1: Int J Dev Biol. 2005;49(7):851-8. PBX1 intracellular localization is independent of MEIS1 in epithelial cells of the developing female genital tract. Dintilhac A, Bihan R, Guerrier D, Deschamps S, Bougerie H, Watrin T, Bonnec G, Pellerin I. UMR 6061, Genetique et Developpement, IFR 140, Universite de Rennes 1, Campus Villejean, Rennes, France. While studies have highlighted the role of HOXA9-13 and PBX1 homeobox genes during the development of the female genital tract, the molecular mechanisms triggered by these genes are incompletely elucidated. In several developmental pathways, PBX1 binds to MEINOX family members in the cytoplasm to be imported into the nucleus where they associate with HOX proteins to form a higher complex that modulates gene expression. This concept has been challenged by a recent report showing that in some cell cultures, PBX1 nuclear localization might be regulated independently of MEINOX proteins (Kilstrup-Nielsen et al., 2003). Our work gives the first illustration of this alternative mechanism in an organogenesis process. Indeed, we show that PBX1 is mostly cytoplasmic in epithelial endometrial cells of the developing female genital tract despite the nuclear localization of MEIS1. We thus provide evidence for a control of PBX1 intracellular distribution which is independent of MEINOX proteins, but is cell cycle correlated. PMID: 16172981 [PubMed - in process] --------------------------------------------------------------- 2: J Biol Chem. 2005 Apr 1;280(13):12359-70. Epub 2005 Jan 28. HOXA9 activates transcription of the gene encoding gp91Phox during myeloid differentiation. Bei L, Lu Y, Eklund EA. Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA. The CYBB gene encodes gp91Phox; a component of the phagocyte respiratory burst oxidase. CYBB transcription is restricted to myeloid cells differentiated beyond the promyelocyte stage. In undifferentiated myeloid cells, the homeodomain (HD) transcription factor HoxA10 represses CYBB transcription via a cis element in the proximal promoter. During myelopoiesis, phosphorylation of conserved tyrosine residues in the HD decreases HoxA10 binding to this CYBB cis element. In the current studies, we found HoxA9 activates CYBB transcription in differentiated myeloid cells via the same cis element. We find HoxA9-mediated CYBB-transcription requires Pbx1 but is inhibited by Meis1. Additionally, phosphorylation of the conserved HD tyrosines increases HoxA9 binding to the CYBB promoter. The HOXA9 gene is involved in leukemia-associated translocations with the gene encoding Nup98, a nucleopore protein. We find expression of a Nup98-hoxA9 fusion protein blocks HoxA9-induced CYBB transcription in differentiating myeloid cells. In comparison to HoxA9, Nup98-hoxA9 has greater binding affinity for the CYBB cis element, but binding is not altered by HD tyrosine phosphorylation. Therefore, these studies identify CYBB as a common target gene repressed by HoxA10 and activated by HoxA9. These studies also suggest overexpression of Meis1 or Nup98-hoxA9 represses myeloid-specific gene transcription, thereby contributing to differentiation block in leukemogenesis. PMID: 15681849 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 3: Blood. 2005 Feb 15;105(4):1456-66. Epub 2004 Nov 2. HOXB6 overexpression in murine bone marrow immortalizes a myelomonocytic precursor in vitro and causes hematopoietic stem cell expansion and acute myeloid leukemia in vivo. Fischbach NA, Rozenfeld S, Shen W, Fong S, Chrobak D, Ginzinger D, Kogan SC, Radhakrishnan A, Le Beau MM, Largman C, Lawrence HJ. Department of Medicine, Veterans Affairs Medical Center, San Francisco, CA 94121, USA. fischba@itsa.ucsf.edu The HOX family of homeobox genes plays an important role in normal and malignant hematopoiesis. Dysregulated HOX gene expression profoundly effects the proliferation and differentiation of hematopoietic stem cells (HSCs) and committed progenitors, and aberrant activation of HOX genes is a common event in human myeloid leukemia. HOXB6 is frequently overexpressed in human acute myeloid leukemia (AML). To gain further insight into