;78:617-624. 69 DiMartino JF, Selleri L, Traver D et al. The Hox cofactor and proto-oncogene Pbx1 is required for maintenance of definitive hematopoiesis in the fetal liver. Blood 2001;98:618-626.
76 Pai CY, Kuo TS, Jaw TJ et al. The Homothorax homeoprotein activates the nuclear localization of another homeoprotein, extradenticle, and suppresses eye development in Drosophila. Genes Dev 1998;12:435-446. 77 Rieckhof GE, Casares F, Ryoo HD et al. Nuclear translocation of extradenticle requires homothorax, which encodes an extradenticle-related homeodomain protein. Cell 1997;91:171183. 78 Saleh M, Huang H, Green NC et al. A conformational change in PBX1A is necessary for its nuclear localization. Exp Cell Res 2000;260:105-115. 79 Mann RS, Abu-Shaar M. Nuclear import of the homeodomain protein extradenticle in response to Wg and Dpp signalling. Nature 1996;383:630-633. 80 Jacobs Y, Schnabel CA, Cleary ML. Trimeric association of Hox and TALE homeodomain proteins mediates Hoxb2 hindbrain enhancer activity. Mol Cell Biol 1999;19:5134-5142. 81 Schnabel CA, Jacobs Y, Cleary ML. HoxA9-mediated immortalization of myeloid progenitors requires functional interactions with TALE cofactors Pbx and Meis. Oncogene 2000;19:608-616. 82 Shen WF, Rozenfeld S, Kwong A et al. HOXA9 forms triple complexes with PBX2 and MEIS1 in myeloid cells. Mol Cell Biol 1999;19:3051-3061. 83 Calvo KR, Sykes DB, Pasillas M et al. Hoxa9 immortalizes a granulocyte-macrophage colony-stimulating factor-dependent promyelocyte capable of biphenotypic differentiation to neutrophils or macrophages, independent of enforced meis expression. Mol Cell Biol 2000;20:3274-3285. 84 Desiderio S. Lymphopoiesis. Transcription factors controlling B-cell development. Curr Biol 1995;5:605-608. 85 Kamps MP, Baltimore D. E2A-Pbx1, the t(1;19) translocation protein of human pre-B-cell acute lymphocytic leukemia, causes acute myeloid leukemia in mice. Mol Cell Biol 1993;13:351-357.
70 Lu Q, Knoepfler PS, Scheele J et al. Both Pbx1 and E2A-Pbx1 bind the DNA motif ATCAATCAA cooperatively with the products of multiple murine Hox genes, some of which are themselves oncogenes. Mol Cell Biol 1995;15:3786-3795.
86 Kamps MP, Wright DD. Oncoprotein E2A-Pbx1 immortalizes a myeloid progenitor in primary marrow cultures without abrogating its factor-dependence. Oncogene 1994;9:3159-3166.
71 van Dijk MA, Peltenburg LT, Murre C. Hox gene products modulate the DNA binding activity of Pbx1 and Pbx2. Mech Dev 1995;52:99-108.
87 Dedera DA, Waller EK, LeBrun DP et al. Chimeric homeobox gene E2A-PBX1 induces proliferation, apoptosis, and malignant lymphomas in transgenic mice. Cell 1993;74:833-843.
72 Chang CP, Shen WF, Rozenfeld S et al. Pbx proteins display hexapeptide-dependent cooperative DNA binding with a subset of Hox proteins. Genes Dev 1995;9:663-674.
88 Chang CP, de Vivo I, Cleary ML. The Hox cooperativity motif of the chimeric oncoprotein E2a-Pbx1 is necessary and sufficient for oncogenesis. Mol Cell Biol 1997;17:81-88.
73 Phelan ML, Rambaldi I, Featherstone MS. Cooperative interactions between HOX and PBX proteins mediated by a conserved peptide motif. Mol Cell Biol 1995;15:3989-3997.
89 Kamps MP, Wright DD, Lu Q. DNA-binding by oncoprotein E2a-Pbx1 is important for blocking differentiation but dispensable for fibroblast transformation. Oncogene 1996;12:19-30.
