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Chandrasekaran FP, Vishal A, Arora U, Kumar S U, George C PD, Nelson EJR. Molecular dynamics simulations corroborate recombinant expression studies carried out on three αIIb β-propeller mutations reported in Indian Glanzmann thrombasthenia patients. J Cell Biochem 2023. [PMID: 37210732 DOI: 10.1002/jcb.30423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 04/27/2023] [Accepted: 05/04/2023] [Indexed: 05/23/2023]
Abstract
Mutations in the αIIb β-propeller domain have long been known to disrupt heterodimerization and intracellular trafficking of αIIbβ3 complexes leading to diminished surface expression and/or function, resulting in Glanzmann thrombasthenia. Our previous study on three β-propeller mutations, namely G128S, S287L, and G357S, showed variable defects in protein transport correlated with the patient's clinical phenotypes. Pulse-chase experiments revealed differences in αIIbβ3 complex maturation among the three mutations. Hence, the current study aims to correlate conformational changes caused by each one of them. Evolutionary conservation analysis, stability analysis, and molecular dynamics simulations of the three mutant structures were carried out. Stability analysis revealed that, while G128S and G357S mutations destabilized the β-propeller structure, S287L retained the stability. Wild-type and mutant β-propeller structures, when subjected to molecular dynamics simulations, confirmed that G128S and G357S were both destabilizing in nature when compared with the wild-type and S287L based on several parameters studied, like RMSD, RMSF, Rg, FEL, PCA, secondary structure, and hydrogen bonds. In our previous study, we demonstrated that mutant S287L αIIbβ3 complexes were more stable than the wild-type αIIbβ3 complexes, as evidenced in pulse-chase experiments. These findings corroborate variable intracellular fates of mutant αIIbβ3 complexes as a result of these β-propeller mutations.
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Affiliation(s)
- Finola Priyadharshini Chandrasekaran
- Gene Therapy Laboratory, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, India
| | - Adarsh Vishal
- Gene Therapy Laboratory, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, India
| | - Udita Arora
- Gene Therapy Laboratory, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, India
| | - Udhaya Kumar S
- Laboratory of Integrative Genomics, Vellore Institute of Technology, Vellore, India
| | - Priya Doss George C
- Laboratory of Integrative Genomics, Vellore Institute of Technology, Vellore, India
| | - Everette Jacob Remington Nelson
- Gene Therapy Laboratory, Department of Integrative Biology, School of Bio Sciences and Technology, Vellore Institute of Technology, Vellore, India
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2
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Koker MY, Sarper N, Albayrak C, Zulfikar B, Zengin E, Saraymen B, Albayrak D, Koc B, Avcilar H, Karakükcü M, Chenet C, Bianchi F, de Brevern AG, Petermann R, Jallu V. New αIIbβ3 variants in 28 Turkish Glanzmann patients; Structural hypothesis for complex activation by residues variations in I-EGF domains. Platelets 2021; 33:551-561. [PMID: 34275420 DOI: 10.1080/09537104.2021.1947481] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Glanzmann thrombasthenia (GT) is a rare autosomal recessive bleeding disorder characterized by impaired platelet aggregation due to defects in integrin αIIbβ3, a fibrinogen receptor. Platelet phenotypes and allelic variations in 28 Turkish GT patients are reported. Platelets αIIbβ3 expression was evaluated by flow cytometry. Sequence analyzes of ITGA2B and ITGB3 genes allowed identifying nine variants. Non-sense variation effect on αIIbβ3 expression was studied by using transfected cell lines. 3D molecular dynamics (MDs) simulations allowed characterizing structural alterations. Five new alleles were described. αIIb:p.Gly423Asp, p.Asp560Ala and p.Tyr784Cys substitutions impaired αIIbβ3 expression. The αIIb:p.Gly128Val substitution allowed normal expression; however, the corresponding NM_000419.3:c.476G>T variation would create a cryptic donor splicing site altering mRNA processing. The β3:p.Gly540Asp substitution allowed αIIbβ3 expression in HEK-293 cells but induced its constitutive activation likely by impairing αIIb and β3 legs interaction. The substitution alters the β3 I-EGF-3 domain flexibility as shown by MDs simulations. GT variations are mostly unique although the NM_000419.3:c.1752 + 2 T > C and NM_000212.2:c.1697 G > A variations identified in 4 and 8 families, respectively, might be a current cause of GT in Turkey. MD simulations suggested how some subtle structural variations in the β3 I-EGF domains might induce constitutive activation of αIIbβ3 without altering the global domain structure.
