Stimulation of cellular alkaline phosphatase activity and its messenger RNA level in a human osteosarcoma cell line by 1,25-dihydroxyvitamin D₃

1,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) significantly stimulated cellular alkaline phosphatase activity in a human osteoblastic osteosarcoma cell line (TE-85 cells) in serum-free medium with 0.1% bovine serum albumin as the hormone carrier in a doseand a time-dependent manner. The extent of the maximal stimulation was greater and the minimal dose that was required for stimulation was lower than those previously reported for TE-85 cells in the presence of serum. The magnitude of the stimulation of alkaline phosphatase activity by 1,25(OH)₂D₃ varied with the cell density. Daily changes of conditioned medium, as compared with no medium changes, significantly reduced the magnitude of the stimulation, suggesting that endogenous factors secreted into culture medium could play an enhancing role. Finally, application of Northern blot analysis using an oligodeoxynucleotide probe corresponding to a unique sequence of the human bone/liver/kidney alkaline phosphatase cDNA coding region revealed that 1,25(OH)₂D₃ increased the alkaline phosphatase mRNA level, suggesting that the increase in alkaline phosphatase activity was a result of either an increase in the rate of transcription or an increase in message stability.