1
|
Gu J, Zhou X, Sutherland L, Kato M, Jaczynska K, Rizo J, McKnight SL. Oxidative regulation of TDP-43 self-association by a β-to-α conformational switch. Proc Natl Acad Sci U S A 2023; 120:e2311416120. [PMID: 37782781 PMCID: PMC10576115 DOI: 10.1073/pnas.2311416120] [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: 07/10/2023] [Accepted: 09/04/2023] [Indexed: 10/04/2023] Open
Abstract
An evolutionarily conserved region of the TDP-43 low-complexity domain (LCD) twenty residues in length can adopt either an α-helical or β-strand conformation. When in the latter conformation, TDP-43 self-associates via the formation of a labile, cross-β structure. Self-association can be monitored via the formation of phase-separated protein droplets. Exposure of droplets to hydrogen peroxide leads to oxidation of conserved methionine residues distributed throughout the LCD. Oxidation disassembles the cross-β structure, thus eliminating both self-association and phase separation. Here, we demonstrate that this process reciprocally enables formation of α-helical structure in precisely the same region formerly functioning to facilitate β-strand-mediated self-association. We further observe that the α-helical conformation allows interaction with a lipid-like detergent and that exposure to lipids enhances the β-to-α conformational switch. We hypothesize that regulation of this oxidative switch will prove to be important to the control of localized translation within vertebrate cells. The experimental observations reported herein were heavily reliant on studies of 1,6-hexanediol, a chemical agent that selectively dissolves labile structures formed via the self-association of protein domains of low sequence complexity. This aliphatic alcohol is shown to exert its dissociative activity primarily via hydrogen-bonding interactions with carbonyl oxygen atoms of the polypeptide backbone. Such observations underscore the central importance of backbone-mediated protein:protein interactions that facilitate the self-association and phase separation of LCDs.
Collapse
Affiliation(s)
- Jinge Gu
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75235
| | - Xiaoming Zhou
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75235
| | - Lillian Sutherland
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75235
| | - Masato Kato
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75235
- Institute for Quantum Life Science, National Institutes for Quantum Science and Technology, Inage-ku, Chiba263-8555, Japan
| | - Klaudia Jaczynska
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75235
| | - Josep Rizo
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX75235
| | - Steven L. McKnight
- Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX75235
| |
Collapse
|
2
|
Gu J, Zhou X, Sutherland L, Kato M, Jaczynska K, Rizo J, McKnight SL. Oxidative regulation of TDP-43 self-association by a β-to-α conformational switch. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.29.555361. [PMID: 37693418 PMCID: PMC10491227 DOI: 10.1101/2023.08.29.555361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/12/2023]
Abstract
An evolutionarily conserved region of the TDP-43 low complexity domain twenty residues in length can adopt either an α-helical or β-strand conformation. When in the latter conformation, TDP-43 self-associates via the formation of a labile, cross-β structure. Self-association can be monitored via the formation of phase separated protein droplets. Exposure of droplets to hydrogen peroxide leads to oxidation of conserved methionine residues distributed throughout the low complexity domain. Oxidation disassembles the cross-β structure, thus eliminating both self-association and phase separation. Here we demonstrate that this process reciprocally enables formation of α-helical structure in precisely the same region formerly functioning to facilitate β-strand mediated self-association. We further observe that the α-helical conformation allows interaction with a lipid-like detergent, and that exposure to lipids enhances the β-to-α conformational switch. We hypothesize that regulation of this oxidative switch will prove to be important to the control of localized translation within vertebrate cells. The experimental observations reported herein were heavily reliant on studies of 1,6-hexanediol, a chemical agent that selectively dissolves labile structures formed via the self-association of protein domains of low sequence complexity. This aliphatic alcohol is shown to exert its dissociative activity primarily via hydrogen bonding interactions with carbonyl oxygen atoms of the polypeptide backbone. Such observations underscore the central importance of backbone-mediated protein:protein interactions that facilitate the self-association and phase separation of low complexity domains. Significance Statement The TDP-43 protein is a constituent of RNA granules involved in regulated translation. TDP-43 contains a C-terminal domain of 150 amino acids of low sequence complexity conspicuously decorated with ten methionine residues. An evolutionarily conserved region (ECR) of 20 residues within this domain can adopt either of two forms of labile secondary structure. Under normal conditions wherein methionine residues are reduced, the ECR forms a labile cross-β structure that enables RNA granule condensation. Upon methionine oxidation, the ECR undergoes a conformational switch to become an α-helix incompatible with self-association and granule integrity. Oxidation of the TDP-43 low complexity domain is hypothesized to occur proximal to mitochondria, thus facilitating dissolution of RNA granules and activation of localized translation.