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Affiliation(s)
- M Y Koker
- Faculty of Medicine, Department of Immunology, Erciyes University, Kayseri, Turkey
| | - N Sarper
- Faculty of Medicine, Department of Pediatrics, Division of Pediatric Hematology, Kocaeli University, Kocaeli, Turkey
| | - C Albayrak
- Faculty of Medicine, Department of Pediatrics, Division of Pediatric Hematology and Oncology, Ondokuz Mayis University, Samsun, Turkey
| | - B Zulfikar
- Oncology Institute, Department of Pediatric Hematology/Oncology, Istanbul University, İstanbul, Turkey
| | - E Zengin
- Faculty of Medicine, Department of Pediatrics, Division of Pediatric Hematology, Kocaeli University, Kocaeli, Turkey
| | - B Saraymen
- Nanotechnology Research and Application Center, Erciyes University, Kayseri, Turkey
| | - D Albayrak
- Faculty of Medicine, Department of Pediatrics, Division of Pediatric Hematology and Oncology, Ondokuz Mayis University, Samsun, Turkey
| | - B Koc
- Oncology Institute, Department of Pediatric Hematology/Oncology, Istanbul University, İstanbul, Turkey
| | - H Avcilar
- Faculty of Medicine, Department of Immunology, Erciyes University, Kayseri, Turkey
| | - M Karakükcü
- Faculty of Medicine, Department of Pediatrics, Division of Pediatric Hematology, Erciyes University, Kayseri, Turkey
| | - C Chenet
- Département d'Immunologie Plaquettaire, Institut National De La Transfusion Sanguine (INTS), Paris, France.,Centre National de Référence en Hémobiologie Périnatale (CNRHP), Site St Antoine, DMU Biologie et Génomique Médicales, AP-HP, Sorbonne Université PARIS, FRANCE
| | - F Bianchi
- Département d'Immunologie Plaquettaire, Institut National De La Transfusion Sanguine (INTS), Paris, France.,Centre National de Référence en Hémobiologie Périnatale (CNRHP), Site St Antoine, DMU Biologie et Génomique Médicales, AP-HP, Sorbonne Université PARIS, FRANCE
| | - A G de Brevern
- Biologie Intégrée du Globule Rouge UMR_S1134, Inserm, DSIMB, Univ. Paris, Univ. De La Réunion, Univ. Des Antilles, Paris, France.,Institut National de la Transfusion Sanguine (INTS), Paris, France.,Laboratoire d'Excellence GR-Ex, Paris, France
| | - R Petermann
- Département d'Immunologie Plaquettaire, Institut National De La Transfusion Sanguine (INTS), Paris, France.,Centre National de Référence en Hémobiologie Périnatale (CNRHP), Site St Antoine, DMU Biologie et Génomique Médicales, AP-HP, Sorbonne Université PARIS, FRANCE.,Centre De Recherche Des Cordeliers, UMRS-1138, INSERM, Sorbone Université De Paris, Equipe ETREs (Ethics, Research, Translations), Paris, France
| | - V Jallu
- Département d'Immunologie Plaquettaire, Institut National De La Transfusion Sanguine (INTS), Paris, France.,Centre National de Référence en Hémobiologie Périnatale (CNRHP), Site St Antoine, DMU Biologie et Génomique Médicales, AP-HP, Sorbonne Université PARIS, FRANCE
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3
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Specifications of the variant curation guidelines for ITGA2B/ITGB3: ClinGen Platelet Disorder Variant Curation Panel. Blood Adv 2021; 5:414-431. [PMID: 33496739 PMCID: PMC7839359 DOI: 10.1182/bloodadvances.2020003712] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 12/08/2020] [Indexed: 12/17/2022] Open
Abstract
Accurate and consistent sequence variant interpretation is critical to the correct diagnosis and appropriate clinical management and counseling of patients with inherited genetic disorders. To minimize discrepancies in variant curation and classification among different clinical laboratories, the American College of Medical Genetics and Genomics (ACMG), along with the Association for Molecular Pathology (AMP), published standards and guidelines for the interpretation of sequence variants in 2015. Because the rules are not universally applicable to different genes or disorders, the Clinical Genome Resource (ClinGen) Platelet Disorder Expert Panel (PD-EP) has been tasked to make ACMG/AMP rule specifications for inherited platelet disorders. ITGA2B and ITGB3, the genes underlying autosomal recessive Glanzmann thrombasthenia (GT), were selected as the pilot genes for specification. Eight types of evidence covering clinical phenotype, functional data, and computational/population data were evaluated in the context of GT by the ClinGen PD-EP. The preliminary specifications were validated with 70 pilot ITGA2B/ITGB3 variants and further refined. In the final adapted criteria, gene- or disease-based specifications were made to 16 rules, including 7 with adjustable strength; no modification was made to 5 rules; and 7 rules were deemed not applicable to GT. Employing the GT-specific ACMG/AMP criteria to the pilot variants resulted in a reduction of variants classified with unknown significance from 29% to 20%. The overall concordance with the initial expert assertions was 71%. These adapted criteria will serve as guidelines for GT-related variant interpretation to increase specificity and consistency across laboratories and allow for better clinical integration of genetic knowledge into patient care.
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Next-Generation Sequencing Based Approach to Identify Underlying Genetic Defects of Glanzmann Thrombasthenia. Indian J Hematol Blood Transfus 2020; 37:414-421. [PMID: 34267460 DOI: 10.1007/s12288-020-01368-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 10/09/2020] [Indexed: 10/23/2022] Open
Abstract
Glanzmann thrombasthenia (GT) is an autosomal recessive platelet function disorder characterized by mucocutaneous bleeding as the most common clinical phenotype. Patients with GT have normal platelet counts, platelet morphology but reduced platelet aggregation in response to various agonists. Homozygosity or compound heterozygosity for variants in the ITGA2B/ITGB3 genes is the genetic basis for GT. Establishing a molecular diagnosis is definitive and is important for predictive testing. Using multi-gene panels is an accurate, faster, and cost-effective mode as compared to Sanger sequencing in large genes. We used a targeted resequencing based approach to identify pathogenic variants in eight cases in seven families. These variants were validated using Sanger sequencing in patients as well as family members and were predicted probably pathogenic using in-silico prediction tools. The variants include three missense (3/7 = 43%) (ITGA2B:c.1028 T > C, ITGA2B:c.1186G > A, ITGB3:c.1388G > C), two deletions (ITGA2B:c.559delG, ITGA2B:c.3092delT), one duplication (ITGA2B:c.1424_1427dupAGGT) and nonsense variant (ITGA2B:c.2578C > T, p.Gln860Ter). Except for one case which was compound heterozygous, the rest of the cases were homozygous. We found two novel variants that are reported for the first time in GT. The targeted resequencing based approach revealed varied genetic variants in North Indian patients, including two novels ones. The high yield of our panel indicates its suitability for usage in larger cohorts for the genetic diagnosis of GT patients. This approach is cost-effective and less cumbersome as compared to Sanger sequencing for these large size genes with multiple exons. The information so obtained is helpful in prenatal testing, carrier analysis, and genetic counseling.
