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O'Donoghue L, Smolenski A. Roles of G proteins and their GTPase-activating proteins in platelets. Biosci Rep 2024; 44:BSR20231420. [PMID: 38808367 PMCID: PMC11139668 DOI: 10.1042/bsr20231420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Revised: 04/30/2024] [Accepted: 05/02/2024] [Indexed: 05/30/2024] Open
Abstract
Platelets are small anucleate blood cells supporting vascular function. They circulate in a quiescent state monitoring the vasculature for injuries. Platelets adhere to injury sites and can be rapidly activated to secrete granules and to form platelet/platelet aggregates. These responses are controlled by signalling networks that include G proteins and their regulatory guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Recent proteomics studies have revealed the complete spectrum of G proteins, GEFs, and GAPs present in platelets. Some of these proteins are specific for platelets and very few have been characterised in detail. GEFs and GAPs play a major role in setting local levels of active GTP-bound G proteins in response to activating and inhibitory signals encountered by platelets. Thus, GEFs and GAPs are highly regulated themselves and appear to integrate G protein regulation with other cellular processes. This review focuses on GAPs of small G proteins of the Arf, Rab, Ras, and Rho families, as well as of heterotrimeric G proteins found in platelets.
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Affiliation(s)
- Lorna O'Donoghue
- UCD School of Medicine, University College Dublin, UCD Conway Institute, Belfield, Dublin 4, Ireland
- Irish Centre for Vascular Biology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green 123, Dublin 2, Ireland
| | - Albert Smolenski
- UCD School of Medicine, University College Dublin, UCD Conway Institute, Belfield, Dublin 4, Ireland
- Irish Centre for Vascular Biology, Royal College of Surgeons in Ireland, 123 St. Stephen’s Green 123, Dublin 2, Ireland
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Lecchi A, La Marca S, Padovan L, Boscarino M, Peyvandi F, Tripodi A. Flow-chamber device (T-TAS) to diagnose patients suspected of platelet function defects. BLOOD TRANSFUSION = TRASFUSIONE DEL SANGUE 2024; 22:55-64. [PMID: 36795343 PMCID: PMC10812895 DOI: 10.2450/2023.0208-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 12/14/2022] [Indexed: 02/17/2023]
Abstract
BACKGROUND Patients suspected of platelet function defects represent a diagnostic challenge for the clinical laboratory, mainly due to the complexity and poor standardization of screening methods. We compared a new flow-based chip-equipped point-of-care (T-TAS) device with lumi-aggregometry and other specific tests. MATERIALS AND METHODS The study included 96 patients suspected of platelet function defects and 26 patients referred to hospital for an evaluation of residual platelet function while on antiplatelet therapy. RESULTS Forty-eight of 96 patients displayed abnormal platelet function by lumi-aggregometry, and 10 of them had defective granule content and were classified as δ-storage pool disease (δ-SPD). T-TAS compared favorably with lumi-aggregometry in detecting the most severe forms of platelet function defects (i.e., δ-SPD) [test agreement (lumi-light transmission aggregometry [lumi-LTA] vs T-TAS) for the δ-SPD subgroup was 80% and K CHOEN 0.695. T-TAS was less sensitive to milder platelet function defects (i.e., primary secretion defects [PSD]). Concerning patients on antiplatelets, test agreement (lumi-LTA vs T-TAS) in detecting patients who were responders to this therapy was 54%; K CHOEN 0.150. DISCUSSION The results indicate that T-TAS can detect the more severe forms of platelet function defects such as δ-SPD. There is limited agreement of T-TAS with lumi-aggregometry in identifying responders to antiplatelets. However, this poor agreement is commonly shared by lumi-aggregometry and other devices owing to the lack of test specificity and of prospective data from clinical trials linking platelet function with therapeutic efficacy.
