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Farman MR, Rehder C, Malli T, Rockman-Greenberg C, Dahir K, Martos-Moreno GÁ, Linglart A, Ozono K, Seefried L, Del Angel G, Webersinke G, Barbazza F, John LK, Delana Mudiyanselage SMA, Högler F, Nading EB, Huggins E, Rush ET, El-Gazzar A, Kishnani PS, Högler W. The Global ALPL gene variant classification project: Dedicated to deciphering variants. Bone 2024; 178:116947. [PMID: 37898381 DOI: 10.1016/j.bone.2023.116947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2023] [Revised: 10/15/2023] [Accepted: 10/17/2023] [Indexed: 10/30/2023]
Abstract
BACKGROUND Hypophosphatasia (HPP) is an inherited multisystem disorder predominantly affecting the mineralization of bones and teeth. HPP is caused by pathogenic variants in ALPL, which encodes tissue non-specific alkaline phosphatase (TNSALP). Variants of uncertain significance (VUS) cause diagnostic delay and uncertainty amongst patients and health care providers. RESULTS The ALPL gene variant database (https://alplmutationdatabase.jku.at/) is an open-access archive for interpretation of the clinical significance of variants reported in ALPL. The database contains coding and non-coding variants, including single nucleotide variants, insertions/deletions and structural variants affecting coding or non-coding sequences of ALPL. Each variant in the database is displayed with details explaining the corresponding pathogenicity, and all reported genotypes and phenotypes, including references. In 2021, the ALPL gene variant classification project was established to reclassify VUS and continuously assess and update genetic, phenotypic, and functional variant information in the database. For this purpose, the database provides a unique submission system for clinicians, geneticists, genetic counselors, and researchers to submit VUS within ALPL for classification. An international, multidisciplinary consortium of HPP experts has been established to reclassify the submitted VUS using a multi-step process adhering to the stringent ACMG/AMP variant classification guidelines. These steps include a clinical phenotype assessment, deep literature research including artificial intelligence technology, molecular genetic assessment, and in-vitro functional testing of variants in a co-transfection model to measure ALP residual activity. CONCLUSION This classification project and the ALPL gene variant database will serve the global medical community, widen the genotypic and phenotypic HPP spectrum by reporting and characterizing new ALPL variants based on ACMG/AMP criteria and thus facilitate improved genetic counseling and medical decision-making for affected patients and families. The project may also serve as a gold standard framework for multidisciplinary collaboration for variant interpretation in other rare diseases.
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Affiliation(s)
- Mariam R Farman
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
| | - Catherine Rehder
- Duke University Medical Center, Department of Pathology, Durham, USA
| | - Theodora Malli
- Laboratory for Molecular Genetic Diagnostics, Ordensklinikum Linz, Linz, Austria
| | - Cheryl Rockman-Greenberg
- Department of Pediatrics and Child Health Max Rady College of Medicine, Rady Faculty of Health Sciences, Winnipeg, Canada
| | - Kathryn Dahir
- Vanderbilt University Medical Center, Program for Metabolic Bone Disorders, Nashville, TN, USA
| | - Gabriel Ángel Martos-Moreno
- Departments of Pediatrics & Pediatric Endocrinology, Hospital Infantil Universitario Niño Jesús, Madrid, Spain
- Department of Pediatrics, Universidad Autónoma de Madrid, Madrid, Spain
- CIBER Fisiopatología de la Obesidad y Nutrición, ISCIII, Madrid, Spain
| | - Agnès Linglart
- AP-HP, Paris Saclay University, INSERM, Bicêtre Paris Saclay hospital, Le Kremlin-Bicêtre, France
| | - Keiichi Ozono
- Department of Pediatrics, Osaka University Graduate School of Medicine, Osaka, Japan
| | | | | | - Gerald Webersinke
- Laboratory for Molecular Genetic Diagnostics, Ordensklinikum Linz, Linz, Austria
| | - Francesca Barbazza
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
| | - Lisa K John
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
| | | | - Florian Högler
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
| | - Erica Burner Nading
- Duke University Medical Center, Division of Medical Genetics, Department of Pediatrics, Durham, USA
| | - Erin Huggins
- Duke University Medical Center, Division of Medical Genetics, Department of Pediatrics, Durham, USA
| | - Eric T Rush
- Division of Clinical Genetics, Children's Mercy Hospital Kansas City, Kansas City, MO, USA
- Department of Internal Medicine, University of Kansas School of Medicine, Kansas City, KS, USA
- Department of Pediatrics, University of Missouri – Kansas City School of Medicine, Kansas City, MO, USA
| | - Ahmed El-Gazzar
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
| | - Priya S Kishnani
- Duke University Medical Center, Division of Medical Genetics, Department of Pediatrics, Durham, USA
| | - Wolfgang Högler
- Department of Paediatrics and Adolescent Medicine, Johannes Kepler University Linz, Linz, Austria
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Molecular and cellular basis of hypophosphatasia. J Oral Biosci 2019; 61:141-148. [PMID: 31400546 DOI: 10.1016/j.job.2019.07.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 07/10/2019] [Accepted: 07/11/2019] [Indexed: 01/09/2023]
Abstract
BACKGROUND Hypophosphatasia (HPP) is an inherited disorder characterized by defective mineralization of the bone and teeth that is also associated with a deficiency of serum alkaline phosphatase (ALP). Patients with HPP exhibit a broad range of symptoms including stillbirth with an unmineralized skeleton, premature exfoliation and dental caries in childhood, and pseudo-fractures in adulthood. The broad clinical spectrum of HPP is attributed to various mutations in the ALPL gene, which encodes tissue-nonspecific alkaline phosphatase (TNSALP). Nevertheless, the molecular mechanisms underlying the genotypic and phenotypic relationship of HPP remain unclear. HIGHLIGHT The expression of HPP-related TNSALP mutants in mammalian cells allows us to determine for the effects of mutations on the properties of TNSALP, which could contribute to a better understanding of the relationship between structure and function of TNSALP. CONCLUSION Molecular characterization of TNSALP mutants helps establish the etiology and onset of HPP.
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Abstract
Hypophosphatasia (HPP) is due to deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNAP). This enzyme cleaves extracellular substrates inorganic pyrophosphates (PPi), pyridoxal-5'-phosphate (PLP), phosphoethanolamine (PEA) and nucleotides, and probably other substrates not yet identified. During the last 15 years the role of TNAP in mineralization, and to a less degree in brain, has been investigated, providing hypotheses and explanations for both bone and neuronal HPP phenotypes. ALPL, the gene encoding TNAP, is subject to many mutations, mostly missense mutations. A few number of mutations are recurrently found and may be quite frequent in particular populations. This reflects founder effects. The great variety of mutations results in a great number of compound heterozygous genotypes and in highly variable clinical expressivity. A good correlation was observed between the severity of the disease and in vitro enzymatic activity of the mutant protein measured after site-directed mutagenesis. Many missense mutations found in severe hypophosphatasia produced a mutant protein that failed to reach the cell membrane , was accumulated in the cis-Golgi and was subsequently degraded in the proteasome. Missense mutations located in the catalytic site or in the homodimer interface were often shown by site-directed mutagenesis to have a dominant negative effect. Currently molecular diagnosis of HPP is based on the sequencing of the coding sequence of ALPL that allows detection of approximately 95 % of mutations in severe cases. In addition, other genes, especially genes encoding proteins involved in the regulation of extracellular PPi concentration, could modify the phenotype (modifier genes).
