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 (ALDH ( br ) 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 ALDH ( br ) and non-tumorigenic ALDH ( lo ) 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 ALDH ( lo ) cells compared with that in ALDH ( br ) cells and the BMPR1B expression in ALDH ( lo ) cells was ∼8-fold higher compared to that in ALDH ( br ) 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 ALDH ( lo ) cells compared to ALDH ( br ) cells, which were mediated by the canonical Smad signaling pathway. In vivo , BMP-2 was identified to induce bone formation in both ALDH ( br ) and ALDH ( lo ) cells. All animals receiving 1×10 ( 4 ) ALDH ( lo ) cells treated with 30 μ g of BMP-2 per animal showed bone formation within 1–2 weeks after injection in mice. Bone formation induced by BMP-2 in ALDH ( lo ) cells showed significantly more bone mineral content compared to that in ALDH ( br ) 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.