WWOX promotes osteosarcoma development via upregulation of Myc

Abstract Osteosarcoma (OS) is an aggressive bone tumor that primarily affects children and adolescents. This malignant tumor is highly aggressive, associated with poor clinical outcomes, and metastasizes mainly to the lungs. Due to its rarity and biological heterogeneity, limited studies of its molecular basis exist, thus hindering the development of effective therapies. WW domain-containing oxidoreductase (WWOX) spans one of the most active and common fragile sites that is frequently altered in human OS. The combined deletion of Wwox and Trp53 using Osterix1-Cre transgenic mice has been shown to accelerate OS development. In this study, we generated a traceable OS mouse model, SKO-Trp53 or DKO-Wwox/Trp53, expressing a tdTomato reporter. By tracking tomato expression at different time points, we detected the early presence of tdTomato-positive cells in the bone marrow (BM) mesenchymal stem cells (MSCs) of non-OS bearing mice, young BM (yBM). We found that DKO yBM cells, but not SKO yBM cells, exhibited tumorigenic traits both in vitro and in vivo. Molecular and cellular characterization of these DKO yBM cells revealed their resemblance to OS tumor cells. Interestingly, one of the observed significant transcriptomic changes in DKO yBM was the upregulation of Myc and its target genes, as compared to SKO yBM cells. Intriguingly, Myc-chromatin immunoprecipitation sequencing (ChIP-Seq) revealed increased enrichment on Myc targets, which were upregulated in DKO yBM cells. Restoration of WWOX in DKO-yBM cells reduced Myc protein levels. As a prototype target, we demonstrated upregulation of MCM7, a known Myc target, in DKO yBM relative to SKO yBM. Inhibition of MCM7 expression using Simvastatin resulted in reduced proliferation and tumor cell growth of DKO yBM cells. Our findings revealed BM-MSCs as a platform to study OS and Myc and its targets as WWOX effectors and early molecular events during osteosarcomagenesis.