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Martins L, Rodrigues TL, Ribeiro MM, Saito MT, Giorgetti APO, Casati MZ, Sallum EA, Foster BL, Somerman MJ, Nociti FH. Novel ALPL genetic alteration associated with an odontohypophosphatasia phenotype. Bone 2013; 56:390-7. [PMID: 23791648 PMCID: PMC3872001 DOI: 10.1016/j.bone.2013.06.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 05/29/2013] [Accepted: 06/13/2013] [Indexed: 01/12/2023]
Abstract
Hypophosphatasia (HPP) is an inherited disorder of mineral metabolism caused by mutations in ALPL, encoding tissue non-specific alkaline phosphatase (TNAP). Here, we report the molecular findings from monozygotic twins, clinically diagnosed with tooth-specific odontohypophosphatasia (odonto-HPP). Sequencing of ALPL identified two genetic alterations in the probands, including a heterozygous missense mutation c.454C>T, leading to change of arginine 152 to cysteine (p.R152C), and a novel heterozygous gene deletion c.1318_1320delAAC, leading to the loss of an asparagine residue at codon 440 (p.N440del). Clinical identification of low serum TNAP activity, dental abnormalities, and pedigree data strongly suggests a genotype-phenotype correlation between p.N440del and odonto-HPP in this family. Computational analysis of the p.N440del protein structure revealed an alteration in the tertiary structure affecting the collagen-binding site (loop 422-452), which could potentially impair the mineralization process. Nevertheless, the probands (compound heterozygous: p.[N440del];[R152C]) feature early-onset and severe odonto-HPP phenotype, whereas the father (p.[N440del];[=]) has only moderate symptoms, suggesting p.R152C may contribute or predispose to a more severe dental phenotype in combination with the deletion. These results assist in defining the genotype-phenotype associations for odonto-HPP, and further identify the collagen-binding site as a region of potential structural importance for TNAP function in the biomineralization.
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Affiliation(s)
- Luciane Martins
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Thaisângela L. Rodrigues
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Mariana Martins Ribeiro
- Department of Morphology, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Miki Taketomi Saito
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Ana Paula Oliveira Giorgetti
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Márcio Z Casati
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Enilson A Sallum
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
| | - Brian L. Foster
- National Institute of Arthritis, Musculoskeletal and Skin Disease (NIAMS), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Martha J. Somerman
- National Institute of Arthritis, Musculoskeletal and Skin Disease (NIAMS), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Francisco H. Nociti
- Department of Prosthodontics and Periodontics, Division of Periodontics, Piracicaba Dental School, University of Campinas - UNICAMP, Piracicaba, SP, Brazil
- National Institute of Arthritis, Musculoskeletal and Skin Disease (NIAMS), National Institutes of Health (NIH), Bethesda, MD, USA
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Hofmann C, Liese J, Schwarz T, Kunzmann S, Wirbelauer J, Nowak J, Hamann J, Girschick H, Graser S, Dietz K, Zeck S, Jakob F, Mentrup B. Compound heterozygosity of two functional null mutations in the ALPL gene associated with deleterious neurological outcome in an infant with hypophosphatasia. Bone 2013; 55:150-7. [PMID: 23454488 DOI: 10.1016/j.bone.2013.02.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Revised: 02/20/2013] [Accepted: 02/21/2013] [Indexed: 10/27/2022]
Abstract
Hypophosphatasia (HPP) is a heterogeneous rare, inherited disorder of bone and mineral metabolism caused by different mutations in the ALPL gene encoding the isoenzyme, tissue-nonspecific alkaline phosphatase (TNAP). Prognosis is very poor in severe perinatal forms with most patients dying from pulmonary complications of their skeletal disease. TNAP deficiency, however, may also result in neurological symptoms such as neonatal seizures. The exact biological role of TNAP in the human brain is still not known and the pathophysiology of neurological symptoms due to TNAP deficiency in HPP is not understood in detail. In this report, we describe the clinical features and functional studies of a patient with severe perinatal HPP which presented with rapidly progressive encephalopathy caused by new compound heterozygous mutations in the ALPL gene which result in a functional ALPL "knock out", demonstrated in vitro. In contrast, an in vitro simulation of the genetic status of his currently asymptomatic parents who are both heterozygous for one mutation, showed a residual in vitro AP activity of above 50%. Interestingly, in our patient, the fatal outcome was due to progressive encephalopathy which was refractory to antiepileptic therapy including pyridoxine, rather than hypomineralization and respiratory insufficiency often seen in HPP patients. The patient's cranial MRI showed progressive cystic degradation of the cortex and peripheral white matter with nearly complete destruction of the cerebrum. To our knowledge, this is the first MRI-based report of a deleterious neurological clinical outcome due to a progressive encephalopathy in an infant harboring a functional human ALPL "knock out". This clinical course of disease suggests that TNAP is involved in development and may be responsible for multiple functions of the human brain. According to our data, a certain amount of residual TNAP activity might be mandatory for normal CNS function in newborns and early childhood.
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Affiliation(s)
- C Hofmann
- Children's Hospital, University of Würzburg, Würzburg, Germany.
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Mentrup B, Marschall C, Barvencik F, Amling M, Plendl H, Jakob F, Beck C. Functional characterization of a novel mutation localized in the start codon of the tissue-nonspecific alkaline phosphatase gene. Bone 2011; 48:1401-8. [PMID: 21419245 DOI: 10.1016/j.bone.2011.03.676] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 03/04/2011] [Accepted: 03/08/2011] [Indexed: 11/16/2022]
Abstract
Hypophosphatasia (HPP) is a rare inborn disease caused by different mutations in the tissue-nonspecific alkaline phosphatase (ALPL) gene. Previous studies showed that gene mutations could exhibit a dominant negative effect leading to a mild HPP phenotype in heterozygous carriers. In the present report we describe the clinical and functional studies of a novel mutation localized in the start codon of transcript variant 1 of the ALPL gene from a female adult heterozygous carrier. The mutation results in translation of an N-terminally truncated protein, which might be identical to the deduced protein from ALPL transcript variant 2. When overexpressed in HEK-293 cells it does not exhibit any enzymatic activity and has no significant effect on the wild type ALPL protein. Furthermore it is not attached to the cell membrane. Due to the loss of the signal peptide an intracellular misrouting and a premature degradation is obvious. Hence the new isoform deposited in the database does not produce an active protein as it is the case in the natural mutation of our patient. Since the mutation does not produce a dominant negative protein in heterozygous carriers, the clinical phenotype in our patient and her relatives is very mild with only unspecific myalgia. However the patient developed bone marrow edema of both femoral heads during lactation after delivery of a healthy child, indicating a risk to develop alterations of bone metabolism in challenge situations. Her sister complains of identical symptoms, her father shows distinct symptoms of odonto-hypophosphatasia. The question if or if not carriers of ALPL mutations in general or only with distinct genotypes can be symptomatic in normal life or in challenge situations requires systematic clinical studies.
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Affiliation(s)
- B Mentrup
- Orthopedic Center for Musculoskeletal Research, Orthopedic Department, University of Würzburg, Wuerzburg, Germany.