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Affiliation(s)
- Anna Lecchi
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
| | - Silvia La Marca
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
| | - Lidia Padovan
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
| | - Marco Boscarino
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
| | - Flora Peyvandi
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
- Università degli Studi di Milano, Department of Pathophysiology and Transplantation, Milan, Italy
| | - Armando Tripodi
- Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center and Fondazione Luigi Villa, Milan, Italy
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Ottesen EW, Singh NN, Luo D, Kaas B, Gillette B, Seo J, Jorgensen H, Singh RN. Diverse targets of SMN2-directed splicing-modulating small molecule therapeutics for spinal muscular atrophy. Nucleic Acids Res 2023; 51:5948-5980. [PMID: 37026480 PMCID: PMC10325915 DOI: 10.1093/nar/gkad259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 03/13/2023] [Accepted: 03/28/2023] [Indexed: 04/08/2023] Open
Abstract
Designing an RNA-interacting molecule that displays high therapeutic efficacy while retaining specificity within a broad concentration range remains a challenging task. Risdiplam is an FDA-approved small molecule for the treatment of spinal muscular atrophy (SMA), the leading genetic cause of infant mortality. Branaplam is another small molecule which has undergone clinical trials. The therapeutic merit of both compounds is based on their ability to restore body-wide inclusion of Survival Motor Neuron 2 (SMN2) exon 7 upon oral administration. Here we compare the transcriptome-wide off-target effects of these compounds in SMA patient cells. We captured concentration-dependent compound-specific changes, including aberrant expression of genes associated with DNA replication, cell cycle, RNA metabolism, cell signaling and metabolic pathways. Both compounds triggered massive perturbations of splicing events, inducing off-target exon inclusion, exon skipping, intron retention, intron removal and alternative splice site usage. Our results of minigenes expressed in HeLa cells provide mechanistic insights into how these molecules targeted towards a single gene produce different off-target effects. We show the advantages of combined treatments with low doses of risdiplam and branaplam. Our findings are instructive for devising better dosing regimens as well as for developing the next generation of small molecule therapeutics aimed at splicing modulation.
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Affiliation(s)
- Eric W Ottesen
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Natalia N Singh
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Diou Luo
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Bailey Kaas
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Benjamin J Gillette
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Joonbae Seo
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Hannah J Jorgensen
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
| | - Ravindra N Singh
- Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA
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Majdalani P, Levitas A, Krymko H, Slanovic L, Braiman A, Hadad U, Dabsan S, Horev A, Zarivach R, Parvari R. A Missense Variation in PHACTR2 Associates with Impaired Actin Dynamics, Dilated Cardiomyopathy, and Left Ventricular Non-Compaction in Humans. Int J Mol Sci 2023; 24:ijms24021388. [PMID: 36674904 PMCID: PMC9864900 DOI: 10.3390/ijms24021388] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 12/24/2022] [Accepted: 01/06/2023] [Indexed: 01/13/2023] Open
Abstract
Dilated cardiomyopathy (DCM) with left ventricular non-compaction (LVNC) is a primary myocardial disease leading to contractile dysfunction, progressive heart failure, and excessive risk of sudden cardiac death. Using whole-exome sequencing to investigate a possible genetic cause of DCM with LVNC in a consanguineous child, a homozygous nucleotide change c.1532G>A causing p.Arg511His in PHACTR2 was found. The missense change can affect the binding of PHACTR2 to actin by eliminating the hydrogen bonds between them. The amino acid change does not change PHACTR2 localization to the cytoplasm. The patient’s fibroblasts showed a decreased globular to fibrillary actin ratio compared to the control fibroblasts. The re-polymerization of fibrillary actin after treatment with cytochalasin D, which disrupts the actin filaments, was slower in the patient’s fibroblasts. Finally, the patient’s fibroblasts bridged a scar gap slower than the control fibroblasts because of slower and indirect movement. This is the first report of a human variation in this PHACTR family member. The knock-out mouse model presented no significant phenotype. Our data underscore the importance of PHACTR2 in regulating the monomeric actin pool, the kinetics of actin polymerization, and cell movement, emphasizing the importance of actin regulation for the normal function of the human heart.
