title: The chimeric oncoproteins E2A-PBX1 and E2A-HLF are concentrated within spherical nuclear domains.
abstract: Oncogenic mutation of nuclear transcription factors often is associated with altered patterns of subcellular localization that may be of functional importance. The leukemogenic transcription factor gene E2A-PBX1 is created through fusion of the genes E2A and PBX1 as a result of t(1;19) in acute lymphoblastic leukemia. We evaluated subcellular localization patterns of E2A-PBX1 protein in transfected cells using immunofluorescence. Full-length E2A-PBX1 was exclusively nuclear and was concentrated in spherical domains denoted chimeric-E2A oncoprotein domains (CODs). In contrast, nuclear fluorescence for wild-type E2A or PBX1 proteins was diffuse. Enhanced concentrations of RNA polymerase II within many CODs and the requirement for an E2A-encoded activation domain suggested transcriptional relevance. However, in situ co-detection of nascent transcripts labeled with bromouridine failed to confirm altered transcriptional activity in relation to CODs. CODs also failed to co-localize with other proteins known to occupy functional nuclear compartments, including the transcription factor PML, the spliceosome-associated protein SC-35 and the adenovirus replication factor DBP, or with foci of DNA replication. Co-transfection of Hoxb7, a homeodomain protein capable of enhancing DNA binding by PBX1, impaired COD formation, suggesting that CODs contain E2A-PBX1 protein not associated with DNA. We conclude that, as a 'gain of function' phenomenon requiring protein elements from both E2A and PBX1, COD formation may be relevant to the biology of E2A-PBX1 in leukemogenesis.
authors.affiliation: Department of Pathology, Queen's University, Kingston, Ontario, Canada.
authors.forename: D P
authors.initials: DP
authors.lastname: LeBrun
authors.forename: B P
authors.initials: BP
authors.lastname: Matthews
authors.forename: B J
authors.initials: BJ
authors.lastname: Feldman
authors.forename: M L
authors.initials: ML
authors.lastname: Cleary
mesh_terms: D016475:3T3 Cells / Q000378:metabolism; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors; D019556:COS Cells / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism*; D012319:RNA Polymerase II / Q000378:metabolism; D012326:RNA Splicing; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C489626:E2a-Hlf fusion protein, mouse; D018398:Homeodomain Proteins; D009363:Neoplasm Proteins; D015514:Oncogene Proteins, Fusion; D014157:Transcription Factors; C089847:E2A-Pbx1 fusion protein; D012319:RNA Polymerase II