MEPE-ASARM Peptides Control Extracellular Matrix Mineralization by Binding to Hydroxyapatite: An Inhibition Regulated by PHEX Cleavage of ASARM
- 1 October 2008
- journal article
- Published by Oxford University Press (OUP) in Journal of Bone and Mineral Research
- Vol. 23 (10), 1638-1649
- https://doi.org/10.1359/jbmr.080601
Abstract
Hyp mice having an inactivating mutation of the phosphate-regulating gene with homologies to endopeptidases on the X-chromosome (Phex) gene have bones with increased matrix extracellular phosphoglycoprotein (MEPE). An acidic, serine- and aspartic acid-rich motif (ASARM) is located in the C terminus of MEPE and other mineralized tissue matrix proteins. We studied the effects of ASARM peptides on mineralization and how PHEX and MEPE interactions contribute to X-linked hypophosphatemia (XLH). ASARM immunoreactivity was observed in the osteoid of wildtype bone and in the increased osteoid of Hyp mice. In wildtype bone, PHEX immunostaining was found particularly in osteoid osteocytes and their surrounding matrix. Treatment of MC3T3-E1 osteoblasts with triphosphorylated (3 phosphoserines) ASARM peptide (pASARM) caused a dose-dependent inhibition of mineralization. pASARM did not affect collagen deposition or osteoblast differentiation, suggesting that pASARM inhibits mineralization by direct binding to hydroxyapatite crystals. Binding of pASARM to mineralization foci in pASARM-treated cultures and to synthetic hydroxyapatite crystals was confirmed by colloidal-gold immunolabeling. Nonphosphorylated ASARM peptide showed little or no binding to hydroxyapatite and did not inhibit mineralization, showing the importance of ASARM phosphorylation in regulating mineralization. PHEX rescued the inhibition of osteoblast culture mineralization by pASARM, and mass spectrometry of cleaved peptides obtained after pASARM-PHEX incubations identified pASARM as a substrate for PHEX. These results, showing that pASARM inhibits mineralization by binding to hydroxyapatite and that this inhibitor can be cleaved by PHEX, provide a mechanism explaining how loss of PHEX activity can lead to extracellular matrix accumulation of ASARM resulting in the osteomalacia of XLH.Keywords
This publication has 52 references indexed in Scilit:
- Phosphorylated acidic serine–aspartate-rich MEPE-associated motif peptide from matrix extracellular phosphoglycoprotein inhibits phosphate regulating gene with homologies to endopeptidases on the X-chromosome enzyme activityJournal of Endocrinology, 2007
- Correction of the mineralization defect in hyp mice treated with protease inhibitors CA074 and pepstatinBone, 2006
- MEPE has the properties of an osteoblastic phosphatonin and minhibinBone, 2004
- Regulation of Fibroblastic Growth Factor 23 Expression but Not Degradation by PHEXPublished by Elsevier BV ,2003
- Human recombinant endopeptidase PHEX has a strict S1' specificity for acidic residues and cleaves peptides derived from fibroblast growth factor-23 and matrix extracellular phosphoglycoproteinBiochemical Journal, 2003
- Biomineralization: An OverviewConnective Tissue Research, 2003
- MEPE, the Gene Encoding a Tumor-Secreted Protein in Oncogenic Hypophosphatemic Osteomalacia, Is Expressed in BoneGenomics, 2001
- Developmental Expression and Tissue Distribution of Phex Protein: Effect of the Hyp Mutation and Relationship to Bone MarkersJournal of Bone and Mineral Research, 2000
- Structure of human neutral endopeptidase (neprilysin) complexed with phosphoramidon 1 1Edited by R. HuberJournal of Molecular Biology, 2000
- Ultrastructural immunolocalization of noncollagenous (osteopontin and osteocalcin) and plasma (albumin and α2HS-glycoprotein) proteins in rat boneJournal of Bone and Mineral Research, 1993