All-trans retinoic acid restored the osteogenic ability of BMP9 in osteosarcoma through the p38 MAPK pathway

Osteosarcoma (OS) is the most common malignant bone tumour and is considered to be a disease caused by a dysfunction in differentiation. Bone morphogenetic protein 9 (BMP9) is the most potent osteogenic factor in mesenchymal stem cells, but it cannot induce osteogenic differentiation in OS cells; this might be one of the determinants in the pathogenesis of OS. All-trans retinoic acid (ATRA) can induce osteogenic differentiation of OS cells and potentiate BMP9-induced osteogenesis in preadipocytes. However, the concomitant effect of ATRA and BMP9 in OS cells is unclear; therefore, in the present study, we focused on this topic. The results showed that BMP9 significantly promoted the proliferation of human OS 143B cells and did not induce osteogenic differentiation of cells in vitro (p