the role of HOXB6 in hematopoiesis, we overexpressed HOXB6 in murine bone marrow using retrovirus-mediated gene transfer. We also explored structure-function relationships using mutant HOXB6 proteins unable to bind to DNA or a key HOX-binding partner, pre-B-cell leukemia transcription factor-1 (PBX1). Additionally, we investigated the potential cooperative interaction with myeloid ecotropic viral integration site 1 homolog (MEIS1). In vivo, HOXB6 expanded HSCs and myeloid precursors while inhibiting erythropoiesis and lymphopoiesis. Overexpression of HOXB6 resulted in AML with a median latency of 223 days. Coexpression of MEIS1 dramatically shortened the onset of AML. Cytogenetic analysis of a subset of HOXB6-induced AMLs revealed recurrent deletions of chromosome bands 2D-E4, a region frequently deleted in HOXA9-induced AMLs. In vitro, HOXB6 immortalized a factor-dependent myelomonocytic precursor capable of granulocytic and monocytic differentiation. These biologic effects of HOXB6 were largely dependent on DNA binding but independent of direct interaction with PBX1. PMID: 15522959 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 4: Blood. 2005 Feb 1;105(3):1222-30. Epub 2004 Oct 12. Meis1-mediated apoptosis is caspase dependent and can be suppressed by coexpression of HoxA9 in murine and human cell lines. Wermuth PJ, Buchberg AM. Department of Microbiology and Immunology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University, 233 S 10th St, Philadelphia, PA 19107-5541, USA. Coexpression of the homeodomain protein Meis1 and either HoxA7 or HoxA9 is characteristic of many acute myelogenous leukemias. Although Meis1 can be overexpressed in bone marrow long-term repopulating cells, it is incapable of mediating their transformation. Although overexpressing HoxA9 alone transforms murine bone marrow cells, concurrent Meis1 overexpression greatly accelerates oncogenesis. Meis1-HoxA9 cooperation suppresses several myeloid differentiation pathways. We now report that Meis1 overexpression strongly induces apoptosis in a variety of cell types in vitro through a caspase-dependent process. Meis1 requires a functional homeodomain and Pbx-interaction motif to induce apoptosis. Coexpressing HoxA9 with Meis1 suppresses this apoptosis and provides protection from several apoptosis inducers. Pbx1, another Meis1 cofactor, also induces apoptosis; however, coexpressing HoxA9 is incapable of rescuing Pbx-mediated apoptosis. This resistance to apoptotic stimuli, coupled with the previously reported ability to suppress multiple myeloid differentiation pathways, would provide a strong selective advantage to Meis1-HoxA9 coexpressing cells in vivo, leading to leukemogenesis. PMID: 15479723 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 5: Genes Dev. 2003 Aug 15;17(16):2060-72. Structure of HoxA9 and Pbx1 bound to DNA: Hox hexapeptide and DNA recognition anterior to posterior. LaRonde-LeBlanc NA, Wolberger C. Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA. The HOX/HOM superfamily of homeodomain proteins controls cell fate and segmental embryonic patterning by a mechanism that is conserved in all metazoans. The linear arrangement of the Hox genes on the chromosome correlates with the spatial distribution of HOX protein expression along the anterior-posterior axis of the embryo. Most HOX proteins bind DNA cooperatively with members of the PBC family of TALE-type homeodomain proteins, which includes human Pbx1. Cooperative DNA binding between HOX and PBC proteins requires a residue N-terminal to the HOX homeodomain termed the hexapeptide, which differs significantly in sequence between anterior- and posterior-regulating HOX proteins. We report here the 1.9-A-resolution structure of a posterior HOX protein, HoxA9, complexed with Pbx1 and DNA, which reveals that the posterior Hox hexapeptide adopts an altered conformation as compared with that seen in previously determined anterior HOX/PBC structures. The additional nonspecific interactions and altered DNA conformation in this structure account for the stronger DNA-binding affinity and altered specificity observed for posterior HOX proteins when compared with anterior HOX proteins. DNA-binding studies of wild-type and mutant HoxA9 and HoxB1 show residues in the N-terminal arm of the homeodomains are critical for proper DNA sequence recognition despite lack of direct contact by these residues to the DNA bases. These results help shed light on the mechanism of transcriptional regulation by HOX proteins and show how DNA-binding proteins may use indirect contacts to determine sequence specificity. PMID: 12923056 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 6: Blood. 