Phosphate Regulates Osteopontin Gene Transcription

• Published in: Journal of dental research Vol. 88; no. 1; pp. 39 - 44
• Main Authors: Fatherazi, S., Matsa-Dunn, D., Foster, B.L., Rutherford, R.B., Somerman, M.J., Presland, R.B.
• Format: Journal Article
• Language: English
• Published: London, England SAGE Publications 01.01.2009; SAGE PUBLICATIONS, INC
• Subjects: Animals; Base Pairing - genetics; Cells, Cultured; Cloning; Dental Cementum - metabolism; Deoxyribonucleic acid; Dexamethasone - pharmacology; DNA; Gene expression; Gene Expression Regulation, Bacterial - genetics; Glucocorticoids; Glucocorticoids - pharmacology; Glycoproteins; Hormone Antagonists - pharmacology; Mice; Mifepristone; Mifepristone - pharmacology; Mineralization; Mutation - genetics; Osteopontin; Osteopontin - genetics; Phosphates - pharmacology; Phosphorus - pharmacology; Promoter Regions, Genetic - drug effects; Promoter Regions, Genetic - genetics; Proteins; Receptors, Glucocorticoid - agonists; Receptors, Glucocorticoid - antagonists & inhibitors; Receptors, Glucocorticoid - genetics; Research Reports; Response Elements - genetics; Signal Transduction - genetics; Transcription; Transcription, Genetic - genetics; Transfection - methods; Up-Regulation - genetics; United States > US; gene transcription; BSP, bone sialoprotein; GRE, glucocorticoid response element; osteopontin; EMSA, Electrophoretic mobility shift assay; OPN, osteopontin; phosphate; ePi, extracellular inorganic phosphate; GR, glucocorticoid receptor; Pi, inorganic phosphate; DMP1, dentin matrix protein 1; Q-PCR, quantitative PCR
• ISSN: 0022-0345; 1544-0591
• DOI: 10.1177/0022034508328072

Extracellular inorganic phosphate (ePi) is a key regulator of cementoblast behavior, both in vivo and in vitro, and results in a marked increase in osteopontin expression in vitro. To examine the molecular mechanisms involved in ePi induction of osteopontin gene expression, we transfected a series of osteopontin promoter-luciferase constructs into OCCM-30 cementoblasts. Our results demonstrate that ePi can directly induce osteopontin gene transcription. The region responsive to ePi signaling was localized to a 53-bp region of the promoter between −1454 and −1401 that contains a glucocorticoid response element (GRE). Mutation of the GRE abolished the ePi response, suggesting that glucocorticoid receptor (GR) signaling is required for ePi-mediated transcription. In addition, treatment of cells with the GR antagonist RU-486 (Mifepristone) prevented promoter activation by ePi. The results presented support a model demonstrating that inorganic phosphate regulates OPN gene transcription in cementoblasts through a pathway that requires a functional GR.