MEPE has the properties of an osteoblastic phosphatonin and minhibin

Abstract

Matrix extracellular phosphoglycoprotein (MEPE) is expressed exclusively in osteoblasts, osteocytes and odontoblasts with markedly elevated expression found in X-linked hypophosphatemic rickets (Hyp) osteoblasts and in oncogenic hypophosphatemic osteomalacia (OHO) tumors. Because these syndromes are associated with abnormalities in mineralization and renal phosphate excretion, we examined the effects of insect-expressed full-length human-MEPE (Hu-MEPE) on serum and urinary phosphate in vivo, 33 PO 4 uptake in renal proximal tubule cultures and mineralization of osteoblast cultures. Dose-dependent hypophosphatemia and hyperphosphaturia occurred in mice following intraperitoneal (IP) administration of Hu-MEPE (up to 400 μg kg -1 31 h -1 ), similar to mice given the phosphaturic hormone PTH (80 μg kg -1 31 h -1 ). Also the fractional excretion of phosphate (FEP) was stimulated by MEPE [65.0% (P < 0.001)] and PTH groups [53.3% (P < 0.001)] relative to the vehicle group [28.7% (SEM 3.97)]. In addition, Hu-MEPE significantly inhibited 33 PO 4 uptake in primary human proximal tubule renal cells (RPTEC) and a human renal cell line (Hu-CL8) in vitro (V max 53.4% inhibition; K m 27.4 ng/ ml, and V max 9.1% inhibition; K m 23.8 ng/ml, respectively). Moreover, Hu-MEPE dose dependently (50-800 ng/ml) inhibited BMP2-mediated mineralization of a murine osteoblast cell line (2T3) in vitro. Inhibition of mineralization was localized to a small (2 kDa) cathepsin B released carboxy-terminal MEPE peptide (protease-resistant) containing the acidic serineaspartate-rich motif (ASARM peptide). We conclude that MEPE promotes renal phosphate excretion and modulates mineralization.

Molecular Regulation of Matrix Extracellular Phosphoglycoprotein Expression by Bone Morphogenetic Protein-2

“…Autosomal-dominant hypophosphatemic rickets is caused by a missense mutation of FGF23, which is resistant to proteolysis by PHEX and increases the half-life of full-length phosphaturic FGF23 (2). Second, X-linked hypophosphatemic rickets (Hyp, OMIM number 307800) is characterized by defective renal phosphate handling, aberrant vitamin D metabolism, and defective calcification of bone (3). X-linked hypophosphatemic is caused by an inactivating mutation in PHEX that increases the uncleaved full-length FGF23 and/or abnormal processing of MEPE.…”

MEPE/OF45 as a new target for sensitizing human tumour cells to DNA damage inducers

“…These cell lines were grown in DMEM medium supplemented with 10% calf serum. The antibody against hMEPE/OF45 was as described (Rowe et al, 2000(Rowe et al, , 2004. Purified HA-tagged JNK2 protein (sc-4062) and antibodies against CHK1 (sc-8408 and sc-7898), HA (sc-805, sc-7392), PCNA (sc-56), a-Tubulin (sc-8035), Cul4 (sc-10782) and ubquitin (Ub) (sc-9133) were purchased from Santa Cruz Biotechnology Inc (Santa Cruz, CA, USA).…”

“…The signals of human MEPE/OF45 showed two bands ( Figure 1A), which might be due to alternatively Whole-cell lyses were prepared. The antibody against hMEPE/OF45 was as described (Rowe et al, 2000(Rowe et al, , 2004. Data shown are the images of western blot analysis.…”

Mycobacterium leprae downregulates the expression of PHEX in Schwann cells and osteoblasts

“…The Zn-metalloendopeptidase phosphate-regulating gene with homologies to endopeptidase on the X chromosome (PHEX) is a key regulatory protein in hydroxyapatite formation and bone mineralization (Rowe et al 2004). The PHEX gene encodes a 749 amino acid protein, which is a member of the M13 family of type II zinc-dependent proteases that is expressed ubiquitously in all vertebrate tissues (Turner & Tanzawa 1997, KiryuSeo & Kiyama 2004.…”

“…The secretion of cathepsin B proteases by osteoblasts is markedly stimulated by parathyroid hormone, a bone-resorbing hormone (Aisa et al 1996), which is known to be elevated in leprosy patients (Ishikawa et al 2001, Ribeiro et al 2007. MEPE proteolysis generates the protease-resistant acidic serine aspartate rich MEPE associated motif (ASARM) peptide, which directly inwhich directly inhibits calcium oxalate crystallization and crystal growth on the extracellular matrix (Hoyer et al 2001) and promotes inhibition of the renal NPT2 phosphate co-trans- Mycobacterium leprae downregulates the expression of PHEX in Schwann cells and osteoblasts porter, affecting renal phosphate handling (Rowe et al 2004). The MEPE-derived ASARM peptide must be phosphorylated to play its role as a PHEX substrate (Addison et al 2008).…”