Smad Mediated Pathways Are Active in Osteosarcoma.
Alexander B Mohseny, Yongping Cai, Pancras CW Hogendoorn, Anne-Marie Cleton-Jansen. Leiden University Medical Center, Netherlands; School of Medicine, Shandong University, China
Background: Conventional osteosarcoma is a highly malignant tumour mainly affecting children and adolescents. The tumour's pathogenesis is largely unknown, however the young age of onset and its metaphyseal location suggest a possible role for impaired pathways deregulating the normal rapid bone growth and renewal. Previously we showed inactivity of the Wnt/β-catenin pathway and that its reactivation could inhibit osteosarcoma growth and promote differentiation (Cai Y et al. J Pathol. 2010 Jan; 220(1):24-33.). Here we aimed to study the role of two other important pathways in skeletogenesis — BMP and TGFβ — in osteosarcoma and to record the effects of their modulation towards potential targets for therapy.
Design: Human osteosarcoma samples (n=127) and osteoblastomas (n=25) were examined for nuclear phosphorylated (p) Smad1 (BMP) and pSmad2 (TGFβ) expression by immunohistochemistry. In addition the activity of both pathways was measured in 4 osteosarcoma cell lines using the BMP-responsive element (BRE)luciferase construct and the TGFβ pathway responsive plasmid containing (CAGA)12luciferase reporter. Furthermore BMP and TGFβ pathways were modulated using BMP4, BMP inhibitor LDN-193189, TGFβ-1 and TGFβ inhibitor SB-431542 and the effects on proliferation and migration of the cells were recorded.
Results: Analysis of pSmad1 and pSmad2 showed high nuclear expression of both proteins in nearly 100% of the osteosarcomas at levels comparable to the osteoblastomas. This indicates that BMP and TGFβ pathways are active in both bone tumour types, which is irrespective of their clinical behavior. The luciferase reporter assays confirmed that the pathways are indeed functionally active. Both pathways could be successfully modulated in the osteosarcoma cell lines; however this did not affect proliferation or migration of the cells.
Conclusions: This study shows that BMP and TGFβ signaling pathways are active in high-grade central osteosarcoma cases tested, in line with the high bone resorption and vascularization seen in these tumours. Inhibiting the pathways did not affect cell proliferation or migration in vitro, however given the importance of interactions of tumour cells with stroma we cannot exclude that these pathways are involved in osteosarcoma genesis in vivo.
Category: Bone & Soft Tissue
Tuesday, March 1, 2011 9:30 AM
Poster Session III # 5, Tuesday Morning