377
90 Monica K, LeBrun DP, Dedera DA et al. Transformation properties of the E2a-Pbx1 chimeric oncoprotein: fusion with E2a is essential, but the Pbx1 homeodomain is dispensable. Mol Cell Biol 1994;14:8304-8314. 91 van Dijk MA, Voorhoeve PM, Murre C. Pbx1 is converted into a transcriptional activator upon acquiring the N-terminal region of E2A in pre-B-cell acute lymphoblastoid leukemia. Proc Natl Acad Sci USA 1993;90:6061-6065. 92 LeBrun DP, Cleary ML. Fusion with E2A alters the transcriptional properties of the homeodomain protein PBX1 in t(1;19) leukemias. Oncogene 1994;9:1641-1647. 93 Lu Q, Wright DD, Kamps MP. Fusion with E2A converts the Pbx1 homeodomain protein into a constitutive transcriptional activator in human leukemias carrying the t(1;19) translocation. Mol Cell Biol 1994;14:3938-3948. 94 Knoepfler PS, Calvo KR, Chen H et al. Meis1 and pKnox1 bind DNA cooperatively with Pbx1 utilizing an interaction surface disrupted in oncoprotein E2a-Pbx1. Proc Natl Acad Sci USA 1997;94:14553-14558.
HOX and Non-HOX Genes in Leukemic Hematopoiesis both primitive and definitive hematopoietic potential. Blood 1998;92:877-887. 107 Allen TD, Zhu YX, Hawley TS et al. TALE homeoproteins as HOX11-interacting partners in T-cell leukemia. Leuk Lymphoma 2000;39:241-256. 108 Zhang N, Shen W, Hawley RG et al. HOX11 interacts with CTF1 and mediates hematopoietic precursor cell immortalization. Oncogene 1999;18:2273-2279. 109 Greene WK, Bahn S, Masson N et al. The T-cell oncogenic protein HOX11 activates Aldh1 expression in NIH 3T3 cells but represses its expression in mouse spleen development. Mol Cell Biol 1998;18:7030-7037. 110 Herzer U, Crocoll A, Barton D et al. The Wilms tumor suppressor gene wt1 is required for development of the spleen. Curr Biol 1999;9:837-840. 111 Koehler K, Franz T, Dear TN. Hox11 is required to maintain normal Wt1 mRNA levels in the developing spleen. Dev Dyn 2000;218:201-206.
95 Krosl J, Baban S, Krosl G et al. Cellular proliferation and transformation induced by HOXB4 and HOXB3 proteins involves cooperation with PBX1. Oncogene 1998;16:3403-3412.
112 Kawabe T, Muslin AJ, Korsmeyer SJ. HOX11 interacts with protein phosphatases PP2A and PP1 and disrupts a G2/M cell-cycle checkpoint. Nature 1997;385:454-458.
96 Knoepfler PS, Sykes DB, Pasillas M et al. HoxB8 requires its Pbx-interaction motif to block differentiation of primary myeloid progenitors and of most cell line models of myeloid differentiation. Oncogene 2001;20:5440-5448.
113 Bernard OA, Busson-LeConiat M, Ballerini P et al. A new recurrent and specific cryptic translocation, t(5;14)(q35;q32), is associated with expression of the Hox11L2 gene in T acute lymphoblastic leukemia. Leukemia 2001;15:1495-1504.
97 Pollard SL, Holland PW. Evidence for 14 homeobox gene clusters in human genome ancestry. Curr Biol 2000;10:1059-1062.
114 Ferrando AA, Neuberg DS, Staunton J et al. Gene expression signatures define novel oncogenic pathways in T cell acute lymphoblastic leukemia. Cancer Cell 2002;1:75-87.
98 Dear TN, Rabbitts TH. A Drosophila melanogaster homologue of the T-cell oncogene HOX11 localises to a cluster of homeobox genes. Gene 1994;141:225-229. 99 Jagla K, Dolle P, Mattei MG et al. Mouse Lbx1 and human LBX1 define a novel mammalian homeobox gene family related to the Drosophila lady bird genes. Mech Dev 1995;53:345-356.
115 Allen JD, Lints T, Jenkins NA et al. Novel murine homeobox gene on chromosome 1 expressed in specific hematopoietic lineages and during embryogenesis. Genes Dev 1991;5:509-520.
100 Roberts CW, Shutter JR, Korsmeyer SJ. Hox11 controls the genesis of the spleen. Nature 1994;368:747-749.
116 Deguchi Y, Moroney JF, Wilson GL et al. Cloning of a human homeobox gene that resembles a diverged Drosophila homeobox gene and is expressed in activated lymphocytes. New Biol 1991;3:353-363.
101 Dear TN, Colledge WH, Carlton MB et al. The Hox11 gene is essential for cell survival during spleen development. Development 1995;121:2909-2915.
117 Lints TJ, Hartley L, Parsons LM et al. Mesoderm-specific expression of the divergent homeobox gene Hlx during murine embryogenesis. Dev Dyn 1996;205:457-470.
