title: Regulation of osterix (Osx, Sp7) and the Osx promoter by parathyroid hormone in osteoblasts.
abstract: Parathyroid hormone (PTH) binds to its receptor on osteoblasts to regulate gene transcription primarily through the elevation of the second messenger cAMP. A number of genes regulated by PTH in osteoblasts contain GC-rich and Sp-binding sites. Osterix (Osx, Sp7) is a transcription factor required for the differentiation of osteoblasts that can bind to Sp-binding sites on gene promoters and regulate their expression. Here, we report the effect of PTH (1-34) on Osx expression in osteoblastic UMR-106-01 cells and murine calvaria. PTH (1-34) and PTH (1-31) inhibited Osx mRNA and protein expression, and this effect could be mimicked by forskolin, 8-bromo-cAMP, or expression of constitutively active Gsalpha (caGsalpha). Treatment of the cells with PTH (3-34) or the EPAC-selective agonist 8CPT-2Me-cAMP had no effect on Osx mRNA, whereas PTH (7-34) or expression of caGqalpha-stimulated Osx mRNA levels. PTH (1-34) treatment did not require new protein synthesis and did not involve changes in Osx mRNA stability. Osx promoter fragments coupled to a luciferase reporter were inhibited by PTH (1-34) treatment in a similar manner to the inhibition of Osx mRNA and protein. Deletion analysis localized PTH inhibition to two regions flanking the Osx1 start site; -304/-119 and -71/+91. These results demonstrate that prolonged exposure to PTH inhibits Osx expression in osteoblasts through sites on its proximal promoter and this suppression occurs through PTH stimulation of cellular cAMP.
authors.affiliation: Department of Pharmacology and Toxicology, University of Toronto, 1 King's College Circle, Room 4342, Ontario, Canada.
authors.forename: Shara H H
authors.initials: SH
authors.lastname: Hong
authors.forename: Xianghuai
authors.initials: X
authors.lastname: Lu
authors.forename: Mark S
authors.initials: MS
authors.lastname: Nanes
authors.forename: Jane
authors.initials: J
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics*; D051381:Rats; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D010281:Parathyroid Hormone; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; C495181:Sp7 protein, rat; D014157:Transcription Factors