Inactive Wnt/β‐catenin pathway in conventional high‐grade osteosarcoma

Abstract

Osteosarcoma is the most common malignant bone tumour, with a peak incidence in children and young adolescents, suggesting a role of rapid bone growth in its pathogenesis. The Wnt/beta-catenin pathway plays a crucial role in skeletal development and is indispensable for osteoblasts' lineage determination. Previous studies suggesting an oncogenic role for the Wnt/beta-catenin pathway in osteosarcoma were based on cytoplasmic staining of beta-catenin or the detection of one component of this pathway. However, those approaches are inappropriate to address whether the Wnt/beta-catenin pathway is functionally active. Therefore, in this study, we examined nuclear beta-catenin expression in 52 human osteosarcoma biopsies, 15 osteoblastomas (benign bone tumours), and four human osteosarcoma cell lines by immunohistochemistry. Furthermore, we modulated Wnt/beta-catenin pathway activity using a GIN (GSK3beta inhibitor) and evaluated its effect on cell growth and osteogenic differentiation. Absence of nuclear beta-catenin staining was found in 90% of the biopsies and all osteosarcoma cell lines, whereas strong nuclear beta-catenin staining was observed in all osteoblastomas. Wnt-luciferase activity was comparable to the negative control in all osteosarcoma cell lines. GIN stimulated the Wnt/beta-catenin pathway, as shown by translocation of beta-catenin into the nucleus and increased Wnt-luciferase activity as well as mRNA expression of AXIN2, a specific downstream target gene. Stimulation of the Wnt/beta-catenin pathway by GIN significantly reduced cell proliferation in the cell lines MG-63 and U-2-OS and enhanced differentiation in the cell lines HOS and SJSA-1, as shown by an increase in alkaline phosphatase (ALP) activity and mineralization. In contrast with the oncogenic role of the Wnt/beta-catenin pathway in osteosarcoma as previous studies suggested, here we demonstrate that this pathway is inactivated in osteosarcoma. Moreover, activation of the Wnt/beta-catenin pathway inhibits cell proliferation or promotes osteogenic differentiation in osteosarcoma cell lines. Our data suggest that loss of Wnt/beta-catenin pathway activity, which is required for osteoblast differentiation, may contribute to osteosarcoma development.

High Wnt Signaling Represses the Proapoptotic Proteoglycan syndecan-2 in Osteosarcoma Cells

“…At present, the role of Wnt signaling in tumorigenesis of osteosarcoma is under debate. Altogether, the facts that Wnt signaling is required for osteoblastic differentiation, that DKK1 was shown to block the differentiation and increase the transformation of mesenchymal stem cells, and the reported inactivation of the canonical Wnt pathway in osteosarcoma support the conclusion that silencing of the Wnt/β-catenin signaling contributes to tumorigenesis (27)(28)(29). In contrast, inhibition of Wnt signaling by a dominant-negative LRP5 was shown to decrease tumorigenicity and metastasis in osteosarcoma in vivo, and Wnt/β-catenin pathway antagonists such as curcumin and PKF118-310 have been shown to have antitumor effects in osteosarcoma cells, indicating a protumoral role of Wnt signaling (30,31).…”

Profiling of high-grade central osteosarcoma and its putative progenitor cells identifies tumourigenic pathways

“…Given the crucial role of this pathway in normal osteogenesis (Hartmann, 2006) and tumourigenesis in general, this observation suggests a role for Wnt signalling that differs from that in colorectal cancer, in which upregulation of the pathway is considered to be crucial for tumourigenesis (Klaus and Birchmeier, 2008). Indeed, we have recently shown with a functional reporter assay that Wnt/b-catenin signalling seems to be absent in osteosarcoma cell lines (Cai et al, 2009). In addition, we showed an absence of nuclear b-catenin staining in primary osteosarcomas, indicative of inactive Wnt/ b-catenin signalling.…”

Oridonin inhibits the proliferation of human osteosarcoma cells by suppressing Wnt/β-catenin signaling

“…Therefore, GSK3β has been identified as a tumor suppressor that is frequently inactivated in various tumors (42). However, studies have provided evidence that the exact role of GSK3β in tumorigenesis of human OS is controversial (43)(44)(45)(46). In the present study, we explored the effect of ORI on GSK-3β and found that the total GSK-3β protein level was significantly elevated in response to the treatment with ORI.…”