1
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Mediator subunit MED1 is required for E2A-PBX1-mediated oncogenic transcription and leukemic cell growth. Proc Natl Acad Sci U S A 2021; 118:1922864118. [PMID: 33542097 DOI: 10.1073/pnas.1922864118] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The chimeric transcription factor E2A-PBX1, containing the N-terminal activation domains of E2A fused to the C-terminal DNA-binding domain of PBX1, results in 5% of pediatric acute lymphoblastic leukemias (ALL). We recently have reported a mechanism for RUNX1-dependent recruitment of E2A-PBX1 to chromatin in pre-B leukemic cells; but the subsequent E2A-PBX1 functions through various coactivators and the general transcriptional machinery remain unclear. The Mediator complex plays a critical role in cell-specific gene activation by serving as a key coactivator for gene-specific transcription factors that facilitates their function through the RNA polymerase II transcriptional machinery, but whether Mediator contributes to aberrant expression of E2A-PBX1 target genes remains largely unexplored. Here we show that Mediator interacts directly with E2A-PBX1 through an interaction of the MED1 subunit with an E2A activation domain. Results of MED1 depletion by CRISPR/Cas9 further indicate that MED1 is specifically required for E2A-PBX1-dependent gene activation and leukemic cell growth. Integrated transcriptome and cistrome analyses identify pre-B cell receptor and cell cycle regulatory genes as direct cotargets of MED1 and E2A-PBX1. Notably, complementary biochemical analyses also demonstrate that recruitment of E2A-PBX1 to a target DNA template involves a direct interaction with DNA-bound RUNX1 that can be further stabilized by EBF1. These findings suggest that E2A-PBX1 interactions with RUNX1 and MED1/Mediator are of functional importance for both gene-specific transcriptional activation and maintenance of E2A-PBX1-driven leukemia. The MED1 dependency for E2A-PBX1-mediated gene activation and leukemogenesis may provide a potential therapeutic opportunity by targeting MED1 in E2A-PBX1+ pre-B leukemia.
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2
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E2A-PBX1 functions as a coactivator for RUNX1 in acute lymphoblastic leukemia. Blood 2021; 136:11-23. [PMID: 32276273 DOI: 10.1182/blood.2019003312] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Accepted: 03/05/2020] [Indexed: 12/13/2022] Open
Abstract
E2A, a basic helix-loop-helix transcription factor, plays a crucial role in determining tissue-specific cell fate, including differentiation of B-cell lineages. In 5% of childhood acute lymphoblastic leukemia (ALL), the t(1,19) chromosomal translocation specifically targets the E2A gene and produces an oncogenic E2A-PBX1 fusion protein. Although previous studies have shown the oncogenic functions of E2A-PBX1 in cell and animal models, the E2A-PBX1-enforced cistrome, the E2A-PBX1 interactome, and related mechanisms underlying leukemogenesis remain unclear. Here, by unbiased genomic profiling approaches, we identify the direct target sites of E2A-PBX1 in t(1,19)-positive pre-B ALL cells and show that, compared with normal E2A, E2A-PBX1 preferentially binds to a subset of gene loci cobound by RUNX1 and gene-activating machineries (p300, MED1, and H3K27 acetylation). Using biochemical analyses, we further document a direct interaction of E2A-PBX1, through a region spanning the PBX1 homeodomain, with RUNX1. Our results also show that E2A-PBX1 binding to gene enhancers is dependent on the RUNX1 interaction but not the DNA-binding activity harbored within the PBX1 homeodomain of E2A-PBX1. Transcriptome analyses and cell transformation assays further establish a significant RUNX1 requirement for E2A-PBX1-mediated target gene activation and leukemogenesis. Notably, the RUNX1 locus itself is also directly activated by E2A-PBX1, indicating a multilayered interplay between E2A-PBX1 and RUNX1. Collectively, our study provides the first unbiased profiling of the E2A-PBX1 cistrome in pre-B ALL cells and reveals a previously unappreciated pathway in which E2A-PBX1 acts in concert with RUNX1 to enforce transcriptome alterations for the development of pre-B ALL.
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3
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Fischer U, Yang JJ, Ikawa T, Hein D, Vicente-Dueñas C, Borkhardt A, Sánchez-García I. Cell Fate Decisions: The Role of Transcription Factors in Early B-cell Development and Leukemia. Blood Cancer Discov 2020; 1:224-233. [PMID: 33392513 DOI: 10.1158/2643-3230.bcd-20-0011] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
B-cells are an integral part of the adaptive immune system and regulate innate immunity. Derived from hematopoietic stem cells they mature through a series of cell fate decisions. Complex transcriptional circuits form and dissipate dynamically during these lineage restrictions. Genomic aberrations of involved transcription factors underlie various B-cell disorders. Acquired somatic aberrations are associated with cancer, whereas germline variations predispose to both malignant and non-malignant diseases. We review the opposing role of transcription factors during B-cell development in health and disease. We focus on early B-cell leukemia and discuss novel causative gene-environment cooperations and their implications for precision medicine.
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Affiliation(s)
- Ute Fischer
- Department of Pediatric Oncology, Hematology and Clinical Immunology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | - Jun J Yang
- Hematological Malignancies Programme, Comprehensive Cancer Center, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Tomokatsu Ikawa
- Division of Immunobiology, Research Institute for Biomedical Sciences, Tokyo University of Science, Noda, Chiba, 278-0022, Japan
| | - Daniel Hein
- Department of Pediatric Oncology, Hematology and Clinical Immunology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | | | - Arndt Borkhardt
- Department of Pediatric Oncology, Hematology and Clinical Immunology, Medical Faculty, Heinrich-Heine-University, Düsseldorf, Germany
| | - Isidro Sánchez-García
- Institute of Biomedical Research of Salamanca (IBSAL), Salamanca, Spain.,Experimental Therapeutics and Translational Oncology Program, Instituto de Biología Molecular y Celular del Cáncer, CSIC/Universidad de Salamanca
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4
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Lin CH, Wang Z, Duque-Afonso J, Wong SHK, Demeter J, Loktev AV, Somervaille TCP, Jackson PK, Cleary ML. Oligomeric self-association contributes to E2A-PBX1-mediated oncogenesis. Sci Rep 2019; 9:4915. [PMID: 30894657 PMCID: PMC6426973 DOI: 10.1038/s41598-019-41393-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2018] [Accepted: 03/04/2019] [Indexed: 11/16/2022] Open
Abstract
The PBX1 homeodomain transcription factor is converted by t(1;19) chromosomal translocations in acute leukemia into the chimeric E2A-PBX1 oncoprotein. Fusion with E2A confers potent transcriptional activation and constitutive nuclear localization, bypassing the need for dimerization with protein partners that normally stabilize and regulate import of PBX1 into the nucleus, but the mechanisms underlying its oncogenic activation are incompletely defined. We demonstrate here that E2A-PBX1 self-associates through the PBX1 PBC-B domain of the chimeric protein to form higher-order oligomers in t(1;19) human leukemia cells, and that this property is required for oncogenic activity. Structural and functional studies indicate that self-association facilitates the binding of E2A-PBX1 to DNA. Mutants unable to self-associate are transformation defective, however their oncogenic activity is rescued by the synthetic oligomerization domain of FKBP, which confers conditional transformation properties on E2A-PBX1. In contrast to self-association, PBX1 protein domains that mediate interactions with HOX DNA-binding partners are dispensable. These studies suggest that oligomeric self-association may compensate for the inability of monomeric E2A-PBX1 to stably bind DNA and circumvents protein interactions that otherwise modulate PBX1 stability, nuclear localization, DNA binding, and transcriptional activity. The unique dependence on self-association for E2A-PBX1 oncogenic activity suggests potential approaches for mechanism-based targeted therapies.