Collapse
Affiliation(s)
- Jinge Gu
- Department of Biochemistry, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| | - Xiaoming Zhou
- Department of Biochemistry, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| | - Lillian Sutherland
- Department of Biochemistry, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| | - Masato Kato
- Department of Biochemistry, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
- Institute for Quantum Life Science, National Institutes for Quantum Science and Technology (QST) 4-9-1, Anagawa, Inage-ku, Chiba, JAPAN 263-8555
| | - Klaudia Jaczynska
- Department of Biophysics, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| | - Josep Rizo
- Department of Biophysics, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| | - Steven L. McKnight
- Department of Biochemistry, UT Southwestern Medical Center 5323 Harry Hines Blvd., Dallas, Texas 75235
| |
Collapse
|
3
|
Zhou X, Sumrow L, Tashiro K, Sutherland L, Liu D, Qin T, Kato M, Liszczak G, McKnight SL. Mutations linked to neurological disease enhance self-association of low-complexity protein sequences. Science 2022; 377:eabn5582. [PMID: 35771920 PMCID: PMC9610444 DOI: 10.1126/science.abn5582] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Protein domains of low sequence complexity do not fold into stable, three-dimensional structures. Nevertheless, proteins with these sequences assist in many aspects of cell organization, including assembly of nuclear and cytoplasmic structures not surrounded by membranes. The dynamic nature of these cellular assemblies is caused by the ability of low-complexity domains (LCDs) to transiently self-associate through labile, cross-β structures. Mechanistic studies useful for the study of LCD self-association have evolved over the past decade in the form of simple assays of phase separation. Here, we have used such assays to demonstrate that the interactions responsible for LCD self-association can be dictated by labile protein structures poised close to equilibrium between the folded and unfolded states. Furthermore, missense mutations causing Charcot-Marie-Tooth disease, frontotemporal dementia, and Alzheimer's disease manifest their pathophysiology in vitro and in cultured cell systems by enhancing the stability of otherwise labile molecular structures formed upon LCD self-association.
Collapse
|
4
|
New perspectives on cytoskeletal dysregulation and mitochondrial mislocalization in amyotrophic lateral sclerosis. Transl Neurodegener 2021; 10:46. [PMID: 34789332 PMCID: PMC8597313 DOI: 10.1186/s40035-021-00272-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Accepted: 10/28/2021] [Indexed: 02/07/2023] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective, early degeneration of motor neurons in the brain and spinal cord. Motor neurons have long axonal projections, which rely on the integrity of neuronal cytoskeleton and mitochondria to regulate energy requirements for maintaining axonal stability, anterograde and retrograde transport, and signaling between neurons. The formation of protein aggregates which contain cytoskeletal proteins, and mitochondrial dysfunction both have devastating effects on the function of neurons and are shared pathological features across several neurodegenerative conditions, including ALS, Alzheimer's disease, Parkinson's disease, Huntington's disease and Charcot-Marie-Tooth disease. Furthermore, it is becoming increasingly clear that cytoskeletal integrity and mitochondrial function are intricately linked. Therefore, dysregulations of the cytoskeletal network and mitochondrial homeostasis and localization, may be common pathways in the initial steps of neurodegeneration. Here we review and discuss known contributors, including variants in genetic loci and aberrant protein activities, which modify cytoskeletal integrity, axonal transport and mitochondrial localization in ALS and have overlapping features with other neurodegenerative diseases. Additionally, we explore some emerging pathways that may contribute to this disruption in ALS.
