Active Beta-Catenin (ABC) promotes an invasive phenotype in pediatric osteosarcoma

Osteosarcoma (OS) is an aggressive primary bone malignancy with peak incidence in children and adolescents. Despite current multimodal treatments, there has been little change in overall survival outcomes in the last two decades. The canonical Wnt/β-catenin pathway is known to be a critical pathway in OS progression. To better understand the molecular basis of OS and potentially provide target/s for new therapies or diagnostics, we investigated the relationship between β-catenin, more specifically, the transcriptionally active form of β-catenin, Activated β-Catenin (ABC), and OS progression. We previously reported an association between ABC and aggressive OS whereby, cellular/nuclear ABC levels, but not cellular/nuclear β-catenin levels, increase with the degree of aggressiveness. However, a direct role for ABC in promoting OS progression has not been shown. In order to directly determine the role/impact of ABC in OS progression, we generated a pEGFP-ABC fusion construct which simulates ABC's phosphorylation pattern. Transfection of pEGFP-ABC, pEGFP-β-catenin, or an empty vector (pEGFP) into OS cell lines showed that wnt pathway transcriptional activity in GFP-ABC-expressing cells was significantly higher than that in both GFP-β-catenin and empty-vector-transfected cells. We also show that the in vitro invasive potential of the pEGFP-ABC-transfected cells was significantly higher compared to both pEGFP-β-catenin and pEGFP-transfected cells. Immunohistochemistry of clinical pediatric OS specimens supported these findings, showing a significant correlation between high ABC levels and invasive disease. To the best of our knowledge, this is the first report that suggest that ABC drive transcriptional activity to enhance invasiveness in OS and could serve as a biomarker of aggressive or metastatic OS.