[Effects of intermittent compressive force on transforming growth factor beta and osteopontin synthesis in cultured bone cells].

It has long been thought that the process of bone remodeling is regulated by the chain reactions of bone cells involving chemical mediators, growth factors and synthesis of extracellular matrix proteins etc. In this context, it has also been recognized that physical stimulation is an important factor in the regulation of bone remodeling. Thus, it is vitally important to understand whether the physical stimulation can induce the cellular events regarding autocrine regulation of protein synthesis. This study was conducted to examine the effects of hydrostatic intermittent compressive force (ICF) on the synthesis of the transforming growth factor beta (TGF-beta) and matrix phosphoproteins which may play an important role in the process of bone remodeling. The rat osteosarcoma cells (ROS 17/2.8) were cultured with DMEM containing 10% FCSP. ICF was applied to sub-confluent cells at 130 mb, 15/min cycle for 48h. ICF increased TGF-beta activity of the conditioned medium. This was assessed by its capacity to promote anchorage independent growth of NRK 49F cells and to inhibit the growth of human hepatoma cells (Hep-3B). Furthermore, ICF stimulated the synthesis of the phosphoproteins with Mr. 75 KDa by about 1.4 fold which was visualized by SDS-PAGE on 5-15% gradient gel. Immunoprecipitation of the phosphoproteins with rat osteopontin antibody revealed that the 75 KDa phosphoprotein was identical to osteopontin. The 75 KDa osteopontin synthesis was inhibited by the addition of TGF-beta antibody in a dose dependent manner. These results suggested that ICF stimulated the synthesis of TGF-beta and osteopontin in ROS 17/2.8 cells and that the osteopontin synthesis could be regulated by TGF-beta.