Collapse
|
5
|
Abstract
Assembly of intermediate filaments (IFs) is reliant upon amino-terminal head domains. These head domains are of low sequence complexity and are assumed to function in the absence of structural order. Herein, we provide evidence that the head domains of the desmin and neurofilament light (NFL) IF proteins self-associate via the formation of labile but structurally specific cross-β interaction. Disease-causing mutations in the head domains of both proteins cause enhanced cross-β interactions. By assembling desmin and NFL IFs bearing isotopically labeled head domains, we provide evidence of structural order in properly assembled biological filaments. We propose that these observations on IF head domains may be instructive to the function of low complexity domains operative in other aspects of cell biology. Low complexity (LC) head domains 92 and 108 residues in length are, respectively, required for assembly of neurofilament light (NFL) and desmin intermediate filaments (IFs). As studied in isolation, these IF head domains interconvert between states of conformational disorder and labile, β-strand–enriched polymers. Solid-state NMR (ss-NMR) spectroscopic studies of NFL and desmin head domain polymers reveal spectral patterns consistent with structural order. A combination of intein chemistry and segmental isotope labeling allowed preparation of fully assembled NFL and desmin IFs that could also be studied by ss-NMR. Assembled IFs revealed spectra overlapping with those observed for β-strand–enriched polymers formed from the isolated NFL and desmin head domains. Phosphorylation and disease-causing mutations reciprocally alter NFL and desmin head domain self-association yet commonly impede IF assembly. These observations show how facultative structural assembly of LC domains via labile, β-strand–enriched self-interactions may broadly influence cell morphology.
Collapse
|
6
|
Stone EJ, Kolb SJ, Brown A. A review and analysis of the clinical literature on Charcot-Marie-Tooth disease caused by mutations in neurofilament protein L. Cytoskeleton (Hoboken) 2021; 78:97-110. [PMID: 33993654 PMCID: PMC10174713 DOI: 10.1002/cm.21676] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Revised: 05/05/2021] [Accepted: 05/06/2021] [Indexed: 01/22/2023]
Abstract
Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders and can be caused by mutations in over 100 different genes. One of the causative genes is NEFL on chromosome 8 which encodes neurofilament light protein (NEFL), one of five proteins that co-assemble to form neurofilaments. At least 34 different CMT-causing mutations in NEFL have been reported which span the head, rod, and tail domains of the protein. The majority of these mutations are inherited dominantly, but some are inherited recessively. The resulting disease is classified variably in clinical reports based on electrodiagnostic studies as either axonal (type 2; CMT2E), demyelinating (type 1; CMT1F), or a form intermediate between the two (dominant intermediate; DI-CMTG). In this article, we first present a brief introduction to CMT and neurofilaments. We then collate and analyze the data from the clinical literature on the disease classification, age of onset and electrodiagnostic test results for the various mutations. We find that mutations in the head, rod, and tail domains can all cause disease with early onset and profound neurological impairment, with a trend toward greater severity for head domain mutations. We also find that the disease classification does not correlate with specific mutation or domain. In fact, different individuals with the same mutation can be classified as having axonal, demyelinating, or dominant intermediate forms of the disease. This suggests that the classification of the disease as CMT2E, CMT1F or DI-CMTG has more to do with variable disease presentation than to differences in the underlying disease mechanism, which is most likely primarily axonal in all cases.
