Find in Library

Glucocorticoid osteoporosis is a serious side effect of long term glucocorticoid uptake and it is caused by osteoblast apoptosis and imbalance in the major bone remodeling pathway RANK/RANKL/OPG. The impact of glucocorticoid on the maintenance of RANK/RANKL/OPG is well explored; dexamethasone was shown to disturb the ratio between <i>OPG</i> and <i>RANKL</i> level by decreasing the expression level of <i>OPG</i> and increasing level of <i>RANKL</i>. Here, were aimed to decipher whether glucocorticoid receptor directly influences <i>RANKL</i> promoter activity and its transcriptional regulation. We demonstrate that overexpression of glucocorticoid receptor (GR) NR3C1 increased <i>RANKL</i> promoter activity in human osteosarcoma, cervical cancer (2-fold) and adenocarcinoma cells (4.5-fold). Mutational analysis revealed that +352 site in the <i>RANKL</i> promoter is functional glucocorticoid responsive element (GRE) since the effect of GR on <i>RANKL</i> promoter activity was diminished by mutation at this site. Overexpression of <i>NR3C1</i> upregulated <i>RANKL</i> mRNA expression 1.5-fold in human A549 and HOS cells. On the other hand silencing of <i>NR3C1</i> caused slight decrease in <i>RANKL</i> mRNA level, suggesting that NR3C1 directly accounts for <i>RANKL</i> transcriptional regulation. Using electrophoretic mobility shift assay we demonstrate that NR3C1 binds to the proximal <i>RANKL</i> promoter region. Our study provides evidences that NR3C1 directly upregulates <i>RANKL</i> transcription in human cell lines and connects the missing link in the mechanism of RANK/RANKL/OPG imbalance of glucocorticoid induced osteoporosis.