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MESH Headings
- Basic Helix-Loop-Helix Transcription Factors/genetics
- Basic Helix-Loop-Helix Transcription Factors/metabolism
- Carcinogenesis/genetics
- Cell Line, Tumor
- Chromosomes, Human, Pair 1/chemistry
- Chromosomes, Human, Pair 19/chemistry
- DNA, Neoplasm/genetics
- DNA, Neoplasm/metabolism
- Gene Expression Regulation, Neoplastic
- HEK293 Cells
- Humans
- Leukemia, Myeloid, Acute/genetics
- Leukemia, Myeloid, Acute/metabolism
- Leukemia, Myeloid, Acute/pathology
- Oncogene Proteins, Fusion/genetics
- Oncogene Proteins, Fusion/metabolism
- Pre-B-Cell Leukemia Transcription Factor 1/genetics
- Pre-B-Cell Leukemia Transcription Factor 1/metabolism
- Protein Binding
- Protein Multimerization
- Protein Stability
- Tacrolimus Binding Proteins/genetics
- Tacrolimus Binding Proteins/metabolism
- Transcription, Genetic
- Translocation, Genetic
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Affiliation(s)
- Chiou-Hong Lin
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Zhong Wang
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA
- Sun Yat-Sen University, School of Pharmaceutical Sciences, Guangzhou, 510006, China
| | - Jesús Duque-Afonso
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA
- Department of Hematology and Oncology, University Medical Center Freiburg, Freiburg, Germany
| | - Stephen Hon-Kit Wong
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Janos Demeter
- Baxter Laboratory for Stem Cell Biology, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Alexander V Loktev
- Baxter Laboratory for Stem Cell Biology, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Tim C P Somervaille
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA
- Leukaemia Biology Laboratory, Cancer Research UK Manchester Institute, The University of Manchester, Manchester, M20 4GJ, UK
| | - Peter K Jackson
- Baxter Laboratory for Stem Cell Biology, Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Michael L Cleary
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, 94305, USA.
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5
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Alsadeq A, Schewe DM. Acute lymphoblastic leukemia of the central nervous system: on the role of PBX1. Haematologica 2018; 102:611-613. [PMID: 28364057 DOI: 10.3324/haematol.2017.165142] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Affiliation(s)
- Ameera Alsadeq
- Institute of Immunology, University Medical Center Ulm, Germany
| | - Denis M Schewe
- Department of Pediatrics I, ALL-BFM Study Group, Christian-Albrechts University Kiel and University Medical Center Schleswig-Holstein, Kiel, Germany
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6
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Abstract
Analysis of chromosomal translocation sequence locations in human lymphomas has provided valuable clues about the mechanism of the translocations and when they occur. Biochemical analyses on the mechanisms of DNA breakage and rejoining permit formulation of detailed models of the human chromosomal translocation process in lymphoid neoplasms. Most human lymphomas are derived from B cells in which a DNA break at an oncogene is initiated by activation-induced deaminase (AID). The partner locus in many cases is located at one of the antigen receptor loci, and this break is generated by the recombination activating gene (RAG) complex or by AID. After breakage, the joining process typically occurs by non-homologous DNA end-joining (NHEJ). Some of the insights into this mechanism also apply to translocations that occur in non-lymphoid neoplasms.
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Affiliation(s)
- Michael R Lieber
- USC Norris Comprehensive Cancer Center, Room 5428, University of Southern California Keck School of Medicine, 1441 Eastlake Avenue, MC9176, Los Angeles, California 90089-9176, USA
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7
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Duque-Afonso J, Feng J, Scherer F, Lin CH, Wong SHK, Wang Z, Iwasaki M, Cleary ML. Comparative genomics reveals multistep pathogenesis of E2A-PBX1 acute lymphoblastic leukemia. J Clin Invest 2015; 125:3667-80. [PMID: 26301816 DOI: 10.1172/jci81158] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 06/18/2015] [Indexed: 12/17/2022] Open
Abstract
Acute lymphoblastic leukemia (ALL) is the most common childhood cancer; however, its genetic diversity limits investigation into the molecular pathogenesis of disease and development of therapeutic strategies. Here, we engineered mice that conditionally express the E2A-PBX1 fusion oncogene, which results from chromosomal translocation t(1;19) and is present in 5% to 7% of pediatric ALL cases. The incidence of leukemia in these mice varied from 5% to 50%, dependent on the Cre-driving promoter (Cd19, Mb1, or Mx1) used to induce E2A-PBX1 expression. Two distinct but highly similar subtypes of B cell precursor ALLs that differed by their pre-B cell receptor (pre-BCR) status were induced and displayed maturation arrest at the pro-B/large pre-B II stages of differentiation, similar to human E2A-PBX1 ALL. Somatic activation of E2A-PBX1 in B cell progenitors enhanced self-renewal and led to acquisition of multiple secondary genomic aberrations, including prominent spontaneous loss of Pax5. In preleukemic mice, conditional Pax5 deletion cooperated with E2A-PBX1 to expand progenitor B cell subpopulations, increasing penetrance and shortening leukemia latency. Recurrent secondary activating mutations were detected in key signaling pathways, most notably JAK/STAT, that leukemia cells require for proliferation. These data support conditional E2A-PBX1 mice as a model of human ALL and suggest targeting pre-BCR signaling and JAK kinases as potential therapeutic strategies.
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8
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Hauer J, Borkhardt A, Sánchez-García I, Cobaleda C. Genetically engineered mouse models of human B-cell precursor leukemias. Cell Cycle 2015; 13:2836-46. [PMID: 25486471 PMCID: PMC4613455 DOI: 10.4161/15384101.2014.949137] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
B-cell precursor acute lymphoblastic leukemias (pB-ALLs) are the most frequent type of malignancies of the childhood, and also affect an important proportion of adult patients. In spite of their apparent homogeneity, pB-ALL comprises a group of diseases very different both clinically and pathologically, and with very diverse outcomes as a consequence of their biology, and underlying molecular alterations. Their understanding (as a prerequisite for their cure) will require a sustained multidisciplinary effort from professionals coming from many different fields. Among all the available tools for pB-ALL research, the use of animal models stands, as of today, as the most powerful approach, not only for the understanding of the origin and evolution of the disease, but also for the development of new therapies. In this review we go over the most relevant (historically, technically or biologically) genetically engineered mouse models (GEMMs) of human pB-ALLs that have been generated over the last 20 years. Our final aim is to outline the most relevant guidelines that should be followed to generate an “ideal” animal model that could become a standard for the study of human pB-ALL leukemia, and which could be shared among research groups and drug development companies in order to unify criteria for studies like drug testing, analysis of the influence of environmental risk factors, or studying the role of both low-penetrance mutations and cancer susceptibility alterations.
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Affiliation(s)
- Julia Hauer
- a Department of Pediatric Oncology ; Hematology and Clinical Immunology ; Heinrich-Heine University Dusseldorf ; Medical Faculty ; Dusseldorf , Germany
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9
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Woodcroft MW, Nanan K, Thompson P, Tyryshkin K, Smith SP, Slany RK, LeBrun DP. Retrovirus-Mediated Expression of E2A-PBX1 Blocks Lymphoid Fate but Permits Retention of Myeloid Potential in Early Hematopoietic Progenitors. PLoS One 2015; 10:e0130495. [PMID: 26098938 PMCID: PMC4476730 DOI: 10.1371/journal.pone.0130495] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Accepted: 05/20/2015] [Indexed: 11/19/2022] Open
Abstract
The oncogenic transcription factor E2A-PBX1 is expressed consequent to chromosomal translocation 1;19 and is an important oncogenic driver in cases of pre-B-cell acute lymphoblastic leukemia (ALL). Elucidating the mechanism by which E2A-PBX1 induces lymphoid leukemia would be expedited by the availability of a tractable experimental model in which enforced expression of E2A-PBX1 in hematopoietic progenitors induces pre-B-cell ALL. However, hematopoietic reconstitution of irradiated mice with bone marrow infected with E2A-PBX1-expressing retroviruses consistently gives rise to myeloid, not lymphoid, leukemia. Here, we elucidate the hematopoietic consequences of forced E2A-PBX1 expression in primary murine hematopoietic progenitors. We show that introducing E2A-PBX1 into multipotent progenitors permits the retention of myeloid potential but imposes a dense barrier to lymphoid development prior to the common lymphoid progenitor stage, thus helping to explain the eventual development of myeloid, and not lymphoid, leukemia in transplanted mice. Our findings also indicate that E2A-PBX1 enforces the aberrant, persistent expression of some genes that would normally have been down-regulated in the subsequent course of hematopoietic maturation. We show that enforced expression of one such gene, Hoxa9, a proto-oncogene associated with myeloid leukemia, partially reproduces the phenotype produced by E2A-PBX1 itself. Existing evidence suggests that the 1;19 translocation event takes place in committed B-lymphoid progenitors. However, we find that retrovirus-enforced expression of E2A-PBX1 in committed pro-B-cells results in cell cycle arrest and apoptosis. Our findings indicate that the neoplastic phenotype induced by E2A-PBX1 is determined by the developmental stage of the cell into which the oncoprotein is introduced.