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Mornet E, Yvard A, Taillandier A, Fauvert D, Simon-Bouy B. A Molecular-Based Estimation of the Prevalence of Hypophosphatasia in the European Population. Ann Hum Genet 2011; 75:439-45. [DOI: 10.1111/j.1469-1809.2011.00642.x] [Citation(s) in RCA: 145] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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9
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Fukunaka A, Kurokawa Y, Teranishi F, Sekler I, Oda K, Ackland ML, Faundez V, Hiromura M, Masuda S, Nagao M, Enomoto S, Kambe T. Tissue nonspecific alkaline phosphatase is activated via a two-step mechanism by zinc transport complexes in the early secretory pathway. J Biol Chem 2011; 286:16363-73. [PMID: 21402707 DOI: 10.1074/jbc.m111.227173] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
A number of enzymes become functional by binding to zinc during their journey through the early secretory pathway. The zinc transporters (ZnTs) located there play important roles in this step. We have previously shown that two zinc transport complexes, ZnT5/ZnT6 heterodimers and ZnT7 homo-oligomers, are required for the activation of alkaline phosphatases, by converting them from the apo- to the holo-form. Here, we investigated the molecular mechanisms of this activation. ZnT1 and ZnT4 expressed in chicken DT40 cells did not contribute to the activation of tissue nonspecific alkaline phosphatase (TNAP). The reduced activity of TNAP in DT40 cells deficient in both ZnT complexes was not restored by zinc supplementation nor by exogenous expression of other ZnTs that increase the zinc content in the secretory pathway. Moreover, we showed that expression of ZnT5/ZnT6 heterodimers reconstituted with zinc transport-incompetent ZnT5 mutant failed to restore TNAP activity but could stabilize the TNAP protein as the apo-form, regardless of zinc status. These findings demonstrate that TNAP is activated not simply by passive zinc binding but by an elaborate two-step mechanism via protein stabilization followed by enzyme conversion from the apo- to the holo-form with zinc loaded by ZnT complexes in the early secretory pathway.
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Affiliation(s)
- Ayako Fukunaka
- Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto, Japan
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Fauvert D, Brun-Heath I, Lia-Baldini AS, Bellazi L, Taillandier A, Serre JL, de Mazancourt P, Mornet E. Mild forms of hypophosphatasia mostly result from dominant negative effect of severe alleles or from compound heterozygosity for severe and moderate alleles. BMC MEDICAL GENETICS 2009; 10:51. [PMID: 19500388 PMCID: PMC2702372 DOI: 10.1186/1471-2350-10-51] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/26/2008] [Accepted: 06/06/2009] [Indexed: 11/24/2022]
Abstract
Background Mild hypophosphatasia (HPP) phenotype may result from ALPL gene mutations exhibiting residual alkaline phosphatase activity or from severe heterozygous mutations exhibiting a dominant negative effect. In order to determine the cause of our failure to detect a second mutation by sequencing in patients with mild HPP and carrying on a single heterozygous mutation, we tested the possible dominant effect of 35 mutations carried by these patients. Methods We tested the mutations by site-directed mutagenesis. We also genotyped 8 exonic and intronic ALPL gene polymorphisms in the patients and in a control group in order to detect the possible existence of a recurrent intronic mild mutation. Results We found that most of the tested mutations exhibit a dominant negative effect that may account for the mild HPP phenotype, and that for at least some of the patients, a second mutation in linkage disequilibrium with a particular haplotype could not be ruled out. Conclusion Mild HPP results in part from compound heterozygosity for severe and moderate mutations, but also in a large part from heterozygous mutations with a dominant negative effect.
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Affiliation(s)
- Delphine Fauvert
- Unité de Pathologie Cellulaire et Génétique EA2493, Université de Versailles-Saint Quentin en Yvelines, 78035 Versailles, France.
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Sogabe N, Oda K, Nakamura H, Orimo H, Watanabe H, Hosoi T, Goseki-Sone M. Molecular effects of the tissue-nonspecific alkaline phosphatase gene polymorphism (787T > C) associated with bone mineral density. ACTA ACUST UNITED AC 2008; 29:213-9. [PMID: 18724009 DOI: 10.2220/biomedres.29.213] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Based on studies of hypophosphatasia, which is a systemic skeletal disorder resulting from tissuenonspecific alkaline phosphatase (TNSALP) deficiency, TNSALP was suggested to be indispensable for bone mineralization. Recently, we demonstrated that there was a significant difference in bone mineral density (BMD) among haplotypes, which was lowest among TNSALP (787T [Tyr-246Tyr]) homozygotes, highest among TNSALP (787T > C [Tyr246His]) homozygotes, and intermediate among heterozygotes. To analyze protein translated from the TNSALP gene 787T > C, we performed the biosynthesis of TNSALPs using TNSALP cDNA expression vectors. TNSALP (787T) and TNSALP (787T > C) were synthesized similarly as a high-mannose-type 66-kDa form, becoming an 80-kDa form. Expression of the human 787T > C TNSALP gene using the cultured mouse marrow stromal cell line ST2 demonstrated that the protein translated from 787T > C exhibited an ALP-specific activity similarly to that of 787T. Interestingly, the Km value for TNSALP in ST2 cells transfected with the 787T > C TNSALP gene was decreased significantly compared to that of cells carrying the 787T gene (P < 0.01). These results suggest that the significant difference in Km values between the proteins translated from 787T > C and 787T may contribute to regulatory effects on bone metabolism.
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Affiliation(s)
- Natsuko Sogabe
- Department of Food and Nutrition, Division of Nutrition, Japan Women's University, Tokyo, Japan
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12
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Abstract
Hypophosphatasia is a rare inherited disorder characterized by defective bone and tooth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The frequency of the disease has been estimated to be one in 100 000 for severe forms, but mild forms of hypophosphatasia may be more common. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early tooth loss without bone symptoms. The transmission of severe forms is autosomal recessive, while milder forms may be transmitted as dominant or recessive autosomal traits. The diagnosis is based on serum alkaline phosphatase assay and molecular analysis of the liver/bone/kidney alkaline phosphatase gene (ALPL). Currently, there is no treatment for the disease. Over the past 10 years, great progress has been made in understanding the structure of tissue non-specific alkaline phosphatase, its function in bone mineralization, and the effect of ALPL mutations responsible for hypophosphatasia.
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Affiliation(s)
- Etienne Mornet
- Laboratoire SESEP, Centre Hospitalier de Versailles, Bâtiment EFS, 2 rue Jean-Louis Forain, 78150 Le Chesnay, France.