2001 Oct 15;98(8):2308-18. Estrogen-dependent E2a/Pbx1 myeloid cell lines exhibit conditional differentiation that can be arrested by other leukemic oncoproteins. Sykes DB, Kamps MP. Department of Molecular Pathology, University of California San Diego School of Medicine, La Jolla 92093-0612, USA. dsykes@ucsd.edu The molecular pathways of normal myeloid differentiation, as well as the mechanisms by which oncogenes disrupt this process, remain poorly understood. A major limitation in approaching this problem has been the lack of suitable cell lines that exhibit normal, terminal, and synchronous differentiation in the absence of endogenous oncoproteins and in response to physiologic cytokines, and whose differentiation can be arrested by ectopically expressed human oncoproteins. This report describes clonal, granulocyte-macrophage colony-stimulating factor-dependent myeloid cell lines that exhibit these properties. The cell lines were established by conditional immortalization of primary murine marrow progenitors with an estrogen-regulated E2a/Pbx1-estrogen receptor fusion protein. Clones were identified that proliferated as immortalized blasts in the presence of estrogen, and that exhibited granulocytic, monocytic, or bipotential (granulocytic and monocytic) differentiation on estrogen withdrawal. Differentiation was normal and terminal as evidenced by morphology, cell surface markers, gene expression, and functional assays. The differentiation of the cells could be arrested by heterologous oncoproteins including AML1/ETO, PML/RARalpha, PLZF/RARalpha, Nup98/HoxA9, and other Hox proteins. Furthermore, the study examined the effects of cooperating oncoproteins such as Ras or Bcr/Abl, which allowed for both factor-independent proliferation and differentiation, or Bcl-2, which permitted factor-independent survival but not proliferation. These myeloid cell lines provide tools for examining the biochemical and genetic pathways that accompany normal differentiation as well as a system in which to dissect how other leukemic oncoproteins interfere with these pathways. PMID: 11588024 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 7: Protein Sci. 2001 Jun;10(6):1244-53. The HoxB1 hexapeptide is a prefolded domain: implications for the Pbx1/Hox interaction. Slupsky CM, Sykes DB, Gay GL, Sykes BD. Protein Engineering Network of Centres of Excellence, Department of Biochemistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada. Hox proteins are transcriptional regulators that bind consensus DNA sequences. The DNA-binding specificity of many of these Hox proteins is modulated by the heterodimerization with partners, such as the Pbx proteins. This cooperative heterodimerization is accomplished through a conserved hexapeptide motif found N-terminal to the Hox DNA-binding homeodomain. Several human leukemias have been associated with a chromosomal translocation involving either the Hox gene (i.e., NUP98/HOXA9) or the gene encoding Pbx1 (E2A/PBX1). The transforming ability of these fusion oncoproteins relies at least partially on the ability to interact with one another through this hexapeptide motif. Herein we describe NMR structural calculations of the hexapeptide of HoxB1 (Nalpha-acetyl-Thr-Phe-Asp-Trp-Met-Lys-amide) that has been shown to mediate binding between HoxB1 and Pbx1 and a hexapeptide consensus sequence (Nalpha-acetyl-Leu-Phe-Pro-Trp-Met-Arg-amide). The consensus peptide exists in two conformations caused by cis-trans isomerization of the Phe-Pro peptide bond. The structures of the HoxB1 peptide and the trans