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Pillois X, Peters P, Segers K, Nurden AT. In silico analysis of structural modifications in and around the integrin αIIb genu caused by ITGA2B variants in human platelets with emphasis on Glanzmann thrombasthenia. Mol Genet Genomic Med 2018; 6:249-260. [PMID: 29385657 PMCID: PMC5902390 DOI: 10.1002/mgg3.365] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Revised: 12/01/2017] [Accepted: 12/20/2017] [Indexed: 01/28/2023] Open
Abstract
BACKGROUND Studies on the inherited bleeding disorder, Glanzmann thrombasthenia (GT), have helped define the role of the αIIbβ3 integrin in platelet aggregation. Stable bent αIIbβ3 undergoes conformation changes on activation allowing fibrinogen binding and its taking an extended form. The αIIb genu assures the fulcrum of the bent state. Our goal was to determine how structural changes induced by missense mutations in the αIIb genu define GT phenotype. METHODS Sanger sequencing of ITGA2B and ITGB3 in the index case followed by in silico modeling of all known GT-causing missense mutations extending from the lower part of the β-propeller, and through the thigh and upper calf-1 domains. RESULTS A homozygous c.1772A>C transversion in exon 18 of ITGA2B coding for a p.Asp591Ala substitution in an interconnecting loop of the lower thigh domain of αIIb in a patient with platelets lacking αIIbβ3 led us to extend our in silico modeling to all 16 published disease-causing missense variants potentially affecting the αIIb genu. Modifications of structuring H-bonding were the major cause in the thigh domain although one mutation gave mRNA decay. In contrast, short-range changes induced in calf-1 appeared minor suggesting long-range effects. All result in severe to total loss of αIIbβ3 in platelets. The absence of mutations within a key Ca2+-binding loop in the genu led us to scan public databases; three potential single allele variants giving major structural changes were identiffied suggesting that this key region is not protected from genetic variation. CONCLUSIONS It appears that the αIIb genu is the object of stringent quality control to prevent platelets from circulating with activated and extended integrin.
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Affiliation(s)
- Xavier Pillois
- Institut de Rhythmologie et de Modélisation Cardiaque, Plateforme Technologique d'Innovation BiomédicaleHôpital Xavier ArnozanBordeauxFrance
- Université de BordeauxINSERM U1034BordeauxFrance
| | - Pierre Peters
- Laboratoire de Thrombose‐HémostaseService d'Hématologie biologique et Immuno‐HématologieCHU Sart TilmanLiègeBelgium
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Ittiwut R, Suchartlikitwong P, Kittikalayawong Y, Ittiwut C, Prasopsanti K, Sosothikul D, Shotelersuk V, Suphapeetiporn K. Novel mutations in Thai patients with glanzmann thrombasthenia. Eur J Haematol 2017; 99:520-524. [PMID: 28888044 DOI: 10.1111/ejh.12965] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/03/2017] [Indexed: 11/29/2022]
Abstract
OBJECTIVES Glanzmann thrombasthenia (GT) is an autosomal recessive platelet disorder, caused by defects of the platelet integrin αIIbβ3 (GPIIb/IIIa) resulting from pathogenic mutations in either ITGA2B or ITGB3. It is characterized by spontaneous mucocutaneous bleeding. The molecular features of GT in Thailand have not been identified. This study aimed to determine the clinical and molecular features of unrelated Thai patients with GT. METHODS Four patients with clinically suspected GT were recruited at the Division of Pediatric Hematology/Oncology, King Chulalongkorn Memorial Hospital. The diagnosis was based on clinical and hematological parameters as well as genetic analysis. Whole exome sequencing (WES) was performed in all cases. RESULTS Of the four patients studied, the median age at first suspicion of GT was 2.5 years. All presented with severe bleeding symptoms (WHO bleeding scale 3). Flow cytometry to assess the surface GPIIb/IIIa complex showed reduced expression. By WES, we successfully identified seven mutant alleles in ITGA2B. One alteration, the c.2915dup (p.Leu973Alafs*63), was detected in two unrelated families. One patient was homozygous for the c.617T>A (p.Val206Asp). Of the five different mutations, three have never been previously described. These include a missense, c.617T>A (p.Val206Asp), a deletion, c.1524_1533del (p.Gln508Hisfs*3), and a nonsense, c.2344C>T (p.Arg782Ter). CONCLUSION This study reported three novel mutations expanding the genotypic spectrum of ITGA2B causing GT.