102 Salvati PD, Ranford PR, Ford J et al. HOX11 expression in pediatric acute lymphoblastic leukemia is associated with T-cell phenotype. Oncogene 1995;11:1333-1338.
118 Deguchi Y, Kehrl JH. Selective expression of two homeobox genes in CD34-positive cells from human bone marrow. Blood 1991;78:323-328.
103 Watt PM, Kumar R, Kees UR. Promoter demethylation accompanies reactivation of the HOX11 proto-oncogene in leukemia. Genes Chromosomes Cancer 2000;29:371-377.
119 Hentsch B, Lyons I, Li R et al. Hlx homeobox gene is essential for an inductive tissue interaction that drives expansion of embryonic liver and gut. Genes Dev 1996;10:70-79.
104 Hawley RG, Fong AZ, Lu M et al. The HOX11 homeoboxcontaining gene of human leukemia immortalizes murine hematopoietic precursors. Oncogene 1994;9:1-12.
120 Quinn LM, Latham SE, Kalionis B. Homeobox gene HB24, a regulator of haematopoiesis, is a candidate for regulating differentiation of the extra-embryonic trophoblast cell lineage. Reprod Fertil Dev 1997;9:617-623.
105 Hough MR, Reis MD, Singaraja R et al. A model for spontaneous B-lineage lymphomas in IgHmu-HOX11 transgenic mice. Proc Natl Acad Sci USA 1998;95:13853-13858. 106 Keller G, Wall C, Fong AZ et al. Overexpression of HOX11 leads to the immortalization of embryonic precursors with
121 Deguchi Y, Agus D, Kehrl JH. A human homeobox gene, HB24, inhibits development of CD4+ T cells and impairs thymic involution in transgenic mice. J Biol Chem 1993;268:36463653.
Owens, Hawley 122 Allen JD, Harris AW, Bath ML et al. Perturbed development of T and B cells in mice expressing an Hlx homeobox transgene. J Immunol 1995;154:1531-1542. 123 Deguchi Y, Kehrl JH. High level expression of the homeobox gene HB24 in a human T-cell line confers the ability to form tumors in nude mice. Cancer Res 1993;53:373-377. 124 Deguchi Y, Thevenin C, Kehrl JH. Stable expression of HB24, a diverged human homeobox gene, in T lymphocytes induces genes involved in T cell activation and growth. J Biol Chem 1992;267:8222-8229. 125 Deguchi Y, Kirschenbaum A, Kehrl JH. A diverged homeobox gene is involved in the proliferation and lineage commitment of human hematopoietic progenitors and highly expressed in acute myelogenous leukemia. Blood 1992;79:2841-2848. 126 Deguchi Y, Yamanaka Y, Theodossiou C et al. High expression of two diverged homeobox genes, HB24 and HB9, in acute leukemias: molecular markers of hematopoietic cell immaturity. Leukemia 1993;7:446-451. 127 Bedford FK, Ashworth A, Enver T et al. HEX: a novel homeobox gene expressed during haematopoiesis and conserved between mouse and human. Nucleic Acids Res 1993;21:1245-1249. 128 Manfioletti G, Gattei V, Buratti E et al. Differential expression of a novel proline-rich homeobox gene (Prh) in human hematolymphopoietic cells. Blood 1995;85:1237-1245. 129 Bogue CW, Ganea GR, Sturm E et al. Hex expression suggests a role in the development and function of organs derived from foregut endoderm. Dev Dyn 2000;219:84-89. 130 Hromas R, Radich J, Collins S. PCR cloning of an orphan homeobox gene (PRH) preferentially expressed in myeloid and liver cells. Biochem Biophys Res Commun 1993;195:976-983. 131 Keng VW, Fujimori KE, Myint Z et al. Expression of Hex mRNA in early murine postimplantation embryo development. FEBS Lett 1998;426:183-186. 132 Tanaka T, Inazu T, Yamada K et al. cDNA cloning and expression of rat homeobox gene, Hex, and functional characterization of the protein. Biochem J 1999;339:111-117. 