title: Regulation of the myeloperoxidase enhancer binding proteins Pu1, C-EBP alpha, -beta, and -delta during granulocyte-lineage specification.
abstract: We have compared the molecular architecture and function of the myeloperoxidase upstream enhancer in multipotential versus granulocyte-committed hematopoietic progenitor cells. We show that the enhancer is accessible in multipotential cell chromatin but functionally incompetent before granulocyte commitment. Multipotential cells contain both Pu1 and C-EBP alpha as enhancer-binding activities. Pu1 is unphosphorylated in both multipotential and granulocyte-committed cells but is phosphorylated in B lymphocytes, raising the possibility that differential phosphorylation may play a role in specifying its lymphoid versus myeloid functions. C-EBP alpha exists as multiple phosphorylated forms in the nucleus of both multipotential and granulocyte-committed cells. C-EBP beta is unphosphorylated and cytoplasmically localized in multipotential cells but exists as a phosphorylated nuclear enhancer-binding activity in granulocyte-committed cells. Granulocyte colony-stimulating factor-induced granulocytic differentiation of multipotential progenitor cells results in activation of C-EBP delta expression and functional recruitment of C-EBP delta and C-EBP beta to the nucleus. Our results implicate Pu1 and the C-EBP family as critical regulators of myeloperoxidase gene expression and are consistent with a model in which a temporal exchange of C-EBP isoforms at the myeloperoxidase enhancer mediates the transition from a primed state in multipotential cells to a transcriptionally active configuration in promyelocytes.
authors.affiliation: Leukaemia Research Fund Centre, Chester Beatty Laboratories, London, United Kingdom.
authors.forename: A M
authors.initials: AM
authors.lastname: Ford
authors.forename: C A
authors.initials: CA
authors.lastname: Bennett
authors.forename: L E
authors.initials: LE
authors.lastname: Healy
authors.forename: M
authors.initials: M
authors.lastname: Towatari
authors.forename: M F
authors.initials: MF
authors.lastname: Greaves
authors.forename: T
authors.initials: T
authors.lastname: Enver
mesh_terms: D000818:Animals; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D006098:Granulocytes / Q000502:physiology*; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000502:physiology*; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism*; D009195:Peroxidase / Q000235:genetics*; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015534:Trans-Activators; D000099232:Proto-Oncogene Protein Spi-1
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009195:Peroxidase; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D000099232:Proto-Oncogene Protein Spi-1