1
|
Zhu S, Ye L, Bennett S, Xu H, He D, Xu J. Molecular structure and function of microfibrillar-associated proteins in skeletal and metabolic disorders and cancers. J Cell Physiol 2020; 236:41-48. [PMID: 32572962 DOI: 10.1002/jcp.29893] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/11/2020] [Accepted: 06/11/2020] [Indexed: 12/16/2022]
Abstract
Microfibrillar-associated proteins (MFAPs) are extracellular matrix glycoproteins, which play a role in microfibril assembly, elastinogenesis, and tissue homeostasis. MFAPs consist of five subfamily members, including MFAP1, MFAP2, MFAP3, MFAP4, and MFAP5. Among these, MFAP2 and MFAP5 are most closely related, and exhibit very limited amino acid sequence homology with MFAP1, MFAP3, and MFAP4. Gene expression profiling analysis reveals that MFAP2, MFAP5, and MFAP4 are specifically expressed in osteoblastic like cells, whereas MFAP1 and MFAP3 are more ubiquitously expressed, indicative of their diverse role in the tropism of tissues. Molecular structural analysis shows that each MFAP family member has distinct features, and functional evidence reveals discrete purposes of individual MFAPs. Animal studies indicate that MFAP2-deficient mice exhibit progressive osteopenia with elevated receptor activator of NF-κB ligand (RANKL) expression, whereas MFAP5-deficient mice are neutropenic, and MFAP4-deficient mice displayed emphysema-like pathology and the impaired formation of neointimal hyperplasia. Emerging data also suggest that MFAPs are involved in cancer progression and fat metabolism. Further understanding of tissue-specific pathophysiology of MFAPs might offer potential novel therapeutic targets for related diseases, such as skeletal and metabolic disorders, and cancers.
Collapse
Affiliation(s)
- Sipin Zhu
- Department of Orthopaedics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, China.,Division of Regenerative Biology, School of Biomedical Sciences, University of Western Australia, Perth, Australia
| | - Lin Ye
- Department of Orthopaedic Surgery, Lishui Municipal Central Hospital, The Fifth Affiliated Hospital of Wenzhou Medical University, Lishui, Zhejiang, China
| | - Samuel Bennett
- Division of Regenerative Biology, School of Biomedical Sciences, University of Western Australia, Perth, Australia
| | - Huazi Xu
- Department of Orthopaedics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, China
| | - Dengwei He
- Department of Orthopaedic Surgery, Lishui Municipal Central Hospital, The Fifth Affiliated Hospital of Wenzhou Medical University, Lishui, Zhejiang, China
| | - Jiake Xu
- Department of Orthopaedics, The Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University, Wenzhou, Zhejiang, China.,Division of Regenerative Biology, School of Biomedical Sciences, University of Western Australia, Perth, Australia
| |
Collapse
|
2
|
Abstract
Microfibril-associated glycoproteins 1 and 2 (MAGP-1, MAGP-2) are protein components of extracellular matrix microfibrils. These proteins interact with fibrillin, the core component of microfibrils, and impart unique biological properties that influence microfibril function in vertebrates. MAGPs bind active forms of TGFβ and BMPs and are capable of modulating Notch signaling. Mutations in MAGP-1 or MAGP-2 have been linked to thoracic aneurysms and metabolic disease in humans. MAGP-2 has also been shown to be an important biomarker in several human cancers. Mice lacking MAGP-1 or MAGP-2 have defects in multiple organ systems, which reflects the widespread distribution of microfibrils in vertebrate tissues. This review summarizes our current understanding of the function of the MAGPs and their relationship to human disease.
Collapse
Affiliation(s)
- Clarissa S Craft
- Division of Bone and Mineral Research, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Thomas J Broekelmann
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, United States
| | - Robert P Mecham
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, United States.
