title: Rapamycin induces the fusion-type independent downregulation of the EWS/FLI-1 proteins and inhibits Ewing's sarcoma cell proliferation.
abstract: Ewing's sarcoma (ES) is the prototype of a family of tumors (ESFT) of neuroectodermal origin formed by small, round cells with limited neural differentiation, which arise most frequently within bones in children or adolescents. The proliferation of ESFT cells is highly dependent on the establishment of, and signaling through several growth factor-mediated autocrine loops. The mammalian target of rapamycin (mTOR) is a central regulator of translation and cell proliferation, involved in the cellular response to various nutritional, stress and mitogenic effectors. As mTOR has recently been associated with certain human cancers, we investigated the possibility that mTOR played a role in the regulation of ES cell proliferation. Results showed that ES cell lines carrying EWS/FLI-1 alleles of different types expressed different levels of total and phosphorylated mTOR protein. We demonstrate that rapamycin, an mTOR inhibitor, efficiently blocked the proliferation of all cell lines by promoting cell cycle arrest at the G1 phase. This was paralleled by the downregulation of the levels of the EWS/FLI-1 proteins, regardless of their fusion type, and the concomitant restoration of the expression of the TGF-beta type 2 receptor (TGFbeta RII), which is known to be repressed by several EWS-ETS fusion proteins. The expression of a rapamycin-resistant mTOR construct prevented both the proliferation blockade and the EWS/FLI-1 downregulation. These data demonstrate that mTOR signaling plays a central role in ES cell pathobiology and strongly suggest that the use of rapamycin as a cytostatic agent may be an efficient tool for the treatment of ES patients.
authors.affiliation: Laboratory of Experimental Carcinogenesis, Department of Radiation Medicine, Georgetown University Medical Center, Washington, DC 20057-1482, USA.
authors.forename: Silvia
authors.initials: S
authors.lastname: Mateo-Lozano
authors.forename: Oscar M
authors.initials: OM
authors.lastname: Tirado
authors.forename: Vicente
authors.initials: V
authors.lastname: Notario
mesh_terms: D000483:Alleles; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis; D002455:Cell Division; D045744:Cell Line, Tumor; D015536:Down-Regulation; D016193:G1 Phase; D006801:Humans; D015514:Oncogene Proteins, Fusion / Q000096:biosynthesis* / Q000235:genetics; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D012512:Sarcoma, Ewing / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000903:Antibiotics, Antineoplastic; C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D018125:Receptors, Transforming Growth Factor beta; D014157:Transcription Factors; D011494:Protein Kinases; C546842:MTOR protein, human; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D020123:Sirolimus