title: A two-step, PU.1-dependent mechanism for developmentally regulated chromatin remodeling and transcription of the c-fms gene.
abstract: Hematopoietic stem cells and multipotent progenitors exhibit low-level transcription and partial chromatin reorganization of myeloid cell-specific genes including the c-fms (csf1R) locus. Expression of the c-fms gene is dependent on the Ets family transcription factor PU.1 and is upregulated during myeloid differentiation, enabling committed macrophage precursors to respond to colony-stimulating factor 1. To analyze molecular mechanisms underlying the transcriptional priming and developmental upregulation of the c-fms gene, we have utilized myeloid progenitors lacking the transcription factor PU.1. PU.1 can bind to sites in both the c-fms promoter and the c-fms intronic regulatory element (FIRE enhancer). Unlike wild-type progenitors, the PU.1(-/-) cells are unable to express c-fms or initiate macrophage differentiation. When PU.1 was reexpressed in mutant progenitors, the chromatin structure of the c-fms promoter was rapidly reorganized. In contrast, assembly of transcription factors at FIRE, acquisition of active histone marks, and high levels of c-fms transcription occurred with significantly slower kinetics. We demonstrate that the reason for this differential activation was that PU.1 was required to promote induction and binding of a secondary transcription factor, Egr-2, which is important for FIRE enhancer activity. These data suggest that the c-fms promoter is maintained in a primed state by PU.1 in progenitor cells and that at FIRE PU.1 functions with another transcription factor to direct full activation of the c-fms locus in differentiated myeloid cells. The two-step mechanism of developmental gene activation that we describe here may be utilized to regulate gene activity in a variety of developmental pathways.
authors.affiliation: University of Leeds, Leeds Institute of Molecular Medicine, St. James's University Hospital, Wellcome Trust Brenner Building, Leeds LS9 7TF, United Kingdom.
authors.forename: Hanna
authors.initials: H
authors.lastname: Krysinska
authors.forename: Maarten
authors.initials: M
authors.lastname: Hoogenkamp
authors.forename: Richard
authors.initials: R
authors.lastname: Ingram
authors.forename: Nicola
authors.initials: N
authors.lastname: Wilson
authors.forename: Hiromi
authors.initials: H
authors.lastname: Tagoh
authors.forename: Peter
authors.initials: P
authors.lastname: Laslo
authors.forename: Harinder
authors.initials: H
authors.lastname: Singh
authors.forename: Constanze
authors.initials: C
authors.lastname: Bonifer
mesh_terms: D000818:Animals; D001483:Base Sequence; D042002:Chromatin Assembly and Disassembly / Q000235:genetics; D003850:Deoxyribonuclease I / Q000378:metabolism; D051767:Early Growth Response Protein 2 / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D018507:Gene Expression Regulation, Developmental; D016236:Genes, fms / Q000235:genetics*; D006657:Histones / Q000378:metabolism; D007700:Kinetics; D008745:Methylation; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D035181:TATA-Box Binding Protein / Q000378:metabolism; D015534:Trans-Activators / Q000172:deficiency / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics*; D015533:Transcriptional Activation; D000099232:Proto-Oncogene Protein Spi-1
chemical_list: D003850:Deoxyribonuclease I; D051767:Early Growth Response Protein 2; D006657:Histones; D011518:Proto-Oncogene Proteins; D012319:RNA Polymerase II; D035181:TATA-Box Binding Protein; D015534:Trans-Activators; D014157:Transcription Factors; D000099232:Proto-Oncogene Protein Spi-1