The effect of transcriptional inhibitors on the bone gamma-carboxyglutamic acid protein response to 1,25-dihydroxyvitamin D3 in osteosarcoma cells.

The stimulation of bone gamma-carboxyglutamic acid protein (BGP) synthesis by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) in clonal osteosarcoma cell culture has been analyzed using specific inhibitors of RNA and protein synthesis. Addition of actinomycin D or alpha-amanitin simultaneously with 1,25-(OH)2D3 prevented hormonal elevation of BGP levels but did not affect basal BGP synthesis. Neither transcriptional inhibitor had any effect on BGP synthesis in cultures which had already been fully stimulated by 1,25-(OH)2D3. In contrast, the protein synthesis inhibitor cycloheximide blocked BGP synthesis in both untreated and 1,25-(OH)2D3-treated cells. Inhibitor effects on media BGP levels corresponded in all cases to effects on the rapidly turned over intracellular BGP pool. These results support a model of transcriptional control for the action of 1,25-(OH)2D3 and suggest that the hormone elicits a transient burst of transcription of the BGP gene.