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Affiliation(s)
- Pierre Majdalani
- The Shraga Segal Department of Microbiology, Immunology & Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- The National Institute for Biotechnology in the Negev, Marcus Campus, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Aviva Levitas
- Department of Pediatric Cardiology, Soroka University Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84101, Israel
| | - Hanna Krymko
- Department of Pediatric Cardiology, Soroka University Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84101, Israel
| | - Leonel Slanovic
- Department of Pediatric Cardiology, Soroka University Medical Center, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84101, Israel
| | - Alex Braiman
- The Shraga Segal Department of Microbiology, Immunology & Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Uzi Hadad
- The Ilse Katz Institute for Nanoscale Science and Technology, Marcus Campus, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Salam Dabsan
- The Shraga Segal Department of Microbiology, Immunology & Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- The National Institute for Biotechnology in the Negev, Marcus Campus, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Amir Horev
- Pediatric Dermatology Service, Soroka University Medical Center, Beer-Sheva 84101, Israel
| | - Raz Zarivach
- The National Institute for Biotechnology in the Negev, Marcus Campus, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- Department of Life Sciences, Faculty of Natural Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
| | - Ruti Parvari
- The Shraga Segal Department of Microbiology, Immunology & Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- The National Institute for Biotechnology in the Negev, Marcus Campus, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel
- Correspondence: ; Tel.: +972-8-647-9967
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Terry LE, Arige V, Neumann J, Wahl AM, Knebel TR, Chaffer JW, Malik S, Liston A, Humblet-Baron S, Bultynck G, Yule DI. Missense mutations in inositol 1,4,5-trisphosphate receptor type 3 result in leaky Ca 2+ channels and activation of store-operated Ca 2+ entry. iScience 2022; 25:105523. [PMID: 36444295 PMCID: PMC9700043 DOI: 10.1016/j.isci.2022.105523] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 10/10/2022] [Accepted: 11/04/2022] [Indexed: 11/09/2022] Open
Abstract
Mutations in all subtypes of the inositol 1,4,5-trisphosphate receptor Ca2+ release channel are associated with human diseases. In this report, we investigated the functionality of three neuropathy-associated missense mutations in IP3R3 (V615M, T1424M, and R2524C). The mutants only exhibited function when highly over-expressed compared to endogenous hIP3R3. All variants resulted in elevated basal cytosolic Ca2+ levels, decreased endoplasmic reticulum Ca2+ store content, and constitutive store-operated Ca2+ entry in the absence of any stimuli, consistent with a leaky IP3R channel pore. These variants differed in channel function; when stably over-expressed the R2524C mutant was essentially dead, V615M was poorly functional, and T1424M exhibited activity greater than that of the corresponding wild-type following threshold stimulation. These results demonstrate that a common feature of these mutations is decreased IP3R3 function. In addition, these mutations exhibit a novel phenotype manifested as a constitutively open channel, which inappropriately gates SOCE in the absence of stimulation.
