1 alpha,25-Dihydroxyvitamin D3 rapidly alters phospholipid metabolism in the nuclear envelope of osteoblasts

1 alpha,25-Dihydroxyvitamin D3 (1 alpha,25-(OH)2D3) has been shown to increase cytosolic calcium and inositol triphosphate levels in rat osteosarcoma cells (ROS 17/2.8) and to increase nuclear calcium in these cells. To determine the mechanism(s) of 1 alpha,25-(OH)2D3-induced changes in nuclear calcium, the effect of the hormone on phospholipid metabolism in isolated osteoblast nuclei was assessed. 1 alpha,25(OH)2D3, 20 nM, increased inositol triphosphate levels in the nuclei after 5 min of treatment. The biologically inactive epimer, 1 beta,25-(OH)2D3, had no significant effect on inositol triphosphate levels. ATP, 1 mM, also increased inositol triphosphate levels in the isolated nuclei after 5 min. 1 alpha,25-(OH)2D3, 20 nM, increased calcium in the isolated nuclei in the presence but not in the absence of extranuclear calcium within 5 min. Nuclear calcium was also increased within 5 min by ATP, 1 mM, and inositol triphosphate, 1 mM. The effect of ATP on nuclear calcium was not additive with 1 alpha,25-(OH)2D3, suggesting that these two agents increase nuclear calcium in these osteoblast-like cells by similar mechanisms. In summary, 1 alpha,25-(OH)2D3 and ATP rapidly increase inositol triphosphate levels in nuclei isolated from ROS 17/2.8 cells. The hormone, the nucleotide, and the inositol phospholipid increase nuclear calcium. Thus, the 1 alpha,25-(OH)2D3 and ATP effects on nuclear calcium may be mediated by changes in phospholipid metabolism in the nuclei of these osteoblast-like cells.