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Osteosarcoma is a highly metastatic form of bone cancer in adolescents and young adults that is resistant to existing treatments. Development of an effective therapy has been hindered by very limited understanding of the mechanisms of osteosarcomagenesis. Here, we used genetically engineered mice to investigate the effects of deleting the tumor suppressor Wwox selectively in either osteoblast progenitors or mature osteoblasts. Mice with conditional deletion of Wwox in preosteoblasts (WwoxΔosx1) displayed a severe inhibition of osteogenesis accompanied by p53 upregulation, effects that were not observed in mice lacking Wwox in mature osteoblasts. Deletion of p53 in WwoxΔosx1 mice rescued the osteogenic defect. In addition, the Wwox;p53Δosx1 double knockout mice developed poorly differentiated osteosarcomas that resemble human osteosarcoma in histology, location, metastatic behavior, and gene expression. Strikingly, the development of osteosarcomas in these mice was greatly accelerated compared with mice lacking p53 only. In contrast, combined WWOX and p53 inactivation in mature osteoblasts did not accelerate osteosarcomagenesis compared with p53 inactivation alone. These findings provide evidence that a WWOX–p53 network regulates normal bone formation and that disruption of this network in osteoprogenitors results in accelerated osteosarcoma. The Wwox;p53Δosx1 double knockout establishes a new osteosarcoma model with significant advancement over existing models. Cancer Res; 76(20); 6107–17. ©2016 AACR.

Supplementary Methods, Figures and Tables

Supplementary Tables 1-10, Figures 1-6, Methods from Frequent Attenuation of the WWOX Tumor Suppressor in Osteosarcoma Is Associated with Increased Tumorigenicity and Aberrant RUNX2 Expression

The WW domain-containing oxidoreductase (WWOX) is a tumor suppressor that is deleted or attenuated in most human tumors. Wwox-deficient mice develop osteosarcoma (OS), an aggressive bone tumor with poor prognosis that often metastasizes to lung. On the basis of these observations, we examined the status of WWOX in human OS specimens and cell lines. In human OS clinical samples, WWOX expression was absent or reduced in 58% of tumors examined (P < 0.0001). Compared with the primary tumors, WWOX levels frequently increased in tumors resected following chemotherapy. In contrast, tumor metastases to lung often exhibited reduced WWOX levels relative to the primary tumor. In human OS cell lines having reduced WWOX expression, ectopic expression of WWOX inhibited proliferation and attenuated invasion in vitro, and suppressed tumorigenicity in nude mice. Expression of WWOX was associated with reduced RUNX2 expression in OS cell lines, whereas RUNX2 levels were elevated in femurs of Wwox-deficient mice. Furthermore, WWOX reconstitution in HOS cells was associated with downregulation of RUNX2 levels and RUNX2 target genes, consistent with the ability of WWOX to suppress RUNX2 transactivation activity. In clinical samples, RUNX2 was expressed in the majority of primary tumors and undetectable in most tumors resected following chemotherapy, whereas most metastases were RUNX2 positive. Our results deepen the evidence of a tumor suppressor role for WWOX in OS, furthering its prognostic and therapeutic significance in this disease. Cancer Res; 70(13); 5577–86. ©2010 AACR.