Modulation of 1,25(OH) 2D 3-induced osteocalcin synthesis in human osteosarcoma cells by other steroidal hormones

Abstract

We have previously shown that osteocalcin synthesis is readily induced by 1,25-dihydroxyvitamin D 3 (1,25(OH) 2D 3) in MG-63 human osteosarcoma cells (Mahonen et al. (1990) Biochim. Biophys. Acta 1048, 30–37). In the present study, the regulation of osteocalcin synthesis by other hormones of the steroid-thyroid hormone family (retinoic acid, 17β-estradiol, triiodothyronine, and dexamethasone) was examined. We found that the other hormones alone had no effects on medium osteocalcin and osteocalcin mRNA concentrations by 96 h of treatment. Compared with 1,25(OH) 2D 3, however, the combination of 1,25(OH) 2D 3 with dexamethasone resulted in a greatly reduced medium osteocalcin concentration. Also estradiol and triiodothyronine diminished the stimulatory effect of 1,25(OH) 2D 3. In contrast, the combination of 1,25(OH) 2D 3 with retinoic acid resulted in an increased medium osteocalcin concentration. The inhibition of osteocalcin synthesis by dexamethasone and triiodothyronine was accompanied by decreased osteocalcin mRNA levels. Retinoic acid and estradiol, however, did not influence the 1,25(OH) 2D 3-induced osteocalcin mRNA levels. To examine the specificity of the hormonal effects, the activity of alkaline phosphatase was determined. Both baseline and 1,25(OH) 2D 3-stimulated alkaline phosphatase activity was found to be inhibited by all other hormones. These results suggest that the steroidal hormones specifically affect osteocalcin synthesis in osteoblastic bone cells, and that complex interactions occur at the level of transcription and/or translation resulting in each case in a finely adjusted rate of osteocalcin sysnthesis.