Abstract 6158: The relevance of endoglin and MMP14 to the metastatic potential of Ewing sarcoma cells

Background: Ewing sarcoma (ES) is a developmental bone/soft tissue neoplasia, for which mesenchymal stem cell (MSC) is the putative cell of origin. Although the outcome of ES patients bearing primary tumors has improved significantly, patients with metastatic ES still have a poor prognosis. The MSC marker endoglin/CD105 (ENG) and the ENG-shedding protease MMP14 have been, respectively, described as cell migration and invasion regulators. In our attempt to better understand the mechanism of ES progression, we are focusing on the role of ENG and MMP14 in ES cells. Methods: In vitro ENG-knockdown (ENG-KD; RM82 and SKNMC cell lines) and ENG-overexpressing (pENG; TC71 cell lines) models were generated by shRNA technology and pDisplay vectors, respectively, and confirmed by qRT-PCR, western blotting and flow cytometry. In vitro MMP14-knockout (MMP14-KO; RM82 and SKNMC) models were generated by CRISPR-Cas9 and confirmed by western blotting and Sanger sequencing. Transwell migration/invasion, adhesion, clonogenicity and proliferation assays were performed in vitro. Actin filament organization was evaluated by immunofluorescence. Extracellular vesicles (EVs) were isolated by ultracentrifugation and density gradient separation. Transcriptomic profiling was performed by Clarion S Human arrays followed by Gene Set Enrichment Analysis. HiPathia tool was used to recode the transcriptomic data into measurements of cell activity by applying mechanistic models. Reverse Phase Protein Array (RPPA) analysis was evaluated on the ENG-KD RM82 model. ENG-targeting immunoprecipitations (IP) from wild type RM82 protein extracts were analyzed by mass spectrometry (MS). Results: The impaired clonogenic potential of ENG-KD RM82 and SKNMC models suggests a role of ENG on the stemness capacity of ES, without affecting the proliferation rate. The reduced migratory and adhesive phenotype of the ENG-KD RM82 model and the transcriptomic profiling of both ENG-KD RM82 and SKNMC cells, suggest a role of ENG in ES cell migration and adhesion. The altered organization of actin filaments in ENG-KD and pENG models could support a role of ENG in actin filament remodeling. The transcriptomic profiling of ENG-KD models and the RPPA results underscore the regulation of FAK signaling by ENG. The IP-MS analysis of ENG partners identifies Integrin-Linked Kinase-Associated serine/threonine Phosphatase (ILKAP) as one of the main interactors of ENG in RM82 cells, suggesting its possible association with the