title: The Ews/Fli-1 fusion gene changes the status of p53 in neuroblastoma tumor cell lines.
abstract: One hallmark of Ewing's sarcoma/peripheral neuroectodermal tumors is the presence of the Ews/Fli-1 chimeric oncogene. Interestingly, infection of neuroblastoma tumor cell lines with Ews/Fli-1 switches the differentiation program of neuroblastomas to Ewing's sarcoma/peripheral neuroectodermal tumors. Here we examined the status of cytoplasmically sequestered wt-p53 in neuroblastomas after stable expression of Ews/Fli-1. Immunofluorescence revealed that in the neuroblastoma-Ews/Fli-1 infectant cell lines, p53 went from a punctate-pattern of cytoplasmic sequestration to increased nuclear localization. Western blot analysis revealed that PARC was down-regulated in one neuroblastoma cell line but not expressed in the second. Therefore, decreased PARC expression could not fully account for relieving p53 sequestration in the neuroblastoma tumor cells. Neuroblastoma-Ews/Fli-1 infectant cell lines showed marked increases in p53 protein expression without transcriptional up-regulation. Interestingly, p53 was primarily phosphorylated, without activation of its downstream target p21(WAF1). Western blot analysis revealed that whereas MDM2 gene expression does not change, p14(ARF), a negative protein regulator of MDM2, increases. These observations suggest that the downstream p53 pathway may be inactivated as a result of abnormal p53. We also found that p53 has an extended half-life in the neuroblastoma-Ews/Fli-1 infectants despite the retention of a wild-type sequence in neuroblastoma-Ews/Fli-1 infectant cell lines. We then tested the p53 response pathway and observed that the neuroblastoma parent cells responded to genotoxic stress, whereas the neuroblastoma-Ews/Fli-1 infectants did not. These results suggest that Ews/Fli-1 can directly abrogate the p53 pathway to promote tumorigenesis. These studies also provide additional insight into the relationship among the p53 pathway proteins.
authors.affiliation: Curriculum in Toxicology and Department of Pathology and Laboratory Medicine, Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: Checo J
authors.initials: CJ
authors.lastname: Rorie
authors.forename: Bernard E
authors.initials: BE
authors.lastname: Weissman
mesh_terms: D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D016158:Genes, p53; D006801:Humans; D009447:Neuroblastoma / Q000235:genetics* / Q000378:metabolism*; D015514:Oncogene Proteins, Fusion / Q000096:biosynthesis / Q000235:genetics*; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53