form of the consensus peptide reveal a turn very similar to that found as part of the HoxB1/Pbx1/DNA complex in the X-ray crystal structure. This observation implies that this region is at least partially 'preformed' and thus ready to interact with Pbx1 and stabilize binding of Pbx1 and HoxB1 to DNA. The structural results presented here provide a starting point for synthesizing potential nonpeptide or cyclical peptide antagonists that mimic the interaction of these transcriptional cofactors resulting in a potential chemotherapeutic for certain types of leukemias. PMID: 11369863 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 8: Mol Cell Biol. 2001 Jan;21(1):224-34. Defining roles for HOX and MEIS1 genes in induction of acute myeloid leukemia. Thorsteinsdottir U, Kroon E, Jerome L, Blasi F, Sauvageau G. Laboratory of Molecular Genetics of Hemopoietic Stem Cells, Clinical Research Institute of Montreal, Montreal, Quebec H2W 1R7, Canada. Complex genetic and biochemical interactions between HOX proteins and members of the TALE (i.e., PBX and MEIS) family have been identified in embryonic development, and some of these interactions also appear to be important for leukemic transformation. We have previously shown that HOXA9 collaborates with MEIS1 in the induction of acute myeloid leukemia (AML). In this report, we demonstrate that HOXB3, which is highly divergent from HOXA9, also genetically interacts with MEIS1, but not with PBX1, in generating AML. In addition, we show that the HOXA9 and HOXB3 genes play key roles in establishing all the main characteristics of the leukemias, while MEIS1 functions only to accelerate the onset of the leukemic transformation. Contrasting the reported functional similarities between PREP1 and MEIS1, such as PBX nuclear retention, we also show that PREP1 overexpression is incapable of accelerating the HOXA9-induced AML, suggesting that MEIS1 function in transformation must entail more than PBX nuclear localization. Collectively, these data demonstrate that MEIS1 is a common leukemic collaborator with two structurally and functionally divergent HOX genes and that, in this collaboration, the HOX gene defines the identity of the leukemia. PMID: 11113197 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 9: Mol Cell Biol. 1999 Sep;19(9):6355-66. The oncoprotein E2A-Pbx1a collaborates with Hoxa9 to acutely transform primary bone marrow cells. Thorsteinsdottir U, Krosl J, Kroon E, Haman A, Hoang T, Sauvageau G. Laboratory of Molecular Genetics of Hemopoietic Stem Cells, Clinical Research Institute of Montreal, Montreal, Quebec, Canada H2W 1R7. A recurrent translocation between chromosome 1 (Pbx1) and 19 (E2A) leading to the expression of the E2A-Pbx1 fusion oncoprotein occurs in approximately 5 to 10% of acute leukemias in humans. It has been proposed that some of the oncogenic potential of E2A-Pbx1 could be mediated through heterocomplex formation with Hox proteins, which are also involved in human and mouse leukemias. To directly test this possibility, mouse bone marrow cells were engineered by retroviral gene transfer to overexpress E2A-Pbx1a together with Hoxa9. The results obtained demonstrated a strong synergistic interaction between E2A-Pbx1a and Hoxa9 in inducing growth factor-independent proliferation of transduced bone marrow cells in vitro and leukemic growth in vivo in only 39 +/- 2 days. The leukemic blasts which coexpress E2A-Pbx1a and Hoxa9 showed little differentiation and produced cytokines such as interleukin-3, granulocyte colony-stimulating factor, and Steel. Together, these studies demonstrate that the Hoxa9 and E2A-Pbx1a gene products collaborate to produce a highly aggressive acute leukemic disease. PMID: 10454582 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 10: Int J Hematol. 