Collapse
Affiliation(s)
- Elizabeth J Stone
- Department of Neuroscience, Ohio State University, Columbus, Ohio, USA.,Neuroscience Graduate Program, Ohio State University, Columbus, Ohio, USA
| | - Stephen J Kolb
- Department of Neurology, Ohio State University, Columbus, Ohio, USA.,Department of Biological Chemistry and Pharmacology, Ohio State University, Columbus, Ohio, USA
| | - Anthony Brown
- Department of Neuroscience, Ohio State University, Columbus, Ohio, USA
| |
Collapse
|
7
|
Schult D, Hölsken A, Buchfelder M, Schlaffer SM, Siegel S, Kreitschmann-Andermahr I, Fahlbusch R, Buslei R. Expression pattern of neuronal intermediate filament α-internexin in anterior pituitary gland and related tumors. Pituitary 2015; 18:465-73. [PMID: 25236435 DOI: 10.1007/s11102-014-0597-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE α-Internexin (INA) is a class IV neuronal intermediate filament protein that maintains the morphogenesis of neurons. It is expressed in developing neuroblasts and represents the major component of the cytoskeleton in cerebellar granule cells of adult central nervous system tissue. Data concerning INA expression in the human frontal pituitary lobe and related adenomas (PA) is missing. METHODS Using immunohistochemistry we examined the distribution pattern of INA in a large cohort of 152 PA, 11 atypical PA, 4 pituitary carcinomas and 20 normal pituitaries (overall n = 187). Quantity of INA protein expression was semi-quantitatively evaluated and grouped into five categories (0 = 0%; 1 = >0-5%; 2 = >5-35%; 3 = >35-80%; 4 = >80% of cells). RESULTS Cellular staining intensity of INA appeared significantly higher in gonadotropinomas (Go, n = 62), null cell adenomas (NC, n = 7) and thyrotropinomas (TSHomas, n = 7) compared to the other tumor subtypes (p ≤ 0.001). Furthermore, Go and NC showed a peculiar pseudorosette-like staining pattern surrounding blood vessels in 85.5% (59/69) of cases. Interestingly, areas exhibiting homogenous INA staining were often associated with oncocytic cell changes and decreased immunohistochemically detectable hormone expression. Only 8.5% (8/94) of other PA showed a comparable INA distribution (p ≤ 0.001). CONCLUSION Go, NC as well as TSHomas exhibit high levels of intracellular INA protein indicating neuronal transdifferentiation. A possible impact on pathogenesis and endocrine activity needs further investigation.
Collapse
Affiliation(s)
- D Schult
- Department of Neuropathology, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Erlangen, Germany
| | | | | | | | | | | | | | | |
Collapse
|
8
|
Order and disorder in intermediate filament proteins. FEBS Lett 2015; 589:2464-76. [PMID: 26231765 DOI: 10.1016/j.febslet.2015.07.024] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 07/21/2015] [Accepted: 07/22/2015] [Indexed: 11/20/2022]
Abstract
Intermediate filaments (IFs), important components of the cytoskeleton, provide a versatile, tunable network of self-assembled proteins. IF proteins contain three distinct domains: an α-helical structured rod domain, flanked by intrinsically disordered head and tail domains. Recent studies demonstrated the functional importance of the disordered domains, which differ in length and amino-acid sequence among the 70 different human IF genes. Here, we investigate the biophysical properties of the disordered domains, and review recent findings on the interactions between them. Our analysis highlights key components governing IF functional roles in the cytoskeleton, where the intrinsically disordered domains dictate protein-protein interactions, supramolecular assembly, and macro-scale order.
Collapse
|
9
|
The tail domain is essential but the head domain dispensable for C. elegans intermediate filament IFA-2 function. PLoS One 2015; 10:e0119282. [PMID: 25742641 PMCID: PMC4351089 DOI: 10.1371/journal.pone.0119282] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 01/19/2015] [Indexed: 01/12/2023] Open
Abstract
The intermediate filament protein IFA-2 is essential for the structural integrity of the Caenorhabditis elegans epidermis. It is one of the major components of the fibrous organelle, an epidermal structure comprised of apical and basal hemidesmosomes linked by cytoplasmic intermediate filaments that serve to transmit force from the muscle to the cuticle. Mutations of IFA-2 result in epidermal fragility and separation of the apical and basal epidermal surfaces during postembryonic growth. An IFA-2 lacking the head domain fully rescues the IFA-2 null mutant, whereas an IFA-2 lacking the tail domain cannot. Conversely, an isolated IFA-2 head was able to localize to fibrous organelles whereas the tail was not. Taken together these results suggest that the head domain contains redundant signals for IF localization, whereas non-redundant essential functions map to the IFA-2, tail, although the tail is unlikely to be directly involved in fibrous organelle localization.