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Affiliation(s)
- Mark W. Woodcroft
- Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
| | - Kyster Nanan
- Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
| | - Patrick Thompson
- Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
| | - Kathrin Tyryshkin
- Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
| | - Steven P. Smith
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Robert K. Slany
- Department of Genetics, University Erlangen, Erlangen, Germany
| | - David P. LeBrun
- Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, Canada
- * E-mail:
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10
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Fusion of the genes EWSR1 and PBX3 in retroperitoneal leiomyoma with t(9;22)(q33;q12). PLoS One 2015; 10:e0124288. [PMID: 25875009 PMCID: PMC4397011 DOI: 10.1371/journal.pone.0124288] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 03/06/2015] [Indexed: 01/17/2023] Open
Abstract
Retroperitoneal leiomyoma is a rare benign smooth muscle tumor almost exclusively found in women and with histopathological features similar to uterine leiomyomas. The pathogenesis of retroperitoneal leiomyoma is unclear and next to nothing is known about the cytogenetics and molecular genetics of the tumor. We present here a retroperitoneal leiomyoma with a t(9;22)(q33;q12) as the sole karyotypic aberration. The translocation resulted in an EWSR1-PBX3 fusion gene in which exon 9 of EWSR1 (nucleotide 1320 accession number NM_013986 version 3) was in-frame fused to exon 5 of PBX3 (nucleotide 824 accession number NM_006195 version 5). The EWSR1-PBX3 fusion transcript codes for a 529 amino acids long chimeric EWSR1-PBX3 protein which contains the N-terminal transactivation part of EWSR1 and the homeodomain of PBX3. The present study, together with our previous finding of a retroperitoneal leiomyoma with t(10;17)(q22;q21) as the sole karyotypic aberration and a KAT6B-KANSL1 fusion gene, indicates that retroperitoneal leiomyomas may be characterized by fusion genes coding for chimeric proteins. However, cytogenetic and molecular heterogeneity exists in these tumors and it is too early to tell how many and which different pathways lead to retroperitoneal leiomyomagenesis.
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11
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Jacoby E, Chien CD, Fry TJ. Murine models of acute leukemia: important tools in current pediatric leukemia research. Front Oncol 2014; 4:95. [PMID: 24847444 PMCID: PMC4019869 DOI: 10.3389/fonc.2014.00095] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2014] [Accepted: 04/18/2014] [Indexed: 01/09/2023] Open
Abstract
Leukemia remains the most common diagnosis in pediatric oncology and, despite dramatic progress in upfront therapy, is also the most common cause of cancer-related death in children. Much of the initial improvement in outcomes for acute lymphoblastic leukemia (ALL) was due to identification of cytotoxic agents that are active against leukemia followed by the recognition that combination of these cytotoxic agents and prolonged therapy are essential for cure. Recent data demonstrating lack of progress in patients for whom standard chemotherapy fails suggests that the ability to improve outcome for these children will not be dramatically impacted through more intensive or newer cytotoxic agents. Thus, much of the recent research focus has been in the area of improving our understanding of the genetics and the biology of leukemia. Although in vitro studies remain critical, given the complexity of a living system and the increasing recognition of the contribution of leukemia extrinsic factors such as the bone marrow microenvironment, in vivo models have provided important insights. The murine systems that are used can be broadly categorized into syngeneic models in which a murine leukemia can be studied in immunologically intact hosts and xenograft models where human leukemias are studied in highly immunocompromised murine hosts. Both of these systems have limitations such that neither can be used exclusively to study all aspects of leukemia biology and therapeutics for humans. This review will describe the various ALL model systems that have been developed as well as discuss the advantages and disadvantages inherent to these systems that make each particularly suitable for specific types of studies.
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Affiliation(s)
- Elad Jacoby
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health , Bethesda, MD , USA
| | - Christopher D Chien
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health , Bethesda, MD , USA
| | - Terry J Fry
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health , Bethesda, MD , USA
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12
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Denis CM, Langelaan DN, Kirlin AC, Chitayat S, Munro K, Spencer HL, LeBrun DP, Smith SP. Functional redundancy between the transcriptional activation domains of E2A is mediated by binding to the KIX domain of CBP/p300. Nucleic Acids Res 2014; 42:7370-82. [PMID: 24682819 PMCID: PMC4066744 DOI: 10.1093/nar/gku206] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The E-protein transcription factors play essential roles in lymphopoiesis, with E12 and E47 (hereafter called E2A) being particularly important in B cell specification and maturation. The E2A gene is also involved in a chromosomal translocation that results in the leukemogenic oncoprotein E2A-PBX1. The two activation domains of E2A, AD1 and AD2, display redundant, independent, and cooperative functions in a cell-dependent manner. AD1 of E2A functions by binding the transcriptional co-activator CBP/p300; this interaction is required in oncogenesis and occurs between the conserved ϕ-x-x-ϕ-ϕ motif in AD1 and the KIX domain of CBP/p300. However, co-activator recruitment by AD2 has not been characterized. Here, we demonstrate that the first of two conserved ϕ-x-x-ϕ-ϕ motifs within AD2 of E2A interacts at the same binding site on KIX as AD1. Mutagenesis uncovered a correspondence between the KIX-binding affinity of AD2 and transcriptional activation. Although AD2 is dispensable for oncogenesis, experimentally increasing the affinity of AD2 for KIX uncovered a latent potential to mediate immortalization of primary hematopoietic progenitors by E2A-PBX1. Our findings suggest that redundancy between the two E2A activation domains with respect to transcriptional activation and oncogenic function is mediated by binding to the same surface of the KIX domain of CBP/p300.
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Affiliation(s)
- Christopher M Denis
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - David N Langelaan
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Alyssa C Kirlin
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Seth Chitayat
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Kim Munro
- Protein Function Discovery Group, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Holly L Spencer
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - David P LeBrun
- Protein Function Discovery Group, Queen's University, Kingston, Ontario, K7L 3N6, Canada Department of Pathology and Molecular Medicine, Queen's University, Kingston, Ontario, K7L 3N6, Canada Division of Cancer Biology and Genetics, Cancer Research Institute, Queen's University, Kingston, Ontario, K7L 3N6, Canada
| | - Steven P Smith
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, K7L 3N6, Canada Protein Function Discovery Group, Queen's University, Kingston, Ontario, K7L 3N6, Canada
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13
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Diakos C, Xiao Y, Zheng S, Kager L, Dworzak M, Wiemels JL. Direct and indirect targets of the E2A-PBX1 leukemia-specific fusion protein. PLoS One 2014; 9:e87602. [PMID: 24503810 PMCID: PMC3913655 DOI: 10.1371/journal.pone.0087602] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Accepted: 12/20/2013] [Indexed: 01/04/2023] Open
Abstract
E2A-PBX1 is expressed as a result of the t(1;19) chromosomal translocation in nearly 5% of cases of childhood acute lymphoblastic leukemia. The E2A-PBX1 chimeric transcription factor contains the N-terminal transactivation domain of E2A (TCF3) fused to the C-terminal DNA-binding homeodomain of PBX1. While there is no doubt of its oncogenic potential, the mechanisms of E2A-PBX1-mediated pre-B cell transformation and the nature of direct E2A-PBX1 target genes and pathways remain largely unknown. Herein we used chromatin immunoprecipitation assays (ChIP-chip) to identify direct targets of E2A-PBX1, and we used gene expression arrays of siRNA E2A-PBX1-silenced cells to evaluate changes in expression induced by the fusion protein. Combined ChIP-chip and expression data analysis gave rise to direct and functional targets of E2A-PBX1. Further we observe that the set of ChIP-chip identified E2A-PBX1 targets show a collective down-regulation trend in the E2A-PBX1 silenced samples compared to controls suggesting an activating role of this fusion transcription factor. Our data suggest that the expression of the E2A-PBX1 fusion gene interferes with key regulatory pathways and functions of hematopoietic biology. Among these are members of the WNT and apoptosis/cell cycle control pathways, and thus may comprise an essential driving force for the propagation and maintenance of the leukemic phenotype. These findings may also provide evidence of potentially attractive therapeutic targets.
