Hormone and growth factor regulation of bone sialoprotein transcription and possible role of these factors on clinical application

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Bone sialoprotein (BSP) is a mineralized tissue-specific protein expressed by differentiated osteoblasts that appears to function in the initial mineralization of bone. Parathyroid hormone (PTH) which regulates serum calcium through its actions on bone cells and fibroblast growth factor 2 (FGF2) is recognized as a potent mitogen for a variety of mesenchymal cells. To determine the molecular mechanism of PTH and FGF2 regulation of BSP, we analyzed the effects of the PTH or FGF2 on the expression of BSP in ROS 17/2.8 cells. At 10^<-8>M PTH stimulation of BSP mRNA was first evident at 3 h (〜3.8 -fold), reached maximal levels at 6 h (〜4.7 -fold), and declined slowly thereafter. At 10ng/ml FGF2, stimulation of BSP mRNA was first evident at 3 h (〜2.6 -fold) and reached maximal levels at 6 h (〜4 -fold).The effects of PTH and FGF2 did not alter the stability of the BSP mRNA.From transient transfection assays using various BSP promoter-luciferase constructs, a pituitary-specific transcription f … More actor-1 regulatory element (Pit-1 ; nts -111 to -105) and a FGF response element (FRE ; nts -92 to -85) were identified as a target of transcriptional activation by PTH and FGF2.Binding of a nuclear protein, recognized by anti-Pit-1 antibodies, to a radiolabelled Pit-1-BSP probe was decreased in nuclear extracts prepared from PTH. Moreover, co-transfection of ROS cells with a double-stranded Pit-1 oligonucleotide also increased luciferase activity. Collectively, these results indicate that PTH acts through a protein kinase A pathway involving cAMP to stimulate BSP transcription by blocking the action of a Pit-1-related nuclear protein that suppresses BSP transcription by binding a cognate element in the BSP promoter. Thus, we have identified a novel Pit-1 suppressor element in the rat BSP gene promoter that is the target of PTH-stimulated transcription of the BSP gene.A protein present in nuclear extracts of ROS 17/2.8 cells, but not in fibroblast extracts, formed a sequence-specific protein-DNA complex with a ds-oligonucleotide probe encompassing the FRE, and was increased following FGF2 stimulation. Several point mutations within the critical FRE sequence abrogated the formation of this complex and suppressed promoter activity. These studies, therefore, have identified a novel FRE in the proximal promoter of the BSP gene that mediates both constitutive and FGF2-induced BSP transcription. Less