| |
Collapse
|
3
|
Mecham RP, Gibson MA. The microfibril-associated glycoproteins (MAGPs) and the microfibrillar niche. Matrix Biol 2015; 47:13-33. [PMID: 25963142 DOI: 10.1016/j.matbio.2015.05.003] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Revised: 03/23/2015] [Accepted: 03/24/2015] [Indexed: 10/23/2022]
Abstract
The microfibril-associated glycoproteins MAGP-1 and MAGP-2 are extracellular matrix proteins that interact with fibrillin to influence microfibril function. The two proteins are related through a 60 amino acid matrix-binding domain but their sequences differ outside of this region. A distinguishing feature of both proteins is their ability to interact with TGFβ family growth factors, Notch and Notch ligands, and multiple elastic fiber proteins. MAGP-2 can also interact with αvβ3 integrins via a RGD sequence that is not found in MAGP-1. Morpholino knockdown of MAGP-1 expression in zebrafish resulted in abnormal vessel wall architecture and altered vascular network formation. In the mouse, MAGP-1 deficiency had little effect on elastic fibers in blood vessels and lung but resulted in numerous unexpected phenotypes including bone abnormalities, hematopoietic changes, increased fat deposition, diabetes, impaired wound repair, and a bleeding diathesis. Inactivation of the gene for MAGP-2 in mice produced a neutropenia yet had minimal effects on bone or adipose homeostasis. Double knockouts had phenotypes characteristic of each individual knockout as well as several additional traits only seen when both genes are inactivated. A common mechanism underlying all of the traits associated with the knockout phenotypes is altered TGFβ signaling. This review summarizes our current understanding of the function of the MAGPs and discusses ideas related to their role in growth factor regulation.
Collapse
Affiliation(s)
- Robert P Mecham
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
| | - Mark A Gibson
- School of Medical Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
| |
Collapse
|
4
|
Hubmacher D, Wang LW, Mecham RP, Reinhardt DP, Apte SS. Adamtsl2 deletion results in bronchial fibrillin microfibril accumulation and bronchial epithelial dysplasia--a novel mouse model providing insights into geleophysic dysplasia. Dis Model Mech 2015; 8:487-99. [PMID: 25762570 PMCID: PMC4415891 DOI: 10.1242/dmm.017046] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 03/05/2015] [Indexed: 12/24/2022] Open
Abstract
Mutations in the secreted glycoprotein ADAMTSL2 cause recessive geleophysic dysplasia (GD) in humans and Musladin–Lueke syndrome (MLS) in dogs. GD is a severe, often lethal, condition presenting with short stature, brachydactyly, stiff skin, joint contractures, tracheal-bronchial stenosis and cardiac valve anomalies, whereas MLS is non-lethal and characterized by short stature and severe skin fibrosis. Although most mutations in fibrillin-1 (FBN1) cause Marfan syndrome (MFS), a microfibril disorder leading to transforming growth factor-β (TGFβ) dysregulation, domain-specific FBN1 mutations result in dominant GD. ADAMTSL2 has been previously shown to bind FBN1 and latent TGFβ-binding protein-1 (LTBP1). Here, we investigated mice with targeted Adamtsl2 inactivation as a new model for GD (Adamtsl2−/− mice). An intragenic lacZ reporter in these mice showed that ADAMTSL2 was produced exclusively by bronchial smooth muscle cells during embryonic lung development. Adamtsl2−/− mice, which died at birth, had severe bronchial epithelial dysplasia with abnormal glycogen-rich inclusions in bronchial epithelium resembling the cellular anomalies described previously in GD. An increase in microfibrils in the bronchial wall was associated with increased FBN2 and microfibril-associated glycoprotein-1 (MAGP1) staining, whereas LTBP1 staining was increased in bronchial epithelium. ADAMTSL2 was shown to bind directly to FBN2 with an affinity comparable to FBN1. The observed extracellular matrix (ECM) alterations were associated with increased bronchial epithelial TGFβ signaling at 17.5 days of gestation; however, treatment with TGFβ-neutralizing antibody did not correct the epithelial dysplasia. These investigations reveal a new function of ADAMTSL2 in modulating microfibril formation, and a previously unsuspected association with FBN2. Our studies suggest that the bronchial epithelial dysplasia accompanying microfibril dysregulation in Adamtsl2−/− mice cannot be reversed by TGFβ neutralization, and thus might be mediated by other mechanisms. Summary: The extracellular protein ADAMTSL2 is a crucial regulator of microfibril composition in the extracellular matrix of bronchial smooth muscle cells and influences bronchial epithelial function.