1998 Dec;68(4):343-53. Homeobox genes in normal hematopoiesis and leukemogenesis. Chiba S. Department of Hematology/Oncology, University of Tokyo Hospital, Japan. schiba-tky@umin.ac.jp Homeobox genes are broadly classified into two subclasses: HOX and non-HOX homeobox genes. A number of genes in both classes are expressed in a variety of hematopoietic cells. Two major categories of evidence implying the involvement of these genes in normal hematopoiesis have been demonstrated. First, the expression pattern of the homeobox genes in hematopoietic cells is lineage- and differentiation-stage specific. Second, enforced and suppressed expression of various homeobox genes cause defects in the hematopoietic cells of specific lineages. The reduction in myeloid, erythroid and B cell progenitors is found in mice with a disrupted HOXA9 gene. The thymuses of HOXB3-overexpressed marrow recipients contain a markedly decreased number of CD4/CD8 double-positive T cells. These examples suggest that the proper level of expression and timely down-regulation of some homeobox genes are necessary for normal hematopoiesis. Homeobox genes are also implicated in human and mouse leukemias. In human leukemias, a HOX gene (HOXA9) and two non-HOX homeobox genes (PBX1 and HOX11) are involved in chromosomal translocations. In mouse leukemias, provirus integrations cause aberrant expression of several HOX and non-HOX genes. Currently available information will be discussed separately on HOX and non-HOX genes, in normal and leukemic hematopoiesis, respectively. Publication Types: Review Review, Tutorial PMID: 9885434 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 11: Mol Cell Biol. 1999 Jan;19(1):764-76. CREB binding protein interacts with nucleoporin-specific FG repeats that activate transcription and mediate NUP98-HOXA9 oncogenicity. Kasper LH, Brindle PK, Schnabel CA, Pritchard CE, Cleary ML, van Deursen JM. Departments of Genetics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA. Genes encoding the Phe-Gly (FG) repeat-containing nucleoporins NUP98 and CAN/NUP214 are at the breakpoints of several chromosomal translocations associated with human acute myeloid leukemia (AML), but their role in oncogenesis is unclear. Here we demonstrate that the NUP98-HOXA9 fusion gene encodes two nuclear oncoproteins with either 19 or 37 NUP98 FG repeats fused to the DNA binding and PBX heterodimerization domains of the transcription factor HOXA9. Both NUP98-HOXA9 chimeras transformed NIH 3T3 fibroblasts, and this transformation required the HOXA9 domains for DNA binding and PBX interaction. Surprisingly, the FG repeats acted as very potent transactivators of gene transcription. This NUP98-derived activity is essential for transformation and can be replaced by the bona fide transactivation domain of VP16. Interestingly, FG repeat-containing segments derived from the nucleoporins NUP153 and CAN/NUP214 functioned similarly to those from NUP98. We further demonstrate that transactivation by FG repeat-rich segments of NUP98 correlates with their ability to interact functionally and physically with the transcriptional coactivators CREB binding protein (CBP) and p300. This finding shows, for the first time, that a translocation-generated fusion protein appears to recruit CBP/p300 as an important step of its oncogenic mechanism. Together, our results suggest that NUP98-HOXA9 chimeras are aberrant transcription factors that deregulate HOX-responsive genes through the transcriptional activation properties of nucleoporin-specific FG repeats that recruit CBP/p300. Indeed, FG repeat-mediated transactivation may be a shared pathogenic function of nucleoporins implicated human AML. PMID: 9858599 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 12: EMBO J. 1998 Jul 1;17(13):3714-25. Hoxa9 transforms primary bone marrow cells through specific collaboration with Meis1a but not Pbx1b. Kroon E, Krosl J, Thorsteinsdottir U, Baban S, Buchberg AM, Sauvageau G. Laboratory of Molecular Genetics of Hemopoietic Stem Cells, Clinical Research Institute of Montreal, Montreal, Quebec, Canada H2W 1R7. Hoxa9, Meis1 and Pbx1 encode homeodomaincontaining proteins implicated in leukemic transformation in both mice and humans. Hoxa9, Meis1 and Pbx1 proteins have been shown to physically interact with each other, as Hoxa9 cooperatively binds consensus DNA sequences with Meis1 and with Pbx1, while Meis1 and Pbx1 form heterodimers in both the presence and