title: The effects of Brn-3a on neuronal differentiation and apoptosis are differentially modulated by EWS and its oncogenic derivative EWS/Fli-1.
abstract: The Brn-3 family of POU (Pit-Oct-Unc) homeodomain transcription factors regulate differentiation of neuronal cell types. The transcriptional activator Brn-3a is expressed in Ewing's sarcomas, which also express characteristic chimaeric proteins as a consequence of fusion of the TET family gene EWS to one of several ETS genes. We have previously demonstrated a physical interaction between Brn-3a and EWS proteins, and show here that the C-terminal POU domain but not N-terminal activation domain of Brn-3a can interact in vitro with the RNA-binding domain of EWS. Likely due to POU domain homology, the related factor Brn-3b can also interact with EWS, but to a lesser extent than Brn-3a. Importantly, Brn-3a but not Brn-3b interacts in vitro with chimaeric EWS/Fli-1, EWS/ATF-1 and EWS/ERG proteins. Furthermore, overexpression of EWS/Fli-1 but not EWS or Fli-1 inhibits Brn-3a-associated growth arrest and neurite outgrowth in neuronal cells, and specifically inhibits Brn-3a-dependent activation of p21 and SNAP-25 transcription. In contrast, upregulation of Bcl-2 expression and inhibition of apoptosis by Brn-3a is antagonized more by EWS than by EWS/Fli-1. These data demonstrate that oncogenic rearrangement of EWS to produce EWS/Fli-1 may enhance the antiapoptotic effect of Brn-3a and inhibit its ability to promote neuronal differentiation.
authors.affiliation: Medical Molecular Biology Unit, Institute of Child Health, UCL, 30 Guilford Street, London WC1N 1EH, UK. d.gascoyne@ich.ucl.ac.uk
authors.forename: Duncan M
authors.initials: DM
authors.lastname: Gascoyne
authors.forename: G Ruth
authors.initials: GR
authors.lastname: Thomas
authors.forename: David S
authors.initials: DS
authors.lastname: Latchman
mesh_terms: D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000032:analysis; D009419:Nerve Tissue Proteins / Q000032:analysis; D016501:Neurites / Q000502:physiology; D009474:Neurons / Q000166:cytology*; D015514:Oncogene Proteins, Fusion / Q000502:physiology*; D011401:Promoter Regions, Genetic; D051789:Proto-Oncogene Protein c-fli-1; D012313:RNA / Q000378:metabolism; D034802:RNA-Binding Protein EWS / Q000502:physiology*; D050825:Synaptosomal-Associated Protein 25; D050818:Transcription Factor Brn-3; D050819:Transcription Factor Brn-3A; D050820:Transcription Factor Brn-3B; D014157:Transcription Factors / Q000502:physiology*
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; C106031:EWS-FLI fusion protein; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015514:Oncogene Proteins, Fusion; C494188:POU4F1 protein, human; C494190:POU4F2 protein, human; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; C494208:SNAP25 protein, human; D050825:Synaptosomal-Associated Protein 25; D050818:Transcription Factor Brn-3; D050819:Transcription Factor Brn-3A; D050820:Transcription Factor Brn-3B; D014157:Transcription Factors; D012313:RNA