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Affiliation(s)
- Christofer Diakos
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
- Department of Pediatrics, St Anna Children’s Hospital, Medical University of Vienna, Vienna, Austria
| | - Yuanyuan Xiao
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
| | - Shichun Zheng
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
- Department of Neurosurgery, University of California San Francisco, San Francisco, California, United States of America
| | - Leo Kager
- Department of Pediatrics, St Anna Children’s Hospital, Medical University of Vienna, Vienna, Austria
| | - Michael Dworzak
- Department of Pediatrics, St Anna Children’s Hospital, Medical University of Vienna, Vienna, Austria
- Children’s Cancer Research Institute, St Anna Kinderkrebsforschung, Vienna, Austria
| | - Joseph L. Wiemels
- Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, United States of America
- * E-mail:
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14
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Gow CH, Guo C, Wang D, Hu Q, Zhang J. Differential involvement of E2A-corepressor interactions in distinct leukemogenic pathways. Nucleic Acids Res 2013; 42:137-52. [PMID: 24064250 PMCID: PMC3874172 DOI: 10.1093/nar/gkt855] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
E2A is a member of the E-protein family of transcription factors. Previous studies have reported context-dependent regulation of E2A-dependent transcription. For example, whereas the E2A portion of the E2A-Pbx1 leukemia fusion protein mediates robust transcriptional activation in t(1;19) acute lymphoblastic leukemia, the transcriptional activity of wild-type E2A is silenced by high levels of corepressors, such as the AML1-ETO fusion protein in t(8;21) acute myeloid leukemia and ETO-2 in hematopoietic cells. Here, we show that, unlike the HEB E-protein, the activation domain 1 (AD1) of E2A has specifically reduced corepressor interaction due to E2A-specific amino acid changes in the p300/CBP and ETO target motif. Replacing E2A-AD1 with HEB-AD1 abolished the ability of E2A-Pbx1 to activate target genes and to induce cell transformation. On the other hand, the weak E2A-AD1-corepressor interaction imposes a critical importance on another ETO-interacting domain, downstream ETO-interacting sequence (DES), for corepressor-mediated repression. Deletion of DES abrogates silencing of E2A activity by AML1-ETO in t(8;21) leukemia cells or by ETO-2 in normal hematopoietic cells. Our results reveal an E2A-specific mechanism important for its context-dependent activation and repression function, and provide the first evidence for the differential involvement of E2A-corepressor interactions in distinct leukemogenic pathways.
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Affiliation(s)
- Chien-Hung Gow
- Department of Cancer Biology, Vontz Center for Molecular Studies, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA
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15
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Mo ML, Chen Z, Zhou HM, Li H, Hirata T, Jablons DM, He B. Detection of E2A-PBX1 fusion transcripts in human non-small-cell lung cancer. JOURNAL OF EXPERIMENTAL & CLINICAL CANCER RESEARCH : CR 2013; 32:29. [PMID: 23688269 PMCID: PMC3661382 DOI: 10.1186/1756-9966-32-29] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 04/15/2013] [Indexed: 01/15/2023]
Abstract
Background E2A-PBX1 fusion gene caused by t(1;19)(q23;p13), has been well characterized in acute lymphoid leukemia (ALL). There is no report on E2A-PBX1 fusion transcripts in non-small-cell lung cancer (NSCLC). Methods We used polymerase chain reaction (PCR) to detect E2A-PBX1 fusion transcripts in human NSCLC tissue specimens and cell lines. We analyzed correlation of E2A-PBX1 fusion transcripts with clinical outcomes in 76 patients with adenocarcinoma in situ (AIS) and other subgroups. We compared mutation status of k-ras, p53 and EGFR in 22 patients with E2A-PBX1 fusion transcripts. Results We detected E2A-PBX1 transcripts in 23 of 184 (12.5%) NSCLC tissue specimens and 3 of 13 (23.1%) NSCLC cell lines. Presence of E2A-PBX1 fusion transcripts correlated with smoking status in female patients (P = 0.048), AIS histology (P = 0.006) and tumor size (P = 0.026). The overall survival was associated with gender among AIS patients (P = 0.0378) and AIS patients without E2A-PBX1 fusion transcripts (P = 0.0345), but not among AIS patients with E2A-PBX1 fusion transcripts (P = 0.6401). The overall survival was also associated with status of E2A-PBX1 fusion transcripts among AIS stage IA patients (P = 0.0363) and AIS stage IA female patients (P = 0.0174). In addition, among the 22 patients with E2A-PBX1 fusion transcripts, 12 (54.5%) patients including all four non-smokers, showed no common mutations in k-ras, p53 and EGFR. Conclusions E2A-PBX1 fusion gene caused by t(1;19)(q23;p13) may be a common genetic change in AIS and a survival determinant for female AIS patients at early stage.
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Affiliation(s)
- Min-Li Mo
- School of Life Sciences, Tsinghua University, Beijing 10084, China
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16
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Chang MJ, Wu H, Achille NJ, Reisenauer MR, Chou CW, Zeleznik-Le NJ, Hemenway CS, Zhang W. Histone H3 lysine 79 methyltransferase Dot1 is required for immortalization by MLL oncogenes. Cancer Res 2011; 70:10234-42. [PMID: 21159644 DOI: 10.1158/0008-5472.can-10-3294] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Chimeric oncoproteins resulting from fusion of MLL to a wide variety of partnering proteins cause biologically distinctive and clinically aggressive acute leukemias. However, the mechanism of MLL-mediated leukemic transformation is not fully understood. Dot1, the only known histone H3 lysine 79 (H3K79) methyltransferase, has been shown to interact with multiple MLL fusion partners including AF9, ENL, AF10, and AF17. In this study, we utilize a conditional Dot1l deletion model to investigate the role of Dot1 in hematopoietic progenitor cell immortalization by MLL fusion proteins. Western blot and mass spectrometry show that Dot1-deficient cells are depleted of the global H3K79 methylation mark. We find that loss of Dot1 activity attenuates cell viability and colony formation potential of cells immortalized by MLL oncoproteins but not by the leukemic oncoprotein E2a-Pbx1. Although this effect is most pronounced for MLL-AF9, we find that Dot1 contributes to the viability of cells immortalized by other MLL oncoproteins that are not known to directly recruit Dot1. Cells immortalized by MLL fusions also show increased apoptosis, suggesting the involvement of Dot1 in survival pathways. In summary, our data point to a pivotal requirement for Dot1 in MLL fusion protein-mediated leukemogenesis and implicate Dot1 as a potential therapeutic target.
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Affiliation(s)
- Ming-Jin Chang
- Department of Biochemistry, Tulane University, New Orleans, Louisiana, USA
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17
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Abstract
Many human cancers are associated with characteristic chromosomal rearrangements, especially hematopoietic cancers such as leukemias and lymphomas. The first and most critical step in the rearrangement process is the induction of two DNA double-strand breaks (DSB). In all cases, at least one of the two DSBs is generated by a pathologic process, such as (1) randomly-positioned breaks due to ionizing radiation, free radical oxidative damage, or spontaneous hydrolysis; (2) breaks associated with topoisomerase inhibitor treatment; or (3) breaks at direct or inverted repeat sequences, mediated by unidentified strand breakage mechanisms. In lymphoid cells, one of the two requisite DSBs is often physiologic, the result of V(D)J recombination or class switch recombination (CSR) at the lymphoid antigen receptor loci. The RAG complex, which causes the DSBs in V(D)J recombination, can cause (4) sequence-specific, pathologic DSBs at sites that fit the consensus of their normal V(D)J recombination signal targets; or (5) structure-specific, pathologic DSBs at regions of single- to double-strand transition. CSR occurs specifically in the B-cell lineage, and requires (6) activation-induced cytidine deaminase (AID) action at sites of single-stranded DNA, which may occur pathologically outside of the normal target loci of class switch recombination regions and somatic hypermutation (SHM) zones. Recent work proposes a seventh mechanism: the sequential action of AID and the RAG complex at CpG sites provides a coherent model for the pathologic DSBs at some of the most common sites of translocation in human lymphoma – the bcl-2 gene in follicular lymphoma and diffuse large B-cell lymphoma, and the bcl-1 gene in mantle cell lymphoma.
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Affiliation(s)
- Albert G Tsai
- USC Norris Comprehensive Cancer Ctr, Rm. 5428 Departments of Pathology, Biochemistry & Molecular Biology, Molecular Microbiology & Immunology, and of Biological Sciences (Section of Molecular & Computational Biology), University of Southern California, Los Angeles, CA 90089-9176, USA.
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18
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Bayly R, Murase T, Hyndman BD, Savage R, Nurmohamed S, Munro K, Casselman R, Smith SP, LeBrun DP. Critical role for a single leucine residue in leukemia induction by E2A-PBX1. Mol Cell Biol 2006; 26:6442-52. [PMID: 16914730 PMCID: PMC1592826 DOI: 10.1128/mcb.02025-05] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
In roughly 5% of cases of acute lymphoblastic leukemia, a chromosomal translocation leads to expression of the oncogenic protein E2A-PBX1. The N-terminal portion of E2A-PBX1, encoded by the E2A gene, is identical in sequence to the corresponding portion of the E proteins E12/E47 and includes transcriptional activation domains. The C terminus consists of most of the HOX interacting transcription factor PBX1, including its DNA-binding homeodomain. Structure-function correlative experiments have suggested that oncogenesis by E2A-PBX1 requires an activation domain, called AD1, at the extreme N terminus. We recently demonstrated that a potentially helical portion of AD1 interacts directly with the transcriptional coactivator protein cyclic AMP response element-binding protein (CBP) and that this interaction is essential in the immortalization of primary bone marrow cells in tissue culture. Here we show that a conserved LXXLL motif within AD1 is required in the interaction between E2A-PBX1 and the KIX domain of CBP. We show by circular dichroism spectroscopy that the LXXLL-containing portion of AD1 undergoes a helical transition upon interacting with the KIX domain and that amino acid substitutions that prevent helix formation prevent both the KIX interaction and cell immortalization by E2A-PBX1. Perhaps most strikingly, substitution of a single, conserved leucine residue (L20) within the LXXLL motif impairs leukemia induction in mice after transplantation with E2A-PBX1-expressing bone marrow. The KIX domain of CBP mediates well-characterized interactions with several transcription factors of relevance to leukemia induction. Circumstantial evidence suggests that the side chain of L20 might interact with a deep hydrophobic pocket in the KIX domain. Therefore, our results serve to identify a potential new drug target.