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Affiliation(s)
- Rungnapa Ittiwut
- Center of Excellence for Medical Genetics, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.,Excellence Center for Medical Genetics, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand
| | | | - Yaowaree Kittikalayawong
- Division of Pediatric Hematology/Oncology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
| | - Chupong Ittiwut
- Center of Excellence for Medical Genetics, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.,Excellence Center for Medical Genetics, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand
| | - Karan Prasopsanti
- Excellence Center for Medical Genetics, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand
| | - Darintr Sosothikul
- Division of Pediatric Hematology/Oncology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
| | - Vorasuk Shotelersuk
- Center of Excellence for Medical Genetics, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.,Excellence Center for Medical Genetics, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand
| | - Kanya Suphapeetiporn
- Center of Excellence for Medical Genetics, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.,Excellence Center for Medical Genetics, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok, Thailand
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7
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Nurden AT, Pillois X, Fiore M, Alessi MC, Bonduel M, Dreyfus M, Goudemand J, Gruel Y, Benabdallah-Guerida S, Latger-Cannard V, Négrier C, Nugent D, Oiron RD, Rand ML, Sié P, Trossaert M, Alberio L, Martins N, Sirvain-Trukniewicz P, Couloux A, Canault M, Fronthroth JP, Fretigny M, Nurden P, Heilig R, Vinciguerra C. Expanding the Mutation Spectrum Affecting αIIbβ3 Integrin in Glanzmann Thrombasthenia: Screening of the ITGA2B and ITGB3 Genes in a Large International Cohort. Hum Mutat 2016; 36:548-61. [PMID: 25728920 DOI: 10.1002/humu.22776] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2014] [Accepted: 02/18/2015] [Indexed: 12/19/2022]
Abstract
We report the largest international study on Glanzmann thrombasthenia (GT), an inherited bleeding disorder where defects of the ITGA2B and ITGB3 genes cause quantitative or qualitative defects of the αIIbβ3 integrin, a key mediator of platelet aggregation. Sequencing of the coding regions and splice sites of both genes in members of 76 affected families identified 78 genetic variants (55 novel) suspected to cause GT. Four large deletions or duplications were found by quantitative real-time PCR. Families with mutations in either gene were indistinguishable in terms of bleeding severity that varied even among siblings. Families were grouped into type I and the rarer type II or variant forms with residual αIIbβ3 expression. Variant forms helped identify genes encoding proteins mediating integrin activation. Splicing defects and stop codons were common for both ITGA2B and ITGB3 and essentially led to a reduced or absent αIIbβ3 expression; included was a heterozygous c.1440-13_c.1440-1del in intron 14 of ITGA2B causing exon skipping in seven unrelated families. Molecular modeling revealed how many missense mutations induced subtle changes in αIIb and β3 domain structure across both subunits, thereby interfering with integrin maturation and/or function. Our study extends knowledge of GT and the pathophysiology of an integrin.
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Affiliation(s)
- Alan T Nurden
- Institut de Rhythmologie et de Modélisation Cardiaque, Plateforme Technologique d'Innovation Biomédicale, Hôpital Xavier Arnozan, Pessac, France
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8
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Kulkarni BP, Nair SB, Vijapurkar M, Mota L, Shanbhag S, Ali S, Shetty SD, Ghosh K. Molecular pathology of rare bleeding disorders (RBDs) in India: a systematic review. PLoS One 2014; 9:e108683. [PMID: 25275492 PMCID: PMC4183524 DOI: 10.1371/journal.pone.0108683] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Accepted: 09/02/2014] [Indexed: 11/20/2022] Open
Abstract
Background Though rare in occurrence, patients with rare bleeding disorders (RBDs) are highly heterogeneous and may manifest with severe bleeding diathesis. Due to the high rate of consanguinity in many caste groups, these autosomal recessive bleeding disorders which are of rare occurrence in populations across the world, may not be as rare in India. Objectives To comprehensively analyze the frequency and nature of mutations in Indian patients with RBDs. Methods Pubmed search was used (www.pubmed.com) to explore the published literature from India on RBDs using the key words “rare bleeding disorders”, “mutations”, “India”, “fibrinogen”, “afibrinogenemia”, “factor II deficiency”, “prothrombin” “factor VII deficiency”, “factor V deficiency”, “factor X deficiency”, “factor XI deficiency”, “combined factor V and VIII deficiency”, “factor XIII deficiency”, “Bernard Soulier syndrome” and “Glanzmanns thrombasthenia” in different combinations. A total of 60 relevant articles could be retrieved. The distribution of mutations from India was compared with that of the world literature by referring to the Human Gene Mutation Database (HGMD) (www.hgmd.org). Results Taken together, 181 mutations in 270 patients with different RBDs have been reported from India. Though the types of mutations reported from India and their percentage distribution with respect to the world data are largely similar, yet much higher percentage of small deletions, duplication mutations, insertions, indels were observed in this analysis. Besides the identification of novel mutations and polymorphisms, several common mutations have also been reported, which will allow to develop a strategy for mutation screening in Indian patients with RBDs. Conclusion There is a need for a consortium of Institutions working on the molecular pathology of RBDs in India. This will facilitate a quicker and cheaper diagnosis of RBDs besides its utility in first trimester prenatal diagnosis of the affected families.
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Affiliation(s)
- Bipin P Kulkarni
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Sona B Nair
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Manasi Vijapurkar
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Leenam Mota
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Sharda Shanbhag
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Shehnaz Ali
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Shrimati D Shetty
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
| | - Kanjaksha Ghosh
- National Institute of Immunohaematology (I.C.M.R.), MS Building, KEM Hospital campus, Parel, Mumbai, India
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9
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Winograd-Katz SE, Fässler R, Geiger B, Legate KR. The integrin adhesome: from genes and proteins to human disease. Nat Rev Mol Cell Biol 2014; 15:273-88. [PMID: 24651544 DOI: 10.1038/nrm3769] [Citation(s) in RCA: 445] [Impact Index Per Article: 44.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The adhesive interactions of cells with their environment through the integrin family of transmembrane receptors have key roles in regulating multiple aspects of cellular physiology, including cell proliferation, viability, differentiation and migration. Consequently, failure to establish functional cell adhesions, and thus the assembly of associated cytoplasmic scaffolding and signalling networks, can have severe pathological effects. The roles of specific constituents of integrin-mediated adhesions, which are collectively known as the 'integrin adhesome', in diverse pathological states are becoming clear. Indeed, the prominence of mutations in specific adhesome molecules in various human diseases is now appreciated, and experimental as well as in silico approaches provide insights into the molecular mechanisms underlying these pathological conditions.
