Abstract
The Ewing sarcoma (ES) EWS-FLI1 chimeric oncoprotein is a prototypic aberrant ETS transcription factor with activating and repressive regulatory functions. We report that EWS-FLI1-repressed promoters are enriched in forkhead box (FOX) recognition motifs, and identify FOXO1 as a EWS-FLI1-suppressed regulator orchestrating a major subset of EWS-FLI1-repressed genes. In addition to FOXO1 regulation by direct promoter binding of EWS-FLI1, its subcellular localization and activity is regulated by cyclin-dependent kinase 2- and AKT-mediated phosphorylation downstream of EWS-FLI1. Restoration of nuclear FOXO1 expression in ES cells impaired proliferation and significantly reduced clonogenicity. Gene-expression profiling revealed a significant overlap between EWS-FLI1-repressed and FOXO1-activated genes. As a proof of principle for a potential therapeutic application of our findings, the treatment of ES cell lines with methylseleninic acid (MSA) reactivated endogenous FOXO1 in the presence of EWS-FLI1 in a dose- and time-dependent manner and induced massive cell death dependent on FOXO1. In an orthotopic xenograft mouse model, MSA increased FOXO1 expression in the tumor paralleled by a significant decrease in ES tumor growth. FOXO1 reactivation by small molecules may therefore serve as a promising strategy for a future ES-specific therapy.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Antineoplastic Agents / pharmacology
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Base Sequence
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Binding Sites
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Bone Neoplasms / drug therapy
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Bone Neoplasms / genetics
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Bone Neoplasms / metabolism*
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Cell Line, Tumor
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Cell Proliferation
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Consensus Sequence
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Cyclin-Dependent Kinase 2 / metabolism
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Forkhead Box Protein O1
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Forkhead Box Protein O3
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Forkhead Transcription Factors / genetics
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Forkhead Transcription Factors / metabolism*
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Gene Expression Regulation, Neoplastic*
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Gene Silencing
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Humans
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Mice
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Oncogene Proteins, Fusion / genetics
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Oncogene Proteins, Fusion / metabolism*
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Organoselenium Compounds / pharmacology
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Phosphorylation
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Promoter Regions, Genetic
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Protein Processing, Post-Translational
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Protein Transport
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Proto-Oncogene Protein c-fli-1 / genetics
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Proto-Oncogene Protein c-fli-1 / metabolism*
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Proto-Oncogene Proteins c-akt / metabolism
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RNA-Binding Protein EWS / genetics
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RNA-Binding Protein EWS / metabolism*
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Sarcoma, Ewing / drug therapy
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Sarcoma, Ewing / genetics
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Sarcoma, Ewing / metabolism*
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Transcription, Genetic
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Tumor Burden / drug effects
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Xenograft Model Antitumor Assays
Substances
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Antineoplastic Agents
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EWS-FLI fusion protein
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FOXO1 protein, human
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FOXO3 protein, human
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Forkhead Box Protein O1
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Forkhead Box Protein O3
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Forkhead Transcription Factors
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Oncogene Proteins, Fusion
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Organoselenium Compounds
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Proto-Oncogene Protein c-fli-1
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RNA-Binding Protein EWS
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methylselenic acid
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Proto-Oncogene Proteins c-akt
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CDK2 protein, human
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Cyclin-Dependent Kinase 2