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Affiliation(s)
- Richard Bayly
- Division of Cancer Biology and Genetics, Cancer Research Institute, Queen's University, Kingston, Ontario K7L 3N6, Canada
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19
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Bijl J, Sauvageau M, Thompson A, Sauvageau G. High incidence of proviral integrations in the Hoxa locus in a new model of E2a-PBX1-induced B-cell leukemia. Genes Dev 2005; 19:224-33. [PMID: 15655112 PMCID: PMC545883 DOI: 10.1101/gad.1268505] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Relevant mouse models of E2a-PBX1-induced pre-B cell leukemia are still elusive. We now report the generation of a pre-B leukemia model using E2a-PBX1 transgenic mice, which lack mature and precursor T-cells as a result of engineered loss of CD3epsilon expression (CD3epsilon(-/-)). Using insertional mutagenesis and inverse-PCR, we show that B-cell leukemia development in the E2a-PBX1 x CD3epsilon(-/-) compound transgenic animals is significantly accelerated when compared to control littermates, and document several known and novel integrations in these tumors. Of all common integration sites, a small region of 19 kb in the Hoxa gene locus, mostly between Hoxa6 and Hoxa10, represented 18% of all integrations in the E2a-PBX1 B-cell leukemia and was targeted in 86% of these leukemias compared to 17% in control tumors. Q-PCR assessment of expression levels for most Hoxa cluster genes in these tumors revealed an unprecedented impact of the proviral integrations on Hoxa gene expression, with tumors having one to seven different Hoxa genes overexpressed at levels up to 6600-fold above control values. Together our studies set the stage for modeling E2a-PBX1-induced B-cell leukemia and shed new light on the complexity pertaining to Hox gene regulation. In addition, our results show that the Hoxa gene cluster is preferentially targeted in E2a-PBX1-induced tumors, thus suggesting functional collaboration between these oncogenes in pre-B-cell tumors.
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Affiliation(s)
- Janet Bijl
- Laboratory of Molecular Genetics of Stem Cells, Institute for Research in Immunology and Cancer, Montréal, Québec H3C 3J7, Canada
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20
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Liu DB, Gu ZD, Cao XZ, Liu H, Li JY. Immunocytochemical detection of HoxD9 and Pbx1 homeodomain protein expression in Chinese esophageal squamous cell carcinomas. World J Gastroenterol 2005; 11:1562-6. [PMID: 15770739 PMCID: PMC4305705 DOI: 10.3748/wjg.v11.i10.1562] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2004] [Revised: 08/18/2004] [Accepted: 10/18/2004] [Indexed: 02/06/2023] Open
Abstract
AIM To evaluate the expression pattern of two novel oncofetal antigens, the HoxD9 and Pbx1 homeoproteins in esophageal squamous cell carcinomas (ESCCs) to determine what role they would play in the carcinogenesis of ESCC. METHODS We obtained tissue samples of ESCC from 56 patients who underwent esophagectomy but not preoperative chemotherapy or radiotherapy. The diagnosis of ESCC was established and confirmed by staff pathologists. We used a highly sensitive, indirect, immunocytochemical method to detect HoxD9 and PbX1 proteins. We qualitatively and quantitatively evaluated cells that exhibited and staining using a light microscope. RESULTS In all observed carcinoma tissue samples, more than 60% of neoplastic cells stained lightly or strongly for HoxD9, and more than 50% of neoplastic cells stained lightly or strongly for Pbx1. CONCLUSION Our data suggest that HoxD9 and Pbx1 are inappropriately expressed in most human esophageal squamous cell carcinoma. Understanding the role of Hox genes in esophageal epithelial cell carcinogenesis may not only augment early detection but also offer new avenues for treatment of this disease.
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Affiliation(s)
- De-Bin Liu
- Department of Thoracic Surgery, Peking University School of Oncology, Beijing Cancer Hospital, Beijing Institute for Cancer Research, Beijing 100036, China.
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21
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Sykes DB, Kamps MP. E2a/Pbx1 induces the rapid proliferation of stem cell factor-dependent murine pro-T cells that cause acute T-lymphoid or myeloid leukemias in mice. Mol Cell Biol 2004; 24:1256-69. [PMID: 14729970 PMCID: PMC321418 DOI: 10.1128/mcb.24.3.1256-1269.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2003] [Revised: 05/27/2003] [Accepted: 10/07/2003] [Indexed: 11/20/2022] Open
Abstract
Oncoprotein E2a/Pbx1 is produced by the t(1;19) chromosomal translocation of human pre-B acute lymphoblastic leukemia. E2a/Pbx1 blocks differentiation of primary myeloid progenitors but, paradoxically, induces apoptosis in established pre-B-cell lines, and no transforming function of E2a/Pbx1 has been reported in cultured lymphoid progenitors. Here, we demonstrate that E2a/Pbx1 induces immortal proliferation of stem cell factor (SCF)-dependent pro-T thymocytes by a mechanism dependent upon both its transactivation and DNA-binding functions. E2a-Pbx1 cooperated with cytokines or activated signaling oncoproteins to induce cell division, as inactivation of conditional E2a/Pbx1 in either factor-dependent pro-T cells or pro-T cells made factor independent by expression of Bcr/Abl resulted in pro-T-cell quiescence, while reactivation of E2a/Pbx1 restored cell division. Infusion of E2a/Pbx1 pro-T cells in mice caused T lymphoblastic leukemia and, unexpectedly, acute myeloid leukemia. The acute lymphoblastic leukemia did not evidence further maturation, suggesting that E2a/Pbx1 establishes an early block in pro-T-cell development that cannot be overcome by marrow or thymic microenvironments. In an E2a/Pbx1 pro-T thymocyte clone that induced only pro-T acute lymphoblastic leukemia, coexpression of Bcr/Abl expanded its leukemic phenotype to include acute myeloid leukemia, suggesting that unique functions of cooperating signaling oncoproteins can influence the lymphoid versus myeloid character of E2a/Pbx1 leukemia and may cooperate with E2a/Pbx1 to dictate the pre-B-cell phenotype of human leukemia containing t(1;19).
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Affiliation(s)
- David B Sykes
- Department of Pathology, University of California-San Diego, La Jolla, California 92093-0612, USA
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22
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Thorsteinsdottir U, Kroon E, Jerome L, Blasi F, Sauvageau G. Defining roles for HOX and MEIS1 genes in induction of acute myeloid leukemia. Mol Cell Biol 2001; 21:224-34. [PMID: 11113197 PMCID: PMC88796 DOI: 10.1128/mcb.21.1.224-234.2001] [Citation(s) in RCA: 222] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2000] [Accepted: 10/12/2000] [Indexed: 11/20/2022] Open
Abstract
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.
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Affiliation(s)
- U Thorsteinsdottir
- Laboratory of Molecular Genetics of Hemopoietic Stem Cells, Clinical Research Institute of Montréal, Montréal, Québec H2W 1R7, Canada
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23
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Abstract
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.
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24
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Bayly R, LeBrun DP. Role for homodimerization in growth deregulation by E2a fusion proteins. Mol Cell Biol 2000; 20:5789-96. [PMID: 10913162 PMCID: PMC86056 DOI: 10.1128/mcb.20.16.5789-5796.2000] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2000] [Accepted: 05/22/2000] [Indexed: 11/20/2022] Open
Abstract
The oncogenic transcription factor E2a-Pbx1 is expressed in some cases of acute lymphoblastic leukemia as a result of chromosomal translocation 1;19. The early observation that E2a-Pbx1 incorporates transcriptional activation domains from E2a and a DNA-binding homeodomain from Pbx1 inspired a model in which E2a-Pbx1 promotes leukemogenic transformation of lymphoid progenitor cells through transcriptional induction of target genes defined by the Pbx1 portion of the molecule. However, the subsequent demonstration that the only known DNA-binding module on the molecule, the Pbx1 homeodomain, is dispensable for the induction of lymphoblastic lymphoma in transgenic mice called into question the contribution made by the Pbx1 portion. In this study, we have used a domain swap approach coupled with a fibroblast-based focus formation assay to evaluate further the requirement for PBX1-encoded peptide elements in growth deregulation by E2a-Pbx1. No impairment of focus formation was observed when the entire Pbx1 portion was replaced with DNA-binding/dimerization domains derived from yeast transcription factor GAL4 or GCN4. Furthermore, replacement of Pbx1 with tandem FKBP domains that mediate homodimerization in the presence of a synthetic ligand led to striking growth deregulation exclusively in the presence of the dimerizing agent. N-terminal elements encoded by E2A, including the AD1 transcriptional activation domain, were required for dimerization-induced focus formation. We conclude that transcriptional target genes defined by heterologous C-terminal DNA-binding modules are not required in growth deregulation by E2a fusion proteins. We speculate that interactions between N-terminal E2a elements and undefined proteins that could function as components of a transcriptional coactivator complex may be more important.
