PI3K/AKT signaling modulates transcriptional expression of EWS/FLI1 through specificity protein 1

• Published in: Oncotarget 2015-10, Vol.6 (30), p.28895-28910
• Main Authors: Giorgi, Chiara, Boro, Aleksandar, Rechfeld, Florian, Lopez-Garcia, Laura A, Gierisch, Maria E, Schäfer, Beat W, Niggli, Felix K
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents - pharmacology; Binding Sites; Bone Neoplasms - drug therapy; Bone Neoplasms - enzymology; Bone Neoplasms - genetics; Bone Neoplasms - pathology; Cell Cycle Checkpoints; Cell Line, Tumor; Dose-Response Relationship, Drug; Gene Expression Regulation, Neoplastic - drug effects; Humans; Imidazoles - pharmacology; Oncogene Proteins, Fusion - genetics; Oncogene Proteins, Fusion - metabolism; Phosphatidylinositol 3-Kinase - genetics; Phosphatidylinositol 3-Kinase - metabolism; Phosphoinositide-3 Kinase Inhibitors; Promoter Regions, Genetic; Protein Binding; Protein Kinase Inhibitors - pharmacology; Proto-Oncogene Protein c-fli-1 - genetics; Proto-Oncogene Protein c-fli-1 - metabolism; Proto-Oncogene Proteins c-akt - metabolism; Quinolines - pharmacology; Research Paper; RNA Interference; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA-Binding Protein EWS - genetics; RNA-Binding Protein EWS - metabolism; Sarcoma, Ewing - drug therapy; Sarcoma, Ewing - enzymology; Sarcoma, Ewing - genetics; Sarcoma, Ewing - pathology; Signal Transduction - drug effects; Sp1 Transcription Factor - genetics; Sp1 Transcription Factor - metabolism; Transcription, Genetic - drug effects; Transfection
• ISSN: 1949-2553; 1949-2553
• DOI: 10.18632/oncotarget.5000

Ewing sarcoma (ES) is the second most frequent bone cancer in childhood and is characterized by the presence of the balanced translocation t(11;22)(q24;q12) in more than 85% of cases, generating a dysregulated transcription factor EWS/FLI1. This fusion protein is an essential oncogenic component of ES development which is necessary for tumor cell maintenance and represents an attractive therapeutic target. To search for modulators of EWS/FLI1 activity we screened a library of 153 targeted compounds and identified inhibitors of the PI3K pathway to directly modulate EWS/FLI1 transcription. Surprisingly, treatment of four different ES cell lines with BEZ235 resulted in down regulation of EWS/FLI1 mRNA and protein by ~50% with subsequent modulation of target gene expression. Analysis of the EWS/FLI1 promoter region (-2239/+67) using various deletion constructs identified two 14 bp minimal elements as being important for EWS/FLI1 transcription. We identified SP1 as modulator of EWS/FLI1 gene expression and demonstrated direct binding to one of these regions in the EWS/FLI1 promoter by EMSA and ChIP experiments. These results provide the first insights on the transcriptional regulation of EWS/FLI1, an area that has not been investigated so far, and offer an additional molecular explanation for the known sensitivity of ES cell lines to PI3K inhibition.