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Numa N, Ishida Y, Nasu M, Sohda M, Misumi Y, Noda T, Oda K. Molecular basis of perinatal hypophosphatasia with tissue-nonspecific alkaline phosphatase bearing a conservative replacement of valine by alanine at position 406. FEBS J 2008; 275:2727-37. [DOI: 10.1111/j.1742-4658.2008.06414.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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14
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Abstract
Hypophosphatasia is a rare inherited disorder characterized by defective bone and teeth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The prevalence of severe forms of the disease has been estimated at 1/100 000. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early loss of teeth without bone symptoms. Depending on the age at diagnosis, six clinical forms are currently recognized: perinatal (lethal), perinatal benign, infantile, childhood, adult and odontohypophosphatasia. In the lethal perinatal form, the patients show markedly impaired mineralization in utero. In the prenatal benign form these symptoms are spontaneously improved. Clinical symptoms of the infantile form are respiratory complications, premature craniosynostosis, widespread demineralization and rachitic changes in the metaphyses. The childhood form is characterized by skeletal deformities, short stature, and waddling gait, and the adult form by stress fractures, thigh pain, chondrocalcinosis and marked osteoarthropathy. Odontohypophosphatasia is characterized by premature exfoliation of fully rooted primary teeth and/or severe dental caries, often not associated with abnormalities of the skeletal system. The disease is due to mutations in the liver/bone/kidney alkaline phosphatase gene (ALPL; OMIM# 171760) encoding the tissue-nonspecific alkaline phosphatase (TNAP). The diagnosis is based on laboratory assays and DNA sequencing of the ALPL gene. Serum alkaline phosphatase (AP) activity is markedly reduced in hypophosphatasia, while urinary phosphoethanolamine (PEA) is increased. By using sequencing, approximately 95% of mutations are detected in severe (perinatal and infantile) hypophosphatasia. Genetic counseling of the disease is complicated by the variable inheritance pattern (autosomal dominant or autosomal recessive), the existence of the uncommon prenatal benign form, and by incomplete penetrance of the trait. Prenatal assessment of severe hypophosphatasia by mutation analysis of chorionic villus DNA is possible. There is no curative treatment for hypophosphatasia, but symptomatic treatments such as non-steroidal anti-inflammatory drugs or teriparatide have been shown to be of benefit. Enzyme replacement therapy will be certainly the most promising challenge of the next few years.
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Affiliation(s)
- Etienne Mornet
- Laboratoire SESEP, Centre Hospitalier de Versailles, Bâtiment EFS, 2 rue Jean-Louis Forain, 78150 Le Chesnay, France.
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Brun-Heath I, Lia-Baldini AS, Maillard S, Taillandier A, Utsch B, Nunes ME, Serre JL, Mornet E. Delayed transport of tissue-nonspecific alkaline phosphatase with missense mutations causing hypophosphatasia. Eur J Med Genet 2007; 50:367-78. [PMID: 17719863 DOI: 10.1016/j.ejmg.2007.06.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Accepted: 06/29/2007] [Indexed: 11/16/2022]
Abstract
Hypophosphatasia is a rare genetic disease characterized by diminished bone and tooth mineralization due to deficient activity of tissue-nonspecific alkaline phosphatase (TNSALP). The disease is clinically heterogeneous due to different mutations in the TNSALP gene. In order to determine whether mutated TNSALP proteins may be sequestered, degraded, or subjected to delay in their transport to the cell membrane, we built a plasmid expressing a YFP-TNSALP fluorescent fusion protein allowing the observation of cellular localization in live cells by fluorescence confocal microscopy at different time points after transfection. We studied five mutants (c. 571G>A, c. 653T>C, c. 746G>T, c. 1363G>A and c. 1468A>T) exhibiting various levels of in vitro residual enzymatic activity. While the wild-type protein reached the membrane within the first 24h after transfection, the mutants reached the membrane with delays of 24, 48 or 72 h. For all of the tested mutations, accumulation of the mutated proteins, mainly in the Golgi apparatus, was observed. We concluded that reduced ALP activity of these TNSALP mutants results from structural disturbances and delay in membrane anchoring, and not from compromised catalytic activity.
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Affiliation(s)
- Isabelle Brun-Heath
- Equipe Structure-Fonction et Génétique, EA 2493, CHU Paris Ile de France Ouest, Université de Versailles-Saint Quentin en Yvelines, France
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Nasu M, Ito M, Ishida Y, Numa N, Komaru K, Nomura S, Oda K. Aberrant interchain disulfide bridge of tissue-nonspecific alkaline phosphatase with an Arg433→Cys substitution associated with severe hypophosphatasia. FEBS J 2006; 273:5612-24. [PMID: 17212778 DOI: 10.1111/j.1742-4658.2006.05550.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Various mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene are responsible for hypophosphatasia characterized by defective bone and tooth mineralization; however, the underlying molecular mechanisms remain largely to be elucidated. Substitution of an arginine at position 433 with a histidine [TNSALP(R433H)] or a cysteine [TNSALP(R433C)] was reported in patients diagnosed with the mild or severe form of hypophosphatasia, respectively. To define the molecular phenotype of the two TNSALP mutants, we sought to examine them in transient (COS-1) and conditional (CHO-K1 Tet-On) heterologous expression systems. In contrast to an 80 kDa mature form of the wild-type and TNSALP(R433H), a unique disulfide-bonded 160 kDa molecular species appeared on the cell surface of the cells expressing TNSALP(R433C). Sucrose density gradient centrifugation demonstrated that TNSALP(R433C) forms a disulfide-bonded dimer, instead of being noncovalently assembled like the wild-type. Of the five cysteine residues per subunit of the wild-type, only Cys102 is thought to be present in a free form. Replacement of Cys102 with serine did not affect the dimerization state of TNSALP(R433C), implying that TNSALP(R433C) forms a disulfide bridge between the cysteine residues at position 433 on each subunit. Although the cross-linking did not significantly interfere with the intracellular transport and cell surface expression of TNSALP(R433C), it strongly inhibited its alkaline phosphatase activity. This is in contrast to TNSALP(R433H), which shows enzyme activity comparable to that of the wild-type. Importantly, addition of dithiothreitol to the culture medium was found to partially reduce the amount of the cross-linked form in the cells expressing TNSALP(R433C), concomitantly with a significant increase in enzyme activity, suggesting that the cross-link between two subunits distorts the overall structure of the enzyme such that it no longer efficiently carries out its catalytic function. Increased susceptibility to proteases confirmed a gross conformational change of TNSALP(R433C) compared with the wild-type. Thus, loss of function resulting from the interchain disulfide bridge is the molecular basis for the lethal hypophosphatasia associated with TNSALP(R433C).
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Affiliation(s)
- Makiko Nasu
- Division of Oral Health in Aging and Fixed Prosthodontics, Niigata University Graduate School of Medical and Dental Sciences, Japan
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Ishihara K, Yamazaki T, Ishida Y, Suzuki T, Oda K, Nagao M, Yamaguchi-Iwai Y, Kambe T. Zinc Transport Complexes Contribute to the Homeostatic Maintenance of Secretory Pathway Function in Vertebrate Cells. J Biol Chem 2006; 281:17743-50. [PMID: 16636052 DOI: 10.1074/jbc.m602470200] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Zinc transporters play important roles in a wide range of biochemical processes. Here we report an important function of ZnT5/ZnT6 hetero-oligomeric complexes in the secretory pathway. The activity of human tissue-nonspecific alkaline phosphatase (ALP) expressed in ZnT5(-)ZnT7(-/-) cells was significantly reduced compared with that expressed in wild-type cells as in the case of endogenous chicken tissue-nonspecific ALP activity. The inactive human tissue-nonspecific ALP in ZnT5(-)ZnT7(-/-) cells was degraded by proteasome-mediated degradation without being trafficked to the plasma membrane. ZnT5(-)ZnT7(-/-) cells showed exacerbation of the unfolded protein response as did the wild-type cells cultured under a zinc-deficient condition, revealing that both complexes play a role in homeostatic maintenance of secretory pathway function. Furthermore, we showed that expression of ZnT5 mRNA was up-regulated by the endoplasmic reticulum stress in various cell lines. The up-regulation of the hZnT5 transcript was mediated by transcription factor XBP1 through the TGACGTGG sequence in the hZnT5 promoter, and this sequence was highly conserved in the ZnT5 genes of mouse and chicken. These results suggest that zinc transport into the secretory pathway is strictly regulated for the homeostatic maintenance of secretory pathway function in vertebrate cells.