Collapse
Affiliation(s)
- Dirk Hubmacher
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Lauren W Wang
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| | - Robert P Mecham
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Dieter P Reinhardt
- Department of Anatomy and Cell Biology and Faculty of Dentistry, McGill University, 3640 University Street, Montreal, Quebec, Canada H3A 0C7
| | - Suneel S Apte
- Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
| |
Collapse
|
5
|
Segade F. Functional evolution of the microfibril-associated glycoproteins. Gene 2009; 439:43-54. [PMID: 19332111 DOI: 10.1016/j.gene.2009.03.013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 03/11/2009] [Accepted: 03/16/2009] [Indexed: 12/19/2022]
Abstract
The microfibril-associated glycoproteins (MAGPs) are cysteine-rich low molecular weight components of the fibrillin-based microfibrillar complex. MAGPs are evolutionarily conserved in vertebrates and have important roles in microfibril and elastic fiber structure, homeostasis, and vascular development. Two MAGPs, designated MAGP1 and MAGP2, are encoded in the mammalian genome. Although MAGP sequences have been identified in several vertebrate species, the extent of conservation and evolutionary history of the MAGPs in vertebrates is unknown. Sequence similarity searches of nucleotide and protein databases identified the first homologs of MAGP1 in monotremes, birds, elasmobranchs and agnathans, and the first MAGP2 genes in marsupials, birds and teleosts. A model for MAGP evolution is presented. Phylogenetic analysis identified the ancient origin of MAGP1 and the evolution of MAGP2 from a gene duplication event early in vertebrate evolution. Phylogenomic analysis shows conservation of synteny between teleosts and tetrapods and suggests a multigene duplication event. The MAGP2 gene has evolved rapidly as an innovation in the bony vertebrate lineage. Estimates of functional divergence and complex nucleotide substitution models suggest that the divergence of MAGP2 took place by relaxation of selective constraints; and that MAGP1 has consistently been constrained by strong purifying selection. Correlated evolution between MAGP1 and the developmental regulator, Notch1, may explain some of the selective forces acting on MAGP2.
Collapse
Affiliation(s)
- Fernando Segade
- Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, 240 S. 40th St., Philadelphia, PA 19104, USA.
| |
Collapse
|
6
|
Weinbaum JS, Broekelmann TJ, Pierce RA, Werneck CC, Segade F, Craft CS, Knutsen RH, Mecham RP. Deficiency in microfibril-associated glycoprotein-1 leads to complex phenotypes in multiple organ systems. J Biol Chem 2008; 283:25533-25543. [PMID: 18625713 DOI: 10.1074/jbc.m709962200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Microfibril-associated glycoprotein-1 (MAGP-1) is a small molecular weight component of the fibrillin-rich microfibril. Gene-targeted inactivation of MAGP-1 reveals a complex phenotype that includes increased body weight and size due to excess body fat, an altered wound healing response in bone and skin, and a bleeding diathesis. Elastic tissues rich in MAGP-1-containing microfibrils develop normally and show normal function. The penetrance of MAGP-1-null phenotypes is highly variable and mouse strain-dependent, suggesting the influence of modifier genes. MAGP-1 was found to bind active transforming growth factor-beta (TGF-beta) and BMP-7 with high affinity, suggesting that it may be an important modulator of microfibril-mediated growth factor signaling. Many of the phenotypic traits observed in MAGP-1-deficient mice are consistent with loss of TGF-beta function and are generally opposite those associated with mutations in fibrillin-1 that result in enhanced TGF-beta signaling. Increased body size and fat deposition in MAGP-1-mutant animals are particularly intriguing given the localization of obesity traits in humans to the region on chromosome 1 containing the MAGP-1 gene.
Collapse
Affiliation(s)
- Justin S Weinbaum
- Departments of Cell Biology and Physiology, St. Louis, Missouri 63110
| | | | - Richard A Pierce
- Medicine, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Claudio C Werneck
- Departamento de Bioquimica, Universidade Estadual de Campinas, Campinas 13084-225, Brazil
| | - Fernando Segade
- Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6030
| | - Clarissa S Craft
- Departments of Cell Biology and Physiology, St. Louis, Missouri 63110
| | - Russell H Knutsen
- Departments of Cell Biology and Physiology, St. Louis, Missouri 63110
| | - Robert P Mecham
- Departments of Cell Biology and Physiology, St. Louis, Missouri 63110.