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Affiliation(s)
- Lara E. Terry
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - Vikas Arige
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - Julika Neumann
- KU Leuven, Department of Microbiology and Immunology, Leuven, Belgium
| | - Amanda M. Wahl
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - Taylor R. Knebel
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - James W. Chaffer
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - Sundeep Malik
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
| | - Adrian Liston
- KU Leuven, Department of Microbiology and Immunology, Leuven, Belgium
| | | | - Geert Bultynck
- KU Leuven, Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - David I. Yule
- Department of Pharmacology and Physiology, University of Rochester, Rochester, NY 14642, USA
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Jha N, Mangukia N, Gadhavi H, Patel M, Bhavsar M, Rawal R, Patel S. Small RNA sequencing and identification of papaya (Carica papaya L.) miRNAs with potential cross-kingdom human gene targets. Mol Genet Genomics 2022; 297:981-997. [PMID: 35570207 PMCID: PMC9107959 DOI: 10.1007/s00438-022-01904-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Accepted: 04/23/2022] [Indexed: 12/11/2022]
Abstract
Several studies have demonstrated potential role of plant-derived miRNAs in cross-kingdom species relationships by transferring into non-plant host cells to regulate certain host cellular functions. How nutrient-rich plants regulate host cellular functions, which in turn alleviate physiological and disease conditions in the host remains to be explored in detail. This computational study explores the potential targets, putative role, and functional implications of miRNAs derived from Carica papaya L., one of the most cultivated tropical crops in the world and a rich source of phytochemicals and enzymes, in human diet. Using the next-generation sequencing, -Illumina HiSeq2500, ~ 30 million small RNA sequence reads were generated from C. papaya young leaves, resulting in the identification of a total of 1798 known and 49 novel miRNAs. Selected novel C. papaya miRNAs were predicted to regulate certain human targets, and subsequent annotation of gene functions indicated a probable role in various biological processes and pathways, such as MAPK, WNT, and GPCR signaling pathways, and platelet activation. These presumptive target gene in humans were predominantly linked to various diseases, including cancer, diabetes, mental illness, and platelet disorder. The computational finding of this study provides insights into how C. papaya-derived miRNAs may regulate certain conditions of human disease and provide a new perspective on human health. However, the therapeutic potential of C. papaya miRNA can be further explored through experimental studies.
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Affiliation(s)
- Neha Jha
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
| | - Naman Mangukia
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
- BioInnovations, Bhayander (West), Mumbai, 401101, Maharashtra, India
| | - Harshida Gadhavi
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
| | - Maulik Patel
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
- Advait Theragnostics Pvt. Ltd., Ahmedabad, Gujarat, India
| | - Mansi Bhavsar
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
| | - Rakesh Rawal
- Department of Biochemistry and Forensic Science, University School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India
| | - Saumya Patel
- Department of Botany, Bioinformatics and Climate Change Impacts Management, School of Sciences, Gujarat University, Ahmedabad, 380009, Gujarat, India.
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Nephroplex: a kidney-focused NGS panel highlights the challenges of PKD1 sequencing and identifies a founder BBS4 mutation. J Nephrol 2021; 34:1855-1874. [PMID: 33964006 PMCID: PMC8610957 DOI: 10.1007/s40620-021-01048-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 04/04/2021] [Indexed: 12/02/2022]
Abstract
Background Genetic testing of patients with inherited kidney diseases has emerged as a tool of clinical utility by improving the patients’ diagnosis, prognosis, surveillance and therapy. Methods The present study applied a Next Generation Sequencing (NGS)-based panel, named NephroPlex, testing 115 genes causing renal diseases, to 119 individuals, including 107 probands and 12 relatives. Thirty-five (poly)cystic and 72 non (poly)cystic individuals were enrolled. The latter subgroup of patients included Bardet-Biedl syndrome (BBS) patients, as major components. Results Disease-causing mutations were identified in 51.5 and 40% of polycystic and non-polycystic individuals, respectively. Autosomal dominant polycystic kidney disease (ADPKD) patients with truncating PKD1 variants showed a trend towards a greater slope of the age-estimated glomerular filtration rate (eGFR) regression line than patients with (i) missense variants, (ii) any PKD2 mutations and (iii) no detected mutations, according to previous findings. The analysis of BBS individuals showed a similar frequency of BBS4,9,10 and 12 mutations. Of note, all BBS4-mutated patients harbored the novel c.332+1G>GTT variant, which was absent in public databases, however, in our internal database, an additional heterozygote carrier was found. All BBS4-mutated individuals originated from the same geographical area encompassing the coastal provinces of Naples. Discussion In conclusion, these findings indicate the potential for a genetic panel to provide useful information at both clinical and epidemiological levels. Graphic abstract ![]()
Supplementary Information The online version contains supplementary material available at 10.1007/s40620-021-01048-4.
