Glucocorticoid regulation of calcitonin receptor in mouse osteoclast-like multinucleated cells

Abstract

Abundant multinucleated cells (MNCs) are formed in cocultures of mouse osteoblastic cells and marrow cells in the presence of 1α, 25‐dihydroxyvitamin D₃ [1α, 25(OH)₂D₃], and these cells have the properties of osteoclasts (OCs). In this study using the mammalian OCs, we tried to clarify the role of glucocorticoids (GCs) in calcitonin receptors (CTR) and CT‐responsive cAMP production in OCs. Dexamethasone (DEX) dose and time dependently enhanced the specific binding of [¹²⁵I]salmon calcitonin (sCT). When the MNCs were preincubated with DEX for 24 h, the effect was evident at 10⁻⁹ M and the maximum effect was obtained at 10⁻⁷ M. The effect developed over 12–48 h at doses of 10⁻⁹ and 10⁻⁶ M DEX. The numbers of CTR‐positive mononuclear cells and MNCs were not altered by the DEX treatment. Prednisolone and triamcinolone reproduced the DEX effect, but 17 β‐estradiol, progesterone, testosterone, aldosterone, and 1α, 25(OH)₂D₃ did not. RU486, a GC receptor antagonist, attenuated the effect of DEX to enhance the specific binding of [¹²⁵I]sCT. From a Scatchard plot analysis, DEX enhanced CTR number (212 ± 64%) with a minimal change in the affinity to sCT. Autoradiographic studies using [¹²⁵I]sCT showed that DEX enhanced the density of the grains on the tartrate‐resistant acid phosphatase (TRAP)‐positive MNCs and mononuclear cells, but not on other types of cells. DEX preincubation also enhanced sCT‐stimulated but not prostaglandin E₂‐ or forskolin‐stimulated cAMP production. Inhibition of enhancement was possible with cycloheximide, indicating this effect was mediated through de novo protein synthesis. The present study showed that GCs play an important role in the regulation of CT effect through the upregulation of CTR on OCs, and this effect would explain, at least partly, a potentiation by GCs of hypocalcemic action of CT in hypercalcemic patients.