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Affiliation(s)
- R Bayly
- Richardson Laboratory, Department of Pathology, Queen's University, Kingston, Ontario K7L 3N6, Canada
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25
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Thorsteinsdottir U, Krosl J, Kroon E, Haman A, Hoang T, Sauvageau G. The oncoprotein E2A-Pbx1a collaborates with Hoxa9 to acutely transform primary bone marrow cells. Mol Cell Biol 1999; 19:6355-66. [PMID: 10454582 PMCID: PMC84606 DOI: 10.1128/mcb.19.9.6355] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
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.
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Affiliation(s)
- U Thorsteinsdottir
- Laboratory of Molecular Genetics of Hemopoietic Stem Cells, Clinical Research Institute of Montréal, Montréal, Québec, Canada H2W 1R7
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26
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Lam PY, Sublett JE, Hollenbach AD, Roussel MF. The oncogenic potential of the Pax3-FKHR fusion protein requires the Pax3 homeodomain recognition helix but not the Pax3 paired-box DNA binding domain. Mol Cell Biol 1999; 19:594-601. [PMID: 9858583 PMCID: PMC83917 DOI: 10.1128/mcb.19.1.594] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/1998] [Accepted: 10/01/1998] [Indexed: 11/20/2022] Open
Abstract
The chimeric transcription factor Pax3-FKHR, produced by the t(2;13)(q35;q14) chromosomal translocation in alveolar rhabdomyosarcoma, consists of the two Pax3 DNA binding domains (paired box and homeodomain) fused to the C-terminal forkhead (FKHR) sequences that contain a potent transcriptional activation domain. To determine which of these domains are required for cellular transformation, Pax3, Pax3-FKHR, and selected mutants were retrovirally expressed in NIH 3T3 cells and evaluated for their capacity to promote anchorage-independent cell growth. Mutational analysis revealed that both the third alpha-helix of the homeodomain and a small region of the FKHR transactivation domain are absolutely required for efficient transformation by the Pax3-FKHR fusion protein. Surprisingly, point mutations in the paired domain that abrogate sequence-specific DNA binding retained transformation potential equivalent to that of the wild-type protein. This finding suggests that DNA binding mediated through the Pax3 paired box is not required for transformation. Our results demonstrate that the integrity of the Pax3 homeodomain recognition helix and the FKHR transactivation domain is necessary for efficient cellular transformation by the Pax3-FKHR fusion protein.
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Affiliation(s)
- P Y Lam
- Departments of Experimental Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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27
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Inukai T, Inaba T, Ikushima S, Look AT. The AD1 and AD2 transactivation domains of E2A are essential for the antiapoptotic activity of the chimeric oncoprotein E2A-HLF. Mol Cell Biol 1998; 18:6035-43. [PMID: 9742120 PMCID: PMC109189 DOI: 10.1128/mcb.18.10.6035] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/1998] [Accepted: 07/01/1998] [Indexed: 11/20/2022] Open
Abstract
The chimeric oncoprotein E2A-HLF, generated by the t(17;19) chromosomal translocation in pro-B-cell acute lymphoblastic leukemia, incorporates the transactivation domains of E2A and the basic leucine zipper (bZIP) DNA-binding and protein dimerization domain of HLF (hepatic leukemic factor). The ability of E2A-HLF to prolong the survival of interleukin-3 (IL-3)-dependent murine pro-B cells after IL-3 withdrawal suggests that it disrupts signaling pathways normally responsible for cell suicide, allowing the cells to accumulate as transformed lymphoblasts. To determine the structural motifs that contribute to this antiapoptotic effect, we constructed a panel of E2A-HLF mutants and programmed their expression in IL-3-dependent murine pro-B cells (FL5.12 line), using a zinc-inducible vector. Neither the E12 nor the E47 product of the E2A gene nor the wild-type HLF protein was able to protect the cells from apoptosis induced by IL-3 deprivation. Surprisingly, different combinations of disabling mutations within the HLF bZIP domain had little effect on the antiapoptotic property of the chimeric protein, so long as the amino-terminal portion of E2A remained intact. In the context of a bZIP domain defective in DNA binding, mutants retaining either of the two transactivation domains of E2A were able to extend cell survival after growth factor deprivation. Thus, the block of apoptosis imposed by E2A-HLF in pro-B lymphocytes depends critically on the transactivating regions of E2A. Since neither DNA binding nor protein dimerization through the bZIP domain of HLF is required for this effect, we propose mechanisms whereby protein-protein interactions with the amino-terminal region of E2A allow the chimera to act as a transcriptional cofactor to alter the expression of genes regulating the apoptotic machinery in pro-B cells.
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Affiliation(s)
- T Inukai
- Department of Experimental Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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28
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Rutherford MN, LeBrun DP. Restricted expression of E2A protein in primary human tissues correlates with proliferation and differentiation. THE AMERICAN JOURNAL OF PATHOLOGY 1998; 153:165-73. [PMID: 9665477 PMCID: PMC1852936 DOI: 10.1016/s0002-9440(10)65557-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
E2A is a basic helix-loop-helix (bHLH) transcription factor required for B cell lymphopoiesis and implicated in myogenesis and the regulation of insulin expression. As E2A is expressed widely in tissues, tissue-specific downstream effects are thought to result primarily from dimerization with other bHLH proteins. To investigate the degree to which regulation of E2A protein abundance may serve to regulate E2A function, expression of E2A was evaluated using immunohistochemistry on histological sections of primary human tissues. Somewhat surprisingly, nuclear staining for E2A was restricted in all tissues examined, often to a small subpopulation of cells. In some tissues, such as adult liver, expression was absent or limited to rare infiltrating lymphocytes. E2A-expressing cells were most abundant in lymphoid tissues. In tonsil, lymph node, and spleen, expression appeared most abundant and prevalent among rapidly proliferating centroblasts of the germinal center dark zone. Scattered E2A-expressing thymocytes were more numerous in the thymic cortex than medulla. In developing skeletal muscle, E2A was detectable in striated myotubes but not in more primitive mononucleated progenitors or mature muscle. Differential E2A expression was also noted in proliferating periventricular neuroepithelial cells in the developing brain. These results suggest that regulation of E2A abundance complements protein-protein interactions in modulating E2A function.
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Affiliation(s)
- M N Rutherford
- Department of Pathology, Richardson Laboratory, Queen's University, Kingston, Ontario, Canada
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Berthelsen J, Zappavigna V, Ferretti E, Mavilio F, Blasi F. The novel homeoprotein Prep1 modulates Pbx-Hox protein cooperativity. EMBO J 1998; 17:1434-45. [PMID: 9482740 PMCID: PMC1170491 DOI: 10.1093/emboj/17.5.1434] [Citation(s) in RCA: 177] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The products of the mammalian Pbx and Drosophila exd genes are able to interact with Hox proteins specifically and to increase their DNA binding affinity and selectivity. In the accompanying paper we show that Pbx proteins exist as stable heterodimers with a novel homeodomain protein, Prep1. Here we show that Prep1-Pbx interaction presents novel structural features: it is independent of DNA binding and of the integrity of their respective homeodomains, and requires sequences in the N-terminal portions of both proteins. The Prep1-Pbx protein-protein interaction is essential for DNA-binding activity. Prep1-Pbx complexes are present in early mouse embryos at a time when Pbx is also interacting with Hox proteins. The use of different interaction surfaces could allow Pbx to interact with Prep1 and Hox proteins simultaneously. Indeed, we observe the formation of a ternary Prep1-Pbx1-HOXB1 complex on a HOXB1-responsive target in vitro. Interaction with Prep1 enhances the ability of the HOXB1-Pbx1 complex to activate transcription in a cooperative fashion from the same target. Our data suggest that Prep1 is an additional component in the transcriptional regulation by Hox proteins.