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Affiliation(s)
- Sabina E Winograd-Katz
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Reinhard Fässler
- Department of Molecular Medicine, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany
| | - Benjamin Geiger
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Kyle R Legate
- 1] Department of Molecular Medicine, Max Planck Institute of Biochemistry, 82152 Martinsried, Germany. [2] Center for Nanosciences, Department of Applied Physics, Ludwig-Maximilians University, 80799 Munich, Germany
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10
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Nurden AT, Pillois X, Nurden P. Understanding the genetic basis of Glanzmann thrombasthenia: implications for treatment. Expert Rev Hematol 2014; 5:487-503. [PMID: 23146053 DOI: 10.1586/ehm.12.46] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Alan T Nurden
- Plateforme Technologique et d'Innovation Biomédicale, Hôpital Xavier Arnozan, Pessac, France.
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11
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Molecular dynamics analysis of a novel β3 Pro189Ser mutation in a patient with glanzmann thrombasthenia differentially affecting αIIbβ3 and αvβ3 expression. PLoS One 2013; 8:e78683. [PMID: 24236036 PMCID: PMC3827234 DOI: 10.1371/journal.pone.0078683] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 09/13/2013] [Indexed: 01/11/2023] Open
Abstract
Mutations in ITGA2B and ITGB3 cause Glanzmann thrombasthenia, an inherited bleeding disorder in which platelets fail to aggregate when stimulated. Whereas an absence of expression or qualitative defects of αIIbβ3 mainly affect platelets and megakaryocytes, αvβ3 has a widespread tissue distribution. Little is known of how amino acid substitutions of β3 comparatively affect the expression and structure of both integrins. We now report computer modelling including molecular dynamics simulations of extracellular head domains of αIIbβ3 and αvβ3 to determine the role of a novel β3 Pro189Ser (P163S in the mature protein) substitution that abrogates αIIbβ3 expression in platelets while allowing synthesis of αvβ3. Transfection of wild-type and mutated integrins in CHO cells confirmed that only αvβ3 surface expression was maintained. Modeling initially confirmed that replacement of αIIb by αv in the dimer results in a significant decrease in surface contacts at the subunit interface. For αIIbβ3, the presence of β3S163 specifically displaces an α-helix starting at position 259 and interacting with β3R261 while there is a moderate 11% increase in intra-subunit H-bonds and a very weak decrease in the global H-bond network. In contrast, for αvβ3, S163 has different effects with β3R261 coming deeper into the propeller with a 43% increase in intra-subunit H-bonds but with little effect on the global H-bond network. Compared to the WT integrins, the P163S mutation induces a small increase in the inter-subunit fluctuations for αIIbβ3 but a more rigid structure for αvβ3. Overall, this mutation stabilizes αvβ3 despite preventing αIIbβ3 expression.
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12
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Nurden AT, Pillois X, Wilcox DA. Glanzmann thrombasthenia: state of the art and future directions. Semin Thromb Hemost 2013; 39:642-55. [PMID: 23929305 DOI: 10.1055/s-0033-1353393] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Glanzmann thrombasthenia (GT) is the principal inherited disease of platelets and the most commonly encountered disorder of an integrin. GT is characterized by spontaneous mucocutaneous bleeding and an exaggerated response to trauma caused by platelets that fail to aggregate when stimulated by physiologic agonists. GT is caused by quantitative or qualitative deficiencies of αIIbβ3, an integrin coded by the ITGA2B and ITGB3 genes and which by binding fibrinogen and other adhesive proteins joins platelets together in the aggregate. Widespread genotyping has revealed that mutations spread across both genes, yet the reason for the extensive variation in both the severity and intensity of bleeding between affected individuals remains poorly understood. Furthermore, although genetic defects of ITGB3 affect other tissues with β3 present as αvβ3 (the vitronectin receptor), the bleeding phenotype continues to dominate. Here, we look in detail at mutations that affect (i) the β-propeller region of the αIIb head domain and (ii) the membrane proximal disulfide-rich epidermal growth factor (EGF) domains of β3 and which often result in spontaneous integrin activation. We also examine deep vein thrombosis as an unexpected complication of GT and look at curative procedures for the diseases, including allogeneic stem cell transfer and the potential for gene therapy.
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Affiliation(s)
- Alan T Nurden
- Plateforme Technologique et d'Innovation Biomédicale, Hôpital Xavier Arnozan, Pessac, France.