Collapse
|
10
|
Liu CH, Chien CL. Molecular cloning and characterization of chicken neuronal intermediate filament protein α-internexin. J Comp Neurol 2013; 521:2147-64. [PMID: 23224860 DOI: 10.1002/cne.23278] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2012] [Revised: 09/19/2012] [Accepted: 11/28/2012] [Indexed: 01/20/2023]
Abstract
α-Internexin is one of the neuronal intermediate filament (IF) proteins, which also include low-, middle-, and high-molecular-weight neurofilament (NF) triplet proteins, designated NFL, NFM, and NFH, respectively. The expression of α-internexin occurs in most neurons as they begin differentiation and precedes the expression of the NF triplet proteins in mammals. However, little is known about the gene sequence and physiological function of α-internexin in avians. In this study we describe the molecular cloning of the mRNA sequence encoding the chicken α-internexin (chkINA) protein from embryonic brains. The gene structure and predicted amino acid sequence of chkINA exhibited high similarity to those of its zebrafish, mouse, rat, bovine, and human homologs. Data from transient-transfection experiments show that the filamentous pattern of chkINA was found in transfected cells and colocalized with other endogenous IFs, as demonstrated via immunocytochemistry using a chicken-specific antibody. The expression of chkINA was detected at the early stage of development and increased during the developmental process of the chicken. chkINA was expressed widely in chicken brains and colocalized with NF triplet proteins in neuronal processes, as assessed using immunohistochemistry. We also found that chkINA was expressed abundantly in the developing cerebellum and was the major IF protein in the parallel processes of granule neurons. Thus, we suggest that chkINA is a neuron-specific IF protein that may be a useful marker for studies of chicken brain development.
Collapse
Affiliation(s)
- Chi-Hsiu Liu
- Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei 10051, Taiwan ROC
| | | |
Collapse
|
11
|
|
12
|
Signaling mechanisms downstream of quinolinic acid targeting the cytoskeleton of rat striatal neurons and astrocytes. Exp Neurol 2011; 233:391-9. [PMID: 22116044 DOI: 10.1016/j.expneurol.2011.11.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2011] [Revised: 10/31/2011] [Accepted: 11/07/2011] [Indexed: 11/22/2022]
Abstract
The studies of signaling mechanisms involved in the disruption of the cytoskeleton homeostasis were performed in a model of quinolinic acid (QUIN) neurotoxicity in vitro. This investigation focused on the phosphorylation level of intermediate filament (IF) subunits of astrocytes (glial fibrillary acidic protein - GFAP) and neurons (low, medium and high molecular weight neurofilament subunits - NFL, NFM and NFH, respectively). The activity of the phosphorylating system associated with the IFs was investigated in striatal slices of rat exposed to QUIN or treated simultaneously with QUIN plus glutamate receptor antagonists, calcium channel blockers or kinase inhibitors. Results showed that in astrocytes, the action of 100 μM QUIN was mainly due to increased Ca(2+) influx through NMDA and L-type voltage-dependent Ca(2+) channels (L-VDCC). In neuronal cells QUIN acted through metabotropic glutamate receptor (mGluR) activation and influx of Ca(2+) through NMDA receptors and L-VDCC, as well as Ca(2+) release from intracellular stores. These mechanisms then set off a cascade of events including activation of PKA, PKCaMII and PKC, which phosphorylate head domain sites on GFAP and NFL. Also, Cdk5 was activated downstream of mGluR5, phosphorylating the KSP repeats on NFM and NFH. mGluR1 was upstream of phospholipase C (PLC) which, in turn, produced diacylglycerol (DAG) and inositol 3,4,5 triphosphate (IP3). DAG is important to activate PKC and phosphorylate NFL, while IP(3) contributed to Ca(2+) release from internal stores promoting hyperphosphorylation of KSP repeats on the tail domain of NFM and NFH. The present study supports the concept of glutamate and Ca(2+) contribution in excitotoxic neuronal damage provoked by QUIN associated to dysfunction of the cytoskeleton homeostasis and highlights the differential signaling mechanisms elicited in striatal astrocytes and neurons.