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Affiliation(s)
- J Berthelsen
- Dipartimento di Genetica e Biologia dei Microrganismi dell'Università, H.S. Raffaele, via Olgettina 58, 20132, Milan, Italy
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Shen WF, Montgomery JC, Rozenfeld S, Moskow JJ, Lawrence HJ, Buchberg AM, Largman C. AbdB-like Hox proteins stabilize DNA binding by the Meis1 homeodomain proteins. Mol Cell Biol 1997; 17:6448-58. [PMID: 9343407 PMCID: PMC232497 DOI: 10.1128/mcb.17.11.6448] [Citation(s) in RCA: 214] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
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.
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Affiliation(s)
- W F Shen
- Department of Medicine, University of California VA Medical Center, San Francisco 94121, USA
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31
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Chang CP, Jacobs Y, Nakamura T, Jenkins NA, Copeland NG, Cleary ML. Meis proteins are major in vivo DNA binding partners for wild-type but not chimeric Pbx proteins. Mol Cell Biol 1997; 17:5679-87. [PMID: 9315626 PMCID: PMC232416 DOI: 10.1128/mcb.17.10.5679] [Citation(s) in RCA: 201] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The Pbx1 and Meis1 proto-oncogenes code for divergent homeodomain proteins that are targets for oncogenic mutations in human and murine leukemias, respectively, and implicated by genetic analyses to functionally collaborate with Hox proteins during embryonic development and/or oncogenesis. Although Pbx proteins have been shown to dimerize with Hox proteins and modulate their DNA binding properties in vitro, the biochemical compositions of endogenous Pbx-containing complexes have not been determined. In the present study, we demonstrate that Pbx and Meis proteins form abundant complexes that comprise a major Pbx-containing DNA binding activity in nuclear extracts of cultured cells and mouse embryos. Pbx1 and Meis1 dimerize in solution and cooperatively bind bipartite DNA sequences consisting of directly adjacent Pbx and Meis half sites. Pbx1-Meis1 heterodimers display distinctive DNA binding specificities and cross-bind to a subset of Pbx-Hox sites, including those previously implicated as response elements for the execution of Pbx-dependent Hox programs in vivo. Chimeric oncoprotein E2a-Pbx1 is unable to bind DNA with Meis1, due to the deletion of amino-terminal Pbx1 sequences following fusion with E2a. We conclude that Meis proteins are preferred in vivo DNA binding partners for wild-type Pbx1, a relationship that is circumvented by its oncogenic counterpart E2a-Pbx1.
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Affiliation(s)
- C P Chang
- Department of Pathology, Stanford University Medical Center, California 94305, USA
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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; 17:81-8. [PMID: 8972188 PMCID: PMC231732 DOI: 10.1128/mcb.17.1.81] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
E2a-Pbx1 chimeric oncoproteins result from fusion of the E2A and PBX1 genes at the sites of t(1;19) chromosomal translocations in a subset acute lymphoblastic leukemias. Experimentally, E2a-Pbx1 transforms a variety of cell types, including fibroblasts, myeloid progenitors, and lymphoblasts. Structure-function studies have shown that contributions from both E2a and Pbx1 are necessary for oncogenesis, but the Pbx1 homeodomain is dispensable and the required portion of Pbx1 has not been delineated. In this study, we used deletional and site-directed mutagenesis to identify portions of Pbx1 necessary for oncogenic and transcriptional activities of E2a-Pbx1. These studies defined a motif (named the Hox cooperativity motif [HCM]) carboxy terminal to the Pbx homeodomain that is required for cooperative DNA binding, cellular transcriptional activity, and the oncogenic potential of E2a-Pbx1. The HCM is highly conserved throughout the Pbx/exd subfamily of divergent homeodomain proteins and functions in DNA-binding assays as a potential contact site for Hox dimerization. E2a-Pbx1 proteins with interstitial deletion or single-point mutations in the HCM could neither activate transcription in cellular assays nor transform NIH 3T3 cells. An E2a-Pbx1 mutant containing 50 amino acids of Pbx1b spanning the HCM but lacking the homeodomain was capable of inducing fibroblast transformation. Thus, the HCM is a necessary and sufficient contribution of Pbx1 for oncogenesis induced by E2a-Pbx1 and accounts for its homeodomain-independent transforming properties. Since subtle alterations of the Pbx HCM result in complete abrogation of transforming activity whereas the homeodomain is entirely dispensable, we conclude that interactions mediated by the HCM are more important for transformation by E2a-Pbx1 than interactions with cognate Pbx DNA sites.
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Affiliation(s)
- C P Chang
- Department of Pathology, Stanford University School of Medicine, California 94305, USA
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Miyamoto A, Cui X, Naumovski L, Cleary ML. Helix-loop-helix proteins LYL1 and E2a form heterodimeric complexes with distinctive DNA-binding properties in hematolymphoid cells. Mol Cell Biol 1996; 16:2394-401. [PMID: 8628307 PMCID: PMC231228 DOI: 10.1128/mcb.16.5.2394] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
LYL1 is a basic helix-loop-helix (HLH) protein that was originally discovered because of its translocation into the beta T-cell receptor locus in an acute lymphoblastic leukemia. LYL1 is expressed in many hematolymphoid cells, with the notable exceptions of thymocytes and T cells. Using the yeast two-hybrid system to screen a cDNA library constructed from B cells, we identified the E-box-binding proteins E12 and E47 as potential lymphoid dimerization partners for LYL1. The interaction of LYL1 with E2a proteins was further characterized in vitro and shown to require the HLH motifs of both proteins. Immunoprecipitation analyses showed that in T-ALL and other cell lines, endogenous LYL1 exists in a complex with E2a proteins. A preferred DNA-binding sequence, 5'-AACAGATG(T/g)T-3', for the LYL1-E2a heterodimer was determined by PCR-assisted site selection. Endogenous protein complexes containing both LYL1 and E2a bound this sequence in various LYL1-expressing cell lines and could distinguish between the LYL1 consensus and muE2 sites. These data demonstrate that E2a proteins serve as dimerization partners for the basic HLH protein LYL1 to form complexes with distinctive DNA-binding properties and support the hypothesis that the leukemic properties of the LYL1 and TAL subfamily of HLH proteins could be mediated by recognition of a common set of target genes as heterodimeric complexes with class I HLH proteins.
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Affiliation(s)
- A Miyamoto
- Laboratory of Experimental Pathology, Stanford University School of Medicine, California 94305, USA
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Chang CP, Brocchieri L, Shen WF, Largman C, Cleary ML. Pbx modulation of Hox homeodomain amino-terminal arms establishes different DNA-binding specificities across the Hox locus. Mol Cell Biol 1996; 16:1734-45. [PMID: 8657149 PMCID: PMC231160 DOI: 10.1128/mcb.16.4.1734] [Citation(s) in RCA: 241] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Pbx cofactors are implicated to play important roles in modulating the DNA-binding properties of heterologous homeodomain proteins, including class I Hox proteins. To assess how Pbx proteins influence Hox DNA-binding specificity, we used a binding-site selection approach to determine high-affinity target sites recognized by various Pbx-Hox homeoprotein complexes. Pbx-Hox heterodimers preferred to bind a bipartite sequence 5'-ATGATTNATNN-3' consisting of two adjacent half sites in which the Pbx component of the heterodimer contacted the 5' half (ATGAT) and the Hox component contacted the more variable 3' half (TNATNN). Binding sites matching the consensus were also obtained for Pbx1 complexed with HoxA10, which lacks a hexapeptide but requires a conserved tryptophan-containing motif for cooperativity with Pbx. Interactions with Pbx were found to play an essential role in modulating Hox homeodomain amino-terminal arm contact with DNA in the core of the Hox half site such that heterodimers of different compositions could distinguish single nucleotide alterations in the Hox half site both in vitro and in cellular assays measuring transactivation. When complexed with Pbx, Hox proteins B1 through B9 and A10 showed stepwise differences in their preferences for nucleotides in the Hox half site core (TTAT to TGAT, 5' to 3') that correlated with the locations of their respective genes in the Hox cluster. These observations demonstrate previously undetected DNA-binding specificity for the amino-terminal arm of the Hox homeodomain and suggest that different binding activities of Pbx-Hox complexes are at least part of the position-specific activities of the Hox genes.