absence of DNA. In this study, we sought to determine if Hoxa9 could transform hemopoietic cells in collaboration with either Pbx1 or Meis1. Primary bone marrow cells, retrovirally engineered to overexpress Hoxa9 and Meis1a simultaneously, induced growth factor-dependent oligoclonal acute myeloid leukemia in <3 months when transplanted into syngenic mice. In contrast, overexpression of Hoxa9, Meis1a or Pbx1b alone, or the combination of Hoxa9 and Pbx1b failed to transform these cells acutely within 6 months post-transplantation. Similar results were obtained when FDC-P1 cells, engineered to overexpress these genes, were transplanted to syngenic recipients. Thus, these studies demonstrate a selective collaboration between a member of the Hox family and one of its DNA-binding partners in transformation of hemopoietic cells. PMID: 9649441 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 13: Mol Cell Biol. 1997 Nov;17(11):6448-58. AbdB-like Hox proteins stabilize DNA binding by the Meis1 homeodomain proteins. Shen WF, Montgomery JC, Rozenfeld S, Moskow JJ, Lawrence HJ, Buchberg AM, Largman C. Department of Medicine, University of California VA Medical Center, San Francisco 94121, USA. Recent studies show that Hox homeodomain proteins from paralog groups 1 to 10 gain DNA binding specificity and affinity through cooperative binding with the divergent homeodomain protein Pbx1. However, the AbdB-like Hox proteins from paralogs 11, 12, and 13 do not interact with Pbx1a, raising the possibility of different protein partners. The Meis1 homeobox gene has 44% identity to Pbx within the homeodomain and was identified as a common site of viral integration in myeloid leukemias arising in BXH-2 mice. These integrations result in constitutive activation of Meis1. Furthermore, the Hoxa-9 gene is frequently activated by viral integration in the same BXH-2 leukemias, suggesting a biological synergy between these two distinct classes of homeodomain proteins in causing malignant transformation. We now show that the Hoxa-9 protein physically interacts with Meis1 proteins by forming heterodimeric binding complexes on a DNA target containing a Meis1 site (TGACAG) and an AbdB-like Hox site (TTTTACGAC). Hox proteins from the other AbdB-like paralogs, Hoxa-10, Hoxa-11, Hoxd-12, and Hoxb-13, also form DNA binding complexes with Meis1b, while Hox proteins from other paralogs do not appear to interact with Meis1 proteins. DNA binding complexes formed by Meis1 with Hox proteins dissociate much more slowly than DNA complexes with Meis1 alone, suggesting that Hox proteins stabilize the interactions of Meis1 proteins with their DNA targets. PMID: 9343407 [PubMed - indexed for MEDLINE] --------------------------------------------------------------- 14: Nat Genet. 1996 Feb;12(2):149-53. Comment in: Nat Genet. 1996 Feb;12(2):113-4. Cooperative activation of Hoxa and Pbx1-related genes in murine myeloid leukaemias. Nakamura T, Largaespada DA, Shaughnessy JD Jr, Jenkins NA, Copeland NG. Mammalian Genetics Laboratory, NCI-Frederick Cancer Research and Development Center, Maryland 21702, USA. Retroviruses induce myeloid leukaemia in BXH-2 mice by the insertional mutation of cellular proto-oncogenes or tumour suppressor genes. Disease genes can thus be identified by proviral tagging through the identification of common viral integration sites in BXH-2 leukaemia. Here, we describe a new approach for proviral tagging that greatly facilitates the identification of BXH-2 leukaemia genes. Using this approach, we identify three genes whose expression is activated by proviral integration in BXH-2 leukaemias; Hoxa7, Hoxa9, and a Pbx1-related homeobox gene, Meis1. Proviral activation of Hoxa7 or Hoxa9 is strongly correlated with proviral activation of Meis1 implying that Hoxa7 and Hoxa9 cooperate with Meis1 in leukaemia formation. These studies provide the first genetic evidence that Pbx1-related genes cooperate with Hox genes in leukaemia formation and identify a number of new murine myeloid leukaemia genes. PMID: 8563752 [PubMed - indexed for MEDLINE] ---------------------------------------------------------------