title: Osteosarcoma cells promote the production of pro-tumor cytokines in mesenchymal stem cells by inhibiting their osteogenic differentiation through the TGF-β/Smad2/3 pathway.
abstract: Mesenchymal stem cells (MSCs) are among the most important components of the osteosarcoma microenvironment and are reported to promote tumor progression. However, the means by which osteosarcoma cells modulate MSC behavior remains unclear. The aim of this study was to determine the effects of osteosarcoma cells on both the production of pro-tumor cytokines by mesenchymal stem cells (MSCs) and the osteogenic differentiation of MSCs. High level of transforming growth factor-β (TGF-β) was detected in three osteosarcoma cell lines. Conditioned media (CM) from the osteosarcoma cell lines Saos-2 and U2-OS were used to stimulate the cultured MSCs. We found that osteosarcoma cells promoted the production of IL-6 and VEGF in MSCs by inhibiting their osteogenic differentiation. Furthermore, TGF-β in tumor CM was proved to be an important factor. The TGF-β neutralizing antibody antagonized the effects induced by osteosarcoma CM. The inhibition of Smad2/3 by siRNA significantly decreased the production of IL-6 and VEGF in MSCs and induced their osteogenic differentiation. We also found that Smad2/3 enhanced the expression of β-catenin in MSCs by decreasing the level of Dickkopf-1 (DKK1). Although the inhibition of β-catenin did not affect the production of IL-6 or VEGF, or the gene expression of the early osteogenic markers Runx2 and ALP, it did enhance the gene expression of osteocalcin. Taken together, our data indicate that osteosarcoma cells secrete TGF-β to maintain the stemness of MSCs and promote the production of pro-tumor cytokines by these cells.
authors.affiliation: Shanghai Key Laboratory of Orthopedic Implant, Department of Orthopedic Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Zhizaoju Road 639, Shanghai 200011, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Tu
authors.forename: Zhao-Xiang
authors.initials: ZX
authors.lastname: Peng
authors.forename: Qi-Ming
authors.initials: QM
authors.lastname: Fan
authors.forename: Lin
authors.initials: L
authors.lastname: Du
authors.forename: Wei
authors.initials: W
authors.lastname: Yan
authors.forename: Ting-Ting
authors.initials: TT
authors.lastname: Tang
mesh_terms: D002454:Cell Differentiation; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000378:metabolism* / Q000473:pathology; D010012:Osteogenesis; D012516:Osteosarcoma / Q000378:metabolism* / Q000473:pathology; D034741:RNA, Small Interfering / Q000494:pharmacology; D051899:Smad2 Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051900:Smad3 Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013329:Structure-Activity Relationship; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D016207:Cytokines; D034741:RNA, Small Interfering; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta
keywords: Cytokines; Mesenchymal stem cells; Osteogenic differentiation; TGF-β/Smad2/3 pathway; Tumor microenvironment