1,25-Dihydroxyvitamin D3 Regulates the Biosynthesis of Osteopontin, a Bone-Derived Cell Attachment Protein, in Clonal Osteoblast-Like Osteosarcoma Cells

We investigated the effects of 1,25-dihydroxyvitamin D3 on the synthesis of osteopontin, a phosphorylated cell attachment glycoprotein, in ROS 17/2.8 cells, a clonal osteoblast-like rat osteosarcoma cell line. We observed a dose dependent increase in uptake of [³²P0₄] into osteopontin secreted into the medium. An increased incorporation of [³⁵S] -methionine into secreted osteopontin suggested the effect was that of increased protein biosynthesis. Using a radioimmunoassay we demonstrated a dose dependent increase in the amount of secreted osteopontin, an increase which could be blocked by Actinomycin D, in response to 1,25-dihydroxyvitamin D3. These results suggest that the hormonal form of vitamin D regulates the biosynthesis of osteopontin, possibly at the level of transcription.