PHEX
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Phosphate-regulating endopeptidase homolog X-linked also known as phosphate-regulating gene with homologies to endopeptidases on the X chromosome or metalloendopeptidase homolog PEX is an enzyme that in humans is encoded by the PHEX gene.[5][6] This gene contains 18 exons and is located on the X chromosome.
Function
[edit]The protein encoded by this gene is a transmembrane endopeptidase that belongs to the type II integral membrane zinc-dependent endopeptidase family. The protein is thought to be involved in bone and dentin mineralization and renal phosphate reabsorption.[7] The bone and dentin protein osteopontin (OPN) which inhibits mineralization in the skeleton and in teeth is a substrate for PHEX.[8] In the absence of functional PHEX in the mouse model (Hyp) of X-linked hypophosphatemia (XLH), and in human XLH where PHEX activity is decreased or absent, increased circulating FGF23 hormone results in low serum phosphate (caused by renal phosphate wasting) such that there is an insufficient level of this mineral ion in the blood in transit to mineralized tissues compared to the normal amount that is required for proper bone and tooth mineralization; this leads to soft bones and teeth.
In addition to renal phosphate wasting, the mineralization-inhibiting phosphoprotein osteopontin and osteopontin fragments accumulate in the extracellular matrix of bones and teeth to contribute locally to the reduction in mineralization, which together with the systemic lower level of circulating serum phosphate, both lead to the decreased mineralization (hypomineralization) characteristic of the osteomalacia and odontomalacia typically seen in XLH/Hyp.[9][10][11][12][13] XLH patients have soft and deformed skeletons, and soft teeth that easily become infected. Osteopontin (OPN) is a substrate protein for the enzyme PHEX whose enzymatic activity degrades/removes the mineralization-inhibiting function of OPN in normal mineralized tissue physiology,[14]
In disease, when the PHEX gene is mutated causing reduced or absent PHEX enzymatic activity, OPN that would normally be degraded and cleared remains behind in the extracellular matrix of bones and teeth, accumulating locally in the tissue to contribute to the osteomalacia and odontomalacia.[15][16] A relationship describing local, physiologic double-negative (inhibiting inhibitors) regulation of mineralization involving OPN has been termed the Stenciling Principle of mineralization, whereby enzyme-substrate pairs imprint mineralization patterns into the extracellular matrix (most notably for bone) by degrading mineralization inhibitors (e.g. TNAP/TNSALP/ALPL enzyme degrading the pyrophosphate inhibition, and PHEX enzyme degrading the osteopontin inhibition).[17][18][19] The Stenciling Principle for mineralization is particularly relevant to the osteomalacia and odontomalacia observed in hypophosphatasia and X-linked hypophosphatemia.[20]
Clinical significance
[edit]Mutation of PHEX leads to X-linked hypophosphatemia.[5]
References
[edit]- ^ a b c GRCh38: Ensembl release 89: ENSG00000102174 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000057457 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ a b Francis F, Hennig S, Korn B, Reinhardt R, De Jong P, Poustka A, et al. (October 1995). "A gene (PEX) with homologies to endopeptidases is mutated in patients with X-linked hypophosphatemic rickets. The HYP Consortium". Nature Genetics. 11 (2): 130–136. doi:10.1038/ng1095-130. PMID 7550339. S2CID 6424732.
- ^ Grieff M, Mumm S, Waeltz P, Mazzarella R, Whyte MP, Thakker RV, Schlessinger D (February 1997). "Expression and cloning of the human X-linked hypophosphatemia gene cDNA". Biochemical and Biophysical Research Communications. 231 (3): 635–639. doi:10.1006/bbrc.1997.6153. PMID 9070861.
- ^ "Entrez Gene: phosphate regulating endopeptidase homolog".
- ^ Barros NM, Hoac B, Neves RL, Addison WN, Assis DM, Murshed M, et al. (March 2013). "Proteolytic processing of osteopontin by PHEX and accumulation of osteopontin fragments in Hyp mouse bone, the murine model of X-linked hypophosphatemia". Journal of Bone and Mineral Research. 28 (3): 688–699. doi:10.1002/jbmr.1766. PMID 22991293.