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Affiliation(s)
- Kaori Ishihara
- Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan
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18
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Goseki-Sone M, Sogabe N, Fukushi-Irie M, Mizoi L, Orimo H, Suzuki T, Nakamura H, Orimo H, Hosoi T. Functional analysis of the single nucleotide polymorphism (787T>C) in the tissue-nonspecific alkaline phosphatase gene associated with BMD. J Bone Miner Res 2005; 20:773-82. [PMID: 15824850 DOI: 10.1359/jbmr.041229] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2004] [Revised: 12/02/2004] [Accepted: 12/17/2004] [Indexed: 11/18/2022]
Abstract
UNLABELLED Polymorphisms of the TNSALP gene have not previously been studied as a possible determinant for variations in BMD or as a predisposing genetic factor for osteoporosis. This study showed a significantly higher association between the 787T>C (Tyr246His) TNSALP gene and BMD among 501 postmenopausal women. Furthermore, the effects of amino acid substitution on the catalytic property of the protein translated from the 787T>C gene were examined. INTRODUCTION Alkaline phosphatase (ALP) is present mainly on the cell membrane in various tissues and hydrolyzes a variety of monophosphate esters into inorganic phosphoric acid and alcohol. Human ALPs are classified into four types: tissue-nonspecific, intestinal, placental, and germ cell types. Based on studies of hypophosphatasia, which is a systemic skeletal disorder resulting from a tissue-nonspecific ALP (TNSALP) deficiency, TNSALP was suggested to be indispensable for bone mineralization. MATERIALS AND METHODS We explored the possibility that the TNSALP gene may contribute to age-related bone loss in humans by examining the association between TNSALP gene polymorphisms and BMD in 501 Japanese postmenopausal women. To analyze the protein translated from the TNSALP gene associated with BMD, we constructed a TNSALP cDNA expression plasmid. RESULTS We genotyped two single nucleotide polymorphisms (787T>C[Tyr246His] and 876A>G[Pro275Pro]), which proved to be in complete linkage disequilibrium. There was a significant difference in BMD and the BMD score adjusted for age and body weight (Z score) among haplotypes (p = 0.041), which was lowest among 787T/876A homozygotes, highest among 787T>C/876A>G homozygotes, and intermediate among heterozygotes. In subgroups divided by age, haplotypes were significantly associated with BMD in older postmenopausal women (>74 years; p = 0.001), but not in younger postmenopausal women (<74 years; p = 0.964). Expression of the 787T>C TNSALP gene using COS-1 cells showed that the protein translated from 787T>C had ALP-specific activity similar to that of 787T. Interestingly, the K(m) value for TNSALP in cells transfected with the 787T>C TNSALP gene was decreased significantly compared with that of cells bearing the 787T gene, reflecting the higher affinity. CONCLUSIONS These results suggest that variation in TNSALP may be an important determinant of age-related bone loss in humans and that the phosphate metabolism pathway may provide a novel target for the prevention and treatment of osteoporosis.
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Affiliation(s)
- Masae Goseki-Sone
- Department of Food and Nutrition, Japan Women's University, Tokyo, Japan.
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Taillandier A, Sallinen SL, Brun-Heath I, De Mazancourt P, Serre JL, Mornet E. Childhood hypophosphatasia due to a de novo missense mutation in the tissue-nonspecific alkaline phosphatase gene. J Clin Endocrinol Metab 2005; 90:2436-9. [PMID: 15671102 DOI: 10.1210/jc.2004-1456] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
Hypophosphatasia is an inherited disorder due to mutations in the bone alkaline phosphatase (ALPL) gene. We report here a patient with childhood hypophosphatasia diagnosed at 1.4 yr because of pectus excavatum, large anterior fontanel, rachitic skeletal changes, and low serum alkaline phosphatase. Sequencing of the ALPL gene produced evidence of two distinct missense mutations, E174K (c.571G>A), of maternal origin, and a de novo mutation, M45I (c.186G>C). The study of various microsatellite polymorphisms ruled out false paternity and therefore confirmed that M45I occurred de novo in the paternal germline or in the early development of the patient. Site-directed mutagenesis showed that M45I results in the absence of in vitro alkaline phosphatase activity, suggesting that the mutation is a severe allele. In conclusion, childhood hypophosphatasia in this patient is the result of compound heterozygosity for the moderate mutation E174K and a novel severe de novo mutation M45I.
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Affiliation(s)
- A Taillandier
- Laboratoire SESEP, Batiment Fermat, Université de Versailles-Saint Quentin en Yvelines, 45 avenue des Etats-Unis, F-78035 Versailles, France
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Komaru K, Ishida Y, Amaya Y, Goseki-Sone M, Orimo H, Oda K. Novel aggregate formation of a frame-shift mutant protein of tissue-nonspecific alkaline phosphatase is ascribed to three cysteine residues in the C-terminal extension. FEBS J 2005; 272:1704-17. [PMID: 15794757 DOI: 10.1111/j.1742-4658.2005.04597.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the majority of hypophosphatasia patients, reductions in the serum levels of alkaline phosphatase activity are caused by various missense mutations in the tissue-nonspecific alkaline phosphatase (TNSALP) gene. A unique frame-shift mutation due to a deletion of T at cDNA number 1559 [TNSALP (1559delT)] has been reported only in Japanese patients with high allele frequency. In this study, we examined the molecular phenotype of TNSALP (1559delT) using in vitro translation/translocation system and COS-1 cells transiently expressing this mutant protein. We showed that the mutant protein not only has a larger molecular size than the wild type enzyme by approximately 12 kDa, reflecting an 80 amino acid-long extension at its C-terminus, but that it also lacks a glycosylphosphatidylinositol anchor. In support of this, alkaline phosphatase activity of the cells expressing TNSALP (1559delT) was localized at the juxtanucleus position, but not on the cell surface. However, only a limited amount of the newly synthesized protein was released into the medium and the rest was polyubiquitinated, followed by degradation in the proteasome. SDS/PAGE and analysis by sucrose-density-gradient analysis indicated that TNSALP (1559delT) forms a disulfide-bonded high-molecular-mass aggregate. Interestingly, the aggregate form of TNSALP (1559delT) exhibited a significant enzyme activity. When all three cysteines at positions of 506, 521 and 577 of TNSALP (1559delT) were replaced with serines, the aggregation disappeared and instead this modified mutant protein formed a noncovalently associated dimer, strongly indicating that these cysteine residues in the C-terminal region are solely responsible for aggregate formation by cross-linking the catalytically active dimers. Thus, complete absence of TNSALP on cell surfaces provides a plausible explanation for a severe lethal phenotype of a homozygote hypophosphatasia patient carrying TNSALP (1559delT).
