Effects of retinoic acid and dexamethasone on proliferation, differentiation, and glucocorticoid receptor expression in cultured human osteosarcoma cells.

HOS-8603 is a newly established human osteosarcoma cell line with phenotypic characteristics of osteoblasts. When these cells were grown in monolayer culture in the presence of dexamethasone (Dex) or retinoic acid (RA), there was a significant inhibition of proliferation in a concentration-dependent manner. The combined effects of Dex and RA depended upon the concentrations: at low concentrations (< 10 nM) the effects of Dex and RA were additive, whereas at high concentrations the effects were antagonistic. Anchorage-independent growth studies performed in methylcellulose culture indicated that Dex or RA inhibited colony formation by HOS-8603 cells. Treatment of HOS-8603 cells with 100 nM Dex induced alkaline phosphatase activity in a time-dependent manner, reaching a maximum of about 6.5-fold over basal levels. All these effects of Dex on HOS-8603 cells could be reversed by RU 486, a potent antiglucocorticoid. Based upon saturation of specific binding and Scatchard plot analysis, we demonstrated that a saturable, high-affinity glucocorticoid receptor (GR) existed in HOS-8603 cells, suggesting that the effects of glucocorticoids on HOS-8603 cells are mediated by the specific GR. Finally, we further investigated the homologous and heterologous regulation of GR in HOS-8603 cells. Treatment of these cells with Dex led to a time-dependent decrease in GR concentrations. This homologous GR downregulation occurred not only at the level of hormone binding but also at the level of GR mRNA. In contrast, RA was capable of increasing GR concentrations in a concentration- and time-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)