133 Thomas PQ, Brown A, Beddington RS. Hex: a homeobox gene revealing peri-implantation asymmetry in the mouse embryo and an early transient marker of endothelial cell precursors. Development 1998;125:85-94. 134 Crompton MR, Bartlett TJ, MacGregor AD et al. Identification of a novel vertebrate homeobox gene expressed in haematopoietic cells. Nucleic Acids Res 1992;20:5661-5667. 135 Ho CY, Houart C, Wilson SW et al. A role for the extraembryonic yolk syncytial layer in patterning the zebrafish embryo suggested by properties of the hex gene. Curr Biol 1999;9:1131-1134. 136 Pellizzari L, D’Elia A, Rustighi A et al. Expression and function of the homeodomain-containing protein Hex in thyroid cells. Nucleic Acids Res 2000;28:2503-2511. 137 Keng VW, Yagi H, Ikawa M et al. Homeobox gene Hex is essential for onset of mouse embryonic liver development and
378
differentiation of the monocyte lineage. Biochem Biophys Res Commun 2000;276:1155-1161. 138 Hansen GM, Justice MJ. Activation of Hex and mEg5 by retroviral insertion may contribute to mouse B-cell leukemia. Oncogene 1999;18:6531-6539. 139 Schaefer LK, Wang S, Schaefer TS. Functional interaction of Jun and homeodomain proteins. J Biol Chem 2001;276:4307443082. 140 Leussink B, Brouwer A, el Khattabi M et al. Expression patterns of the paired-related homeobox genes MHox/Prx1 and S8/Prx2 suggest roles in development of the heart and the forebrain. Mech Dev 1995;52:51-64. 141 Bergwerff M, Gittenberger-de Groot AC, DeRuiter MC et al. Patterns of paired-related homeobox genes PRX1 and PRX2 suggest involvement in matrix modulation in the developing chick vascular system. Dev Dyn 1998;213:59-70. 142 Kataoka K, Yoshitomo-Nakagawa K, Shioda S et al. A set of Hox proteins interact with the Maf oncoprotein to inhibit its DNA binding, transactivation, and transforming activities. J Biol Chem 2001;276:819-826. 143 Wiggan O, Taniguchi-Sidle A, Hamel PA. Interaction of the pRB-family proteins with factors containing paired-like homeodomains. Oncogene 1998;16:227-236. 144 Shimamoto T, Nakamura S, Bollekens J et al. Inhibition of DLX-7 homeobox gene causes decreased expression of GATA-1 and c-myc genes and apoptosis. Proc Natl Acad Sci USA 1997;94:3245-3249. 145 Haga SB, Fu S, Karp JE et al. BP1, a new homeobox gene, is frequently expressed in acute leukemias. Leukemia 2000;14:1867-1875. 146 Chase MB, Fu S, Haga SB et al. BP1, a homeodomain-containing isoform of DLX4, represses the beta-globin gene. Mol Cell Biol 2002;22:2505-2514. 147 Fu S, Stevenson H, Strovel JW et al. Distinct functions of two isoforms of a homeobox gene, BP1 and DLX7, in the regulation of the beta-globin gene. Gene 2001;278:131-139. 148 Roberson MS, Schoderbek WE, Tremml G et al. Activation of the glycoprotein hormone alpha-subunit promoter by a LIM-homeodomain transcription factor. Mol Cell Biol 1994;14:2985-2993. 149 Xu Y, Baldassare M, Fisher P et al. LH-2: a LIM/homeodomain gene expressed in developing lymphocytes and neural cells. Proc Natl Acad Sci USA 1993;90:227-231. 150 Porter FD, Drago J, Xu Y et al. Lhx2, a LIM homeobox gene, is required for eye, forebrain, and definitive erythrocyte development. Development 1997;124:2935-2944. 151 Wu HK, Heng HH, Siderovski DP et al. Identification of a human LIM-Hox gene, hLH-2, aberrantly expressed in chronic myelogenous leukaemia and located on 9q33-34.1. Oncogene 1996;12:1205-1212. 152 Wu HK, Minden MD. Transcriptional activation of human LIM-HOX gene, hLH-2, in chronic myelogenous leukemia is due to a cis-acting effect of Bcr-Abl. Biochem Biophys Res Commun 1997;233:806-812.