Collapse
|
13
|
Perrot R, Berges R, Bocquet A, Eyer J. Review of the Multiple Aspects of Neurofilament Functions, and their Possible Contribution to Neurodegeneration. Mol Neurobiol 2008; 38:27-65. [DOI: 10.1007/s12035-008-8033-0] [Citation(s) in RCA: 205] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Accepted: 06/14/2008] [Indexed: 10/21/2022]
|
14
|
Goryunov D, Nightingale A, Bornfleth L, Leung C, Liem RKH. Multiple disease-linked myotubularin mutations cause NFL assembly defects in cultured cells and disrupt myotubularin dimerization. J Neurochem 2007; 104:1536-52. [PMID: 17973976 DOI: 10.1111/j.1471-4159.2007.05103.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Charcot-Marie-Tooth disease (CMT) is an inherited peripheral neuropathy that has been linked to mutations in multiple genes. Mutations in the neurofilament light (NFL) chain gene lead to the CMT2E form whereas mutations in the myotubularin-related protein 2 and 13 (MTMR2 and MTMR13) genes lead to the CMT4B form. These two forms share characteristic pathological hallmarks on nerve biopsies including concentric sheaths ('onion bulbs') and, in at least one case, myelin loops. In addition, MTMR2 protein has been shown to interact physically with both NFL and MTMR13. Here, we present evidence that CMT-linked mutations of MTMR2 can cause NFL aggregation in a cell line devoid of endogenous intermediate filaments, SW13vim(-). Mutations in the protein responsible for X-linked myotubular myopathy (myotubularin, MTM1) also induced NFL abnormalities in these cells. We also show that two MTMR2 mutant proteins, G103E and R283W, are unable to form dimers and undergo phosphorylation in vivo, implicating impaired complex formation in myotubularin-related pathology.
Collapse
Affiliation(s)
- Dmitry Goryunov
- Department of Pathology and Cell Biology, Columbia University College of Physicians & Surgeons, New York, New York 10032, USA
| | | | | | | | | |
Collapse
|
15
|
Sihag RK, Inagaki M, Yamaguchi T, Shea TB, Pant HC. Role of phosphorylation on the structural dynamics and function of types III and IV intermediate filaments. Exp Cell Res 2007; 313:2098-109. [PMID: 17498690 PMCID: PMC2570114 DOI: 10.1016/j.yexcr.2007.04.010] [Citation(s) in RCA: 194] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Revised: 04/04/2007] [Accepted: 04/06/2007] [Indexed: 12/19/2022]
Abstract
Phosphorylation of types III and IV intermediate filaments (IFs) is known to regulate their organization and function. Phosphorylation of the amino-terminal head domain sites on types III and IV IF proteins plays a key role in the assembly/disassembly of IF subunits into 10 nm filaments, and influences the phosphorylation of sites on the carboxyl-terminal tail domain. These phosphorylation events are largely under the control of second messenger-dependent protein kinases and provide the cells a mechanism to reorganize the IFs in response to the changes in second messenger levels. In mitotic cells, Cdk1, Rho kinase, PAK1 and Aurora-B kinase are believed to regulate vimentin and glial fibrillary acidic protein phosphorylation in a spatio-temporal manner. In neurons, the carboxyl-terminal tail domains of the NF-M and NF-H subunits of heteropolymeric neurofilaments (NFs) are highly phosphorylated by proline-directed protein kinases. The phosphorylation of carboxyl-terminal tail domains of NFs has been suspected to play roles in forming cross-bridges between NFs and microtubules, slowing axonal transport and promoting their integration into cytoskeleton lattice and, in doing so, to control axonal caliber and stabilize the axon. The role of IF phosphorylation in disease pathobiology is discussed.
Collapse
Affiliation(s)
- Ram K Sihag
- Laboratory of Neurochemistry, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, Bldg. 49 Room 2A28, MD 20892, USA.
| | | | | | | | | |
Collapse
|
16
|
Leung CL, Nagan N, Graham TH, Liem RKH. A novel duplication/insertion mutation of NEFL in a patient with Charcot-Marie-Tooth disease. Am J Med Genet A 2006; 140:1021-5. [PMID: 16619203 DOI: 10.1002/ajmg.a.31242] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
17
|
Gros-Louis F, Larivière R, Gowing G, Laurent S, Camu W, Bouchard JP, Meininger V, Rouleau GA, Julien JP. A frameshift deletion in peripherin gene associated with amyotrophic lateral sclerosis. J Biol Chem 2004; 279:45951-6. [PMID: 15322088 DOI: 10.1074/jbc.m408139200] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Peripherin is a neuronal intermediate filament associated with inclusion bodies in motor neurons of patients with amyotrophic lateral sclerosis (ALS). A possible peripherin involvement in ALS pathogenesis has been suggested based on studies with transgenic mouse overexpressors and with a toxic splicing variant of the mouse peripherin gene. However, the existence of peripherin gene mutations in human ALS has not yet been documented. Therefore, we screened for sequence variants of the peripherin gene (PRPH) in a cohort of ALS patients including familial and sporadic cases. We identified 18 polymorphic variants of PRPH detected in both ALS and age-matched control populations. Two additional PRPH variants were discovered in ALS cases but not in 380 control individuals. One variant consisted of a nucleotide insertion in intron 8 (PRPH(IVS8)(-36insA)), whereas the other one consisted of a 1-bp deletion within exon 1 (PRPH(228delC)), predicting a truncated peripherin species of 85 amino acids. Remarkably, expression of this frameshift peripherin mutant in SW13 cells resulted in disruption of neurofilament network assembly. These results suggest that PRPH mutations may be responsible for a small percentage of ALS, cases and they provide further support of the view that neurofilament disorganization may contribute to pathogenesis.
