Dissecting the Molecular Mechanisms of Osteosacomagenesis

Osteosarcoma (OS) is the most common primary malignant bone tumor in children and adolescents. OS frequently metastasizes to the lungs. The most prominent studied gene in OS is p53, with other genes like Rb, c-Myc, c-Fos and Runx2 . WWOX (WW domain-containing oxidoreductase) is frequently inactivated in human OS, and WWOX restoration in WWOX-negative OS cells suppresses tumorigenicity. Our lab has recently demonstrated that depletion of murine Wwox at pre-osteoblast using Osterix1-cre transgenic mouse in p53-deficient background (DKO) accelerates OS development. The DKO tumors display more aggressive and poorly differentiated phenotype as compared with single p53 KO tumors. RNA sequencing analysis of DKO tumors showed an upregulation of several genes among which c-Fos was noted. These results suggested that WWOX dysregulation is associated with dysregulation of c-Fos. Here, we confirmed increased levels of c-Fos in the majority of human OS cases and its negative correlation with WWOX levels (P value=0.006). To test whether c-Fos is an effector of WWOX/p53 deletion, we generated a conditional triple knockout mouse of Wwox, Trp53 and c-Fos (TKO) in committed osteoblast using the Osterix1-Cre transgenic mouse. Our findings revealed i) prolonged tumor-free survival of TKO compared to DKO mice ii) decreased Ki67 staining iii) increased differentiation in TKO tumors as demonstrated by more bony tissue in H&E staining, more collagen staining using Sirius red stain, and more calcium deposition in Alizarin red stain. These findings suggest a novel functional cross talk between c-Fos, WWOX and p53 in osteosarcomagenesis and indispensable role in osteoblasts differentiation process.