| |
Collapse
|
7
|
Segade F, Suganuma N, Mychaleckyj JC, Mecham RP. The intracellular form of human MAGP1 elicits a complex and specific transcriptional response. Int J Biochem Cell Biol 2007; 39:2303-13. [PMID: 17692555 PMCID: PMC2083557 DOI: 10.1016/j.biocel.2007.06.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Revised: 05/14/2007] [Accepted: 06/23/2007] [Indexed: 12/13/2022]
Abstract
Microfibril-associated glycoprotein-1 (MAGP1) is found associated with microfibrils in the extracellular matrix (ECM). In humans, MAGP1 is expressed as two alternatively spliced isoforms: MAGP1A, the extracellular microfibril-associated form; and MAGP1B, an exclusively intracellular isoform derived from the skipping of exon 3. The biological function of MAGP1B is unknown. We performed gene expression profiling to study the cellular response to MAGP1B using whole-genome genechips. We found that MAGP1B specifically induces the expression of genes linked to cell adhesion, motility, metabolism, gene expression, development and signal transduction. Versican, a gene product involved in the structure and functional regulation of the ECM, showed the highest up-regulation in response to MAGP1B. These studies suggest a dual role for MAGP1, with extracellular MAGP1A involved in ECM function, and intracellular MAGP1B modulating the expression of genes that function in cell adhesion, migration and control of ECM deposition.
Collapse
Affiliation(s)
- Fernando Segade
- Center for Human Genomics, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
| | | | | | | |
Collapse
|
8
|
Kobayashi N, Watanabe M, Kijimoto T, Fujimura K, Nakazawa M, Ikeo K, Kohara Y, Gojobori T, Okada N. magp4 gene may contribute to the diversification of cichlid morphs and their speciation. Gene 2006; 373:126-33. [PMID: 16517097 DOI: 10.1016/j.gene.2006.01.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2005] [Revised: 01/19/2006] [Accepted: 01/22/2006] [Indexed: 11/15/2022]
Abstract
Lake Victoria harbors more than 300 species of cichlid fish, which are adapted to a variety of ecological niches with various morphological species-specific features. However, it is believed that these species arose explosively within the last 14,000 years and transcripts among Lake Victoria cichlid species are almost identical in sequence. These data prompted us to develop a DNA chip assay to compare patterns of gene expression among cichlid species. We prepared a DNA chip spotted with 6240 elements derived from cichlid expressed sequence tag (EST) clones and successfully characterized gene expression differences between the cichlid species Haplochromis chilotes and Haplochromis sp. "rockkribensis". We identified 14 transcripts that were differentially expressed between these species at an early developmental stage, 15 days post-fertilization (dpf), and several were further analyzed using quantitative real-time PCR (qPCR). One of these differentially expressed transcripts was a homolog of microfibril-associated glycoprotein 4 (magp4), a putative causative gene for the human inherited disease, Smith-Magenis syndrome (SMS), for which facial defects are among the phenotypic features. Further analysis of magp4 expression showed that magp4 was expressed in the jaw portion of cichlid fry and that expression profiles between Haplochromis chilotes and Haplochromis sp. "rockkribensis" differed during development. These data suggest that the differential expression of a gene associated with human cranial morphogenesis may be involved in the diversification of cichlid jaw morphs.
Collapse
Affiliation(s)
- Naoki Kobayashi
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259-B21, Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Chen E, Larson JD, Ekker SC. Functional analysis of zebrafish microfibril-associated glycoprotein-1 (Magp1) in vivo reveals roles for microfibrils in vascular development and function. Blood 2006; 107:4364-74. [PMID: 16469878 PMCID: PMC1895789 DOI: 10.1182/blood-2005-02-0789] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Mutations in fibrillin-1 (FBN1) result in Marfan syndrome, demonstrating a critical requirement for microfibrils in vessel structure and function. However, the identity and function of many microfibril-associated molecules essential for vascular development and function have yet to be characterized. In our morpholino-based screen for members of the secretome required for vascular development, we identified a key player in microfibril formation in zebrafish embryogenesis. Microfibril-associated glycoprotein-1 (MAGP1) is a conserved protein found in mammalian and zebrafish microfibrils. Expression of magp1 mRNA is detected in microfibril-producing cells. Analysis of a functional Magp1-mRFP fusion protein reveals localization along the midline and in the vasculature during embryogenesis. Underexpression and overexpression analyses demonstrate that specific Magp1 protein levels are critical for vascular development. Integrin function is compromised in magp1 morphant embryos, suggesting that reduced integrin-matrix interaction is the main mechanism for the vascular defects in magp1 morphants. We further show that Magp1 and fibrillin-1 interact in vivo. This study implicates MAGP1 as a key player in microfibril formation and integrity during development. The essential role for MAGP1 in vascular morphogenesis and function also supports a wide range of clinical applications, including therapeutic targets in vascular disease and cardiovascular tissue engineering.
