title: BRD-NUT oncoproteins: a family of closely related nuclear proteins that block epithelial differentiation and maintain the growth of carcinoma cells.
abstract: An unusual group of carcinomas, here termed nuclear protein in testis (NUT) midline carcinomas (NMC), are characterized by translocations that involve NUT, a novel gene on chromosome 15. In about 2/3rds of cases, NUT is fused to BRD4 on chromosome 19. Using a candidate gene approach, we identified two NMCs harboring novel rearrangements that result in the fusion of NUT to BRD3 on chromosome 9. The BRD3-NUT fusion gene encodes a protein composed of two tandem chromatin-binding bromodomains, an extra-terminal domain, a bipartite nuclear localization sequence, and almost the entirety of NUT that is highly homologous to BRD4-NUT. The function of NUT is unknown, but here we show that NUT contains nuclear localization and export sequences that promote nuclear-cytoplasmic shuttling via a leptomycin-sensitive pathway. In contrast, BRD3-NUT and BRD4-NUT are strictly nuclear, implying that the BRD moiety retains NUT in the nucleus via interactions with chromatin. Consistent with this idea, FRAP studies show that BRD4, BRD4-NUT and BRD3-NUT have significantly slower rates of lateral nuclear diffusion than that of NUT. To investigate the functional role of BRD-NUT fusion proteins in NMCs, we investigated the effects of siRNA-induced BRD3-NUT and BRD4-NUT withdrawal. Silencing of these proteins in NMC cell lines resulted in squamous differentiation and cell cycle arrest. Together, these data suggest that BRD-NUT fusion proteins contribute to carcinogenesis by associating with chromatin and interfering with epithelial differentiation.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: French
authors.forename: C L
authors.initials: CL
authors.lastname: Ramirez
authors.forename: J
authors.initials: J
authors.lastname: Kolmakova
authors.forename: T T
authors.initials: TT
authors.lastname: Hickman
authors.forename: M J
authors.initials: MJ
authors.lastname: Cameron
authors.forename: M E
authors.initials: ME
authors.lastname: Thyne
authors.forename: J L
authors.initials: JL
authors.lastname: Kutok
authors.forename: J A
authors.initials: JA
authors.lastname: Toretsky
authors.forename: A K
authors.initials: AK
authors.lastname: Tadavarthy
authors.forename: U R
authors.initials: UR
authors.lastname: Kees
authors.forename: J A
authors.initials: JA
authors.lastname: Fletcher
authors.forename: J C
authors.initials: JC
authors.lastname: Aster
mesh_terms: D001483:Base Sequence; D002277:Carcinoma / Q000235:genetics / Q000473:pathology*; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000235:genetics*; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D002843:Chromatin / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D005810:Multigene Family; D009363:Neoplasm Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015514:Oncogene Proteins, Fusion / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D013736:Testicular Neoplasms / Q000235:genetics / Q000473:pathology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D014407:Tumor Cells, Cultured; D000092468:Bromodomain Containing Proteins
chemical_list: D018797:Cell Cycle Proteins; D002843:Chromatin; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D015514:Oncogene Proteins, Fusion; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D014157:Transcription Factors; C109106:BRD3 protein, human; D000092468:Bromodomain Containing Proteins; C441289:BRD4 protein, human; C000630260:NUTM1 protein, human