Collapse
Affiliation(s)
- François Gros-Louis
- Centre for Research in Neuroscience, McGill University Health Centre, Montreal General Hospital Research Institute, Montreal, Québec H3G 1A4, Canada
| | | | | | | | | | | | | | | | | |
Collapse
|
18
|
Woo WM, Goncharov A, Jin Y, Chisholm AD. Intermediate filaments are required for C. elegans epidermal elongation. Dev Biol 2004; 267:216-29. [PMID: 14975728 DOI: 10.1016/j.ydbio.2003.11.007] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2003] [Revised: 11/06/2003] [Accepted: 11/11/2003] [Indexed: 10/26/2022]
Abstract
Cytoplasmic intermediate filaments (cIFs) are thought to provide mechanical strength to vertebrate cells; however, their function in invertebrates has been largely unexplored. The Caenorhabditis elegans genome encodes multiple cIFs. The C. elegans ifb-1 locus encodes two cIF isoforms, IFB-1A and IFB-1B, that differ in their head domains. We show that both IFB-1 isoforms are expressed in epidermal cells, within which they are localized to muscle-epidermal attachment structures. Reduction in IFB-1A function by mutation or RNA interference (RNAi) causes epidermal fragility, abnormal epidermal morphogenesis, and muscle detachment, consistent with IFB-1A providing mechanical strength to epidermal attachment structures. Reduction in IFB-1B function causes morphogenetic defects and defective outgrowth of the excretory cell. Reduction in function of both IFB-1 isoforms results in embryonic arrest due to muscle detachment and failure in epidermal cell elongation at the 2-fold stage. Two other cIFs, IFA-2 and IFA-3, are expressed in epidermal cells. We show that loss of function in IFA-3 results in defects in morphogenesis indistinguishable from those of embryos lacking ifb-1. In contrast, IFA-2 is not required for embryonic morphogenesis. Our data indicate that IFB-1 and IFA-3 are likely the major cIF isoforms in embryonic epidermal attachment structures.
Collapse
Affiliation(s)
- Wei-Meng Woo
- Sinsheimer Laboratories, Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Cruz, CA 95064, USA
| | | | | | | |
Collapse
|
19
|
Zheng YL, Li BS, Pant HC. Phosphorylation of the head domain of neurofilament protein (NF-M): a factor regulating topographic phosphorylation of NF-M tail domain KSP sites in neurons. J Biol Chem 2003; 278:24026-32. [PMID: 12695506 DOI: 10.1074/jbc.m303079200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In neurons the phosphorylation of neurofilament (NF) proteins NF-M and NF-H is topographically regulated. Although kinases and NF subunits are synthesized in cell bodies, extensive phosphorylation of the KSP repeats in tail domains of NF-M and NF-H occurs primarily in axons. The nature of this regulation, however, is not understood. As obligate heteropolymers, NF assembly requires interactions between the core NF-L with NF-M or NF-H subunits, a process inhibited by NF head domain phosphorylation. Phosphorylation of head domains at protein kinase A (PKA)-specific sites seems to occur transiently in cell bodies after NF subunit synthesis. We have proposed that transient phosphorylation of head domains prevents NF assembly in the soma and inhibits tail domain phosphorylation; i.e. assembly and KSP phosphorylation in axons depends on prior dephosphorylation of head domain sites. Deregulation of this process leads to pathological accumulations of phosphorylated NFs in the soma as seen in some neurodegenerative disorders. To test this hypothesis, we studied the effect of PKA phosphorylation of the NF-M head domain on phosphorylation of tail domain KSP sites. In rat cortical neurons we showed that head domain phosphorylation of endogenous NF-M by forskolin-activated PKA inhibits NF-M tail domain phosphorylation. To demonstrate the site specificity of PKA phosphorylation and its effect on tail domain phosphorylation, we transfected NIH3T3 cells with NF-M mutated at PKA-specific head domain serine residues. Epidermal growth factor stimulation of cells with mutant NF-M in the presence of forskolin exhibited no inhibition of NF-tail domain phosphorylation compared with the wild type NF-M-transfected cells. This is consistent with our hypothesis that transient phosphorylation of NF-M head domains inhibits tail domain phosphorylation and suggests this as one of several mechanisms underlying topographic regulation.