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Nicolaou N, Margadant C, Kevelam SH, Lilien MR, Oosterveld MJS, Kreft M, van Eerde AM, Pfundt R, Terhal PA, van der Zwaag B, Nikkels PGJ, Sachs N, Goldschmeding R, Knoers NVAM, Renkema KY, Sonnenberg A. Gain of glycosylation in integrin α3 causes lung disease and nephrotic syndrome. J Clin Invest 2012; 122:4375-87. [PMID: 23114595 DOI: 10.1172/jci64100] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 09/06/2012] [Indexed: 12/23/2022] Open
Abstract
Integrins are transmembrane αβ glycoproteins that connect the extracellular matrix to the cytoskeleton. The laminin-binding integrin α3β1 is expressed at high levels in lung epithelium and in kidney podocytes. In podocytes, α3β1 associates with the tetraspanin CD151 to maintain a functional filtration barrier. Here, we report on a patient homozygous for a novel missense mutation in the human ITGA3 gene, causing fatal interstitial lung disease and congenital nephrotic syndrome. The mutation caused an alanine-to-serine substitution in the integrin α3 subunit, thereby introducing an N-glycosylation motif at amino acid position 349. We expressed this mutant form of ITGA3 in murine podocytes and found that hyperglycosylation of the α3 precursor prevented its heterodimerization with β1, whereas CD151 association with the α3 subunit occurred normally. Consequently, the β1 precursor accumulated in the ER, and the mutant α3 precursor was degraded by the ubiquitin-proteasome system. Thus, these findings uncover a gain-of-glycosylation mutation in ITGA3 that prevents the biosynthesis of functional α3β1, causing a fatal multiorgan disorder.
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Affiliation(s)
- Nayia Nicolaou
- Department of Medical Genetics, University Medical Center Utrecht, Utrecht, The Netherlands
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Pillois X, Fiore M, Heilig R, Pico M, Nurden AT. A novel amino acid substitution of integrin αIIb in Glanzmann thrombasthenia confirms that the N-terminal region of the receptor plays a role in maintaining β-propeller structure. Platelets 2012; 24:77-80. [DOI: 10.3109/09537104.2012.665278] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Ghosh K. Coagulation disorders seen through the window of molecular biology. INDIAN JOURNAL OF HUMAN GENETICS 2011; 13:81-7. [PMID: 21957353 PMCID: PMC3168142 DOI: 10.4103/0971-6866.38980] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Coagulation disorders have been traditionally worked up by their clinical phenotypes and coagulation factor assays which are dependent on APTT- and PT-based techniques. Development of chromogenic substrates in the late seventies and early eighties allowed coagulation factors to be measured like enzymes. There was still a major lacuna in the understanding of the biology of different coagulation disorders. Modern molecular biology - which developed as an unique synthesis of biochemistry, immunology, cell biology, and genetics - allowed us to have a more comprehensive understanding of the pathobiology of many of these coagulation disorders. This overview presents several examples which show how we have enriched our understanding about the varied clinical phenotypes of different coagulation disorders.
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Affiliation(s)
- Kanjaksha Ghosh
- Institute of Immunohematology, 13 Floor, KEM Hospital Campus, Parel, Mumbai - 400 012, India
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Glanzmann thrombasthenia: a review of ITGA2B and ITGB3 defects with emphasis on variants, phenotypic variability, and mouse models. Blood 2011; 118:5996-6005. [PMID: 21917754 DOI: 10.1182/blood-2011-07-365635] [Citation(s) in RCA: 159] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Characterized by mucocutaneous bleeding arising from a lack of platelet aggregation to physiologic stimuli, Glanzmann thrombasthenia (GT) is the archetype-inherited disorder of platelets. Transmitted by autosomal recessive inheritance, platelets in GT have quantitative or qualitative deficiencies of the fibrinogen receptor, αIIbβ3, an integrin coded by the ITGA2B and ITGB3 genes. Despite advances in our understanding of the disease, extensive phenotypic variability with respect to severity and intensity of bleeding remains poorly understood. Importantly, genetic defects of ITGB3 also potentially affect other tissues, for β3 has a wide tissue distribution when present as αvβ3 (the vitronectin receptor). We now look at the repertoire of ITGA2B and ITGB3 gene defects, reexamine the relationship between phenotype and genotype, and review integrin structure in the many variant forms. Evidence for modifications in platelet production is assessed, as is the multifactorial etiology of the clinical expression of the disease. Reports of cardiovascular disease and deep vein thrombosis, cancer, brain disease, bone disorders, and pregnancy defects in GT are discussed in the context of the results obtained for mouse models where nonhemostatic defects of β3-deficiency or nonfunction are being increasingly described.
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Nurden AT, Fiore M, Nurden P, Heilig R, Pillois X. Are bone defects in rare patients with Glanzmann's thrombasthenia associated with ITGB3 or ITGA2B mutations? Platelets 2011; 22:547-51. [PMID: 21557682 DOI: 10.3109/09537104.2011.573600] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The question as to whether Glanzmann thrombasthenia patients with ITGB3 defects and deficiencies of both αIIbβ3 and αvβ3 show phenotypic differences to those with abnormalities exclusive to αIIbβ3 is unresolved. Studies on β3-deficient mice have shown an increased bone mass. Here we review the literature on bone defects in thrombasthenia patients and report the molecular analysis of a patient associating a lifelong thrombasthenia-like syndrome with skeletal defects. We show that the patient is compound heterozygote for Arg327His and Gly391Arg mutations in αIIb, with one mutation inherited from each parent. Modelling strongly suggested that both mutations act by destabilizing the αIIb beta propeller. So it appears likely that this patient has a combination of co-expressed genetic defects.
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Affiliation(s)
- Alan T Nurden
- Centre de Référence des Pathologies Plaquettaires, Plateforme Technologique et d'Innovation Biomédicale, Hôpital Xavier Arnozan, Pessac, France.
