1719P - Fusion of immortalized myoblasts induces genomic instability that drives tumour development and progression

Abstract

BackgroundSarcoma are a heterogeneous group of tumor which can be split into two subgroups with distinct genetics. Half of sarcoma presents an important genomic reorganization correlated to tumor aggressiveness. At this stage, the origin of this instability is still unknown. Cell fusion is a physiological mechanism involved in several processes including myoblast differentiation and already described to be involved in aneuploidy generation and genomic instability. We thus hypothesized that cell fusion could participate to sarcoma oncogenesis by generating genomic instability. MethodsWe established cell line of hybrids from spontaneous fusion of immortalized myoblasts. Tumor and metastasis development were evaluated upon grafting and whole genome and transcriptome sequencing with in-vitro mechanistic studies were performed to decipher phenotypes acquired by hybrids upon fusion. ResultsIn vitro hybrid cell lines show a more aggressive phenotype than parental cell lines by increasing proliferation and clonogenic capacities. Only hybrids form tumors upon grafting and may develop also metastasis. Aneuploidy triggered by cell fusion induces genome reorganization and in vivo tumor genome show alterations corresponding to those observed in human rhabdomyosarcoma. Indeed, 85% of hybrid tumors harbor DMD deletions as observed in sarcoma with myogenic origin. The study of this protein reveals that tumors lose the expression of Dp427 isoform which is the one reported as a tumor suppressor. This malignant transformation of hybrids is associated to transcriptomic remodeling toward a decrease of the expression of genes involved in muscle differentiation. ConclusionsTo our knowledge, this is the first model able to reproduce the complex genomic of sarcoma. The detection of those hybrid cells in sarcoma tumor allowed us to push forward they are involved in sarcoma development and progression and their quantification in tumors or in circulating cells could thus establish an early prognostic marker. Finally, specific therapeutic targeting of this hybrids could represent new approach. Legal entity responsible for the studyFrederic Chibon. FundingAssociation pour la Recherche contre le Cancer (ARC) Fondation pour la Recherche Médicale (FRM). DisclosureAll authors have declared no conflicts of interest.