title: PTHrP(1-34)-mediated repression of the PHEX gene in osteoblastic cells involves the transcriptional repressor E4BP4.
abstract: PHosphate-regulating gene with homology to Endopeptidase on the X chromosome (PHEX) has been identified as the gene mutated in X-linked hypophosphatemia (XLH) syndrome, the most prevalent form of rickets in humans. The predominant expression of PHEX in bones and teeth, and the defective mineralization of these tissues in XLH patients indicate that PHEX is an important regulator of mineralization. Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are known to regulate the expression of numerous genes in osteoblastic cells through activation of the protein kinase A pathway, including repression of PHEX. PTH also activates the transcriptional repressor E4BP4 through the same pathway, suggesting that PTH or PTHrP-mediated repression of PHEX expression could involve E4BP4. To evaluate this possibility, we treated UMR-106 osteoblastic cells with PTHrP(1-34), and used RT-PCR and immunoblotting to analyze PHEX and E4BP4 expression. E4BP4 mRNA and protein levels were rapidly increased in cells treated with PTHrP(1-34), with a concomitant decrease in PHEX expression. This downregulation of PHEX could be reproduced by overexpression of E4BP4. Moreover, PTHrP(1-34)-mediated PHEX repression was blocked when cells were transfected with a siRNA targeting E4BP4 mRNA. Finally, DNA pull-down and luciferase assays showed that two E4BP4 response elements located in PHEX promoter were functional. These results underline the important role of E4BP4 in osteoblastic cells and further define the repression mechanism of PHEX gene by PTHrP(1-34).
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Université de Montréal, Montréal, Québec, Canada.
authors.forename: Martin
authors.initials: M
authors.lastname: Pellicelli
authors.forename: Maryam
authors.initials: M
authors.lastname: Taheri
authors.forename: Mathieu
authors.initials: M
authors.lastname: St-Louis
authors.forename: Véronique
authors.initials: V
authors.lastname: Bériault
authors.forename: Luc
authors.initials: L
authors.lastname: Desgroseillers
authors.forename: Guy
authors.initials: G
authors.lastname: Boileau
authors.forename: Alain
authors.initials: A
authors.lastname: Moreau
mesh_terms: D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D015153:Blotting, Western; D015536:Down-Regulation; D017930:Genes, Reporter; D047468:Immunoprecipitation; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D053402:PHEX Phosphate Regulating Neutral Endopeptidase / Q000235:genetics / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D060888:Real-Time Polymerase Chain Reaction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; C497441:Nfil3 protein, mouse; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D012333:RNA, Messenger; C054296:parathyroid hormone-related protein (1-34); D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506231:PHEX protein, human; D013755:Tetradecanoylphorbol Acetate