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Nurden P, Stritt S, Favier R, Nurden AT. Inherited platelet diseases with normal platelet count: phenotypes, genotypes and diagnostic strategy. Haematologica 2021; 106:337-350. [PMID: 33147934 PMCID: PMC7849565 DOI: 10.3324/haematol.2020.248153] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Accepted: 08/12/2020] [Indexed: 12/16/2022] Open
Abstract
Inherited platelet disorders resulting from platelet function defects and a normal platelet count cause a moderate or severe bleeding diathesis. Since the description of Glanzmann thrombasthenia resulting from defects of ITGA2B and ITGB3, new inherited platelet disorders have been discovered, facilitated by the use of high throughput sequencing and genomic analyses. Defects of RASGRP2 and FERMT3 responsible for severe bleeding syndromes and integrin activation have illustrated the critical role of signaling molecules. Important are mutations of P2RY12 encoding the major ADP receptor causal for an inherited platelet disorder with inheritance characteristics that depend on the variant identified. Interestingly, variants of GP6 encoding the major subunit of the collagen receptor GPVI/FcRassociate only with mild bleeding. The numbers of genes involved in dense granule defects including Hermansky-Pudlak and Chediak Higashi syndromes continue to progress and are updated. The ANO6 gene encoding a Ca2+-activated ion channel required for phospholipid scrambling is responsible for the rare Scott syndrome and decreased procoagulant activity. A novel EPHB2 defect in a familial bleeding syndrome demonstrates a role for this tyrosine kinase receptor independent of the classical model of its interaction with ephrins. Such advances highlight the large diversity of variants affecting platelet function but not their production, despite the difficulties in establishing a clear phenotype when few families are affected. They have provided insights into essential pathways of platelet function and have been at the origin of new and improved therapies for ischemic disease. Nevertheless, many patients remain without a diagnosis and requiring new strategies that are now discussed.
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Affiliation(s)
| | - Simon Stritt
- Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala
| | - Remi Favier
- French National Reference Center for Inherited Platelet Disorders, Armand Trousseau Hospital, Assistance Publique-Hôpitaux de Paris, Paris
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Terry LE, Alzayady KJ, Wahl AM, Malik S, Yule DI. Disease-associated mutations in inositol 1,4,5-trisphosphate receptor subunits impair channel function. J Biol Chem 2020; 295:18160-18178. [PMID: 33093175 PMCID: PMC7939385 DOI: 10.1074/jbc.ra120.015683] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 10/21/2020] [Indexed: 01/27/2023] Open
Abstract
The inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs), which form tetrameric channels, play pivotal roles in regulating the spatiotemporal patterns of intracellular calcium signals. Mutations in IP3Rs have been increasingly associated with many debilitating human diseases such as ataxia, Gillespie syndrome, and generalized anhidrosis. However, how these mutations affect IP3R function, and how the perturbation of as-sociated calcium signals contribute to the pathogenesis and severity of these diseases remains largely uncharacterized. Moreover, many of these diseases occur as the result of autosomal dominant inheritance, suggesting that WT and mutant subunits associate in heterotetrameric channels. How the in-corporation of different numbers of mutant subunits within the tetrameric channels affects its activities and results in different disease phenotypes is also unclear. In this report, we investigated representative disease-associated missense mutations to determine their effects on IP3R channel activity. Additionally, we designed concatenated IP3R constructs to create tetrameric channels with a predefined subunit composition to explore the functionality of heteromeric channels. Using calcium imaging techniques to assess IP3R channel function, we observed that all the mutations studied resulted in severely attenuated Ca2+ release when expressed as homotetramers. However, some heterotetramers retained varied degrees of function dependent on the composition of the tetramer. Our findings suggest that the effect of mutations depends on the location of the mutation in the IP3R structure, as well as on the stoichiometry of mutant subunits assembled within the tetrameric channel. These studies provide insight into the pathogenesis and penetrance of these devastating human diseases.
