Regulation of calcitonin receptor by glucocorticoid in human osteoclast-like cells prepared in vitro using receptor activator of nuclear factor-kappaB ligand and macrophage colony-stimulating factor

Using mouse osteoclast-like cells (OCs), we have shown that treatment with glucocorticoids (GCs) resulted in an increase in calcitonin (CT) binding by enhancing CT receptor (CTR) gene transcription. Additionally, treatment wi th GCs demonstrated increased sensitivity to CT. There is, however, scant i nformation on the effects of GC or CTR regulation by GCs in human osteoclas ts, In this study we examined CTR regulation by GCs and the effects of GCs and CT together in human OCs. OCs were prepared by treatment of peripheral blood mononuclear cells in vitro with soluble receptor activator of nuclear factor-kappaB ligand and macrophage colony-stimulating factor. Treatment o f mature OCs with dexamethasone (Dex) resulted in a dose-and time-dependent increase in [I-125]salmon CT (sCT) binding capacity. Treatment with Dex en hanced CTR messenger RNA (mRNA) expression, suggesting that CTR up-regulati on is at least partly due to an increase in de novo CTR synthesis. Triamcin olone and prednisolone reproduced the Dex effect on [I-125]sCT-specific bin ding and CTR mRNA expression, but 17 beta -estradiol, progesterone, dehydro epiandrosterone, and aldosterone did not. A Scatchard plot analysis showed that Dex enhanced CTR number with a minimal change in the affinity to sCT. Autoradiographic studies using [I-125] sCT showed that Dex enhanced the CTR density on individual multinuclear OCs. Upregulation of [125I]sCT-specific binding and CTR mRNA expression was seen even in the presence of sCT, but the enhancement diminished subsequently at later times (36-48 h after sCT r emoval), which was consistent with our previous observation in mouse OCs. T his suggests that GCs and CTs act on CTR expression differently, consistent with our previous work using mouse OCs, in which we found that GCs increas ed transcription of CTR gene expression, whereas CT reduced CTR mRNA stabil ity. The results obtained in this study show that GC increased CTR expressi on and sensitivity to CT in cells of the human osteoclast lineage and provi de the basis for understanding the beneficial effects of combination treatm ent with GCs and CTs in malignancy-associated hypercalcemia.