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Affiliation(s)
- Keiichi Komaru
- Division of Biochemistry, Niigata University Graduate School of Medical and Dental Sciences, Gakkocho-dori, Niigata, Japan
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Watanabe H, Takinami H, Goseki-Sone M, Orimo H, Hamatani R, Ishikawa I. Characterization of the mutant (A115V) tissue-nonspecific alkaline phosphatase gene from adult-type hypophosphatasia. Biochem Biophys Res Commun 2005; 327:124-9. [PMID: 15629439 DOI: 10.1016/j.bbrc.2004.11.155] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2004] [Indexed: 10/26/2022]
Abstract
Hypophosphatasia (HOPS) is a clinically heterogeneous heritable disorder characterized by defective skeletal mineralization, deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) activity, and premature loss of deciduous teeth. To date, various mutations in the TNSALP gene have been identified. Especially, A115V located in exon 5 has been detected in a Japanese patient with severe periodontitis and adult-type HOPS. In this study, we have characterized the protein translated from the mutant A115V gene. Wild-type and A115V mutant-type TNSALP cDNA expression vector pcDNA3 have been constructed and transfected to COS-1 cells by lipofectin technique. After 48-h transfection, the cells were subjected to assay ALP activity. In order to identify possible dominant effect of the mutation, we performed co-transfections of wild-type and mutated cDNA, and evaluated the residual activities of each mutation. Detection of TNSALP synthesized by COS-1 cells transfected with the wild- or the mutated-type was also performed by using an immunofluorescent method. ALP activity of cell transfected with the mutant cDNA (A115V) plasmid after 48-h transfection exhibited 0.399+/-0.021 U/mg. As the enzymatic activity of the wild type was taken as 100%, the value of the mutant was estimated as 16.9%. When co-transfected this mutant showed no inhibition of the wild-type enzyme. TNSALP in COS-1 cells with transfected with the mutant exhibited strong fluorescence at the surface of cells as wild-type. This study indicated that the mutant (A115V) TNSALP gene produced the defective ALP enzyme and it could be recessively transmitted and be a disease-causing mutation of the adult-type hypophosphatasia.
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Affiliation(s)
- Hisashi Watanabe
- Department of Hard Tissue Engineering (Periodontology), Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
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22
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Mornet E, Simon-Bouy B. [Genetics of hypophosphatasia]. Arch Pediatr 2004; 11:444-8. [PMID: 15135429 DOI: 10.1016/j.arcped.2004.01.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2003] [Accepted: 01/02/2004] [Indexed: 11/30/2022]
Abstract
Hypophosphatasia is a rare inherited disorder characterized by defective bone and teeth mineralization and deficiency of serum and bone alkaline phosphatase activity. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early loss of teeth without bone symptoms. Currently, there is no treatment for the disease. Recent developments in molecular biology allow to better understand the genetics of the disease, especially its transmission that may be recessive or dominant, to improve genetic counseling and molecular diagnosis, and offer new perspectives of treatment.
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Affiliation(s)
- E Mornet
- Centre d'études de biologie prénatale, laboratoire SESEP, université de Versailles-Saint-Quentin en Yvelines, bâtiment Fermat, 45, avenue des Etats-Unis, 78035 Versailles, France.
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Sawai H, Kanazawa N, Tsukahara Y, Koike K, Udagawa H, Koyama K, Mornet E. Severe perinatal hypophosphatasia due to homozygous deletion of T at nucleotide 1559 in the tissue nonspecific alkaline phosphatase gene. Prenat Diagn 2003; 23:743-6. [PMID: 12975786 DOI: 10.1002/pd.696] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
OBJECTIVES Hypophosphatasia is an inherited disorder characterized by defective bone mineralization and deficiency of tissue nonspecific alkaline phosphatase (TNSALP) activity. This disorder is caused by various mutations in the TNSALP gene. We report here hypophosphatasia in two siblings, both of them severely affected by the perinatal (lethal) type. METHODS We diagnosed the first infant by clinical and radiologic manifestations, and laboratory findings. Laboratory findings were characterized by deficiency of serum alkaline phosphatase. Both parents and the second infant were then analyzed by molecular techniques. RESULTS The radiograph of the first infant showed severe hypomineralization of the skeleton. Molecular analysis of the second infant showed that this condition was caused by a homozygous single T nucleotide deletion at cDNA number 1559 (1559delT). Both parents were heterozygous carriers for this mutation, although they were not consanguineous. CONCLUSION This mutation has been frequently found in Japanese hypophosphatasia patients, but this is the first observation of a homozygous deletion. This report shows that homozygosity for the 1559delT mutation of the TNSALP gene results in a severe lethal phenotype.
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Affiliation(s)
- Hideaki Sawai
- Laboratory of Developmental Biology and Reproduction, Institute for Advanced Medical Sciences, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan.
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Di Mauro S, Manes T, Hessle L, Kozlenkov A, Pizauro JMJ, Hoylaerts MF, Millán JL. Kinetic characterization of hypophosphatasia mutations with physiological substrates. J Bone Miner Res 2002; 17:1383-91. [PMID: 12162492 DOI: 10.1359/jbmr.2002.17.8.1383] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We have analyzed 16 missense mutations of the tissue-nonspecific AP (TNAP) gene found in patients with hypophosphatasia. These mutations span the phenotypic spectrum of the disease, from the lethal perinatal/ infantile forms to the less severe adult and odontohypophosphatasia. Site-directed mutagenesis was used to introduce a sequence tag into the TNAP cDNA and eliminate the glycosylphosphatidylinositol (GPI)-anchor recognition sequence to produce a secreted epitope-tagged TNAP (setTNAP). The properties of GPI-anchored TNAP (gpiTNAP) and setTNAP were found comparable. After introducing each single hypophosphatasia mutation, the setTNAP and mutant TNAP cDNAs were expressed in COS-1 cells and the recombinant flagged enzymes were affinity purified. We characterized the kinetic behavior, inhibition, and heat stability properties of each mutant using the artificial substrate p-nitrophenylphosphate (pNPP) at pH 9.8. We also determined the ability of the mutants to metabolize two natural substrates of TNAP, that is, pyridoxal-5'-phosphate (PLP) and inorganic pyrophosphate (PPi), at physiological pH. Six of the mutant enzymes were completely devoid of catalytic activity (R54C, R54P, A94T, R206W, G317D, and V365I), and 10 others (A16V, A115V, A160T, A162T, E174K, E174G, D277A, E281K, D361V, and G439R) showed various levels of residual activity. The A160T substitution was found to decrease the catalytic efficiency of the mutant enzyme toward pNPP to retain normal activity toward PPi and to display increased activity toward PLP. The A162T substitution caused a considerable reduction in the pNPPase, PPiase, and PLPase activities of the mutant enzyme. The D277A mutant was found to maintain high catalytic efficiency toward pNPP as substrate but not against PLP or PPi. Three mutations ( E174G, E174K, and E281K) were found to retain normal or slightly subnormal catalytic efficiency toward pNPP and PPi but not against PLP. Because abnormalities in PLP metabolism have been shown to cause epileptic seizures in mice null for the TNAP gene, these kinetic data help explain the variable expressivity of epileptic seizures in hypophosphatasia patients.