Collapse
Affiliation(s)
- Eleanor Chen
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | | | | |
Collapse
|
10
|
Segade F, Mecham RP. Regulatory elements of microfibril-associated glycoprotein-1 gene expression in muscle cells. ACTA ACUST UNITED AC 2005; 1731:215-24. [PMID: 16321658 DOI: 10.1016/j.bbaexp.2005.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Revised: 10/17/2005] [Accepted: 10/19/2005] [Indexed: 11/22/2022]
Abstract
The Mfap2 gene encodes the microfibril-associated glycoprotein-1 (MAGP1), an extracellular matrix protein of microfibrillar structures. The gene is transcribed from a major transcription start site embedded in a CpG island. Mapping of transcriptionally active regions in the 5' flanking sequence identified a region, located between nucleotides -339 and -109 as the Mfap2 basal promoter. Site-directed and random mutagenesis demonstrated that a KLF sequence motif at -256/-270, an E-box at -222/-229, and a GC-box at -117/-125, are critical for the promoter function. Using electrophoresis mobility shift assays, we find that the KLF motif mediates the binding of GKLF/KLF4, whereas the E-box is a target for both Upstream Stimulatory Factors 1 and 2, and the GC box at -117/-125 forms complexes with Sp1 and Sp3, but not with Sp4 or AP2alpha. A sequence element spanning position -150 may represent the binding motif of an uncharacterized transcription factor. The basal transcriptional regulation of Mfap2 in muscle cells is discussed.
Collapse
Affiliation(s)
- Fernando Segade
- Department of Internal Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
| | | |
Collapse
|
11
|
Segade F, Trask BC, Broekelmann TJ, Pierce RA, Mecham RP. Identification of a matrix-binding domain in MAGP1 and MAGP2 and intracellular localization of alternative splice forms. J Biol Chem 2002; 277:11050-7. [PMID: 11796718 DOI: 10.1074/jbc.m110347200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MAGP1 is a small molecular mass protein associated with microfibrils in the extracellular matrix (ECM). To identify the molecular basis of its interaction with other microfibrillar proteins, deletion constructs of MAGP1 were expressed in a mammalian cell system that served as a model for microfibril assembly. This study identified a 54-amino acid sequence in the carboxyl-terminal region of the protein that defines a matrix-binding domain that is sufficient to target MAGP1 to the ECM. Site-directed mutagenesis demonstrated that binding activity is dependent on the presence of 7 cysteine residues in this sequence. MAGP2 contains a sequence similar to the matrix-binding domain of MAGP1, but could not associate with the ECM because of a single amino acid change. Two naturally occurring MAGP1 splice variants, MAGP1B (human-specific) and MAGP1D (found in mice), localized intracellularly when expressed as chimeric proteins with green fluorescent protein in rat lung fibroblasts. This suggests a second action site for MAGP1.
Collapse
Affiliation(s)
- Fernando Segade
- Department of Cell Biology and Physiology and the Division of Pulmonary and Critical Care Medicine, Barnes-Jewish Hospital and Washington University School of Medicine, St. Louis, Missouri 63110, USA
| | | | | | | | | |
Collapse
|
12
|
Pianese L, Tammaro A, Turano M, De Biase I, Monticelli A, Cocozza S. Identification of a novel transcript of X25, the human gene involved in Friedreich ataxia. Neurosci Lett 2002; 320:137-40. [PMID: 11852181 DOI: 10.1016/s0304-3940(02)00048-4] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Friedreich ataxia (FRDA) is caused by a GAA triplet expansion in the first intron of the X25 gene. The X25 gene encodes a 210-amino acid protein, frataxin (A isoform). Here, we report the identification of a new transcript of the X25 gene generated by alternative splicing by the use of a second donor splice site in the intron 4. Full-length cDNA transcript sequence revealed an insertion of 8 bp between 4 and 5a exon sequence. This event leads to a frameshift in the mRNA reading frame and introduces a new stop codon at position 589. Therefore, this X25 transcript variant may encode a 196-amino acid protein, the A1 isoform, that structurally differs from the main A isoform of 210 amino acids after residue 160. In all human tissues analyzed, reverse transcription-polymerase chain reaction experiments demonstrated that the A1 isoform was expressed at low levels compared with the predominant A isoform. No difference in A and A1 isoform expression rate was detected between FRDA patients and normal controls. We did not find an A1 like splice variant in rodents.
Collapse
Affiliation(s)
- Luigi Pianese
- BioGeM, c/o Department of Molecular and Cellular Biology and Pathology, Federico II University, Via S. Pansini, 580131 Naples, Italy.
| | | | | | | | | | | |
Collapse
|