- ^ Boukpessi T, Gaucher C, Léger T, Salmon B, Le Faouder J, Willig C, et al. (August 2010). "Abnormal presence of the matrix extracellular phosphoglycoprotein-derived acidic serine- and aspartate-rich motif peptide in human hypophosphatemic dentin". The American Journal of Pathology. 177 (2): 803–812. doi:10.2353/ajpath.2010.091231. PMC 2913338. PMID 20581062.
- ^ Boukpessi T, Hoac B, Coyac BR, Leger T, Garcia C, Wicart P, et al. (February 2017). "Osteopontin and the dento-osseous pathobiology of X-linked hypophosphatemia". Bone. 95: 151–161. doi:10.1016/j.bone.2016.11.019. PMID 27884786.
- ^ Barros NM, Hoac B, Neves RL, Addison WN, Assis DM, Murshed M, et al. (March 2013). "Proteolytic processing of osteopontin by PHEX and accumulation of osteopontin fragments in Hyp mouse bone, the murine model of X-linked hypophosphatemia". Journal of Bone and Mineral Research. 28 (3): 688–699. doi:10.1002/jbmr.1766. PMID 22991293.
- ^ McKee MD, Hoac B, Addison WN, Barros NM, Millán JL, Chaussain C (October 2013). "Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia". Periodontology 2000. 63 (1): 102–122. doi:10.1111/prd.12029. PMC 3766584. PMID 23931057.
- ^ Salmon B, Bardet C, Coyac BR, Baroukh B, Naji J, Rowe PS, et al. (August 2014). "Abnormal osteopontin and matrix extracellular phosphoglycoprotein localization, and odontoblast differentiation, in X-linked hypophosphatemic teeth". Connective Tissue Research. 55 (Suppl 1): 79–82. doi:10.3109/03008207.2014.923864. PMID 25158186. S2CID 19702315.
- ^ Barros NM, Hoac B, Neves RL, Addison WN, Assis DM, Murshed M, et al. (March 2013). "Proteolytic processing of osteopontin by PHEX and accumulation of osteopontin fragments in Hyp mouse bone, the murine model of X-linked hypophosphatemia". Journal of Bone and Mineral Research. 28 (3): 688–699. doi:10.1002/jbmr.1766. PMID 22991293. S2CID 20840491.
- ^ Boukpessi T, Hoac B, Coyac BR, Leger T, Garcia C, Wicart P, et al. (February 2017). "Osteopontin and the dento-osseous pathobiology of X-linked hypophosphatemia". Bone. 95: 151–161. doi:10.1016/j.bone.2016.11.019. PMID 27884786.
- ^ Barros NM, Hoac B, Neves RL, Addison WN, Assis DM, Murshed M, et al. (March 2013). "Proteolytic processing of osteopontin by PHEX and accumulation of osteopontin fragments in Hyp mouse bone, the murine model of X-linked hypophosphatemia". Journal of Bone and Mineral Research. 28 (3): 688–699. doi:10.1002/jbmr.1766. PMID 22991293. S2CID 20840491.
- ^ McKee MD, Buss DJ, Reznikov N (December 2021). "Mineral tessellation in bone and the stenciling principle for extracellular matrix mineralization". Journal of Structural Biology. 214 (1): 107823. doi:10.1016/j.jsb.2021.107823. PMID 34915130. S2CID 245187449.
- ^ Buss DJ, Reznikov N, McKee MD (November 2020). "Crossfibrillar mineral tessellation in normal and Hyp mouse bone as revealed by 3D FIB-SEM microscopy". Journal of Structural Biology. 212 (2): 107603. doi:10.1016/j.jsb.2020.107603. PMID 32805412. S2CID 221164596.
- ^ Reznikov N, Hoac B, Buss DJ, Addison WN, Barros NM, McKee MD (September 2020). "Biological stenciling of mineralization in the skeleton: Local enzymatic removal of inhibitors in the extracellular matrix". Bone. 138: 115447. doi:10.1016/j.bone.2020.115447. PMID 32454257. S2CID 218909350.
- ^ McKee MD, Buss DJ, Reznikov N (December 2021). "Mineral tessellation in bone and the stenciling principle for extracellular matrix mineralization". Journal of Structural Biology. 214 (1): 107823. doi:10.1016/j.jsb.2021.107823. PMID 34915130. S2CID 245187449.
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