title: Transformation of bone marrow B-cell progenitors by E2a-Hlf requires coexpression of Bcl-2.
abstract: The chimeric transcription factor E2a-Hlf is an oncoprotein associated with a subset of acute lymphoblastic leukemias of early B-lineage derivation. We employed a retroviral transduction-transplantation approach to evaluate the oncogenic effects of E2a-Hlf on murine B-cell progenitors harvested from adult bone marrow. Expression of E2a-Hlf induced short-lived clusters of primary hematopoietic cells but no long-term growth on preformed bone marrow stromal cell layers comprised of the AC6.21 cell line. Coexpression with Bcl-2, however, resulted in the sustained self-renewal of early preB-I cells that required stromal and interleukin-7 (IL-7) support for growth in vitro. Immortalized cells were unable to induce leukemias after transplantation into nonirradiated syngeneic hosts, unlike the leukemic properties and cytokine independence of preB-I cells transformed by p190(Bcr-Abl) under identical in vitro conditions. However, bone marrow cells expressing E2a-Hlf in combination with Bcl-2, but not E2a-Hlf alone, induced leukemias in irradiated recipients with long latencies, demonstrating both a requirement for suppression of apoptosis and the need for further secondary mutations in leukemia pathogenesis. Coexpression of IL-7 substituted for Bcl-2 to induce the in vitro growth of pre-B cells expressing E2a-Hlf, but leukemic conversion required additional abrogation of undefined stromal requirements and was associated with alterations in the Arf/Mdm2/p53 pathway. Thus, E2a-Hlf enhances the self-renewal of bone marrow B-cell progenitors without inciting a p53 tumor surveillance response or abrogating stromal and cytokine requirements for growth, which are nevertheless abrogated during progression to a leukemogenic phenotype.
authors.affiliation: Department of Pathology, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Smith
authors.forename: Joon Whan
authors.initials: JW
authors.lastname: Rhee
authors.forename: Michael L
authors.initials: ML
authors.lastname: Cleary
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology*; D050976:Basic-Leucine Zipper Transcription Factors; D015139:Blotting, Southern; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002455:Cell Division; D002469:Cell Separation; D002471:Cell Transformation, Neoplastic; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018450:Disease Progression; D005434:Flow Cytometry; D005838:Genotype; D015851:Interleukin-7 / Q000378:metabolism; D007938:Leukemia / Q000209:etiology / Q000378:metabolism; D008747:Methylcellulose / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008957:Models, Genetic; D009154:Mutation; D015514:Oncogene Proteins, Fusion / Q000378:metabolism*; D010641:Phenotype; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012190:Retroviridae / Q000235:genetics; D013234:Stem Cells / Q000166:cytology*; D013997:Time Factors; D019076:Transgenes; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C489626:E2a-Hlf fusion protein, mouse; D015851:Interleukin-7; D015514:Oncogene Proteins, Fusion; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D008747:Methylcellulose; D004247:DNA