Collapse
Affiliation(s)
- Ya-Li Zheng
- Laboratory of Neurochemistry, National Institute of Neurological Diseases and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | |
Collapse
|
20
|
Riederer IM, Robert P, Porchet R, Eyer J, Riederer BM. Selective changes in the neurofilament and microtubule cytoskeleton of NF-H/LacZ mice. J Neurosci Res 2003; 71:196-207. [PMID: 12503082 DOI: 10.1002/jnr.10485] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
This study focused mainly on changes in the microtubule cytoskeleton in a transgenic mouse where beta-galactosidase fused to a truncated neurofilament subunit led to a decrease in neurofilament triplet protein expression and a loss in neurofilament assembly and abolished transport into neuronal processes in spinal cord and brain. Although all neurofilament subunits accumulated in neuronal cell bodies, our data suggest an increased solubility of all three subunits, rather than increased precipitation, and point to a perturbed filament assembly. In addition, reduced neurofilament phosphorylation may favor an increased filament degradation. The function of microtubules seemed largely unaffected, in that tubulin and microtubule-associated proteins (MAP) expression and their distribution were largely unchanged in transgenic animals. MAP1A was the only MAP with a reduced signal in spinal cord tissue, and differences in immunostaining in various brain regions corroborate a relationship between MAP1A and neurofilaments.
Collapse
Affiliation(s)
- Irène M Riederer
- Institut de Biologie Cellulaire et de Morphologie, Lausanne, Switzerland
| | | | | | | | | |
Collapse
|
21
|
Asch WS, Schechter N. Plasticin, a type III neuronal intermediate filament protein, assembles as an obligate heteropolymer: implications for axonal flexibility. J Neurochem 2000; 75:1475-86. [PMID: 10987827 DOI: 10.1046/j.1471-4159.2000.0751475.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The assembly characteristics of the neuronal intermediate filament protein plasticin were studied in SW13 cells in the presence and absence of a cytoplasmic filament network. Full-length plasticin cannot polymerize into homopolymers in filament-less SW13c1.2Vim(-) cells but efficiently coassembles with vimentin in SW13c1.1Vim(-) cells. By cotransfecting plasticin and vimentin in SW13c1.1Vim(-) cells, we show that plasticin assembly requires vimentin in noncatalytic amounts. Differing effects on assembly were seen with point mutations of plasticin monomers that were analogous to the keratin mutations that cause epidermolysis bullosa simplex (EBS). In particular, plasticin monomers with point mutations analogous to those in EBS do not uniformly inhibit neurofilament (NF) network formation. A point mutation in the helix termination sequence resulted in complete filament aggregation when coexpressed with vimentin but showed limited coassembly with low- and medium-molecular-weight NF proteins (NF-L and NF-M, respectively). In transfected SW13c1.1Vim(+) cells, a point mutation in the first heptad of the alpha-helical coil region formed equal amounts of filaments, aggregates, and a mixture of filaments and aggregates. Furthermore, coexpression of this point mutation with NF-L and NF-M was associated with a shift toward increased numbers of aggregates. These results suggest that there are important structural differences in assembly properties between homologous fish and mammalian intermediate filament proteins. These structural differences may contribute to the distinctive growth characteristics of the teleost visual pathway.
Collapse
Affiliation(s)
- W S Asch
- Department of Biochemistry and Cell Biology, Health Sciences Center, State University of New York, Stony Brook, New York 11794, USA
| | | |
Collapse
|