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Affiliation(s)
- Lara E Terry
- Department of Pharmacology and Physiology, University of Rochester, Rochester, New York, USA
| | - Kamil J Alzayady
- Department of Pharmacology and Physiology, University of Rochester, Rochester, New York, USA
| | - Amanda M Wahl
- Department of Pharmacology and Physiology, University of Rochester, Rochester, New York, USA
| | - Sundeep Malik
- Department of Pharmacology and Physiology, University of Rochester, Rochester, New York, USA
| | - David I Yule
- Department of Pharmacology and Physiology, University of Rochester, Rochester, New York, USA.
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10
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Coste de Bagneaux P, von Elsner L, Bierhals T, Campiglio M, Johannsen J, Obermair GJ, Hempel M, Flucher BE, Kutsche K. A homozygous missense variant in CACNB4 encoding the auxiliary calcium channel beta4 subunit causes a severe neurodevelopmental disorder and impairs channel and non-channel functions. PLoS Genet 2020; 16:e1008625. [PMID: 32176688 PMCID: PMC7176149 DOI: 10.1371/journal.pgen.1008625] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 04/22/2020] [Accepted: 01/23/2020] [Indexed: 12/27/2022] Open
Abstract
P/Q-type channels are the principal presynaptic calcium channels in brain functioning in neurotransmitter release. They are composed of the pore-forming CaV2.1 α1 subunit and the auxiliary α2δ-2 and β4 subunits. β4 is encoded by CACNB4, and its multiple splice variants serve isoform-specific functions as channel subunits and transcriptional regulators in the nucleus. In two siblings with intellectual disability, psychomotor retardation, blindness, epilepsy, movement disorder and cerebellar atrophy we identified rare homozygous variants in the genes LTBP1, EMILIN1, CACNB4, MINAR1, DHX38 and MYO15 by whole-exome sequencing. In silico tools, animal model, clinical, and genetic data suggest the p.(Leu126Pro) CACNB4 variant to be likely pathogenic. To investigate the functional consequences of the CACNB4 variant, we introduced the corresponding mutation L125P into rat β4b cDNA. Heterologously expressed wild-type β4b associated with GFP-CaV1.2 and accumulated in presynaptic boutons of cultured hippocampal neurons. In contrast, the β4b-L125P mutant failed to incorporate into calcium channel complexes and to cluster presynaptically. When co-expressed with CaV2.1 in tsA201 cells, β4b and β4b-L125P augmented the calcium current amplitudes, however, β4b-L125P failed to stably complex with α1 subunits. These results indicate that p.Leu125Pro disrupts the stable association of β4b with native calcium channel complexes, whereas membrane incorporation, modulation of current density and activation properties of heterologously expressed channels remained intact. Wildtype β4b was specifically targeted to the nuclei of quiescent excitatory cells. Importantly, the p.Leu125Pro mutation abolished nuclear targeting of β4b in cultured myotubes and hippocampal neurons. While binding of β4b to the known interaction partner PPP2R5D (B56δ) was not affected by the mutation, complex formation between β4b-L125P and the neuronal TRAF2 and NCK interacting kinase (TNIK) seemed to be disturbed. In summary, our data suggest that the homozygous CACNB4 p.(Leu126Pro) variant underlies the severe neurological phenotype in the two siblings, most likely by impairing both channel and non-channel functions of β4b.
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Affiliation(s)
| | - Leonie von Elsner
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Tatjana Bierhals
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Marta Campiglio
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Jessika Johannsen
- Childrens Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Gerald J. Obermair
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
- Division Physiology, Karl Landsteiner University of Health Sciences, Krems, Austria
| | - Maja Hempel
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Bernhard E. Flucher
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Kerstin Kutsche
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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