Calcium hydroxide regulates transcription of the bone sialoprotein gene via a calcium-sensing receptor in osteoblast-like ROS 17/2.8 cells.

Bone sialoprotein (BSP) is a glycoprotein associated with mineralized tissues. In this study, we investigated the regulation of Bsp transcription by calcium hydroxide [Ca(OH)2 ] in rat osteosarcoma-derived osteoblast-like ROS 17/2.8 cells and stromal bone marrow cells. Application of Ca(OH)2 (0.4 mM) increased the levels of runt-related transcription factor 2 (Runx2) and BspmRNAs at 3 and 6 h and the level of BSP protein at 12 h. Transient transfection analyses were performed using chimeric constructs encompassing different regions of the rat Bsp gene promoter ligated to a luciferase reporter gene. It was found that Ca(OH)2 increased the luciferase activities of the pLUC3 and pLUC4 constructs. Introduction of 2-bp mutations to the luciferase construct showed that the effects of Ca(OH)2 were mediated by cAMP response-element (CRE) and fibroblast growth factor 2 (FGF2) response element (FRE). Luciferase activities induced by Ca(OH)2 were blocked by protein kinase C (PKC), protein kinase A (PKA), phosphoinositide-3-kinase (PI3-K), and extracellular signal-regulated kinase 1/2 (ERK1/2) inhibitors and by calcium-sensing receptor (CASR) antagonists. Gel-shift analyses showed that Ca(OH)2 increased binding of nuclear protein to CRE and FRE. Dexamethasone-induced mineralization in stromal bone marrow cells was abrogated by CASR antagonists. These studies demonstrate that Ca(OH)2 regulates Bsp transcription via the CASR by targeting CRE and FRE in the rat Bsp gene promoter.