title: Inactive Wnt/beta-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.
authors.affiliation: Department of Pathology, School of Medicine, Shandong University, Jinan 250012, PR China.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Cai
authors.forename: Alexander B
authors.initials: AB
authors.lastname: Mohseny
authors.forename: Marcel
authors.initials: M
authors.lastname: Karperien
authors.forename: Pancras C W
authors.initials: PC
authors.lastname: Hogendoorn
authors.forename: Gengyin
authors.initials: G
authors.lastname: Zhou
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Cleton-Jansen
mesh_terms: D000818:Animals; D001859:Bone Neoplasms / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000502:physiology; D000071679:Glycogen Synthase Kinase 3 beta; D053823:Hedgehog Proteins / Q000502:physiology; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D009363:Neoplasm Proteins / Q000378:metabolism / Q000502:physiology; D010006:Osteoblasts / Q000473:pathology; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured; D051153:Wnt Proteins / Q000494:pharmacology / Q000502:physiology*; D060508:Wnt3 Protein; D051176:beta Catenin / Q000378:metabolism*
chemical_list: C501126:DKK1 protein, human; D053823:Hedgehog Proteins; D036341:Intercellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; D051153:Wnt Proteins; D060508:Wnt3 Protein; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3