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Abstract
Glanzmann's thrombasthenia (GT) is an autosomal recessive inherited bleeding disorder due to a defect in platelet function. The hallmark of this disease is severely reduced/absent platelet aggregation in response to multiple physiological agonists. Bleeding signs in GT include epistaxis, bruising, gingival hemorrhage, gastrointestinal hemorrhage, hematuria, menorrhagia, and hemarthrosis. Homozygous or compound heterozygous mutations in the genes of GPIIb and GPIIIa lead to GT. A patient with GT, with no possible causative mutations in GPIIb and GPIIIa genes, may harbor defects in a regulatory element affecting the transcription of these 2 genes. GT occurs in high frequency in certain ethnic populations with an increased incidence of consanguinity such as in Indians, Iranians, Iraqi Jews, Palestinian and Jordanian Arabs, and French Gypsies. Carrier detection in GT is important to control the disorder in family members. Carrier detection can be done both by protein analysis and direct gene analysis.
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Affiliation(s)
- Meganathan Kannan
- Department of Hematology, All India Institute of Medical Sciences, New Delhi, India
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Afrasiabi A, Gelain F, Artoni A, Mannucci PM. AlphaIIbG236E causes Glanzmann thrombasthenia by impairing association with beta3. Platelets 2008; 19:322-7. [PMID: 18791937 DOI: 10.1080/09537100802123365] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Glanzmann thrombasthenia (GT) is a recessively inherited bleeding disorder caused by the quantitative or qualitative deficiency of the platelet fibrinogen receptor, integrin alphaIIbbeta3. The N-terminal domain of the alphaIIb subunit is folded in a beta-propeller that plays the role of binding fibrinogen and associating with the ligand-binding region of beta3. Analysing the mutations of Italian GT patients we found that a patient had a alphaIIb G236E missense substitution that substitutes a glycine from the highly conserved PhiPhiGPhi motif of blade 4 of the beta-propeller. To verify experimentally the effect of the substitution of glycine 236 human embryonic kidney (HEK) cells were transfected with normal or mutated alphaIIb in conjunction with normal beta3. Using flow cytometry analysis we found the percentage of HEK cells transfected with alphaIIbG236Ebeta3 that reacted with anti alphaIIbbeta3 was very low. In HEK cells transfected with either alphaIIbbeta3 or alphaIIbG236Ebeta3 and lysed, when immunoblotting was done in non-reducing conditions a band reacting with an antibody against alphaIIb was present in both lysates, although less intense in cells transfected with alphaIIbG236Ebeta3. In reducing condition alphaIIb from cells transfected with alphaIIbbeta3 was nearly all mature, while in cells transfected with alphaIIbG236Ebeta3 the ratio pro-alphaIIb: alphaIIb was 1 : 1, with signs of degradation of the mutated protein. Cell lysates were then immunoprecipitated with antibodies against alphaIIb and immunoblotted with an antibody reacting with beta3. While in immunoblots from cells transfected with alphaIIbbeta3 a band corresponding to beta3 was strongly detectable, in immunoblots originating from cells transfected with alphaIIbG236Ebeta3 no band at the same level of normal beta3 was detected. Immunofluorescence studies showed accumulation of alphaIIbG236Ebeta3 in the endoplasmic reticulum and minimal transport to the Golgi. In conclusion we demonstrated that the alphaIIbG236E mutation causes GT by impairing the association with beta3 during biogenesis of the receptor.
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Affiliation(s)
- A Afrasiabi
- Hematology and Thrombosis Unit, Hematology Research Center, Shiraz University of Medical Sciences, Nemazee Hospital, Shiraz, Iran
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Murcia M, Jirouskova M, Li J, Coller BS, Filizola M. Functional and computational studies of the ligand-associated metal binding site of beta3 integrins. Proteins 2008; 71:1779-91. [PMID: 18175315 DOI: 10.1002/prot.21859] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
A combination of experimental and computational approaches was used to provide a structural context for the role of the beta3 integrin subunit ligand-associated metal binding site (LIMBS) in the binding of physiological ligands to beta3 integrins. Specifically, we have carried out (1) adhesion assays on cells expressing normal alphaIIbeta3, normal alphaVbeta3, or the corresponding beta3 D217A LIMBS mutants; and (2) equilibrium and nonequilibrium (steered) molecular dynamics (MD) simulations of eptifibatide in complex with either a fully hydrated normal alphaIIbeta3 integrin fragment (alphaIIb beta-propeller and the beta3 betaA (I-like), hybrid, and PSI domains) or the equivalent beta3 D217A mutant. Normal alphaIIbeta3 expressing cells adhered to immobilized fibrinogen and echistatin, whereas cells expressing the alphaIIbeta3 D217A LIMBS mutant failed to adhere to either ligand. Similarly, the equivalent alphaVbeta3 mutant was unable to support adhesion to vitronectin or fibrinogen. The alphaIIbeta3 D217A mutation increased the binding of mAb AP5, which recognizes a ligand-induced binding site (LIBS) in the beta3 PSI domain, indicating that this mutation induced allosteric changes in the protein. Steered MD simulating the unbinding of eptifibatide from either normal alphaIIbeta3 or the equivalent beta3 D217A mutant suggested that the reduction in ligand binding caused by the LIMBS mutant required the loss of both the LIMBS and the metal ion-dependent adhesion site (MIDAS) metal ions. Our computational results indicate that the LIMBS plays a crucial role in ligand binding to alphaIIbeta3 by virtue of its effects on the coordination of the MIDAS.
