title: The possible role of EWS-Fli1 in evasion of senescence in Ewing family tumors.
abstract: The chromosomal translocation t(11;22) yields the EWS-Fli1 fusion gene and is associated with oncogenesis of Ewing family tumors (EFT). In this study, using the RNA interference method, we show that EWS-Fli1-targeting small interfering RNAs (siRNA) depleted EWS-Fli1 protein and caused growth inhibition in EFT cells with the accumulation of p27 protein and the down-regulation of Skp2 protein in dose-dependent, time-dependent, and sequence-specific manners. Depletion of EWS-Fli1 subacutely elicited a senescence-like phenotype, but not apoptosis, in EFT cells. Furthermore, not only the knockdown of p27, but also the forced expression of Skp2, reduced the expression levels of p27 protein and partially rescued senescence-like phenotype caused by EWS-Fli1-targeting siRNAs. The accumulation of p27 protein in EWS-Fli1-depleted cells inhibited cdk2 kinase activity and was related to the stability of p27 protein, which resulted from a decrease in Skp2 protein. Immunohistochemical analysis of p27 and Skp2 proteins in EFT samples revealed that there was an inverse relationship between the expression profiles of p27 and Skp2 proteins. These findings indicate an important role of EWS-Fli1 in the prevention of senescence, leading to the unlimited growth and oncogenesis of EFT cells through a decrease in the stability of p27 protein due to increased action of Skp2-mediated 26S proteasome degradation.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, 812-8582 Fukuoka, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Matsunobu
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tanaka
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nakamura
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Nakatani
authors.forename: Riku
authors.initials: R
authors.lastname: Sakimura
authors.forename: Masuo
authors.initials: M
authors.lastname: Hanada
authors.forename: Xu
authors.initials: X
authors.lastname: Li
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Okada
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Oda
authors.forename: Masazumi
authors.initials: M
authors.lastname: Tsuneyoshi
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D017209:Apoptosis; D002471:Cell Transformation, Neoplastic; D016922:Cellular Senescence; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000096:biosynthesis; D015536:Down-Regulation; D006801:Humans; D015514:Oncogene Proteins, Fusion / Q000502:physiology*; D010641:Phenotype; D051789:Proto-Oncogene Protein c-fli-1 / Q000502:physiology*; D034622:RNA Interference; D034741:RNA, Small Interfering; D034802:RNA-Binding Protein EWS; D044786:S-Phase Kinase-Associated Proteins / Q000096:biosynthesis; D012512:Sarcoma, Ewing / Q000235:genetics* / Q000503:physiopathology
chemical_list: C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034741:RNA, Small Interfering; D034802:RNA-Binding Protein EWS; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27