17β-Oestradiol enhances the stimulatory effect of 1,25-dihydroxyvitamin D3 on alkaline phosphatase activity in human osteosarcoma SaOS-2 cells in a differentiation-dependent manner

Abstract

We tested the effect of osteoblastic differentiation on the interactive effects of 17β-oestradiol (E₂) and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on alkaline phosphatase activity. As cell models we utilized the more differentiated human osteosarcoma (SaOS) cells that had been cultured for 6 days in medium containing 10 nm dexamethasone (Dex) (SaOS+Dex cells) and the less differentiated cells cultured in the absence of Dex (SaOS−Dex cells). The cells were challenged with 1,25(OH)₂D₃ in the presence or absence of Dex for 24 h and then with E₂ for an additional 24 h. In SaOS−Dex cells, alkaline phosphatase activity remained constant over the 48-h period and was not significantly affected by E₂, 1,25(OH)₂D₃ or 1,25(OH)₂D₃+E₂ treatment. On the other hand, in SaOS+Dex cells, 1,25(OH)₂D₃ and E₂+1,25(OH)₂D₃ stimulated alkaline phosphatase activity (ANOVA, F= 154·2, PP2D₃ had dose-dependent stimulatory effects which were strongly enhanced by 10 nm E₂ (ANOVA, F=46·0, P2, in the presence or absence of 100 nm 1,25(OH)₂D₃, revealed that in the presence of 1,25(OH)₂D₃, the E₂ dose-response curve was biphasic in SaOS+Dex cells (ANOVA, F=3·40, P2 (P2 was verified using the inactive 17α-oestradiol and the oestrogen antagonist, tamoxifen. These data indicate that E₂ and 1,25(OH)₂D₃ have positive interactive effects on alkaline phosphatase activity in human osteoblasts, and suggest that the expression of this interaction is dependent on the stage of differentiation of the cells. Journal of Endocrinology (1996) 148, 181–187