title: Lysyl oxidase is downregulated by the EWS/FLI1 oncoprotein and its propeptide domain displays tumor supressor activities in Ewing sarcoma cells.
abstract: Ewing sarcoma is the second most common bone malignancy in children and young adults. It is driven by oncogenic fusion proteins (i.e. EWS/FLI1) acting as aberrant transcription factors that upregulate and downregulate target genes, leading to cellular transformation. Thus, identificating these target genes and understanding their contribution to Ewing sarcoma tumorigenesis are key for the development of new therapeutic strategies. In this study we show that lysyl oxidase (LOX), an enzyme involved in maintaining structural integrity of the extracellular matrix, is downregulated by the EWS/FLI1 oncoprotein and in consequence it is not expressed in Ewing sarcoma cells and primary tumors. Using a doxycycline inducible system to restore LOX expression in an Ewing sarcoma derived cell line, we showed that LOX displays tumor suppressor activities. Interestingly, we showed that the tumor suppressor activity resides in the propeptide domain of LOX (LOX-PP), an N-terminal domain produced by proteolytic cleavage during the physiological processing of LOX. Expression of LOX-PP reduced cell proliferation, cell migration, anchorage-independent growth in soft agar and formation of tumors in immunodeficient mice. By contrast, the C-terminal domain of LOX, which contains the enzymatic activity, had the opposite effects, corroborating that the tumor suppressor activity of LOX is mediated exclusively by its propeptide domain. Finally, we showed that LOX-PP inhibits ERK/MAPK signalling pathway, and that many pathways involved in cell cycle progression were significantly deregulated by LOX-PP, providing a mechanistic explanation to the cell proliferation inhibition observed upon LOX-PP expression. In summary, our observations indicate that deregulation of the LOX gene participates in Ewing sarcoma development and identify LOX-PP as a new therapeutic target for one of the most aggressive paediatric malignancies. These findings suggest that therapeutic strategies based on the administration of LOX propeptide or functional analogues could be useful for the treatment of this devastating paediatric cancer.
authors.affiliation: Unidad de Tumores Sólidos Infantiles, Área de Genética Humana, Instituto de Investigación de Enfermedades Raras, Instituto de Salud Carlos III, Majadahonda, Madrid, Spain.
authors.forename: Noelia
authors.initials: N
authors.lastname: Agra
authors.forename: Florencia
authors.initials: F
authors.lastname: Cidre
authors.forename: Laura
authors.initials: L
authors.lastname: García-García
authors.forename: Juan
authors.initials: J
authors.lastname: de la Parra
authors.forename: Javier
authors.initials: J
authors.lastname: Alonso
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015536:Down-Regulation; D005260:Female; D006801:Humans; D051379:Mice; D015514:Oncogene Proteins, Fusion / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D008249:Protein-Lysine 6-Oxidase / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D051789:Proto-Oncogene Protein c-fli-1 / Q000737:chemistry / Q000378:metabolism*; D034802:RNA-Binding Protein EWS / Q000737:chemistry / Q000378:metabolism*; D012512:Sarcoma, Ewing / Q000473:pathology*; D025521:Tumor Suppressor Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism
chemical_list: C106031:EWS-FLI fusion protein; D015514:Oncogene Proteins, Fusion; D051789:Proto-Oncogene Protein c-fli-1; D034802:RNA-Binding Protein EWS; D025521:Tumor Suppressor Proteins; D008249:Protein-Lysine 6-Oxidase