Bone formation induced by BMP-2 in human osteosarcoma cells

Our previous studies demonstrated that BMP-2 inhibits the tumorigenicity of cancer stem cells identified as cells with high aldehyde dehydrogenase activity (ALDHbr cells) from the human osteosarcoma cell line OS99-1. We further investigated whether BMP-2 is capable of inducing bone formation in OS99-1 cells. Flow cytometry sorting was used to isolate tumorigenic ALDHbr and non-tumorigenic ALDHlo cells. qRT-PCR was used to quantify the gene expression. A xenograft model was used to verify the bone formation in vivo. There was significantly higher mRNA expression of BMPR1B and BMPR2 in ALDHlo cells compared with that in ALDHbr cells and the BMPR1B expression in ALDHlo cells was ~8-fold higher compared to that in ALDHbr cells. BMP-2 was also found to induce higher transcription of osteogenic markers Runx-2, Osterix (Osx), alkaline phosphatase (ALP) and collagen type I in ALDHlo cells compared to ALDHbr cells, which were mediated by the canonical Smad signaling pathway. In vivo, BMP-2 was identified to induce bone formation in both ALDHbr and ALDHlo cells. All animals receiving 1x104 ALDHlo cells treated with 30 ?g of BMP-2 per animal showed bone formation within 1-2 weeks after injection in mice. Bone formation induced by BMP-2 in ALDHlo cells showed significantly more bone mineral content compared to that in ALDHbr cells. BMP-2 induces bone formation in heterogeneous osteosarcoma cells and BMP-2 may have a promising therapeutic role for treating human osteosarcoma by inducing differentiation along an osteogenic pathway.