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Ito M, Amizuka N, Ozawa H, Oda K. Retention at the cis-Golgi and delayed degradation of tissue-non-specific alkaline phosphatase with an Asn153-->Asp substitution, a cause of perinatal hypophosphatasia. Biochem J 2002; 361:473-80. [PMID: 11802776 PMCID: PMC1222329 DOI: 10.1042/0264-6021:3610473] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Tissue-non-specific alkaline phosphatase (TNSALP) is an ectoenzyme anchored to the plasma membrane via glycosylphosphatidylinositol (GPI). A TNSALP mutant with an Asn(153)-->Asp (N153D) substitution was reported in a foetus diagnosed with perinatal hypophosphatasia (Mornet, Taillandier, Peyramaure, Kaper, Muller, Brenner, Bussiere, Freisinger, Godard, Merrer et al. (1998) Eur. J. Hum. Genet. 6, 308-314). When expressed ectopically in COS-1 cells, the wild-type TNSALP formed active non-covalently associated dimers, whereas TNSALP (N153D) formed aberrant disulphide-bonded high-molecular-mass aggregates devoid of enzyme activity. Cell-surface biotinylation and digestion with phosphatidylinositol-specific phospholipase C showed that TNSALP (N153D) failed to reach the cell surface. Instead, double immunofluorescence demonstrated that TNSALP (N153D) partially co-localized with a cis-Golgi marker (GM-130) at the steady-state. Upon treatment with brefeldin A, TNSALP (N153D) was still co-localized with GM-130, further supporting the finding that this mutant is localized in the cis-Golgi. Consistent with morphological results, pulse-chase experiments showed that newly synthesized TNSALP (N153D) remained endo-beta-N-acetylglucosaminidase H-sensitive throughout the chase. Eventually, after a prolonged chase time, the mutant was found to be partly degraded in a proteasome-dependent manner. Since the mutant TNSALP was significantly labelled with [3H]ethanolamine, a component of GPI, comparable with the wild-type enzyme, it is unlikely that the abortive synthesis of the mutant is due to a defect in GPI-attachment. Interestingly, when asparagine was replaced by glutamine at position 153 (N153D), TNSALP (N153Q) was indistinguishable from the wild-type enzyme in terms of its molecular properties, suggesting the possible importance of amino acids with a polar amide group at position 153. Taken together, these findings indicate that replacing asparagine with aspartic acid at position 153 causes misfolding and incorrect assembly of TNSALP, which results in its retention at the cis-Golgi en route to the cell surface, followed by a delayed degradation, presumably as part of a quality-control process. We postulate that the molecular basis of the perinatal hypophosphatasia associated with TNSALP (N153D) is due to the absence of mature TNSALP at the cell surface.
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Affiliation(s)
- Masahiro Ito
- Division of Biochemistry, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Niigata, 951-8514, Japan
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Orimo H, Girschick HJ, Goseki-Sone M, Ito M, Oda K, Shimada T. Mutational analysis and functional correlation with phenotype in German patients with childhood-type hypophosphatasia. J Bone Miner Res 2001; 16:2313-9. [PMID: 11760847 DOI: 10.1359/jbmr.2001.16.12.2313] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The tissue-nonspecific alkaline phosphatase (TNSALP) gene from five German family members with childhood-type hypophosphatasia (HOPS) was analyzed using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP)-direct sequencing method. Four novel missense mutations (T51M, R54S, L258P, and R374H) and two that had been described previously (A160T and R206W) were detected in the respective patients. Mutation A160T was detected in 3 distinct patients, and a polymorphism V505A that had been described previously was detected in the same allele as L258P mutation in 1 patient and in 2 fathers whose V505A alleles were not transmitted to the probands. No other mutations were found in 2 patients. Transient expression of the mutant proteins in COS-1 cells showed that the four novel mutations and R206W were severe alleles, whereas A160T was a moderate allele. Analysis of its enzymatic activity and genetic transmission patterns confirmed that V505A was a polymorphism. Immunoprecipitation of the transiently expressed proteins showed that levels of the 80-kDa mature form of the enzyme were diminished or absent with the severe alleles; instead, levels of high-molecular mass disulfide-linked aggregates were increased. These results suggest that in compound heterozygotes, the combination of severe and moderate alleles may combine to cause the mild phenotype seen in childhood-type HOPS.
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Affiliation(s)
- H Orimo
- Department of Biochemistry and Molecular Biology, Nippon Medical School, Tokyo, Japan
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Mornet E, Stura E, Lia-Baldini AS, Stigbrand T, Ménez A, Le Du MH. Structural evidence for a functional role of human tissue nonspecific alkaline phosphatase in bone mineralization. J Biol Chem 2001; 276:31171-8. [PMID: 11395499 DOI: 10.1074/jbc.m102788200] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human tissue nonspecific alkaline phosphatase (TNAP) is found in liver, kidney, and bone. Mutations in the TNAP gene can lead to Hypophosphatasia, a rare inborn disease that is characterized by defective bone mineralization. TNAP is 74% homologous to human placental alkaline phosphatase (PLAP) whose crystal structure has been recently determined at atomic resolution (Le Du, M. H., Stigbrand, T., Taussig, M. J., Ménez, A., and Stura, E. A. (2001) J. Biol. Chem, 276, 9158-9165). The degree of homology allowed us to build a reliable TNAP model to investigate the relationship between mutations associated with hypophosphatasia and their probable consequences on the activity or the structure of the enzyme. The mutations are clustered within five crucial regions, namely the active site and its vicinity, the active site valley, the homodimer interface, the crown domain, and the metal-binding site. The crown domain and the metal-binding domain are mammalian-specific and were observed for the first time in the PLAP structure. The crown domain contains a collagen binding loop. A synchrotron radiation x-ray fluorescence study confirms that the metal in the metal-binding site is a calcium ion. Several severe mutations in TNAP occur around this calcium site, suggesting that calcium may be of critical importance for the TNAP function. The presence of this extra metal-binding site gives new insights on the controversial role observed for calcium.
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Affiliation(s)
- E Mornet
- Centre d'Etudes de Biologie Prénatale-SESEP, Université de Versailles-Saint Quentin en Yvelines, 78000 Versailles, France
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Johnson KA, Hessle L, Vaingankar S, Wennberg C, Mauro S, Narisawa S, Goding JW, Sano K, Millan JL, Terkeltaub R. Osteoblast tissue-nonspecific alkaline phosphatase antagonizes and regulates PC-1. Am J Physiol Regul Integr Comp Physiol 2000; 279:R1365-77. [PMID: 11004006 DOI: 10.1152/ajpregu.2000.279.4.r1365] [Citation(s) in RCA: 131] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tissue-nonspecific alkaline phosphatase (TNAP) is essential for bone matrix mineralization, but the central mechanism for TNAP action remains undefined. We observed that ATP-dependent (45)Ca precipitation was decreased in calvarial osteoblast matrix vesicle (MV) fractions from TNAP-/- mice, a model of infantile hypophosphatasia. Because TNAP hydrolyzes the mineralization inhibitor inorganic pyrophosphate (PP(i)), we assessed phosphodiesterase nucleotide pyrophosphatase (PDNP/NTPPPH) activity, which hydrolyzes ATP to generate PP(i). Plasma cell membrane glycoprotein-1 (PC-1), but not the isozyme B10 (also called PDNP3) colocalized with TNAP in osteoblast MV fractions and pericellular matrix. PC-1 but not B10 increased MV fraction PP(i) and inhibited (45)Ca precipitation by MVs. TNAP directly antagonized inhibition by PC-1 of MV-mediated (45)Ca precipitation. Furthermore, the PP(i) content of MV fractions was greater in cultured TNAP-/- than TNAP+/+ calvarial osteoblasts. Paradoxically, transfection with wild-type TNAP significantly increased osteoblast MV fraction NTPPPH. Specific activity of NTPPPH also was twofold greater in MV fractions of osteoblasts from TNAP+/+ mice relative to TNAP-/- mice. Thus TNAP attenuates PC-1/NTPPPH-induced PP(i) generation that would otherwise inhibit MV-mediated mineralization. TNAP also paradoxically regulates PC-1 expression and NTPPPH activity in osteoblasts.