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Affiliation(s)
- C P Chang
- Department of Pathology, Stanford University, California 94305, USA
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Lu Q, Kamps MP. Selective repression of transcriptional activators by Pbx1 does not require the homeodomain. Proc Natl Acad Sci U S A 1996; 93:470-4. [PMID: 8552663 PMCID: PMC40260 DOI: 10.1073/pnas.93.1.470] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
PBX1 is a homeobox-containing gene identified as the chromosome 1 participant of the t(1;19) chromosomal translocation of childhood pre-B-cell acute lymphoblastic leukemia. This translocation produces a fusion gene encoding the chimeric oncoprotein E2A-Pbx1, which can induce both acute myeloid and T-lymphoid leukemia in mice. The binding of Pbx1 to DNA is weak; however, both Pbx1 and E2A-Pbx1 exhibit tight binding to specific DNA motifs in conjunction with certain other homeodomain proteins, and E2A-Pbx1 activates transcription through these motifs, whereas Pbx1 does not. In this report, we investigate potential transcriptional functions of Pbx1, using transient expression assays. While no segments of Pbx1 activated transcription, an internal domain of Pbx1 repressed transcription induced by the activation domain of Sp1, but not by the activation domains of VP16 or p53. This Pbx1 domain, which lies upstream of the homeodomain and is highly conserved among Pbx proteins, is thus predicted to bind a specific transcription factor. Surprisingly, the repression activity of Pbx1 did not require homeodomain-dependent DNA binding. Thus, Pbx1 may be able to alter gene transcription by both DNA-binding-dependent and DNA-binding-independent mechanisms.
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Affiliation(s)
- Q Lu
- Department of Pathology, University of California, San Diego, School of Medicine, La Jolla 92093, USA
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36
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Massari ME, Jennings PA, Murre C. The AD1 transactivation domain of E2A contains a highly conserved helix which is required for its activity in both Saccharomyces cerevisiae and mammalian cells. Mol Cell Biol 1996; 16:121-9. [PMID: 8524288 PMCID: PMC230985 DOI: 10.1128/mcb.16.1.121] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
A conserved region, designated the AD1 domain, is present in a class of helix-loop-helix (HLH) proteins, E proteins, that includes E12, E47, HEB, E2-2, and a Xenopus laevis HLH protein closely related to E12. We demonstrate that the AD1 domain in E2A and the conserved region of E2-2 activate transcription in both yeast and mammalian cells. The AD1 domain contains a highly conserved putative helix that is crucial for its transactivation properties. Circular dichroism spectroscopy data show that AD1 is structured and contains distinctive helical properties. In addition, we show that a synthetic peptide corresponding to the conserved region is unstructured in aqueous solution at neutral pH but can adopt an alpha-helical conformation in the presence of the hydrophobic solvent trifluoroethanol. Amino acid substitutions that destabilize the helix abolish the transactivation ability of the AD1 domain. Both structural and functional analyses of AD1 reveal striking similarities to the acidic class of activators. Remarkably, when wild-type and mutant proteins are expressed in mammalian cells and Saccharomyces cerevisiae, identical patterns of transactivation are observed, suggesting that the target molecule is conserved between S. cerevisiae and mammals. These data show that transactivation by E proteins is mediated, in part, by a strikingly conserved peptide that has the ability to form a helix in a hydrophobic solvent. We propose that the unstructured domain may become helical upon interaction with its cellular target molecule.
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Affiliation(s)
- M E Massari
- Department of Biology, University of California, San Diego, La Jolla 92093, USA
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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; 15:5811-9. [PMID: 7565734 PMCID: PMC230833 DOI: 10.1128/mcb.15.10.5811] [Citation(s) in RCA: 135] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The vertebrate Hox genes, which represent a subset of all homeobox genes, encode proteins that regulate anterior-posterior positional identity during embryogenesis and are cognates of the Drosophila homeodomain proteins encoded by genes composing the homeotic complex (HOM-C). Recently, we demonstrated that multiple Hox proteins bind DNA cooperatively with both Pbx1 and its oncogenic derivative, E2A-Pbx1. Here, we show that the highly conserved pentapeptide motif F/Y-P-W-M-R/K, which occurs in numerous Hox proteins and is positioned 8 to 50 amino acids N terminal to the homeodomain, is essential for cooperative DNA binding with Pbx1 and E2A-Pbx1. Point mutational analysis demonstrated that the tryptophan and methionine residues within the core of this motif were critical for cooperative DNA binding. A peptide containing the wild-type pentapeptide sequence, but not one in which phenylalanine was substituted for tryptophan, blocked the ability of Hox proteins to bind cooperatively with Pbx1 or E2A-Pbx1, suggesting that the pentapeptide itself provides at least one surface through which Hox proteins bind Pbx1. Furthermore, the same peptide, but not the mutant peptide, stimulated DNA binding by Pbx1, suggesting that interaction of Hox proteins with Pbx1 through the pentapeptide motif raises the DNA-binding ability of Pbx1.
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Affiliation(s)
- P S Knoepfler
- Department of Pathology, School of Medicine, University of California, San Diego, La Jolla 92093, USA
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Phelan ML, Rambaldi I, Featherstone MS. Cooperative interactions between HOX and PBX proteins mediated by a conserved peptide motif. Mol Cell Biol 1995; 15:3989-97. [PMID: 7623795 PMCID: PMC230638 DOI: 10.1128/mcb.15.8.3989] [Citation(s) in RCA: 185] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Homeoprotein products of the Hox/HOM gene family pattern the animal embryo through the transcriptional regulation of target genes. We have previously shown that the labial group protein HOXA-1 has intrinsically weak DNA-binding activity due to residues in the N-terminal arm of its homeodomain (M. L. Phelan, R. Sadoul, and M. S. Featherstone, Mol. Cell. Biol. 14:5066-5075, 1994). This observation, among others, suggests that HOX and HOM proteins require cofactors for stable interactions with DNA. We have demonstrated that a putative HOX cofactor, PBX1A, participates in cooperative DNA binding with HOXA-1 and the Deformed group protein HOXD-4. Three Abdominal-B class HOX proteins failed to cooperate with PBX1A. We mapped the interacting domain of HOXD-4 to the YPWMK pentapeptide motif, a conserved sequence found N terminal to the homeodomain of HOXA-1 and many other homeoproteins but absent from the Abdominal-B class. The naturally occurring fusion of the transcriptional activation domain of E2A with PBX1 creates an oncoprotein implicated in human pre-B-cell leukemias (M. P. Kamps, C. Murre, X.-H. Sun, and D. Baltimore, Cell 60:547-555, 1990; J. Nourse, J. D. Mellentin, N. Galili, J. Wilkinson, E. Starbridge, S. D. Smith, and M. L. Cleary, Cell 60:535-545, 1990). A pentapeptide mutation that abolished cooperative interaction with PBX1A in vitro also abrogated synergistic transcriptional activation with the E2A/PBX oncoprotein. The direct contact of PBX family members by the HOX pentapeptide is likely to play an important role in developmental and oncogenic processes.
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Affiliation(s)
- M L Phelan
- McGill Cancer Centre, McGill University, Montreal, Québec, Canada
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Lu Q, Knoepfler PS, Scheele J, Wright DD, Kamps MP. 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; 15:3786-95. [PMID: 7791786 PMCID: PMC230617 DOI: 10.1128/mcb.15.7.3786] [Citation(s) in RCA: 126] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
E2A-PBX1 is the oncogene produced at the t(1;19) chromosomal breakpoint of pediatric pre-B-cell leukemia. Expression of E2A-Pbx1 induces fibroblast transformation and myeloid and T-cell leukemia in mice and arrests differentiation of granulocyte macrophage colony-stimulating factor-dependent myeloblasts in cultured marrow. Recently, the Drosophila melanogaster protein Exd, which is highly related to Pbx1, was shown to bind DNA cooperatively with the Drosophila homeodomain proteins Ubx and Abd-A. Here, we demonstrate that the normal Pbx1 homeodomain protein, as well as its oncogenic derivative, E2A-Pbx1, binds the DNA sequence ATCAATCAA cooperatively with the murine Hox-A5, Hox-B7, Hox-B8, and Hox-C8 homeodomain proteins, which are themselves known oncoproteins, as well as with the Hox-D4 homeodomain protein. Cooperative binding to ATCAATCAA required the homeodomain-dependent DNA-binding activities of both Pbx1 and the Hox partner. In cotransfection assays, Hox-B8 suppressed transactivation by E2A-Pbx1. These results suggest that (i) Pbx1 may participate in the normal regulation of Hox target gene transcription in vivo and therein contribute to aspects of anterior-posterior patterning and structural development in vertebrates, (ii) that E2A-Pbx1 could abrogate normal differentiation by altering the transcriptional regulation of Hox target genes in conjunction with Hox proteins, and (iii) that the oncogenic mechanism of certain Hox proteins may require their physical interaction with Pbx1 as a cooperating, DNA-binding partner.
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Affiliation(s)
- Q Lu
- Department of Pathology, School of Medicine, University of California, San Diego, La Jolla 92093, USA
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