379
153 Al Jehani F, Hochhaus A, Spencer A et al. Expression of the LH2 gene in chronic myeloid leukaemia cells. Leukemia 1996;10:1122-1126. 154 Pinto do OP, Kolterud A, Carlsson L. Expression of the LIM-homeobox gene LH2 generates immortalized steel factor-dependent multipotent hematopoietic precursors. EMBO J 1998;17:5744-5756. 155 Pinto do OP, Richter K, Carlsson L. Hematopoietic progenitor/stem cells immortalized by Lhx2 generate functional hematopoietic cells in vivo. Blood 2002;99:3939-3946. 156 Lin X, Swaroop A, Vaccarino FM et al. Characterization and sequence analysis of the human homeobox-containing gene GBX2. Genomics 1996;31:335-342. 157 Gao AC, Isaacs JT. Expression of homeobox gene-GBX2 in human prostatic cancer cells. Prostate 1996;29:395-398. 158 Kowenz-Leutz E, Herr P, Niss K et al. The homeobox gene GBX2, a target of the myb oncogene, mediates autocrine growth and monocyte differentiation. Cell 1997;91:185-195. 159 Mallo GV, Rechreche H, Frigerio JM et al. Molecular cloning, sequencing and expression of the mRNA encoding human Cdx1 and Cdx2 homeobox. Down-regulation of Cdx1 and Cdx2 mRNA expression during colorectal carcinogenesis. Int J Cancer 1997;74:35-44. 160 da Costa LT, He TC, Yu J et al. CDX2 is mutated in a colorectal cancer with normal APC/beta-catenin signaling. Oncogene 1999;18:5010-5014. 161 Wicking C, Simms LA, Evans T et al. CDX2, a human homologue of Drosophila caudal, is mutated in both alleles in a replication error positive colorectal cancer. Oncogene 1998;17:657-659. 162 Yagi OK, Akiyama Y, Yuasa Y. Genomic structure and alterations of homeobox gene CDX2 in colorectal carcinomas. Br J Cancer 1999;79:440-444.
HOX and Non-HOX Genes in Leukemic Hematopoiesis 167 Blobel GA. CREB-binding protein and p300: molecular integrators of hematopoietic transcription. Blood 2000;95:745-755. 168 Goodman RH, Smolik S. CBP/p300 in cell growth, transformation, and development. Genes Dev 2000;14:1553-1577. 169 Chariot A, van Lint C, Chapelier M et al. CBP and histone deacetylase inhibition enhance the transactivation potential of the HOXB7 homeodomain-containing protein. Oncogene 1999;18:4007-4014. 170 Asahara H, Dutta S, Kao HY et al. Pbx-Hox heterodimers recruit coactivator-corepressor complexes in an isoformspecific manner. Mol Cell Biol 1999;19:8219-8225. 171 Kamps MP, Look AT, Baltimore D. The human t(1;19) translocation in pre-B ALL produces multiple nuclear E2APbx1 fusion proteins with differing transforming potentials. Genes Dev 1991;5:358-368. 172 Saleh M, Rambaldi I, Yang XJ et al. Cell signaling switches HOX-PBX complexes from repressors to activators of transcription mediated by histone deacetylases and histone acetyltransferases. Mol Cell Biol 2000;20:8623-8633. 173 Shen WF, Krishnan K, Lawrence HJ et al. The HOX homeodomain proteins block CBP histone acetyltransferase activity. Mol Cell Biol 2001;21:7509-7522. 174 Catron KM, Zhang H, Marshall SC et al. Transcriptional repression by Msx-1 does not require homeodomain DNA-binding sites. Mol Cell Biol 1995;15:861-871. 175 Li C, Manley JL. Even-skipped represses transcription by binding TATA binding protein and blocking the TFIIDTATA box interaction. Mol Cell Biol 1998;18:3771-3781. 176 Um M, Li C, Manley JL. The transcriptional repressor evenskipped interacts directly with TATA-binding protein. Mol Cell Biol 1995;15:5007-5016.
163 Chase A, Reiter A, Burci L et al. Fusion of ETV6 to the caudal-related homeobox gene CDX2 in acute myeloid leukemia with the t(12;13)(p13;q12). Blood 1999;93:1025-1031.
177 Zhang H, Catron KM, Abate-Shen C. A role for the Msx-1 homeodomain in transcriptional regulation: residues in the N-terminal arm mediate TATA binding protein interaction and transcriptional repression. Proc Natl Acad Sci USA 1996;93:1764-1769.
164 Lorentz O, Suh ER, Taylor JK et al. CREB-binding protein interacts with the homeodomain protein Cdx2 and enhances transcriptional activity. J Biol Chem 1999;274:7196-7199.
178 Newberry EP, Latifi T, Battaile JT et al. Structure-function analysis of Msx2-mediated transcriptional suppression. Biochemistry 1997;36:10451-10462.
165 Bromleigh VC, Freedman LP. p21 is a transcriptional target of HOXA10 in differentiating myelomonocytic cells. Genes Dev 2000;14:2581-2586.
179 Shetty S, Takahashi T, Matsui H et al. Transcriptional autorepression of Msx1 gene is mediated by interactions of Msx1 protein with a multi-protein transcriptional complex containing TATA-binding protein, Sp1 and cAMP-response-element-binding protein-binding protein (CBP/p300). Biochem J 1999;339:751-758.
166 Raman V, Martensen SA, Reisman D et al. Compromised HOXA5 function can limit p53 expression in human breast tumours. Nature 2000;405:974-978.