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Affiliation(s)
- Marta Murcia
- Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York, New York 10029-6574, USA
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Gupta V, Alonso JL, Sugimori T, Essafi M, Issafi M, Xiong JP, Arnaout MA. Role of the beta-subunit arginine/lysine finger in integrin heterodimer formation and function. THE JOURNAL OF IMMUNOLOGY 2008; 180:1713-8. [PMID: 18209068 DOI: 10.4049/jimmunol.180.3.1713] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Formation of the integrin alphabeta heterodimer is essential for cell surface expression and function. At the core of the alphabeta interface is a conserved Arg/Lys "finger" from the beta-subunit that inserts into a cup-like "cage" formed of two layers of aromatic residues in the alpha-subunit. We evaluated the role of this residue in heterodimer formation in an alphaA-lacking and an alphaA-containing integrin alphaVbeta3 and alphaMbeta2 (CD11b/CD18), respectively. Arg261 of beta3 was mutated to Ala or Glu; the corresponding Lys252 of beta2 was mutated to Ala, Arg, Glu, Asp, or Phe; and the effects on heterodimer formation in each integrin examined by ELISA and immunoprecipitation in HEK 293 cells cotransfected with plasmids encoding the alpha- and beta-subunits. The Arg261Glu (but not Arg261Ala) substitution significantly impaired cell surface expression and heterodimer formation of alphaVbeta3. Although Lys252Arg, and to a lesser extent Lys252Ala, were well tolerated, each of the remaining substitutions markedly reduced cell surface expression and heterodimer formation of CD11b/CD18. Lys252Arg and Lys252Ala integrin heterodimers displayed a significant increase in binding to the physiologic ligand iC3b. These data demonstrate an important role of the Arg/Lys finger in formation of a stable integrin heterodimer, and suggest that subtle changes at this residue affect the activation state of the integrin.
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Affiliation(s)
- Vineet Gupta
- Division of Nephrology, Leukocyte Biology and Inflammation Program, Structural Biology Program, Massachusetts General Hospital and Harvard Medical School, 149 13th Street, Charlestown, MA 02129, USA
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Silencing of OB-RGRP in mouse hypothalamic arcuate nucleus increases leptin receptor signaling and prevents diet-induced obesity. Proc Natl Acad Sci U S A 2007; 104:19476-81. [PMID: 18042720 DOI: 10.1073/pnas.0706671104] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Obesity is a major public health problem and is often associated with type 2 diabetes mellitus, cardiovascular disease, and metabolic syndrome. Leptin is the crucial adipostatic hormone that controls food intake and body weight through the activation of specific leptin receptors (OB-R) in the hypothalamic arcuate nucleus (ARC). However, in most obese patients, high circulating levels of leptin fail to bring about weight loss. The prevention of this "leptin resistance" is a major goal for obesity research. We report here a successful prevention of diet-induced obesity (DIO) by silencing a negative regulator of OB-R function, the OB-R gene-related protein (OB-RGRP), whose transcript is genetically linked to the OB-R transcript. We provide in vitro evidence that OB-RGRP controls OB-R function by negatively regulating its cell surface expression. In the DIO mouse model, obesity was prevented by silencing OB-RGRP through stereotactic injection of a lentiviral vector encoding a shRNA directed against OB-RGRP in the ARC. This work demonstrates that OB-RGRP is a potential target for obesity treatment. Indeed, regulators of the receptor could be more appropriate targets than the receptor itself. This finding could serve as the basis for an approach to identifying potential new therapeutic targets for a variety of diseases, including obesity.
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Nelson EJR, Nair SC, Peretz H, Coller BS, Seligsohn U, Chandy M, Srivastava A. Diversity of Glanzmann thrombasthenia in southern India: 10 novel mutations identified among 15 unrelated patients. J Thromb Haemost 2006; 4:1730-7. [PMID: 16879215 DOI: 10.1111/j.1538-7836.2006.02066.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND Glanzmann thrombasthenia (GT) is a congenital bleeding disorder caused by either a lack or dysfunction of the platelet integrin alphaIIbbeta3. OBJECTIVES To determine the molecular basis of GT in patients from southern India. PATIENTS Fifteen unrelated patients whose diagnosis was consistent with GT were evaluated. RESULTS Platelet surface expression of alphaIIbbeta3 was < 10%, 10%-50%, and > 50% of controls in five, nine, and one patient(s), respectively. Immunoblotting of the platelet lysates showed no alphaIIb in 14 patients, and no beta3 in 10 patients, although severely reduced in four patients. Platelet fibrinogen was undetectable in 13 patients, and severely reduced in one patient. One patient showed normal surface alphaIIbbeta3 expression, and normal alphaIIb, beta3 and fibrinogen levels in the lysate. Ten novel candidate disease-causing mutations were identified in 11 patients. The missense mutations included Gly128Ser, Ser287Leu, Gly357Ser, Arg520Trp, Leu799Arg in alphaIIb, and Cys575Gly in beta3. We have already shown that Gly128Ser, Ser287Leu, and Gly357Ser mutations variably affect alphaIIbbeta3 surface expression. The Cys575Gly mutation may disrupt the disulphide link with Cys586 to cause the GT phenotype. The molecular pathology of the other missense mutations is not clear. Two nonsense mutations, Trp-16Stop and Glu715Stop in alphaIIb, and a 7-bp deletion (330-336TCCCCAG) in beta3 are predicted to result in truncated proteins. An IVS15(-1)G --> A mutation in alphaIIb induced a cryptic splice site as confirmed by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Thirteen polymorphisms were also identified (five in alphaIIb and eight in beta3), among which five were novel. CONCLUSIONS While identifying a significant number of novel mutations causing GT, this study confirms the genetic heterogeneity of the disorder in southern India.
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Affiliation(s)
- E J R Nelson
- Department of Hematology, Christtian Medical College, Vellore, India
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