Thrombospondin-2 stimulates MMP-9 production and promotes osteosarcoma metastasis via the PLC, PKC, c-Src and NF-κB activation

Osteosarcoma is an extremely common primary bone malignancy that is highly metastatic, with most deaths resulting from pulmonary metastases. The extracellular matrix protein thrombospondin-2 (TSP-2) is key to many biological processes, such as inflammation, wound repair and tissue remodelling. However, it is unclear as to what biological role TSP-2 plays in human metastatic osteosarcoma. The immunochemistry analysis from osteosarcoma specimens identified marked up-regulation of TSP-2 in late-stage osteosarcoma. Furthermore, we found that TSP-2 increased the levels of matrix metallopeptidase 9 (MMP-9) expression and thereby increased the migratory potential of human osteosarcoma cells. Osteosarcoma cells pre-treated with an MMP-9 monoclonal antibody (mAb), an MMP-9 inhibitor, or transfected with MMP-9 small interfering RNA (siRNA) reduced the capacity of TSP-2 to potentiate cell migration. TSP-2 treatment activated the PLCβ, PKCα, c-Src and nuclear kappa factor B (NF-κB) signalling pathways, while the specific siRNA, inhibitors and mutants of these cascades reduced TSP-2-induced stimulation of migration activity. Knockdown of TSP-2 expression markedly reduced cell metastasis in cellular and animal experiments. It appears that an interaction between TSP-2 and integrin αvβ3 activates the PLCβ, PKCα and c-Src signalling pathways and subsequently activates NF-κB signalling, increasing MMP-9 expression and stimulating migratory activity amongst human osteosarcoma cells.