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Affiliation(s)
- K A Johnson
- Veterans Affairs Medical Center/University of California San Diego, La Jolla 92161, USA
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Amizuka N, Fukushi-Irie M, Sasaki T, Oda K, Ozawa H. Inefficient function of the signal sequence of PTHrP for targeting into the secretory pathway. Biochem Biophys Res Commun 2000; 273:621-9. [PMID: 10873655 DOI: 10.1006/bbrc.2000.2913] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Parathyroid hormone-related peptide (PTHrP) is not only secreted out of cells, but also targeted to the nucleoli due to a nucleolar targeting signal (NTS). We assessed the molecular mechanism underlying the dual targeting of PTHrP by constructing a series of truncated forms of rat PTHrP cDNA and expressing them in CHO cells. Immunostaining was observed in both the Golgi apparatus and nucleoli in the same cell expressing PTHrP with the N-terminal full-length signal sequence. When PTHrP molecules were translated from CUGs downstream of the AUG-initiator codon in the signal sequences, potential alternative initiators of the translation, they were exclusively localized in the nucleoli. In contrast, when a construct containing only the ATG-initiator codon was expressed, PTHrP was found to localize in both the nucleolus and the Golgi apparatus. No nucleolar staining of PTHrP was observed in the CHO cells transfected with PTH/PTHrP receptors even after incubating with a conditioned medium containing PTHrP, ruling out a possibility that PTHrP is, once secreted, internalized via receptor-mediated endocytosis and subsequently conveyed to nucleoli. Compatible with these morphological observations, a preproform of PTHrP was found in the cells expressing PTHrP in addition to proPTHrP, indicative of molecules along the secretory pathway. These results strongly indicate that the signal sequence of PTHrP is not sufficient to direct all the newly synthesized molecules across the endoplasmic reticulum, resulting in part of it being delivered to the nucleoli due to the NTS.
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Affiliation(s)
- N Amizuka
- 1st Department of Oral Anatomy, Department of Oral Biochemistry, Niigata University Faculty of Dentistry, 5274, 2-Bancho, Gakkocho-dori, Niigata, 951-8514, Japan.
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Abstract
Hypophosphatasia is an inborn error of metabolism caused by a deficiency of liver-, bone- or kidney-type alkaline phosphatase due to mutations in the tissue-nonspecific alkaline phosphatase (ALPL) gene. Most of the 65 distinct mutations described to date are missense mutations, a result which must be correlated with the great variability of clinical expression ranging from stillbirth without mineralized bone to pathologic fractures developing only late in adulthood. Correlations of genotype and phenotype have been established on the basis of clinical data exhibited by the patients, transfection studies, computer-assisted modeling, and examination of biochemical properties of ALP in cultured fibroblasts of patients. Screening for mutations in the TNSALP gene allows genetic counseling and prenatal diagnosis of the disease in families with severe forms of hypophosphatasia, and screening may also be helpful in confirming diagnosis of hypophosphatasia when biochemical and clinical data are not clear. Screening is also the necessary first step in further studies to elucidate dominant transmission of the disease and of liver-, bone- and kidney-type alkaline phosphatase activity mechanism.
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Affiliation(s)
- E Mornet
- Centre d'Etudes de Biologie Prénatale-SESEP, Université de Versailles-Saint Quentin en Yvelines, Versailles, France.
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Gehring B, Mornet E, Plath H, Hansmann M, Bartmann P, Brenner RE. Perinatal hypophosphatasia: diagnosis and detection of heterozygote carriers within the family. Clin Genet 1999; 56:313-7. [PMID: 10636450 DOI: 10.1034/j.1399-0004.1999.560409.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
We report on two families in which one or two children had a severe disorder of skeletal development detected by prenatal ultrasonography. The children died postnatally and showed typical radiological and biochemical findings of perinatal hypophosphatasia. Biochemical analysis revealed a low activity of alkaline phosphatase (AP) and a high value of pyridoxal-5-phosphate (PLP), one of its natural substrates. The screening for mutations of the tissue nonspecific alkaline phosphatase (TNSALP) gene showed homozygosity for a point mutation (G 317 --> D) in the two affected children of the first family. The affected child of the second family was homozygous for a nonsense mutation (R 411 --> X). Family screening revealed that the determination of AP and PLP is helpful for detection of heterozygotes. However, heterozygote children had values of AP in the lower normal range during phases of rapid growth. The determination of PLP proved to be more sensitive in these cases. It should be kept in mind that during the last trimester of gestation there is an increase in maternal AP activity and a normalization of PLP due to placental AP, which is not affected. Therefore, in the course of a prenatal diagnosis in an index case, paternal blood should be analyzed in parallel. For detailed genetic counseling and early prenatal diagnosis in following pregnancies, the possibility of mutation analysis should be used.
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Affiliation(s)
- B Gehring
- Department of Neonatology, University of Bonn, Germany
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Johnson K, Vaingankar S, Chen Y, Moffa A, Goldring MB, Sano K, Jin-Hua P, Sali A, Goding J, Terkeltaub R. Differential mechanisms of inorganic pyrophosphate production by plasma cell membrane glycoprotein-1 and B10 in chondrocytes. ARTHRITIS AND RHEUMATISM 1999; 42:1986-97. [PMID: 10513816 DOI: 10.1002/1529-0131(199909)42:9<1986::aid-anr26>3.0.co;2-o] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
OBJECTIVE Increased nucleoside triphosphate pyrophosphohydrolase (NTPPPH) activity in chondrocytes is associated with cartilage matrix inorganic pyrophosphate (PPi) supersaturation in chondrocalcinosis. This study compared the roles of the transforming growth factor beta (TGFbeta)-inducible plasma cell membrane glycoprotein-1 (PC-1) and the closely related B10 NTPPPH activities in chondrocyte PPi metabolism. METHODS NTPPPH expression was studied using reverse transcriptase-polymerase chain reaction and Western blotting. Transmembrane PC-1 (tmPC-1), water-soluble secretory PC-1 (secPC-1), and transmembrane B10 were expressed by adenoviral gene transfer or plasmid transfection, and expression of PPi was assessed in cultured articular chondrocytes and immortalized NTPPPH-deficient costal chondrocytes (TC28 cells). RESULTS PC-1 and B10 messenger RNA were demonstrated in articular cartilages in situ, in untreated cultured normal articular chondrocytes, and in TC28 cells. Expression of tmPC-1 and secPC-1, but not B10, rendered the NTPPPH-deficient TC28 cells able to increase expression of extracellular PPi, with or without addition of TGFbeta (10 ng/ml) to the media. More plasma membrane NTPPPH activity was detected in cells transfected with tmPC-1 than in cells transfected with B10. Furthermore, confocal microscopy with immunofluorescent staining of articular chondrocytes confirmed preferential plasma membrane localization of PC-1, relative to B10. Finally, both PC-1 and B10 increased the levels of intracellular PPi, but PC-1 and B10 appeared to act principally in different intracellular compartments (Golgi and post-Golgi versus pre-Golgi, respectively). CONCLUSION PC-1 and B10 NTPPPH activities were not redundant in chondrocytes. Although increased PC-1 and B10 expression caused elevations in intracellular PPi, the major effects of PC-1 and B10 were exerted in distinct subcellular compartments. Moreover, PC-1 (transmembrane and secreted), but not B10, increased the levels of extracellular PPi. Differential expression of PC-1 and B10 could modulate cartilage mineralization in degenerative joint diseases.
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Affiliation(s)
- K Johnson
- Department of Veterans Affairs Medical Center, University of California, San Diego 92161, USA
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