title: EWS/FLI1 suppresses retinoblastoma protein function and senescence in Ewing's sarcoma cells.
abstract: Ewing's Family Tumors (EFTs) most commonly harbor a specific t(11;22) translocation that generates the EWS/FLI1 fusion protein responsible for malignant transformation. Many potential downstream targets of EWS/FLI1 have been identified but a detailed mechanism by which the fusion protein brings about transformation remains unknown. In this report, we show that depletion of EWS/FLI1 in Ewing's cell lines results in a senescence phenotype, a marked increase in expression of the G1/S regulatory proteins p27(kip1) and p57(kip2), and a significant decrease in cyclin D1 and CDK2. We also demonstrate for the first time, to our knowledge, that knockdown of EWS/FLI1 leads to hypophosphorylation and functional activation of the retinoblastoma (pRb) family of proteins. Consistent with activation of the pRb proteins, E2F-responsive genes such as cyclin A are repressed in EWS/FLI1-depleted cells. Together, these results support the role of EWS/LI1 as an inhibitor of cellular senescence and implicate the retinoblastoma family of proteins as key mediators of this inhibition.
authors.affiliation: Department of Orthopedics and Sports Medicine, School of Medicine, University of Washington, 1660 S. Columbian Way, ORT112, Seattle, Washington 98108, USA.
authors.forename: Hsien-Ming
authors.initials: HM
authors.lastname: Hu
authors.forename: Anna
authors.initials: A
authors.lastname: Zielinska-Kwiatkowska
authors.forename: Karen
authors.initials: K
authors.lastname: Munro
authors.forename: Jason
authors.initials: J
authors.lastname: Wilcox
authors.forename: Daniel Y
authors.initials: DY
authors.lastname: Wu
authors.forename: Liu
authors.initials: L
authors.lastname: Yang
authors.forename: Howard A
authors.initials: HA
authors.lastname: Chansky
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D016922:Cellular Senescence / Q000502:physiology*; D056741:Cyclin D; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000235:genetics / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D005810:Multigene Family / Q000502:physiology; D015514:Oncogene Proteins, Fusion / Q000378:metabolism*; D010641:Phenotype; D051789:Proto-Oncogene Protein c-fli-1 / Q000378:metabolism*; D034622:RNA Interference; D034802:RNA-Binding Protein EWS; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase / Q000502:physiology; D012512:Sarcoma, Ewing / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology*
chemical_list: C436291:CDKN1B protein, human; D056741:Cyclin D; D050761:Cyclin-Dependent Kinase Inhibitor p57; D016213:Cyclins; C106031:EWS-FLI fusion protein; D047908:Intracellular Signaling Peptides and Proteins; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D016160:Retinoblastoma Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4